Electron Beam Facility Research Articles

Repair of heat load damaged plasma–facing material using the wire-based laser metal deposition process

Due to its unique properties tungsten is a promising candidate as plasma-facing-material (PFM) in future nuclear fusion reactors. Tungsten features an exceptionally high melting point, high thermal conductivity, low tritium inventory and comparatively low erosion rate under plasma loading [1]. But given the extreme loads on the PFM during operation of a fusion reactor, the lifetime of plasma-facing components (PFC)s is limited. Currently, it is planned to replace damaged PFCs when they reach the end of their service life. However, the lifetime of PFCs could be increased by in situ repair using additive manufacturing technology (AM) in the form of direct-energy-deposition (DED). The wire–based laser metal deposition process (LMD-w) meets several necessary conditions for operation in the vessel and could be used for performing such in situ repairs.It was investigated if the LMD-w process is able to heal thermal induced surface cracks and roughening by remelting the substrate during deposition of tungsten. For this purpose, tungsten samples of 12 × 12 × 5mm3, which later served as substrate plates for the LMD-w experiments, were treated with combined steady-state and transient thermal loads in the electron beam facility JUDITH 2. These samples were brazed to a copper cooling structure and exposed to 105 thermal shocks of 0.5 ms duration and an intensity of Labs = 0.55 GW m−2 (FHF = 12 MW s0.5 m−2) at a base temperature of Tbase = 700 °C. This way, edge localized mode (ELM) like thermal load damage was induced on the tungsten samples. On these samples, different LMD-w and laser remelting process strategies were performed. Subsequently, these samples were analyzed, and it was examined that the healing of the pre-damaged substrate material was successful. In parallel, the laser remelting process was modeled in a thermal transient finite element method(FEM) simulation in order to gain an insight into the temperatures prevailing in the material during the process.

Development and manufacturing of beryllium-armoring ITER enhanced heat flux FW toward series production in China

ITER’s enhanced heat flux (EHF) first wall (FW) provides thermal shielding to the other components behind it and limits its plasma boundary, consequently bearing high surface heat loads up to 4.7 MW m−2. China developed the EHF FW technologies in steady stages by making small mock-ups, semi-prototypes and a full-scale prototype (FSP), working toward series production at the Southwestern Institute of Physics. All the key technologies for bimetallic diffusion bonding, welding and assembly have been fully qualified. The Be armor tile size effects on thermal-fatigue performance have been evaluated using a pulsed high heat flux test with an EMS-400 electron beam facility. It was found that both the Be/CuCrZr bonding and its thermal-fatigue life are highly dependent on the tile size, and 12 × 12 mm2 Be tiles are acceptable for the required performance, either as individual tiles or in castellation by cutting larger ones. Small-scale mock-ups with such Be tiles survived 16 000 thermal cycles at 4.7 MW m−2, while EHF FW fingers with 16 × 16 mm2 Be tiles demonstrated unstable performance. In contrast, only BE tiles larger than 24 × 12 mm2 showed reliable diffusion bonding with the CuCrZr heat sink by hot isostatic pressing and consequently should be castellated into smaller ones. The manufacturing of the FSP finger goes through complex thermal cycles, using CuCrZr alloys in age-strengthening plus cold-rolling states, enabling it to maintain its tensile strength to the level of 285 MPa and its mean grain size less than 100 µm. The pipe welding for finger pairing and its assembly with the central beam are demonstrated, including enabling welding to be carried out twice for repair in a narrow space. The FSP showed good finger alignment, dimensional control and reliable vacuum tightness without any blockage of cooling channels.

Finite Element Analysis and Experimental Verification of Thermal Fatigue of W-PFM with Stacked Structure

As the prime candidate for plasma-facing materials (PFM), the response of tungsten (W) to thermal shock loads is an important research topic for future fusion devices. Under heat loads, the surface of tungsten plasma-facing materials (W-PFM) can experience thermal damage, including brittle cracking and fatigue cracks. Therefore, exploring solutions for thermal damage of W-PFM remains one of the current research focuses. We propose a novel approach to mitigate thermal radiation damage in PFM, namely, the stacked structure W-PFM. The surface thermal stress distribution of the stacked structure W-PFM under heat loads was simulated and analyzed by the finite element method. As the foil thickness decreases, both the peak thermal stresses in the normal direction (ND) and rolling direction (RD) decrease. When the thickness decreases to a certain value, the peak thermal stress in the RD decreases to about 1384 MPa and no longer decreases; while the peak thermal stress in the ND approaches 0 MPa and can be neglected. In the range of approximately 5–100 mm, the accumulated equivalent plastic strain decreases sharply as the thickness decreases; in other thickness ranges, it decreases slowly. Thermal fatigue experiments were conducted on the stacked structure W composed of W foils with different thicknesses and bulk W using an electron beam facility. The samples were applied with a power density of 30 MW/m2 for 10,000 and 20,000 pulses. The cracks on the surface of the stacked structure W extended along the ND direction, while on the surface of bulk W, besides the main crack in the ND direction, a crack network also formed. The experimental results were consistent with finite element simulations. When the pulse number was 10,000, as the thickness of the W foil decreased, the number and width of the cracks on the surface of the stacked structure W decreased. Only four small cracks were present on the surface of stacked structure W (0.05 mm). When the pulse number increased to 20,000, the plastic deformation and number of cracks on the surface of all samples increased. However, the stacked structure W (0.05 mm) only added one small crack and had the smallest surface roughness (Ra = 1.536 μm). Quantitative analysis of the fatigue cracks showed that the stacked structure W-PFM (0.05 mm) exhibited superior thermal fatigue performance.

Development of a high current electron beam facility for compact accelerator neutron source target thermal tests

Target thermal capabilities are one of the major key points for CANS (Compact Accelerator-based Neutron Source) developments. Indeed, high energy (few MeV) and high average current (few tens of mA) proton or deuteron beams are required to produce high thermal neutron flux of 101³ n.cm⁻2.s⁻1 or greater. The targets must therefore absorb and dissipate a high thermal power. In order to make progress on their designs without deuteron or proton beams, we developed a compact electron beamline based on an Electron Cyclotron Resonance (ECR) source that permits testing of targets under relevant thermal conditions at power densities up 3 kW. cm⁻2.

Neutron irradiation effects on the low cycle thermal fatigue performance of first wall mock-ups

For the first wall (FW) of ITER, beryllium will be the plasma facing material and has to sustain high thermal, particle and neutron loads. In order to assess the synergistic effects of thermal and neutron loads in total ten Be-armored FW normal heat flux (NHF) mock-ups were produced consisting of two Be flat tiles each joined via hot isostatic pressing (HIP) to a CuCrZr heat sink and a steel support structure by different manufacturing routes to assess the most promising ones. Five of them were neutron irradiated, two at Centrum Výzkumu Řež in Czech Republic and three in the High Flux Reactor at NRG in the Netherlands. The remaining mock-ups were kept as reference. All flat-tile mock-ups had two Be-tiles and were exposed to cyclic steady state heat loads in the electron beam facilities JUDITH 1 and 2 up to a maximum power density of 3.75 MW/m2, in order to find the damaging threshold. A screening step using 1 MW/m2 was performed after finishing each loading step and after failure for direct comparison and detection of any deterioration caused by the cycling. Despite being still in the early development phase of Be joining, all mock-ups sustained the cycling up to at least 2.75 MW/m2 and clear differences in the performance of irradiated vs. non-irradiated mock-ups were observed.

Dark matter search with the BDX-MINI experiment

BDX-MINI is a beam dump experiment optimized to search for Light Dark Matter produced in the interaction of the intense CEBAF 2.176 GeV electron beam with the Hall A beam dump at Jefferson Lab. The BDX-MINI detector consists of a PbWO$_4$ electromagnetic calorimeter surrounded by a hermetic veto system for background rejection. The experiment accumulated $2.56 \times 10^{21}$ EOT in six months of running. Simulations of fermionic and scalar Dark Matter interactions with electrons of the active volume of the BDX-MINI detector were used to estimate the expected signal. Data collected during the beam-off time allowed us to characterize the background dominated by cosmic rays. A blind data analysis based on a maximum-likelihood approach was used to optimize the experiment sensitivity. An upper limit on the production of light dark matter was set using the combined event samples collected during beam-on and beam-off configurations. In some kinematics, this pilot experiment is sensitive to the parameter space covered by some of the most sensitive experiments to date, which demonstrates the discovery potential of the next generation beam dump experiment planned at intense electron beam facilities.

Evaluation of heat removal property in W/Cu/RAFM steel joint by using electron beam facility

• The durability of the W/Cu/JLF-1 joint sample fabricated by brazing was confirmed by performing steady-state and repetitive heat loading experiments. • The W/Cu/JLF-1 showed excellent heat removal performance under the steady-state heat loading. • A degradation of the heat removal performance was confirmed during the repetitive heat loading. • The delamination which could lead to the barrier of efficient heat transfer was confirmed after the repetitive heat loading of ∼6.0 MW/m 2 . A reliable technique for creating joints between tungsten (W) and Reduced Activated Ferritic/Martensitic (RAFM) steel with a pure-copper (Cu) interlayer (W/Cu/RAFM steel) has been explored for developing the heat removal component in the baffle and dome of a divertor. The first joint sample of W/Cu/RAFM steel was fabricated by using a brazing technique described in our previous work. In this work, to evaluate the heat removal property, a joint sample was subjected to a steady-state and a repetitive heat loading test with an electron beam facility (ACT2). In the steady-state heat loading test, a step-wised static heat load with ∼0.7, ∼1.0, ∼1.9, ∼2.7, ∼3.6, ∼4.4 and ∼6.0 MW/m 2 was applied to the joint sample. The temperatures on the W and RAFM steel showed a linear increasing tendency, as a function of the heat loading value. Also, in the repetitive heat loading test, a 30 s pulse width of 100 cycles was applied with a maximum heat loading value of ∼2.8 and ∼6.0 MW/m 2 . The obvious temperature excursion, while increasing the heat cycles, was confirmed at ∼6.0 MW/m 2 . After the heat loading, a major crack in the vicinity of the interface between the W and Cu was confirmed. This crack led to the degradation of the heat removal performance over ∼6.0 MW/m 2 .

Improving the mechanical properties and thermal shock resistance of W-Y2O3 composites by two-step high-energy-rate forging

Yttria dispersion-strengthened tungsten composites with enhanced thermal and mechanical properties were fabricated by powder metallurgical methods in this work. The processing route involves the doping of yttria particles in the tungsten powders by liquid-liquid doping process, followed by hot pressing and two-step high-energy-rate forging (HERF). The microstructure, thermal conductivity, mechanical properties and thermal shock resistance of the hot-pressed W-Y2O3 composites and the HERF processed W-Y2O3 composites were comparatively investigated. The bending strengths of the HERF processed W-Y2O3 composites increased significantly compared with that of the hot-pressed W-Y2O3 billets. The HERF W-Y2O3 material presented a ductile behavior even at room temperature with a maximum flexural strain of 4.4% and a yield stress of 2324.5 MPa. At 100°C, the material also exhibits evident plasticity with a flexural strain of 5.9% and the yield stress is up to 1931.9 MPa. The thermal conductivity of the W-Y2O3 composite is 170 W/mK, which is close to the deformed pure W. The thermal shock response of the HERF processed W-Y2O3 is also evaluated by applying edge-localized mode like high heat loads (100 pulses) with an energy density of 0.16–1 GWm−2 at various temperatures in an electron beam facility. The thermal shock results indicate that the cracking threshold of the HERF processed W-Y2O3 at RT is between 0.55 GWm−2 and 0.66 GWm−2. The cracking threshold of the HERF W-Y2O3 at 100°C and above is higher than 1 GWm−2.

Progress in additive manufacturing of pure tungsten for plasma-facing component applications

In the present paper, recent progress regarding additive manufacturing (AM) of pure tungsten (W) by means of laser powder bed fusion (LPBF) is discussed. In this context, several aspects are highlighted: The influence of the raw powder material characteristics on the resulting W part quality is briefly discussed, examples for complexly shaped additively manufactured W lattice structure samples are shown, the application of an additively manufactured W structure as preform for a tungsten-copper (W-Cu) composite is illustrated and thermal shock experiments on additively manufactured bulk W samples with the electron beam facility JUDITH 2 are described. The latter demonstrates that W material consolidated by means of LPBF is capable of surviving intense thermal shock loads. This is an encouraging result indicating that the thermal performance and stability of W fabricated by means of LPBF is comparable to that of conventionally fabricated W which in turn implies that the further investigation of additively manufactured W as candidate material with regard to applications in highly loaded plasma-facing components (PFCs) of future magnetic confinement thermonuclear fusion devices can be considered worthwhile.

Sustainable lubrication: low molecular weight PTFE micro-particles as extreme pressure additives for heavy duty grease applications

Purpose The purpose of this paper is to formulate heavy-duty lithium complex grease using low molecular weight poly tetra fluoro ethylene (PTFE) micro-particles as extreme pressure (EP) additive manufactured by E-beam scissoring and ultra-high speed grinding process of pre-sintered PTFE scrap. Design/methodology/approach Lithium complex grease is formulated with PTFE micro-particles, and optimum treat rate was studied by standard bench tests by ASTM D 2266 and IP-239 for tribological properties and compared with commercially available Molybdenum Di sulphide (Moly)-based lithium complex grease. The performance of the grease was further evaluated by a cyclic load test at varying speeds and loads to simulate the operational field conditions. Findings The lithium complex PTFE grease was manufactured using PTFE micro-particles as EP additive. The PTFE micro-particles dispersed in the lithium complex grease significantly improve the anti-wear performance and load bearing properties. Further, when the product was tested under a cyclic load conditions on standard tribological bench test against commercially available Moly lithium complex grease, shows stable anti-wear properties and reduced coefficient of friction. Originality/value The low molecular weight PTFE micro-particles, manufactured in the in-house electron beam (E-beam) and ultra-high speed micronizer facility from a pre-sintered PTFE scrap has been used as EP additive for grease applications for the first time. The results on the cyclic load tests indicate significant performance improvement in retaining the anti-wear and friction properties. Thus, value addition is done in formulating superior performance grease and evaluating under cyclic load conditions similar to field operating conditions and also in creating value added additives by converting the pre-sintered PTFE scarp which is environmental hazard due to poor biodegradability, creating a cyclic economy and a sustainable concept.

Numerical Research of Design Solutions for the Bending Magnets of the Electron Beam Facility GESA-1M

Numerical Research of Design Solutions for the Bending Magnets of the Electron Beam Facility GESA-1M

High heat flux testing of newly developed tungsten components for WEST

In preparation of the production of the actively cooled tungsten targets for the lower divertor of WEST (W -for tungsten- Environment in Steady-state Tokamak), the qualification of suppliers is done by exposing small-scale mock-ups to cyclic high heat flux tests in the electron beam facility JUDITH 1 at Forschungszentrum Jülich. Thereby, the small-scale mock-ups are based on the ITER design, consisting of 7 monoblocks mounted on a CuCrZr cooling tube and connected via a soft Cu-interlayer.The results presented herein focus on the high heat flux test results of two mock-ups produced by AT&M in China. The testing was performed by thermal cycling at 10 MW/m2 and 20 MW/m2 with a maximum of 1200 cycles at 10 MW/m2 followed by 500 cycles at 20 MW/m2 without obvious damage formation.The qualification is supported by subsequent hardness tests and microstructural analyses. The latter focus on local variation of tungsten recrystallization and macro-crack formation and deformation induced changes in the heat sink materials.

Conceptual design and heat transfer performance of a flat-tile water-cooled divertor target

The divertor target components for the Chinese fusion engineering test reactor (CFETR) and the future experimental advanced superconducting tokamak (EAST) need to remove a heat flux of up to ∼20 MW m−2. In view of such a high heat flux removal requirement, this study proposes a conceptual design for a flat-tile divertor target based on explosive welding and brazing technology. Rectangular water-cooled channels with a special thermal transfer structure (TTS) are designed in the heat sink to improve the flat-tile divertor target’s heat transfer performance (HTP). The parametric design and optimization methods are applied to study the influence of the TTS variation parameters, including height (H), width (W*), thickness (T), and spacing (L), on the HTP. The research results show that the flat-tile divertor target’s HTP is sensitive to the TTS parameter changes, and the sensitivity is T > L > W* > H. The HTP first increases and then decreases with the increase of T, L, and W* and gradually increases with the increase of H. The optimal design parameters are as follows: H = 5.5 mm, W* = 25.8 mm, T = 2.2 mm, and L = 9.7 mm. The HTP of the optimized flat-tile divertor target at different flow speeds and tungsten tile thicknesses is studied using the numerical simulation method. A flat-tile divertor mock-up is developed according to the optimized parameters. In addition, high heat flux (HHF) tests are performed on an electron beam facility to further investigate the mock-up HTP. The numerical simulation calculation results show that the optimized flat-tile divertor target has great potential for handling the steady-state heat load of 20 MW m−2 under the tungsten tile thickness <5 mm and the flow speed ≥7 m s−1. The heat transfer efficiency of the flat-tile divertor target with rectangular cooling channels improves by ∼13% and ∼30% compared to that of the flat-tile divertor target with circular cooling channels and the ITER-like monoblock, respectively. The HHF tests indicate that the flat-tile divertor mock-up can successfully withstand 1000 cycles of 20 MW m−2 of heat load without visible deformation, damage, and HTP degradation. The surface temperature of the flat-tile divertor mock-up at the 1000th cycle is only ∼930 °C. The flat-tile divertor target’s HTP is greatly improved by the parametric design and optimization method, and is better than the ITER-like monoblock and the flat-tile mock-up for the WEST divertor. This conceptual design is currently being applied to the engineering design of the CFETR and EAST flat-tile divertors.

Single pi ^0 production off neutrons bound in deuteron with linearly polarized photons

The quasifree overrightarrow{gamma } drightarrow pi ^0n(p) photon beam asymmetry, varSigma , has been measured at photon energies, E_gamma , from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49^circ to 148^circ . In this kinematic region, polarization observables are sensitive to contributions from the varDelta (1232) and N(1440) resonances. The extracted values of varSigma have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID and Bonn–Gatchina analyses; while a revised SAID fit, including the new varSigma measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict pi ^0n photoproduction observables, based on fits to published data in the channels pi ^0p, pi ^+n and pi ^-p.

Radiation sterilization of Honey and Honey-Alginate Wound Dressing from Stingless Bee (Tetragonula biroi) Collected from Sta. Maria, Laguna, Philippines

This study was conducted to determine the effect of radiation sterilization on alginate wound dressing containing honey from the Philippine stingless bee, Tetragonula biroi. Our results show that a radiation dose of 30 kGy did not affect the antibacterial property of honey against Staphylococcus aureus. Electron-beam irradiation did not produce significant alterations in the physicochemical properties (pH, total soluble solids, and flavonoids); however, the total phenolics was significantly increased in honey with higher irradiation doses. Demonstrating that irradiation can be applied to honey with negligible physicochemical effects, honey was incorporated in alginate and exposed to a sterilization dose of 25 kGy using an electron beam facility. Irradiation did not affect the physicochemical properties (pH, moisture content, gel fraction, moisture vapor transmission rate (MVTR), and fluid handling capacity) of the honey alginate wound dressing (HAWD). The perspectives for the potential use of irradiated HAWD as a natural product-based substitute for commercial wound care products may be considered.

Studying of in-vessel component materials under high power electron beam and steady-state plasma loads

Combined tests of tungsten mock-ups with thermocyclic test in the electron beam facility with the load up to 50 MW/m² and subsequent irradiation with steady-state plasma load up to 1 MW/m² in PLM device have been carried out to simulate a material degradation under loads expected in a fusion reactor. Cracks of 1–5 microns and more have been formed on the surface of the tungsten during e-beam test. Melted layer observed in the area of e-beam hot spot load. Plasma load led to a formation of nanostructured layers on the surface.

Studying in-vessel component materials under heat and plasma loads relevant to fusion installations

The results of studies of materials under extreme thermal and plasma-beam loads, carried out to justify existing technological solutions in the design of thermonuclear reactors, are presented. The study of materials under plasma and beam loads and the intensifying heat transfer of in-vessel cooled components of fusion devices is reported. Tests of limiter and divertor mock-ups irradiated with high heat fluxes in electron beam and plasma facilities are described. Methods for cooling in-vessel components using advanced approaches with dispersed gas-liquid flow for heat removal, including at loads of up to 15 MW/m2 have been developed and tested.

Strain life analysis of the first wall mock up under ITER-relevant heat flux conditions

Abstract The ITER first wall (FW) panels consist of plasma facing Be tiles, the CuCrZr alloy heat sink, and the stainless steel structural material. A copper layer of 1−2 mm is used between the Be tile and the CuCrZr for stress compensation. The results of cyclic high heat flux (HHF) tests employing an electron beam facility indicate that the failure/weak spot usually occurs at the joint corners between the Be tile and the copper layer. 3-D FEM (finite element method) thermo-mechanical analysis utilizing ANSYS software has been conducted to simulate the performance of a FW mock up (MU) under cyclic HHF test. The elastoplastic analysis results indicate that the copper layer is most sensitive to plastic deformation, and eventually the most risky location for failures. With the ANSYS strain-life fatigue module, based on the strain-life relation of copper from the ITER handbook, the fatigue life of the MU was predicted via FEM simulation. The results show that, when loaded with 2 MW/m², the small scale MU and the semi-prototype MU have a predicted life time of 12,220 cycles and 10,834 cycles, respectively. Although the shortest life time is located at the upper surface of copper which is joined to the Be tile, the major part of the copper has a life time of the same scale, which lies in the range of 10000–30000 cycles. When loaded with 2.5 MW/m², the life times of the MUs are 7432 cycles and 7343 cycles, respectively.

Thermal shock behavior of potassium doped and rhenium added tungsten alloys

High ductile-to-brittle transition temperature, recrystallization-induced embrittlement, and neutron-irradiation-induced embrittlement are potential drawbacks related to the mechanical properties of tungsten (W) for plasma facing materials of fusion reactor divertors. To improve the mechanical properties, resistance to recrystallization and neutron irradiation, W materials modified by potassium doping and alloying by rhenium have been developed. In this paper, thermal shock behaviors of these W materials under high heat flux tests were investigated, which simulated an edge localized mode of plasma occurring in fusion reactors as a transient event. The thermal shock tests were performed with an electron beam facility, JUDITH 1, and post-mortem analyses to evaluate the damage caused by the thermal shock tests were carried out.

Development of the GridPix detector quad

We have developed the gaseous GridPix detector quad made from four Timepix3 chips. To provide the required charge amplification a Micromegas-like grid has been deposited on the chip surface by MEMS technology. The grid holes are precisely aligned to the chip pixels and have a pitch of 55 μm while the high time resolution of 1.56 ns of the Timepix3 chip enables the precise reconstruction of each individual primary ionization electron in the detector gas. The chip is coated by a high resistivity protection layer to prevent damage by unavoidable discharges. Using the GridPix technology, the full position of the ionization cloud is measured. As such the ultimate resolution of a gaseous detector is achieved, mainly limited by diffusion. The quad has all services located under the detection surface. Multiple quads can be simply joined together to create a large readout plane of a TPC. In this paper we show details about the construction of the quad and the preliminary results from a recent test beam experiment at the ELSA electron beam facility in Bonn.