MLZ Conference 2025: Neutrons for Fusion and Nuclear Applications

28 Jul 2025, 09:00 → 31 Jul 2025, 14:15 Europe/Berlin

Schloss Fürstenried (Munich)

Neutrons are pivotal in shaping the future of fusion energy and nuclear technology, offering unparalleled opportunities to address challenges in materials science, energy production, and sustainability. This research field explores the development of advanced materials and technical components tailored to withstand the extreme operating conditions of nuclear fusion reactors, driving progress towards industrial-scale deployment. 

Cutting-edge analytical methods utilising neutrons and positrons provide powerful tools for material characterisation on an atomic scale, enabling detailed investigations of structural integrity and radiation effects. Key efforts are directed at understanding and mitigating radiation damage, optimising material properties, and extending the lifespan of critical components. The study of fast neutrons, their interactions, and their role in inducing radiation damage and transmutation processes is central to improving the material performance. Beyond materials, this field delves into research on fundamental plasma properties using positrons. These endeavors lay the groundwork to ensure the efficiency and stability of fusion reactions, for industrial-scale and reliable fusion energy.

Together, the holistic approach of these research areas underscores the multifaceted roles of neutrons and positrons in advancing both fusion energy and nuclear technologies towards a sustainable energy future.

Topics:

  ·   Fusion reactors – towards industrialisation 

  ·   Materials and technical components for fusion reactors

  ·   Advanced materials for nuclear applications

  ·   Fast neutrons, radiation damage and transmutation

  ·   Cutting-edge analytical methods using neutrons and positrons

  ·   Creation and stabilisation of plasmas

  ·   Simulations and theoretical calculations of plasma and material properties

The MLZ Conference Neutrons for Fusion and Nuclear Applications is meant to be a forum for experts from research and industry to enhance and tap the potential of neutron and positron methods in combination with complementary techniques for the characterisation and the development of advanced materials in the field of fusion reactors and nuclear applications. Series of presentations (talks and posters) will be presented by renowned international researchers in the field to demonstrate forefront research, cutting-edge analytical methods and applications including simulations.

Monday 28 July

11:45 → 12:00 Welcome

Welcome

12:00 → 13:00 Lunch

13:00 → 14:40 Session 1

Convener: Christian Pfleiderer (TUM FRM II)

13:00 Current status and challenges of the development of plasma-facing components

The severe operating conditions for Plasma Facing-Components (PFCs) in future power-generating fusion devices require the development of advanced materials and components. PFCs must not only withstand high steady state power loads of up to 20 MW/m², but also a high number of thermal cycles and shocks. In addition, the design of PFCs and the selection of appropriate armour and structural materials must consider the change in thermo-mechanical properties due to damage, activation and transmutation by fusion neutrons. At present, water-cooled PFCs are foreseen in most future fusion devices to provide reliable heat removal capability and to allow only moderate extrapolation of the technologies developed and tested for the ITER, which is presently the largest fusion device under construction the south of France. However, attempts have been made to optimise the design, as well as the armour and heat sink materials, with a view to future applications under even harsher conditions. This contribution gives an overview of the requirements for plasma facing components and the state-of-the-art solutions. In addition, new concepts and materials will be presented, including investigations on W composites and alloys as well as innovative fabrication methods such as additive manufacturing and cold spray coating of PFC mock-ups.

Speaker: Rudolf Neu (MPI for Plasma Physics)

13:40 X-ray and neutron diffraction for characterizing lattice defects in irradiated structural materials

Structural materials in the nuclear industry operate within harsh environmental conditions. Cooling substances pose corrosion, irradiation produces a high density of lattice defects, and external strains cause fracture. The large density of lattice defects generated by irradiation causes embrittlement, leading to early fracture. The analysis of diffraction peak broadening, called line profile analysis (LPA), has been used successfully to characterize the quantity, nature, and size distribution of dislocation loops induced by proton or neutron irradiation in Zr alloys [1-3]. In [1] it was shown that at lower irradiation temperatures the loops created by irradiation are smaller with larger densities. This result was used to explain the discrepancy observed in the difference of dislocation densities determined either by TEM or LPA. TEM counting revealed larger dislocation densities in cladding than in channel materials, whereas LPA showed the opposite in neutron-irradiated Zircaloy-2. In [2] it was shown that while in TEM investigations the fraction of loops smaller than a critical size escapes counting, LPA is providing the total dislocation density including the smallest fraction. Using the two different dislocation density values, the size distribution of irradiation-induced loops was determined, indicating the excellent synergy between TEM and LPA investigations. In [3], a method was developed to determine the partial dislocation densities and the fractional activities of different slip modes in plastically deformed and neutron-irradiated Zr alloys. It was shown that neutron irradiation can totally eradicate the lattice dislocations produced by the fabrication procedure of Zr-based structural components. In post-irradiation tensile deformed Zr alloys, the LPA-determined dislocation densities were in good correlation with the strain-localized deformation mechanism observed by TEM or digital image correlation techniques. The experience in analyzing irradiation-induced defects in Zr alloys can readily be used in structural materials used in the fusion-based energy industry.

[1] M. Topping et al., The effect of irradiation temperature on damage structures in proton-irradiated zirconium alloys, J. Nucl. Mater. 514 (2019) 358-367.
[2] T. Ungár et al., Size-distribution of irradiation-induced dislocation-loops in materials used in the nuclear industry, J. Nucl. Mater. 550 (2021) 152945-10.
[3] T. Ungár et al., Fractional densities and character of dislocations in different slip modes from powder diffraction patterns, J. Nucl. Mater. 589 (2024) 154828-16.

Speaker: Tamas Ungar (The University of Miskolc, Miskolc, Hungary)

14:00 Review of the tungsten thermal conductivity in a fusion power reactor

Tungsten is considered a main candidate plasma facing material (PFM) for nuclear fusion power reactors. Its high thermal conductivity is considered a major advantage compared to other PFMs. Under reactor conditions, the thermal conductivity will deteriorate significantly below the 170 W/(mK) usually agreed at room temperature and without irradiation damage. In a fusion reactor, PFMs have to be operated within a temperature window restricted, among others, by the mechanical limits and the irradiation damage annealing. This work reviews existing literature on tungsten conductivity and its operational temperature window to provide an estimate for the thermal conductivity in a fusion reactor and evaluate it in a fusion reactor component.
At temperatures relevant for reactor operation, which the displacement defect annealing requires to be above ~900 K, the conductivity drops to ~120 W/(mK) in the pristine state. Irradiation damage, in particular the transmutation to Re and the subsequent W-Re precipitation, is expected to reduce the thermal conductivity to ~50 W/(mK) after an irradiation damage in the order of 10 DPA, corresponding to about two full power years of a DEMO type power reactor.
The impact of this reduction on component design will be discussed. A lower thermal conductivity results in higher temperature gradients across the material thickness, therefore inducing higher stress to the PFC. In combination with the operational window, this limits the tungsten armour thickness and the available set of cooling pipe materials, since an overlap in the operational windows is required for joint materials.
An equation is presented to estimate the thermal conductivity of tungsten, as a function of operational time and temperature. FEM simulations using Ansys 20 and this equation are conducted for monoblock and flat tile plasma-facing components to investigate the effect of the reduced thermal conductivity on the temperature and stress distributions under different power loadings and coolant temperature scenarios. The results and their implications on joining tungsten with CuCrZr, steels, or Mo-based materials will be presented in the contribution.

Speaker: Sören Möller (FZJ)

14:20 Tritium Breeding Testing with an Intense DT Neutron Source

SHINE Technologies operates the Fusion Linear Accelerator for Radiation Effects (FLARE) high flux, steady state, 14 MeV neutron radiation effects testing facility in Janesville, Wisconsin, USA. FLARE is comprised of a neutron generator, a tritium purification system, an irradiation bunker, and related facility infrastructure. SHINE has evaluated the use of the FLARE facility to perform tritium breeding experiments. A preliminary analysis suggests that the FLARE facility could generate 100’s of MBq of tritium in the FLiBe or PbLi during a 50-hour experiment within a 30 cm tall annular vessel with 50 cm thickness. This would result in 100’s of MBq of tritium per liter at the end of irradiation. This concentration of tritium in solution should be readily quantifiable, whether measured during a post-irradiation evaluation or via an online measurement of flowing FLiBe during irradiation. This indicates that such experiments should provide good validation of breeding ratios and related parameters in blankets being irradiated with DT neutrons. This paper will discuss full results of this analysis and SHINE's experimental plans.
Additionally, SHINE has been selected as the DT neutron source supplier for the United Kingdom Atomic Energy Authority (UKAEA) Lithium Breeding Tritium Innovation (LIBRTI) program. As part of the UKAEA’s broader Fusion Futures initiative, LIBRTI focuses on pioneering fusion fuel advancements and stimulating general industry capacity through international collaboration. Over its four-year span, the program aims to demonstrate controlled tritium breeding, which is a critical step for future fusion power plants. The paper will discuss SHINE’s contribution to the LIBRTI program and interface considerations between the neutron source and breeding test blanket.

Speaker: Ross Radel (SHINE Technologies)

14:40 → 15:10 Coffee

15:10 → 16:50 Session 2

Convener: Dr Christian Reiter

15:10 Testing Needs for the Development and Qualification of Fusion Breeding Blankets

Achieving tritium self-sustainment in the breeding blanket will require a form of breeder within the engineering design of the machine which must produce an acceptable ratio of tritium to fusion neutrons to allow for a closed fuel cycle, with surplus to start up subsequent power plants. The design of the breeder and associated tritium plant must be maintainable and must be demonstrably safe with regards to the release of tritium into the environment. However, no fusion blanket has ever been built or tested. Hence, its crucial integrated functions and reliability in DEMO and future power plants are by no means assured.
Large feasibility concerns and performance uncertainties exist for all the concepts investigated to date. A vigorous research, development, and demonstration programme is urgently needed to fill the remaining outstanding gaps. This includes the accomplishment of a nuclear qualification programme involving the use of relevant new n-irradiation testing facilities or some other means, where developers will need to be able to test breeding blanket components in a neutron flux like what would be present in in the fusion reactor itself.
Currently, focus is on define the testing requirements and the testing and qualification strategy to increase the maturity level of this critical component. Validating and qualifying an essential fusion core component, like the breeding blanket, requires adequate facilities which are yet to be developed and cannot occur as part of the testing and development of pilot plants or first-of-a-kind facility. Just as wind tunnels for airplanes, launch pads for space rockets or test tracks for new railroad locomotives have been built and used to confirm the performance of the tested solutions, to determine their reliability and correct possible design faults, advancing the development and qualification of the breeding blanket would need adequate testing capabilities and facilities.
The testing issues together with the options being considered for possible qualification facilities are discussed in this talk.

Speaker: Dr Gianfranco Federici (EUROfusion Consortium)

15:50 Fission neutrons to support fusion research

Developing nuclear fusion as a viable energy source requires demonstrating sustained plasma conditions and validating associated technologies, such as tritium breeding, as well as qualifying structural materials under extreme conditions. Future fusion reactors will operate in an intense neutron environment dominated by 14.1 MeV neutrons from deuterium-tritium reactions. These high-energy neutrons must be utilized for energy recovery and triggering nuclear processes such as neutron multiplication and tritium production from lithium. At the same time, they will cause significant radiation damage to structural and functional materials, including high-performance steels and superconductors. Therefore, understanding and validating the behavior of these materials is essential for designing robust, long-lasting fusion systems.
Although fusion-specific neutron sources are limited, fission reactors provide accessible, well-characterized neutron spectra ranging from fast (~2 MeV) to thermal (~25 meV). This enables targeted experimental investigations. Such studies include research on radiation damage in structural materials beyond the first wall, helium accumulation and blistering effects in steels, neutron multiplication, tritium breeding in specific blankets, and advanced component degradation, such as that of high-temperature superconductors, under irradiation.
There are experimental opportunities available at various facilities, including the MEDAPP beamline at the FRM II. The MEDAPP beamline offers a fast neutron flux of 10⁹ n/(cm² s) over areas larger than 10 × 10 cm². Despite its relatively moderate flux, the accessibility of MEDAPP makes it attractive for systematic investigations. Complementary neutron scattering techniques, such as wide-angle and small-angle diffraction, enable characterizing radiation-induced defects and helium accommodation at the microstructural level. In addition, material test irradiations in specialized test facilities like the BR2 at SCK•CEN in Belgium can reach fast neutron fluxes exceeding 10¹⁴ n/(cm² s), enabling accelerated neutron damage studies. These already available capabilities for fast fission neutrons provide a powerful foundation for experimental research on fusion materials and tritium breeding.

Speaker: Winfried Petry (FRM II - TUM)

16:10 Database for thermal neutron induced prompt gamma rays

Prompt Gamma Activation Analysis (PGAA) is based on the detection and analysis of gamma rays induced by neutron capture. This versatile nuclear analytical technique started propagating after the 1990s not just because of the difficulties of the spectrum evaluation, but also due to the lack of the proper analytical database. The first comprehensive spectroscopy database with the ambition of reliably supporting chemical analysis for all naturally occurring elements was published in 2004—2007 based on the measurements performed at Budapest. It contains energy and partial gamma-ray production cross section data for all stable elements for 25-100 strongest lines derived from spectra of pure elements, calibrated using stoichiometric compounds and special mixtures. Using this database, an analytical method was also developed to determine the composition from the PGAA spectra. After 20 years of minor upgrades in both the database and the analytical method, the database is ti be upgrade based on the new measurements in FRM2’s strong cold beam with improved statistic.
Besides chemical analysis, the collection of spectra together with the capture-gamma database can be used for many other purposes in the field of nuclear science and industry, e.g. for shielding calculations, nuclear physics etc.

Speaker: Dr Zsolt Revay (PGAA)

16:30 The use of ion beam irradiation to simulate neutron-induced displacement damage in tungsten

Tungsten (W) is considered as a promising plasma-facing material for future fusion reactors. W components will be subjected to an intense flux of 14 MeV neutrons. This will result in creation of radiation defects, production of H, He and transmutation elements. Radiation defects can trap the tritium fuel, posing safety and economic concerns.
MeV heavy ion irradiation is widely used for simulating the displacement damage created by 14 MeV neutrons because it induces dense collision cascades and does not alter the material composition. This contribution will give an overview of the studies performed at IPP Garching over the last decade. It will focus on the influence of irradiation temperature and damage dose in W. The irradiated samples are exposed to a low-flux of low-energy deuterium (D) ions extracted from an ECR plasma at low material temperature (370 K). This allows to decorate the irradiation-induced defects with D without introducing additional damage and deduce the total trap densities. Trapped D concentration profiles are measured using D(3He, p)4He nuclear reaction analysis. The D binding states in the defects are analysed using thermal desorption spectroscopy (TDS). This is accompanied by reaction-diffusion simulations to derive D binding energies with the defects.

Speaker: Mikhail Zibrov (Max-Planck-Institut für Plasmaphysik)

16:50 → 17:10 Coffee

17:10 → 18:10 Session 3

Convener: Christoph Hugenschmidt

17:10 The Effect of Rhenium on Irradiation Induced Defects in W-Re Alloys Studied by Positron Annihilation Spectroscopy

The plasma-facing components in a nuclear fusion reactor have to withstand irradiation by 14 MeV neutrons, which are released in the fusion reaction of deuterium and tritium. A critical requirement of a future fusion reactor will be tritium self-sufficiency. A primary concern of tritium management is the potential for tritium trapping within or diffusion through the first wall of the reactor. Tungsten is considered to be the most suitable plasma-facing material, due to its high melting point, high thermal conductivity and low erosion under fusion reactor operating conditions. In addition to radiation damage, neutron irradiation of tungsten induces nuclear transmutation reactions, resulting in the formation of further elements such as rhenium. This work investigates the effect of rhenium on the defects produced during the irradiation of tungsten. Irradiation with W-ions mimics the radiation damage caused by 14 MeV neutrons and Re-ion irradiation is used to investigate simultaneous rhenium addition and damage creation. Positron annihilation spectroscopy provides a non-destructive, atomic scale resolution measurement of the irradiation damage, as positrons are efficiently trapped in vacancy-type defects. The annihilation radiation of positions and electrons is detected and subsequently analyzed. The Doppler-broadening of the 511 keV annihilation peak reflects the electron momentum distribution at the annihilation site, which provides a measure for the defect concentration in the material. Coincidence Doppler-broadening spectroscopy provides element sensitive measurements of vacancy-type defects. We find that rhenium reduces the defect concentration and/or changes the defect type for irradiation at high temperature.

Speaker: Lisa-Marie Krug (MLZ / TUM)

17:30 Deuterium Desorption from Irradiated Tungsten Studied by In-situ Temperature Dependent Positron Annihilation Spectroscopy

The materials in a nuclear fusion reactor will face extreme conditions of particle bombardment and power load. Tungsten is widely considered the only appropriate material for plasma facing components due to its high melting temperature, good thermal conductivity and low sputter yield. The interaction of ionizing radiation with tungsten will lead to atomic displacements and thus to the formation of lattice defects. The loading of these defects with deuterium, tritium and helium affects mechanical properties and thermal conductivity which are key to the successful operation of a fusion reactor. Furthermore, the extent to which foreign atoms are trapped at defects in tungsten will directly affect the tritium budget of a fusion reactor.

We present an in-situ, temperature dependent, investigation of deuterium desorption from self-ion irradiated tungsten. Positron Annihilation Lifetime Spectroscopy (PALS) allows the measurement of vacancy type defects down to single vacancies as well as the loading of these defects with deuterium. Tungsten samples, which have been irradiated with self-ions and then deuterium loaded, are heated during PALS measurements. Spectra composed of the characteristic lifetimes of different defect types allow identification of the specific trapping locations from which deuterium is desorbed. These data will provide critical benchmarking for rate equation codes which are used to predict tritium transport under fusion reactor conditions.

Speaker: Danny Russell (Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München)

17:50 High-current accelerator-based neutron sources – Fusion materials and testing

The neutron damage of structural materials in fusion reactors is a crucial challenge. Present knowledge of the accumulated neutron doses and neutron fluxes indicates that new materials need to be developed and experimentally proved. For this purpose neutron source facilities for material tests are strongly required. They have to be capable of offering (i) continuous irradiation to get required accumulated dose of neutrons and (ii) pulsed irradiation relevant to test the inertial-energy fusion regime.
High-current accelerator-based neutron sources rely on pulsed proton beams with tens of milliamp proton current and energies of several tens of MeV. This kind of non-fission neutron sources have been developed, and main components have been tested in recent years offering the path to neutron fluences comparable to fission reactors for irradiation and material testing purposes as requested by fusion materials.
We will present and discuss the options of high-current accelerator-based neutrons sources like the HBS project and similar neutron facilities discussed to offer the fusion community access to required neutron beams to develop and test fusion materials e.g. of lead blanket sub-assemblies or breeding blankets, and to solve important challenges in the design, construction and operation of such facilities.

Speaker: Thomas Gutberlet (Forschungszentrum Jülich)

18:10 → 19:10 Dinner

Tuesday 29 July

09:00 → 10:20 Session 4

Convener: Ralph Gilles

09:00 Nuclear fission and fusion power plants: Validating models

Nuclear fission and fusion power plants share many features: complex, often welded structural elements; aggressive environments and service loading; and high safety and economic consequences of structural degradation and failure. Computational modelling of structural performance plays an important role in the safe operation of fission reactors, and fusion plant will be no different.

Much research effort has been expended, both on extending materials and structural modelling over multiple length scales, and on modelling the whole of life, from component manufacture through to final failure in service. This multi-scale, whole life modelling offers the prospect of more reliable and less conservative prediction of component behaviour, with less unpleasant surprises in service.

Modelling is of little use without validation – proof that its predictions match the behaviour of real components. This talk discusses the challenges involved in validation of multi-scale models, via a set of case studies, starting with “conventional” finite element predictions of weld residual stress, and then considering lower length scale techniques that aim to predict microstructure development, such as solid state phase transformation in steels, crystal plasticity , and phase field methods.

Speaker: Michael Smith (The University of Manchester)

09:40 Residual stress determination in structural materials for fusion and fission reactors using neutron diffraction

In structural integrity assessments of components residual stresses play a crucial role as they interact with load stresses during operation and thus directly affect the lifetime of the component. Therefore, reliable and accurate characterization of these stresses is of high relevance in the design of structural components for future fission or fusion reactors. In this respect, neutron diffraction methods have become a key technique for bulk and operando characterization given their unique combination of non-destructive nature and penetration power in comparison to other characterization methods.

The diffractometer STRESS-SPEC is the dedicated instrument for residual stress determination at the German neutron source Heinz Maier-Leibnitz (FRM II). In this contribution we will show two examples of measurements performed at STRESS-SPEC to demonstrate the capabilities of residual stress determination with neutron diffraction for components in nuclear applications. The first example elucidates the stress state in a W-monoblock plasma-facing component (PFC) under high heat-flux (HHF) loads [1], while in the second example the effect of welding in a stainless-steel material earmarked as possible structural material for future GEN-IV fission reactors is investigated [2].

[1] J.-H. You, H. Chae, R. Coppola, W. Gan, H. Greuner, M. Hofmann, S. Roccella, W. Woo, Neutron diffraction measurement of residual stresses in an ITER-like tungsten-monoblock type plasma-facing component, Fusion Engineering and Design 146 (2019) 701–704
[2] P.Agostini, R. Coppola, M. Hofmann, C. Ohms, K. Tucek, Stress distribution in a 316L(N) steel narrow gap TIG model weld for Gen IV nuclear applications, Nuclear Materials and Energy 32 (2022) 101203

Speaker: Michael Hofmann

10:00 Unique capabilities of neutron imaging in analyzing structural components in fusion reactors

Building a fusion reactor places the structural components, particularly the plasma-facing wall, under enormous mechanical and thermal stress while being bombarded by high-energy radiation. Developing and characterizing materials able to withstand these stresses is a crucial step in building and operating a nuclear fusion reactor.
Neutron imaging is a uniquely capable technique for analyzing the materials used in the plasma-facing wall as well as in the structural components. Due to their interaction with the atomic nucleus, neutrons penetrate deeply into these materials and enable the visualization of sub-millimeter-sized pores as well as the distribution of hydrogen in the material.
Using advanced imaging techniques, further contrast modalities can be unlocked. In the case of plasma-facing walls and structural components, additional information about the microstructure can be extracted by mapping the scattering under ultra-small angles which provides insight into the distributions of porosities in the sub-micrometer regime and the formation of cracks. By also analyzing the energy-dependent transmission, the grain and stress distribution, as well as phase transitions, are mapped.
In our contribution, we will illustrate the versatility and power of neutron imaging in materials research in general and fusion research in particular using selected examples.

Speaker: Tobias Neuwirth

10:20 → 10:50 Coffee

10:50 → 11:50 Session 5

Convener: Michael Smith (The University of Manchester)

10:50 Neutron irradiation micro-structural effects in standard and B-alloyed EUROFER97 steel

The low activation ferritic/martensitic steel EUROFER97 (9 Cr, 0.12 C, 1.08 W, 0.12 Ta, 0.48 Mn, 0.2 Ta Fe bal wt%) is currently considered as the reference structural material for the fabrication of the first-wall, directly facing the burning plasma, in future fusion reactors. Small-angle neutron scattering (SANS) has been utilized to characterize the micro-structural effects of neutron irradiation in this steel, both in its standard composition and doped with B contents up to 5600 appm; such B contents are introduced by mechanical alloying to artificially increase the content of helium, produced by transmutation, to levels representative of the fusion reactor. The SANS measurements have been carried out at ILL-Grenoble and at FRM II-Garching, always utilizing an external magnetic field of at least 1 T and un-irradiated EUROFER97 reference samples. In standard EUROFER97 samples irradiated at HFR Petten, at 250°C and 300°C for doses up to 16 dpa (displacement per atom) an increase of the SANS cross-sections with the dose is observed, tentatively attributed to the evolution of micro-voids distributions, with volume fractions in the order of 10-3 and average radii of a few Å. In B-alloyed EUROFER97, HFR neutron irradiated to 16 dpa at various temperatures, a huge increase of the SANS cross-section and a strong decrease of the magnetic SANS component are observed, both enhanced increasing the irradiation temperature: these effects are attributed to the increased production of helium bubbles and to the occurrence of empty halos in the martensitic matrix, following the dissolution of the large B carbides. All these results will be discussed with reference to TEM observation of the same samples investigated by SANS.

Speaker: Roberto Coppola (ENEA-Casaccia)

11:10 Advanced characterization of tungsten-steel multi materials for plasma facing components produced with additive manufacturing techniques.

AM has a high potential to become one of the leading manufacturing methods in the nuclear industry, especially for complex components for fission and fusion reactors that are difficult to machine with conventional techniques and are not considered for mass production, but only in a limited number. Among proposed Plasma Facing Components (PFCs) materials in fusion reactors, tungsten (W) is the leading first-wall armor candidate to cover and shield the structural Reduced-Activation Ferritic-Martensitic (RAFM) steel structural components of the reactor core. However, joining two very dissimilar materials like steel and tungsten implies a number of challenges. Laser Powder Bed Fusion (LPBF) or Laser Directed Energy Deposition (L-DED) processes are envisioned to produce such parts, however, the properties of alloys produced with these techniques can strongly differ from those produced by conventional methods, which in turn can affect their performance in the context of nuclear applications. Therefore, it is crucial to understand the possible formation of minor crystalline phases, as well as the internal residual stresses in as-built components or columnar/anisotropic grain structures. Minor phases, such as retained austenite grains and intermetallic precipitates in the steel, as well as intermetallic phases at the W-steel interface affect the mechanical, corrosion and irradiation resistance and can act as nucleation sites for radiation damage.
We aim to gain fundamental understanding of the microstructure and morphology development in such materials produced using AM, with a focus on the interface between steel and tungsten. This is realized by using multimodal imaging of the produced samples. μXRD and μXRF microscopy performed at beamlines of SLS and DESY synchrotrons provided the insight into formation of the minor phases and chemical composition with spatial resolution. Neutron Bragg Edge Imaging performed at the POLDI instrument of SINQ neutron source allowed to get insight into texture and residual strains in the vicinity of the interface. Additionally, we are developing methodology for operando synchrotron and neutron studies of AM processes, which includes development of a new infrastructure for operando studies of laser-based AM. The results of the ex-situ advanced characterization, as well as the first results from the commissioning of the operando infrastructure will be presented.

Speaker: Malgorzata Makowska

11:30 Effect of laser beam shaping on the crystallographic texture and residual stress distribution of 316L stainless steel manufactured using Laser Powder Bed Fusion

Laser Powder Bed Fusion (PBF-LB) has attracted significant attention in aerospace, automotive, and biomedical applications due to its highly flexible and near-net-shape fabrication capabilities for complex structures. While PBF-LB overcomes the limitations of conventional manufacturing methods by enabling lightweight and functionally integrated designs, traditional Gaussian laser-based L-PBF suffers from low productivity and high residual stresses due to small melt pools, rapid cooling rates, and steep thermal gradients. Laser beam shaping techniques, such as ring-mode lasers, offer improved energy distribution, enhanced melt pool stability, and potentially higher build rates. However, their effects on residual stress, microstructural texture, and mechanical properties remain unclear. This study systematically investigates the influence of Gaussian versus ring-mode lasers on the as-built microstructure (e.g., dislocation structures, elemental segregation), crystallographic texture, and residual stress in 316L austenitic stainless steel using advanced characterization techniques, including electron backscatter diffraction (EBSD) and neutron diffraction. The findings aim to optimize process parameters for superior mechanical performance, providing critical insights for the potential application of beam-shaped PBF-LB on fusion energy and nuclear industrial components.

Speaker: Dr Weimin Gan (Helmholtz-Zentrum Hereon)

12:00 → 13:00 Lunch

13:00 → 18:00 FRM II Guided Tours (via Bus Transfer)

18:00 → 19:00 Dinner

19:00 → 21:00 Poster Session and Beer

19:00 Advanced characterization of high temperature structural materials for fusion reactor environments

High temperature structural materials are of key importance for many traditional applications such as gas turbines for stationary power plants and jet engines, rocket engines, components for the chemical and oil & gas industry but also for fusion reactors under development and future applications. Materials used in fusion reactors are exposed to severe conditions, including intense thermal loads, high neutron flux, radiation damage and hydrogen implantation. These extreme environments highlight the urgent need for the development and improvement of advanced structural materials that can endure such harsh factors. To address this challenge, it is essential to characterize and understand both known and new materials in terms of their microstructure, defect structures, mechanical properties and damage correlations. This comprehensive approach allows researchers to identify the relationships between the material’s microstructural features and its performance under extreme conditions. In this contribution, several examples will be presented to illustrate these correlations and highlight the significance of advancing material science in the context of fusion technologies. It will be shown how the changing chemical composition of intermetallics or irradiated W affects their fracture toughness, how hydrogen leads to an embrittlement of superalloys, how lattice misfits of two-phase materials can be precisely analysed by diffraction techniques, and how small-scale testing allows to measure mechanical properties locally and of small specimens. Therefore, various characterization techniques such as mechanical testing at different length scales, (high resolution transmission) electron microscopy, atom probe tomography, neutron and high energy X-ray diffraction and thermal desorption spectroscopy are employed. These examples should illustrate how studying the microstructure-mechanical properties-correlation enables us to get a deeper understanding of the used materials and how they can be further improved and new alloys can be developed to ensuring the integrity and longevity of fusion reactors and to avoid CO2 emissions for our future society.

Speaker: S. Neumeier

19:00 Chemical Analysis with Neutrons at MLZ

Chemical analysis with neutrons offers a range of methods for element determination. The sample matrix can be characterized as well as the smallest traces. In certain cases, neutron activation analysis (NAA) reaches detection limits down to the ppt/ppq (weight) range. Prompt Gamma Activation Analysis (PGAA) enables a completely non-destructive measurement of the sample bulk. A combination of PGAA and neutron tomography (PGAI-NT) enables spatially resolved analyses. PGAA and NAA are to a certain extent complementary and can be also combined effectively to significantly increase the number of detectable elements. Further possibilities are neutron depth profiling (NDP) and cyclic in-beam activation analysis (cib-NAA). Chemical analysis with neutrons is a useful analytical toolbox for the development of novel materials that require a specific composition or a certain grade of purity. For example, it can be used in the development of fusion reactors or new concepts in nuclear fission technology. We present the capabilities of these methods at MLZ.

Speaker: Dr Christian Stieghorst (TUM / FRM II)

19:00 Effects of Hydrogen Loading on Lattice Defects in Nickel-Based Superalloys Studied by Positron Annihilation

Positron annihilation spectroscopy (PAS) is a highly sensitive technique for the detection and characterization of vacancy-like defects in crystalline solids, making it an ideal tool for studying radiation damage and hydrogen-related degradation processes in materials. In this work, we employ PAS to investigate the interaction between hydrogen and open-volume defects in hydrogen-loaded nickel-based superalloys. Pure nickel samples, annealed and loaded with hydrogen, were used as a reference.
Depth-resolved Doppler broadening spectroscopy (DBS) of the positron electron annihilation line allows for the differentiation between (near-) surface and bulk phenomena, while coincidence DBS (CDBS) provides insights into the chemical environment of the positron annihilation sites. The depth-resolved experiments were conducted using the Setup for Low-energy Positron Experiments (SLOPE) of the positron research group at TUM. By variation of the pressure and temperature hydrogen loading was applied to systematically study the interaction of hydrogen with defect structures in nickel-based superalloys. First results will be presented — especially obtained by the depth-resolved methods — to visualize and quantify microstructural changes induced by hydrogen.
This study demonstrates the unique capability of positron annihilation techniques in benchmarking defect models and improving the understanding of hydrogen effects in materials. Such methods are of particular importance to study the (temperature dependent) influence of hydrogen as well as the irradiation-induced defects in materials relevant for nuclear and fusion applications.

Speaker: Kilian Porth (Nepomuc)

19:00 How can Sample Environment help

We present an overview of the possibilities of the sample environment groups equipment at MLZ. Sample Environment can offer a wide range of parameters for measuring your samples. Low and high temperatures, magnetic fields, pressure, to name few, as well as combinations thereof. Feel free to prompt us with your special demands and we can discuss the different options.

Speaker: Dr Alexander Weber (Forschungszentrum Jülich GmbH)

19:00 In situ high temperature sample environment @ MLZ

The Heinz Maier-Leibnitz Zentrum (MLZ) is a leading centre for cutting-edge research with neutrons and positrons. As part of the user operation at the MLZ, the Sample Environment (SE) group assists in the installation and operation of complex SE equipment on instruments, providing experimental support to MLZ scientists as well as design, manufacturing, maintenance and repair of equipment.
One of the key aspects is the provision of high temperature (HT) sample environment of different configurations. Furthermore, the option of combining high temperature with other techniques is possible, such as HT and gas supply, HT in combination with magnetic fields or HT and mechanical stress.
In this poster, you will have the opportunity to learn and discuss about the capabilities and technical features of the MLZ sample environment equipment suitable for the study of materials in the fields of fusion reactors and nuclear energy.

Speaker: Dr Manuel Suarez Anzorena (Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München (TUM))

19:00 Neutron grating interferometry – an advanced neutron imaging method

Neutron imaging is an established technique to non-destructively map the spatial distribution of the elemental composition and density of bulk materials in the sub-millimeter region.
This is achieved by measuring the spatial distribution of the neutron attenuation coefficient in a 2D radiography or 3D computed tomography.
By adding an intensity modulation to the beam additional contrast modalities can be accessed such as phase contrast in the differential phase contrast image (DPCI) or (ultra-) small-angle scattering contrast in the dark field image (DFI).
The most common way to introduce the aforementioned intensity modulation to a neutron imaging beam is a Talbot-Lau grating interferometer.
The DFI contrast contains information of scattering under small angles in form of the slit-smeared real-space correlation function and the total scattering probability.
The correlation function of the sample system is probed at a specific correlation length which can be adjusted depending on the neutron wavelength and position of the sample.
This enables to extract the average (ultra-) small-angle scattering contrast with the spatial resolution of typical neutron imaging instrumentation.
The materials used for plasma-facing components of fusion plasmas are typically dense and consist of heavy elements. This severely limits the applicability of many established techniques of non-destructive testing, especially X-Ray methods. However, neutron radiation is uniquely suited here due to it primarily interacting with the nuclei and thus showing high penetration and good contrast over a large range of elements.
Neutron grating interferometry (nGI) is exceptionally suited to combat the challenges of non-destructive testing and material characterization as it adds information about micro-meter sized porosities and other defects to the pure attenuation signal.
We will showcase the possibilities of this technique on composite tungsten-copper components intended as divertor material showing pores of varying size.
With this poster we want to give an overview over the technique of Talbot-Lau nGI and the methods applied to obtain quantitative results from small-angle scattering with DFI as well as highlight limitations.

Speaker: Simon Sebold (MLZ)

19:00 Neutron powder diffraction at instruments SPODI, ERWIN and FIREPOD

In this contribution, the capabilities of the three powder diffractometers—SPODI, ERWIN, and FIREPOD—are presented in the context of potential studies on fusion-relevant materials. Neutron diffraction enables the determination of phase fractions in multiphase systems and allows for the refinement of structural parameters for each constituent phase. Furthermore, microstructural features can be identified and analyzed. Compared to X-ray diffraction, neutron diffraction offers advantages in the investigation of coarse-grained materials due to superior grain statistics.

Speaker: Markus Hoelzel

19:00 Rotating Quantum Droplets in Low Dimensions

Quantum droplets formed by rubidium, lithium, and sodium atoms have been analyzed in this paper by using a logarithmic-type Gross-Pitaevskii equation. Variational methods and numerical techniques were employed to solve nonlinear equations. A disk-shaped BEC was analyzed to assess its radial evolution. Additionally, free expansion under rotation of the BEC was studied. Compression and expansion around the equilibrium radius were observed in different scenarios, predicting self-confinement, which implies the formation of quantum droplets originating from a BEC state. Briefly, the physical aspects of the system and the possible formation of Bose-nova are discussed.

Speaker: Mr Kevin Hernandez (Universidad de El Salvador)

19:00 The MEDAPP instrument as test site for fast neutron radiation damage

At the FRM II medical application instrument MEDAPP, fast neutrons are available for radiation therapy and radiation hardness testing of electronic components and materials. In a unique set-up, thermal neutrons from the reactor core are converted to fast neutrons by fission of uranium-235 and transported through the beam tube with direct sight on the fission source.
With optional filtering, three neutron spectra are available at MEDAPP. The fast fission spectrum for medical applications is filtered with a thermal filter and has a mean energy of 1.9 MeV and a total flux of 3.2e8 n/(cm² sec) at reference position in the irradiation room. The maximum neutron energy of the fast spectrum is at around 10 MeV. When the thermal filter is removed a mixed thermal and fast fission spectrum with a significant intermediate component is available. In addition, the converter can be removed entirely for irradiation with thermal neutrons from the reactor core. While information on the filtered fast fission spectrum is available from both measurements and simulations, the last two are only available from simulations.
The medical beam is well characterized in terms of flux and the separation of the neutron and gamma component and a well-established dosimetry method is available for reference measurements at the irradiation position.
Furthermore, the large available field size of around 30 cm x 20 cm can be limited with a multi leaf collimator to adjust the irradiated region of the sample.
With the broad range of energies and especially the fast neutron beam, MEDAPP can serve as test side for radiation hardness testing and characterization of radiation damage due to fast neutrons. With neutrons from fusion having higher energies that are not available at MEDAPP, the applicability will depend on the location of the investigated material in the fusion reactor. Thus, MEDAPP holds great potential for the investigation of radiation damage due to fast neutrons and can substitute higher energy neutron sources respecting the limitation due to the available neutron energy.

Speaker: Lucas Sommer

19:00 The Small-Angle Neutron Scattering Instrument SANS-1 at MLZ

The Instrument
SANS-1, a joint project of the Technical University of Munich and the Helmholtz-Zentrum Hereon, is a classical pinhole-geometry small-angle neutron scattering (SANS) instrument optimized for a broad range of applications, particularly in strongly correlated electron systems and materials science. Designed as a general-purpose tool, SANS-1 offers a wide dynamic Q-range with tunable resolution and supports full polarization analysis.
A chopper-based TISANE (Time-Resolved Small-Angle Neutron Scattering) setup provides microsecond time resolution, enabling real-time kinetic studies. For in-situ and in-operando measurements under extreme conditions, SANS-1 features a spacious, modular sample area equipped with a heavy-duty six-axis goniometer. This setup accommodates a wide range of complex sample environments—including superconducting magnets, high-temperature furnaces, and a custom quenching dilatometer—handling loads up to 1000 kg and dimensions of up to 125 cm × 250 cm with sub-millimeter and sub-degree precision.
The detector system at SANS-1 is housed in a 22-meter-long vacuum tube with an inner diameter of approximately 2.4 meters. The main detector (1 m × 1 m), consisting of 128 position-sensitive ³He tubes (1 m active length, 8 mm × 8 mm resolution), is mounted off-center relative to the beam axis and can be laterally shifted by up to 0.5 meters. This, combined with the ability to tilt the detection plane, significantly extends the accessible Q-range—particularly beneficial for time-resolved and in-operando experiments—and reduces anisotropic solid-angle effects and parallax artifacts. Extensive shielding minimizes background noise and edge scattering, optimizing signal-to-noise ratios.
Scientific Applications and Industrial Relevance
SANS-1 probes structural inhomogeneities in bulk materials on mesoscopic length scales (10–3000 Å), making it a vital tool for materials science, soft matter, and magnetism research. Applications range from polymers, biological macromolecules, and colloids to porous materials, ceramics, and metallic alloys, including precipitates and composite structures. Its advanced capabilities and flexible design make SANS-1 highly relevant for both fundamental research and industrial applications, particularly in the context of energy materials and fusion-related studies.

Speaker: Dr Gilles Wittmann (ADVMAT)

19:00 X-Ray Diffraction as a Tool for Structure Analysis of Functional Materials including Fusion Materials

X-ray diffraction (XRD) analysis is an important method for characterizing materials in fusion reactors, particularly for understanding their microstructure and properties under the extreme conditions of fusion. This method can be applied to assess the effects of radiation damage, high temperatures, and other factors on materials such as steel and composites. These materials are used in the first reactor wall, the reactor roof, and other components. It is important for XRD experiments that the samples do not have high radioactivation to enable sample handling. Literature on tungsten showed the significance of understanding the radiation damage of fusion materials causing defects, cracking and microstructural changes inside the materials inside the fusion reactor.[1,2]
In the Advanced Materials group XRD measurements are used to investigate formed phases during synthesis via conventional melting, chemical reaction or additive manufacturing. The phase and element composition are important to know e.g., during the steel production, different elements like Mn, Cr and Ni are mixed in the steel to enhance mechanical properties and corrosion resistances, due to the formation of different intermetallic phases and alloys. In addition, investigations on the crystal size plays a crucial role in precipitation hardening materials, too large particles can agglomerate or cause fracture points along their crystal borders. Further information can be obtained from XRD measurement at elevated temperatures with our high temperature sample stage, it is possible to take XRD patterns below, at and above phase transitions or reactions. XRD can reveal changes in grain size, dislocation density, and other microstructural features caused by irradiation and other factors. Residual stress studies are of great importance to investigate materials that tend to cracking. Besides measuring at elevated temperatures, also measurements can be acquired during loading and unloading of alloys with hydrogen an interesting field in fusion research, which can lead to changes in the phase composition or if the hydrogen gets intercalated to changes in the lattice parameters, the diffusion process of the loading and unloading can be tracked with our hydrogen detection device. Lastly, XRD measurements are used for pre-characterization and optimization of large samples (~cm3) for neutron scattering experiments.
[1] Wielunska B. D., Dissertation, Characterization of Radiation Damage in Tungsten, Technical University Munich, Munich, 2020.
[2] Papadakis D., Manios E., Mergia K. Metals 2025, 15, 2, 172.

Speaker: Stefan Engel (Heinz Maier-Leibnitz Zentrum (MLZ))

Wednesday 30 July

09:00 → 10:20 Session 6

Convener: Winfried Petry (FRM II - TUM)

09:00 Consequences of neutron irradiation of fusion plasma-facing materials and components

Plasma-facing materials and components are the interface between the fusion plasma and the reactor’s material structure. In a burning fusion reactor, they are directly exposed to the neutrons from the D-T fusion reaction. Neutron-exposed materials undergo changes in their composition due to transmutation reactions, both towards light elements (H, He) and heavy isotopes. In addition, neutron-induced collision cascades displace atoms in the solid material. As a consequence, the first wall materials are not only activated, but also modified in their material properties, e.g. thermal conductivity. For some effects like the erosion by sputtering or hydrogen isotope retention, the consequences of neutron irradiation are not well known. In the fusion environment, the consequences of neutron irradiation need to be considered for the prediction of the lifetime of plasma-facing components, as this directly influences safety and the economy of a fusion reactor. This presentation will describe altered material properties and methods to study the behavior of first wall components after neutron irradiation.

Speaker: Prof. Christian Linsmeier (Forschungszentrum Jülich GmbH, Institute of Fusion Energy and Nuclear Waste Management – Plasma Physics, Jülich, Germany)

09:40 Neutron Imaging of Nuclear Fuel Cladding Tubes

The employment of neutron radiography and tomography allow non-destructive visualization of hydrogen distribution in cladding tubes due to the strong neutron attenuation by hydrogen compared to the weak attenuation by zirconium. The excellent spatial resolution of neutron radiography and sensitivity enable a precise characterization of hydride morphology and hydrogen gradients in 2D and 3D. Experiments allow for hydrogen studies under various thermal and mechanical loading conditions, but also for hydrogen diffusion tests within different cladding tubes and different metallic structure directions. Post-test hydrogen quantification can always be performed additionally via carrier gas hot extraction (CGHE) and validated against the neutron imaging results using calibration samples of a known hydrogen content.

Zirconium alloys are widely employed as cladding materials for nuclear fuel rods due to their low neutron absorption cross-section, high corrosion resistance, and adequate mechanical strength during and after reactor operation. However, during operation, hydrogen is absorbed by cladding corrosion processes involving reactor coolant. The hydrogen influence on the claddings is investigated by means of neutron imaging referring to different scenarios: loss-of-coolant accident (LOCA) conditions and dry storage similar conditions. The LOCA scenario includes a rapid temperature rise that causes ballooning of the cladding tubes and may lead to bursting. Further, the influence of secondary hydriding phenomena on the applicability of cladding embrittlement criteria is tested during this scenario. The formation of ballooning regions, cladding wall thinning and hydrogen enrichments can be revealed by 3D neutron tomographies, where local hydrogen concentrations up to 1800 wt.ppm were measured. On the other hand, dry storage related hydrogen effects arise after operation upon cooling, when the hydrogen solubility limit is exceeded and hydrogen precipitates. These hydrides have a profound impact on the mechanical integrity of the cladding, particularly due to their orientation, morphology, and distribution. In dry storage conditions, hydrogen redistribution and hydride precipitation continue to evolve over time, influenced by temperature gradients and residual mechanical stresses. Understanding this behavior is essential for long-term safety assessments of SNF in interim storage.

This paper presents the diverse neutron imaging possibilities to investigate zirconium based nuclear fuel cladding tubes with regard to hydrogen/ hydrides.

Speaker: Sarah Weick (KIT)

10:00 Time-of-Flight Neutron Imaging for Material Identification and Characterization

Neutron imaging is a non-destructive, spatially resolved technique that is frequently employed to analyze samples for which x-rays have a low penetration capability or provide poor contrast. While in many cases even complex structures can be mapped using a broad neutron energy spectrum without energy-resolution (white beam imaging), some sample properties only provide sufficient contrast at selected neutron energies. In addition, energy-resolution is frequently required to obtain quantitative information on a sample. Energy-resolved neutron imaging is even capable of probing information that is completely inaccessible to x-ray techniques, such as the atomic composition down to the isotope level.

For neutrons with energies up to the thermal region, velocity selectors and monochromators can be used to generate monoenergetic neutron beams. However, these components reduce the neutron flux significantly. A much more efficient approach to obtain energy-resolved information is to use the time-of-flight (ToF) technique at a pulsed beamline. The ToF approach is also viable for the higher energy neutrons where velocity selectors and monochromators stop working but which are required for example to measure the atomic composition via neutron resonance imaging. While ToF is a standard technique for neutron diffraction, most neutron imaging detectors do not provide the necessary timing resolution. In recent years, the development of different types of event-mode imaging detectors that provide significantly better timing resolution increased the use of ToF also in the imaging community.

This presentation will focus on the material properties that can be probed with ToF neutron imaging, showcasing different measurements where the techniques have been used. This includes the mapping of crystallographic information via Bragg-edge imaging, magnetic fields via polarized neutron imaging, and atomic composition of light and heavy elements via fast and epithermal neutron imaging. While for example the atomic composition measurements have already been used for of nuclear fuel characterization, the presentation should mainly provide a basis for discussions on new ways in which ToF neutron imaging can be used to support fusion and nuclear applications.

Speaker: Alexander Wolfertz (TUM FRM2)

10:20 → 10:50 Coffee

10:50 → 11:50 Session 7

Convener: Rudolf Neu (MPI for Plasma Physics)

10:50 Neutron and X-ray Diffraction as a Tool to Study High-Temperature Materials for Fusion Applications

For the fusion of hydrogen isotopes, plasma temperatures of around 100 million °C are required. Although the plasma does not come into direct contact with the reactor walls, the surrounding materials are subjected to extreme thermal loads, high neutron flux, and hydrogen implantation. Consequently, advanced structural materials must be developed to withstand these harsh conditions.
Diffraction techniques—both neutron and synchrotron-based—are well suited to investigate candidate materials in situ and non-destructively under relevant environmental conditions. Especially, the high penetration depth of neutrons allows bulk studies for industrial applications. In this study, we demonstrate how diffraction can be employed to gain insight into the behavior of high-temperature materials that may be used in fusion reactors.
Hydrogen incorporation into the crystal lattice can be tracked indirectly by monitoring changes in the lattice parameter, as interstitial hydrogen increases the spacing between metal atoms. Furthermore, irradiation-induced defects such as vacancies and dislocations influence peak shapes and broadening, and can likewise be characterized via diffraction. Also, microstrains induced by the hydrogen can be tracked by diffraction. [1]
We present results on the recently developed polycrystalline superalloy VDM® Alloy 780, studied under hydrogen exposure and elevated temperatures. In situ diffraction experiments were performed to monitor hydrogen effusion during continuous heating. The observed decrease in lattice parameters confirms hydrogen effusion, indicating reversible hydrogen uptake. [2]
Complementary tensile tests with a self-developed testing machine (up to 100 kN and 1300°C) revealed the influence of hydrogen on the mechanical properties. Hydrogen-charged specimens exhibited reduced elongation at fracture compared to uncharged reference samples. Subsequent annealing at 500 °C for various durations led to a partial recovery of ductility, further validating the reversibility of hydrogen embrittlement. These findings highlight the potential of diffraction methods to support the development and qualification of structural materials for future fusion energy systems.
[1] O. Nagel, M. Fritton, A. Mutschke, R. Gilles, S. Neumeier, Scr. Mater. Volume 260, 2025.
[2] M.Fritton, A. Mutschke, O. Nagel, M. Hafez-Haghighat, B. Gehrmann, S. Neumeier, R. Gilles, J. Alloys Compd. Volume1014, 2025.

Speaker: Massimo Fritton

11:10 Pulsed Low Energy Positron Beams for Fusion Materials

Pulsed low-energy positron beams of variable energy are powerful tools for non-destructive defect depth profiling of small open volume defects such as vacancies, vacancy-clusters, dislocations, grain boundaries, internal surfaces, and voids in materials relevant to fusion and fission with positron annihilation lifetime spectroscopy (PALS) [1].

The Pulsed Low-Energy Positron System (PLEPS) at the NEPOMUC positron source at the MLZ in Garching (FRM-II), developed and operated by the University of the Bundeswehr München, is a pioneering instrument for one-dimensional depth-resolved defect profiling with PALS [1].

In this contribution we describe the operational principles of PLEPS in its current configuration. Selected applications of PLEPS in characterizing irradiation damage in fusion and fission materials are then presented to highlight the unique capabilities of our pulsed beam technology [2-4]. Finally, we provide an outlook on future developments.

References:
[1] W. Egger, in Proc. Int. School of Physics “Enrico Fermi” CLXXIV (2010) 419. DOI:10.3254/978-1-60750-647-8-419.
[2] M. Zibrov et al., Nucl. Mater. Energy 23 (2020) 100747
[3] Q. Yang et al., J. Nucl. Materials 571 (2022) 154019
[4] V. Krsjak et al., Journal of Materials Science & Technology 105 (2022) 172-181

Speaker: Werner Egger (Universität der Bundeswehr München)

11:30 A Scanning Positron Microscope for 3D defect mapping

Positron annihilation lifetime spectroscopy (PALS) is a powerful tool for defect investigation at the atomic scale in a wide variety of materials. To investigate inhomogeneous defect distributions with PALS, for example in the vicinity of fatigue cracks or irradiated wall materials, it is necessary to employ a monochromatic pulsed positron beam of variable energy, with a diameter in the range of 1 µm and a pulse width of 150 ps FWHM.
$\quad$To this aim, the Scanning Positron Microscope (SPM) [1-2] was developed and built at the Universität der Bundeswehr München. To overcome the limit of low count-rates in the laboratory the SPM has been transferred to the intense positron source NEPOMUC at the MLZ in Garching (FRM II) where it will be operated as a user facility.
$\quad$A sophisticated beam preparation, including multiple remoderation steps, is needed to reach a lateral resolution in the micro-meter range. The SPM finally prepares a monochromatic pulsed positron beam suited for position resolved PALS measurements [3]. By varying the implantation energy and the position of the beam over an area of 1x1 mm$^2$ 3D-mapping of defect distributions down to ~250 nm below the surface becomes possible for the first time.
$\quad$This contribution will provide a comprehensive overview of the SPM, with a focus on its future applications.

References:
[1] A. David et al., Phys. Rev. Lett. Volume 87, 067402 (2001)
[2] G. Kögel et al., Appl. Surf. Sci., Volume 116, Pages 108-113, (1997).
[3] J. Mitteneder, PhD Thesis UniBwM (2025).

Speaker: Johannes Mitteneder

11:50 → 12:50 Lunch

14:00 → 18:30 Excursion to Flugwerft Schleißheim (via Bus Transfer)

18:30 → 22:00 Conference Dinner at Schlosswirtschaft Schleißheim

Thursday 31 July

09:00 → 10:20 Session 8

Convener: Christian Linsmeier (Forschungszentrum Jülich GmbH, Institute of Fusion Energy and Nuclear Waste Management – Plasma Physics, Jülich, Germany)

09:00 Development of a Scalable Platform for Fusion Neutron Irradiation and Next Generation Nuclear Applications

In the 2nd half of the 20th century, research fission reactors were deployed across the world in the form of OPAL and TRIGA designs, among others. The profound positive effect on nuclear research into materials science, training, fundamental particle physics, and nuclear medicine still endures today. However, many of those old reactors have already come to the end of their life with very few still running and even fewer being built to replace those lost. Historically, there has been little resource put towards the development of a fusion-based research reactor equivalent as most attention is aimed at the noble goal of demonstrating the feasibility of fusion energy.

Our focus over the last few years has been on making neutrons available in an economical, reliable, and scalable form factor. Many of the old positive impact areas in science and engineering are still relevant for a fusion-based equivalent, but many new applications and next-generation opportunities are unlocked by this novel platform.
More specifically, the qualification of fusion reactor components and tritium breeding materials, medical radionuclide production, and nuclear waste transmutation are just a few of the most pressing challenges that can be addressed.

Speaker: Tom Wallace-Smith

09:40 Assmement of Bunker Suitability for a Fusion Neutron Source using Serpent 2

Fusion research has gained significant ground in Bavaria as the Masterplan “Kernfusion und neuartiger Kerntechnologien” moves forward and presents the goal of significantly pushing nuclear technology. In addition, TUM held a symposium on Novel Nuclear Technologies with the clear recommendation to further study high energy fusion neutrons.
Thus, it is important to have a detailed understanding of the effects of such highly energetic 14.1 MeV fusion neutrons that carry most of the energy from a fusion reaction. To study such effects, e.g., interaction with materials or the knowledge of cross sections, the TUM Center for Nuclear Safety and Innovation (TUM.CNSI) consider buying and commissioning a fusion neutron generator. A prerequisite to installing such a neutron source however, includes ensuring proper shielding is in place to protect the users from the fast neutrons, gamma rays emitted from the device, below dosage limits set by the legal framework. This talk presents how the Monte Carlo code Serpent 2 is used to design a suitable bunker for a fusion neutron source. For a given neutron source rate, the thickness and type of concrete, moderator, and absorber materials are assessed. It is found that a bunker at one of the TUM.CNSI laboratories would be feasible.

Speaker: Christopher Ehrich (Technical University of Munich)

10:00 Neutron computed tomography and liquid contrast agents for the examination of materials

Neutron computed tomography penetrates many metals easily while showing good contrast for many light elements, often showing contrast pretty much complementary to X-rays.
Neutron CT also provides the possibility of using liquid contrast agents containing Gadolinium that has extreme contrast for neutrons, and can be used to detect cracks and capillary properties of materials. In the past, Carbon-fiber based plasma delimiters have been examined for IPP, and delamination between the carbon fiber matrix and the copper base was shown. The talk will show these previous examinations and other examples for the use of neutron CT.

Speaker: Dr Burkhard Schillinger (MLZ /FRM II, TU München)

10:20 → 10:50 Coffee

10:50 → 11:50 Session 9

Convener: Tom Wallace-Smith (Astral Systems)

10:50 Development of non-planar, HTS, tabletop-sized-stellarator coils

Stellarators are a leading concept for magnetic confinement of plasmas -- usually with the goal of enabling terrestrial fusion power plants. At small scales, they are also attractive for fundamental science, such as studies of non-neutral plasmas or matter-antimatter plasmas; this is the goal of EPOS (Electrons and Positrons in an Optimized Stellartor), part of the APEX Collaboration, which aims to study low-temperature (eV-scale) e+e- plasmas confined in compact (~10-liter), ultra-high vacuum (UHV) traps using modest magnetic fields (up to 1-3 T). Stellarator magnetic configurations are typically achieved with coil shapes that are significantly non-planar, in addition to requiring sophisticated numerical optimization methods. The non-planarity presents challenges for the design and development of HTS stellarator coils, due to HTS tapes’ anisotropic bending properties and critical current dependence. To help tackle these challenges, our group and others have developed numerical tools for incorporating winding angle optimization into stellarator coil design -- i.e., adjusting winding pack orientation along the coil path to stay within HTS strain limits [1]. The coil shapes themselves can also be adjusted to be more HTS-compatible, while still together generating a confining magnetic field with the desired properties [2]. Having used these tools to calculate that small (10-cm-scale) HTS coils based on 3-mm ReBCO tape are indeed feasible for EPOS, we then designed winding frames for test coils, which we conductively cool in UHV down to 20 K and energize [3]. This contribution will present results from the test coil campaign, design choices for the EPOS experiment, and plans for higher-field test coils that can further inform HTS stellarator coil development.

[1] “A Non-planar ReBCO Test Coil with 3D-printed Aluminum Support Structure for the EPOS Stellarator.” P. Huslage, et al. arXiv:2505.08488

[2] “Strain Optimization for ReBCO High-Temperature Superconducting Stellarator Coils in SIMSOPT.” P. Huslage, et al. Journal of Plasma Physics. 2025;91(2):E71. doi:10.1017/S0022377825000224

[3] “Winding angle optimization and testing of small-scale, non-planar, high-temperature superconducting stellarator coils.” P Huslage et a, Supercond. Sci. Technol. 37 085010 (2024). DOI 10.1088/1361-6668/ad5382

Speaker: E. V. Stenson (MPI for Plasma Physics)

11:10 A compact levitated dipole trap for the confinement of electron-positron pair plasma

Over the past ~40 years, many theoretical papers have predicted the remarkable stability properties of magnetized pair plasmas – largely due to the mass symmetry of the opposite charge species. However, there is a nearly complete lack of experimental validation. The mission of the APEX (A Positron-Electron eXperiment) collaboration is to confine and study a low-temperature, long-lived, magnetically-confined electron-positron pair plasma, thereby opening a new frontier in laboratory physics [1]. To achieve quasineutral plasma conditions, positrons, provided by the reactor-based positron source NEPOMUC (NEutron induced POsitron source MUniCh), are collected in a series of linear traps, then transferred to one of two compact (~10 liter) magnetic traps: an optimized, quasi-axisymmetric stellarator (EPOS, currently under construction), or a levitated dipole (APEX-LD). Focusing on the latter device, the requirements for this application posed a number of challenges for experiment design and engineering (including, e.g., the need for the compact [R=7.5 cm] superconducting "floating coil" [F-coil] to repeatedly make and break thermal contact with cryogenically cooled components in a vacuum environment; excitation of the persistent current in the F-coil, followed by long-duration, feedback-stabilized levitation; and a demand for robustness to repeated quenches and possible mechanical shocks). A comparable number of experiment design and engineering solutions have been found and implemented, and APEX-LD has successfully started operation, enabling initial electron plasma experiments. This talk will outline the design of the APEX-LD systems, then present the highlights of the experiment commissioning (including, e.g., efficient persistent current induction to ~0.5 T on-axis, levitation times in excess of three hours with a stability of $σ_z=18$ µm [2], and "gentle" quenching of the no-insulation [NI] rare-earth barium copper oxide [ReBCO] high-temperature superconducting [HTS] coil). Finally, it will describe results from first experiments (i.e., visualization of electron injection) and next steps for future injection of cold, dense pulses of positrons.

[1] Stoneking M.R., et al. (2020) A new frontier in laboratory physics: magnetized electron–positron plasmas. Journal of Plasma Physics, 86(6):155860601
[2] Card, A., et al (2024) FPGA-Stabilized Magnetic Levitation of the APEX-LD High-Temperature Superconducting Coil. IEEE Transactions on Applied Superconductivity, 34.9, pp. 1-9

Speaker: Alexander Card (MLZ (NEPOMUC))

11:30 Fusion's Fast Neutrons: Measurement, Management and Tritium Breeding

Nuclear fusion offers the promise of a sustainable, low-carbon energy future. However, the success of this technology hinges on our ability to understand and manage the intense neutron environment within a fusion reactor. Unlike fission systems, fusion reactors generate high-energy neutrons (approximately 14.1 MeV) that interact with structural materials, leading to activation and potentially enabling tritium breeding through neutron-lithium reactions.
This talk provides an overview of the role of neutron balance in fusion reactors, with a focus on its use for tritium breeding and the potential extraction of energy to power a steam turbine. Special emphasis is placed on the metrology of measuring neutron fluxes in fusion-relevant environments. As part of earlier work, the author conducted high-precision flux wire measurements at the McMaster Nuclear Reactor (MNR), which serve as a benchmark for characterizing the neutron field. This well-established fission reactor diagnostic technique may also be adapted for metrological tasks in fusion reactors, such as ITER and IFMIF-DONES.
The presentation will outline the principles of neutron flux measurements and potential adaptations for fusion contexts. It will also illustrate possible applications, including validating blanket module simulations, supporting materials testing campaigns, and assessing tritium breeding efficiency.

Speaker: Peter Reichel (Center for Nuclear Safety and Innovation)

11:50 → 12:50 Lunch