Pub Date : 2025-02-03DOI: 10.1016/j.nme.2025.101888
M.G. Burke , F. Scotti , S.L. Allen , W.H. Meyer , A. Holm , M. Zhao , A.G. McLean , M. Fenstermacher , H.Q. Wang , R. Wilcox
This paper presents experimental measurements of the location of the impurity flow stagnation point in the scrape-off-layer (SOL) of a tokamak plasma. Coherence imaging of carbon-2+ emission (465 nm) is used to track the main-chamber impurity velocity of DIII-D L-mode plasmas with out of the divertor. The flow stagnates near the top or crown of the plasma when an open divertor (no baffling) is used. In contrast, with matched conditions and using a divertor with baffling, the flow stagnates near the outer divertor leg (X-point). The poloidal emission is hollow, peaking near the divertor legs, in the open configuration. In contrast, in the closed configuration, the emission is flat through most of the main-chamber SOL. Changing divertor dissipation from attached to detached conditions had only a minor effect on the main-chamber midplane impurity velocity. Numerical simulations using the multi-fluid edge transport code UEDGE including cross-field drifts show qualitative agreement with the open divertor experimental result.
{"title":"The effect of divertor closure on the impurity stagnation point in detached L-mode discharges on DIII-D","authors":"M.G. Burke , F. Scotti , S.L. Allen , W.H. Meyer , A. Holm , M. Zhao , A.G. McLean , M. Fenstermacher , H.Q. Wang , R. Wilcox","doi":"10.1016/j.nme.2025.101888","DOIUrl":"10.1016/j.nme.2025.101888","url":null,"abstract":"<div><div>This paper presents experimental measurements of the location of the impurity flow stagnation point in the scrape-off-layer (SOL) of a tokamak plasma. Coherence imaging of carbon-2+ emission (465 nm) is used to track the main-chamber impurity velocity of DIII-D L-mode plasmas with <span><math><mrow><mi>B</mi><mo>×</mo><mo>∇</mo><mi>B</mi></mrow></math></span> out of the divertor. The <span><math><msup><mrow><mi>C</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></math></span> flow stagnates near the top or crown of the plasma when an open divertor (no baffling) is used. In contrast, with matched conditions and using a divertor with baffling, the <span><math><msup><mrow><mi>C</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></math></span> flow stagnates near the outer divertor leg (X-point). The <span><math><msup><mrow><mi>C</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></math></span> poloidal emission is hollow, peaking near the divertor legs, in the open configuration. In contrast, in the closed configuration, the <span><math><msup><mrow><mi>C</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></math></span> emission is flat through most of the main-chamber SOL. Changing divertor dissipation from attached to detached conditions had only a minor effect on the main-chamber midplane impurity velocity. Numerical simulations using the multi-fluid edge transport code UEDGE including cross-field drifts show qualitative agreement with the open divertor experimental result.</div></div>","PeriodicalId":56004,"journal":{"name":"Nuclear Materials and Energy","volume":"42 ","pages":"Article 101888"},"PeriodicalIF":2.3,"publicationDate":"2025-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143403221","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-01DOI: 10.1016/j.nme.2025.101892
Z.H. Huang , L.W. Yan , K.Y. Yi , Na Wu , W.J. Chen , W.C. Wang , Yu He , J. Chen , J. Cheng , W. Zhao , J.M. Gao , L. Nie , Z.B. Shi , X.Q. Ji , W.L. Zhong
Newly flush-mounted Langmuir probe arrays are fabricated and applied in the HL-3 tokamak to investigate its advanced divertor physics such as snowflake and tripod divertors. Three sets of flush probe arrays are installed on toroidal ports 4, 10 and 18. Each port has 43 × 4 = 172 probe tips, which are composed of 43 triple and single probe arrays. Each array consists of 4 tips with the same major radius and height. A total of 516 CFC (carbon fiber composite) tips with diameter of dp = 4 mm are mounted at 3 ports. Their minimum spatial separation is 1.8 cm poloidally, while temporal resolution for ion saturation currents is 1 μs. The toroidal separation of a triple probe is 1.8 ∼ 3.8 cm or 10.2 ∼ 14.8 cm. It gradually increases with major radius. A novel design of ceramic isolation ring with a labyrinth can ensure reliable electrical insulation between the CFC tip and the divertor target plate where plasma dust and impurities are continuously deposited into their gaps due to long experimental operation. A large spring washer improves the heat conduction from each tip through a ceramic insulator into a cooled divertor copper plate. Every probe body is embedded into a divertor plate then brazed to a copper wire to ensure good electrical connection, and finally fixed on a stainless-steel support. Forty-three signal wires at the same toroidal angle are combined into a manifold copper tube to vacuum feedthrough, which can dramatically shield noise and resist the high baking temperature of 300 °C. Moreover, the discharge monitoring and mode conversion between the triple and single probes could be freely performed via a remote-control workstation. The first application results indicate that the target probe arrays can measure highly temporal plasma parameters, including electron temperature and density, particle and heat fluxes in H-mode discharges on HL-3 tokamak. The tripod divertor configuration has been confirmed by the new flush probe arrays.
{"title":"The first application of flush probe arrays on HL-3 tokamak","authors":"Z.H. Huang , L.W. Yan , K.Y. Yi , Na Wu , W.J. Chen , W.C. Wang , Yu He , J. Chen , J. Cheng , W. Zhao , J.M. Gao , L. Nie , Z.B. Shi , X.Q. Ji , W.L. Zhong","doi":"10.1016/j.nme.2025.101892","DOIUrl":"10.1016/j.nme.2025.101892","url":null,"abstract":"<div><div>Newly flush-mounted Langmuir probe arrays are fabricated and applied in the HL-3 tokamak to investigate its advanced divertor physics such as snowflake and tripod divertors. Three sets of flush probe arrays are installed on toroidal ports 4, 10 and 18. Each port has 43 × 4 = 172 probe tips, which are composed of 43 triple and single probe arrays. Each array consists of 4 tips with the same major radius and height. A total of 516 CFC (carbon fiber composite) tips with diameter of <em>d</em><sub>p</sub> = 4 mm are mounted at 3 ports. Their minimum spatial separation is 1.8 cm poloidally, while temporal resolution for ion saturation currents is 1 μs. The toroidal separation of a triple probe is 1.8 ∼ 3.8 cm or 10.2 ∼ 14.8 cm. It gradually increases with major radius. A novel design of ceramic isolation ring with a labyrinth can ensure reliable electrical insulation between the CFC tip and the divertor target plate where plasma dust and impurities are continuously deposited into their gaps due to long experimental operation. A large spring washer improves the heat conduction from each tip through a ceramic insulator into a cooled divertor copper plate. Every probe body is embedded into a divertor plate then brazed to a copper wire to ensure good electrical connection, and finally fixed on a stainless-steel support. Forty-three signal wires at the same toroidal angle are combined into a manifold copper tube to vacuum feedthrough, which can dramatically shield noise and resist the high baking temperature of 300 °C. Moreover, the discharge monitoring and mode conversion between the triple and single probes could be freely performed via a remote-control workstation. The first application results indicate that the target probe arrays can measure highly temporal plasma parameters, including electron temperature and density, particle and heat fluxes in H-mode discharges on HL-3 tokamak. The tripod divertor configuration has been confirmed by the new flush probe arrays.</div></div>","PeriodicalId":56004,"journal":{"name":"Nuclear Materials and Energy","volume":"42 ","pages":"Article 101892"},"PeriodicalIF":2.3,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143174243","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-31DOI: 10.1016/j.nme.2025.101883
Mounir Alfazzaa , Federica Pappalardo , Andrea Campos , Gilles Cartry , Marco Minissale , Céline Martin
The impact of grain orientation and surface temperature on helium bubble growth at tungsten surfaces exposed to low-pressure helium plasmas was investigated by analyzing the nanoholes formed at the surface. Polycrystalline tungsten samples were exposed to a 2 Pa RF plasma at 400 W and 79 eV positive ion bombardment energy. Through detailed SEM imaging before and after plasma exposure and a developed image analysis protocol, we assessed quantitatively the size and density of helium bubbles that have burst on the surface upon plasma exposure. The results demonstrate a clear temperature dependence, with surface bubble density and size increasing at higher temperatures, and a dependence on grain orientation, with the (111) orientation giving slightly larger and denser surfaces of burst bubbles.
{"title":"Grain orientation and temperature dependences of bubbles at tungsten surfaces upon helium plasma exposure","authors":"Mounir Alfazzaa , Federica Pappalardo , Andrea Campos , Gilles Cartry , Marco Minissale , Céline Martin","doi":"10.1016/j.nme.2025.101883","DOIUrl":"10.1016/j.nme.2025.101883","url":null,"abstract":"<div><div>The impact of grain orientation and surface temperature on helium bubble growth at tungsten surfaces exposed to low-pressure helium plasmas was investigated by analyzing the nanoholes formed at the surface. Polycrystalline tungsten samples were exposed to a 2<!--> <!-->Pa RF plasma at 400<!--> <!-->W and 79<!--> <!-->eV positive ion bombardment energy. Through detailed SEM imaging before and after plasma exposure and a developed image analysis protocol, we assessed quantitatively the size and density of helium bubbles that have burst on the surface upon plasma exposure. The results demonstrate a clear temperature dependence, with surface bubble density and size increasing at higher temperatures, and a dependence on grain orientation, with the (111) orientation giving slightly larger and denser surfaces of burst bubbles.</div></div>","PeriodicalId":56004,"journal":{"name":"Nuclear Materials and Energy","volume":"42 ","pages":"Article 101883"},"PeriodicalIF":2.3,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143343831","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-31DOI: 10.1016/j.nme.2025.101891
T. Wauters , G.J.M. Hagelaar , R.A. Pitts
The ITER re-baseline proposes changing the first wall material from beryllium to tungsten and incorporating a boronization system to mitigate plasma operation risks associated with tungsten. This system aims to deposit a 50 nm boron coating on plasma facing surfaces by fuelling diborane with a carrier gas (He, H2, or D2) in a glow discharge, based on the extensive experience from present devices. This paper analyzes the optimal number and distribution of anodes and gas injection locations for achieving a uniform boron coating in ITER. Using Monte Carlo simulations of diborane molecules in the ITER glow discharge plasma, the study examines the spatial distribution of diborane ionization and dissociation reactions, for different anode and gas injection configurations, neutral pressure, and hydrogen versus helium carrier gas concentration. The glow discharge plasma backgrounds are obtained by adapting an existing axisymmetric glow model to simulate helium–hydrogen gas mixtures. The simulation results, initially conducted with a maximum of 2 anodes, are scaled to represent a realistic anode configuration for the ITER equatorial plane. Key findings include that a low hydrogen content in helium, achieved with 5 % diborane in the carrier gas, and a low total pressure yields the best uniform boron deposition. However, thinner layers are expected where ports cannot accommodate additional anodes. Uniform gas injection points, including at the high field side, and separation of gas injection points from anodes are crucial for uniform coatings. These modeling efforts support the design of the ITER boronization system and justify expanding the ITER GDC hardware to include more anodes and gas feed points. Despite the widespread use of boronization in modern tokamaks, boron layer uniformity and its impact on plasma performance remains under-researched, highlighting the need for dedicated experiments and model benchmarking against results from current devices.
{"title":"Modeling input to the ITER glow discharge boronization system design","authors":"T. Wauters , G.J.M. Hagelaar , R.A. Pitts","doi":"10.1016/j.nme.2025.101891","DOIUrl":"10.1016/j.nme.2025.101891","url":null,"abstract":"<div><div>The ITER re-baseline proposes changing the first wall material from beryllium to tungsten and incorporating a boronization system to mitigate plasma operation risks associated with tungsten. This system aims to deposit a 50 nm boron coating on plasma facing surfaces by fuelling diborane with a carrier gas (He, H<sub>2</sub>, or D<sub>2</sub>) in a glow discharge, based on the extensive experience from present devices. This paper analyzes the optimal number and distribution of anodes and gas injection locations for achieving a uniform boron coating in ITER. Using Monte Carlo simulations of diborane molecules in the ITER glow discharge plasma, the study examines the spatial distribution of diborane ionization and dissociation reactions, for different anode and gas injection configurations, neutral pressure, and hydrogen versus helium carrier gas concentration. The glow discharge plasma backgrounds are obtained by adapting an existing axisymmetric glow model to simulate helium–hydrogen gas mixtures. The simulation results, initially conducted with a maximum of 2 anodes, are scaled to represent a realistic anode configuration for the ITER equatorial plane. Key findings include that a low hydrogen content in helium, achieved with 5 % diborane in the carrier gas, and a low total pressure yields the best uniform boron deposition. However, thinner layers are expected where ports cannot accommodate additional anodes. Uniform gas injection points, including at the high field side, and separation of gas injection points from anodes are crucial for uniform coatings. These modeling efforts support the design of the ITER boronization system and justify expanding the ITER GDC hardware to include more anodes and gas feed points. Despite the widespread use of boronization in modern tokamaks, boron layer uniformity and its impact on plasma performance remains under-researched, highlighting the need for dedicated experiments and model benchmarking against results from current devices.</div></div>","PeriodicalId":56004,"journal":{"name":"Nuclear Materials and Energy","volume":"42 ","pages":"Article 101891"},"PeriodicalIF":2.3,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143422084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-31DOI: 10.1016/j.nme.2025.101885
A. Antony , L. Carbajal , T.D. Rognlien , M.V. Umansky , A. Froese , S. Howard , C. Ribeiro , R. Ivanov , C. Dunlea , C.P. McNally
Boundary plasma and plasma-material interactions are investigated for magnetised target fusion (MTF) applications. The General Fusion magnetised target fusion technology uses coaxial helicity injection (CHI) start-up which forms a spherical tokamak in a cavity with liquid lithium walls that will subsequently be compressed to fusion conditions Laberge, J. Fusion Energy (2019) The Plasma Injector 3 (PI3) experiment at General Fusion is a non-compressing experiment with solid lithium walls that studies the formation and quasi-steady state operation of a CHI spherical tokamak Carbajal et al. (2023). An explorative study is carried out for wall-limited versus diverted configurations for PI3 using the fluid edge transport code UEDGE. Experimental edge temperature and density profiles from triple Langmuir probes are used to establish realistic temperature and density profiles in UEDGE Rognlien et al. (1992) by adjusting the transport coefficients. In UEDGE, we model the wall-limited plasma via a thin limiter with various insertion depths. It is found that limiter depth and location are key parameters in determining radial profiles and sputtered lithium behaviour. Furthermore, it is found that the total sputtering of the limiter is significantly lower than the sputtering of the wall in some of the limiter configurations studied. Lithium ions and neutral behaviour are compared between limited and diverted configurations.
{"title":"Boundary plasma studies for a spherical tokamak with lithium walls","authors":"A. Antony , L. Carbajal , T.D. Rognlien , M.V. Umansky , A. Froese , S. Howard , C. Ribeiro , R. Ivanov , C. Dunlea , C.P. McNally","doi":"10.1016/j.nme.2025.101885","DOIUrl":"10.1016/j.nme.2025.101885","url":null,"abstract":"<div><div>Boundary plasma and plasma-material interactions are investigated for magnetised target fusion (MTF) applications. The General Fusion magnetised target fusion technology uses coaxial helicity injection (CHI) start-up which forms a spherical tokamak in a cavity with liquid lithium walls that will subsequently be compressed to fusion conditions Laberge, J. Fusion Energy (2019) The Plasma Injector 3 (PI3) experiment at General Fusion is a non-compressing experiment with solid lithium walls that studies the formation and quasi-steady state operation of a CHI spherical tokamak Carbajal et al. (2023). An explorative study is carried out for wall-limited versus diverted configurations for PI3 using the fluid edge transport code UEDGE. Experimental edge temperature and density profiles from triple Langmuir probes are used to establish realistic temperature and density profiles in UEDGE Rognlien et al. (1992) by adjusting the transport coefficients. In UEDGE, we model the wall-limited plasma via a thin limiter with various insertion depths. It is found that limiter depth and location are key parameters in determining radial profiles and sputtered lithium behaviour. Furthermore, it is found that the total sputtering of the limiter is significantly lower than the sputtering of the wall in some of the limiter configurations studied. Lithium ions and neutral behaviour are compared between limited and diverted configurations.</div></div>","PeriodicalId":56004,"journal":{"name":"Nuclear Materials and Energy","volume":"42 ","pages":"Article 101885"},"PeriodicalIF":2.3,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143174235","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-30DOI: 10.1016/j.nme.2025.101890
Xin-Dong Pan , Xiao-Chun Li , Jing Wang , Rongmei Yu , Chunying Pu , Hai-Shan Zhou , Guang-Nan Luo
FeAl/Al2O3 is considered the most promising candidate material for tritium permeation barrier (TPB) due to numerous advantages. γ-Al2O3 phase structure is commonly found in FeAl/Al2O3, and is crucial to its effectiveness. In fusion reactors, high-energy neutrons generate a large number of irradiation-induced defects, significantly affecting the performance of γ-Al2O3. The underlying mechanism is still unclear. This study focuses on the influence of irradiation-induced point defects on the dissolution and diffusion of H in γ-Al2O3 using first-principles theory. Our results show that the irradiation-induced point defect exhibit a strong ability to capture dissolved H atoms, leading to higher hydrogen retention. When dissolved H atoms are captured by vacancy-type defects, the diffusion barrier becomes so high that isolated vacancy-type irradiation-induced point defects can hinder the diffusion of H atoms. This in turn enhances the effectiveness of TPB in preventing H permeation. Furthermore, the impediment effect of Al vacancies on H diffusion in γ-Al2O3 is higher than that in α-Al2O3, whereas O vacancies have the opposite effect, impeding H diffusion in γ-Al2O3 less than in α-Al2O3. However, the diffusion barrier of O interstitial atoms and H as a bound entity is only 0.11 eV, which is even far lower than that in α-Al2O3 (0.44 eV). Therefore, O interstitial atoms can accelerate the diffusion process of H, which can reduce the efficiency of protection against H permeation through γ-Al2O3 TPB. The accelerating effect in γ-Al2O3 is higher than that in α-Al2O3. These findings provide valuable insights into the influence of irradiation-induced point defects on H behavior in γ-Al2O3, which is essential for improving the efficiency of FeAl/Al2O3 tritium permeation barriers.
{"title":"First-principles calculations for the effect of irradiation-induced point defects on the hydrogen dissolution and diffusion in γ-Al2O3","authors":"Xin-Dong Pan , Xiao-Chun Li , Jing Wang , Rongmei Yu , Chunying Pu , Hai-Shan Zhou , Guang-Nan Luo","doi":"10.1016/j.nme.2025.101890","DOIUrl":"10.1016/j.nme.2025.101890","url":null,"abstract":"<div><div>FeAl/Al<sub>2</sub>O<sub>3</sub> is considered the most promising candidate material for tritium permeation barrier (TPB) due to numerous advantages. γ-Al<sub>2</sub>O<sub>3</sub> phase structure is commonly found in FeAl/Al<sub>2</sub>O<sub>3</sub>, and is crucial to its effectiveness. In fusion reactors, high-energy neutrons generate a large number of irradiation-induced defects, significantly affecting the performance of γ-Al<sub>2</sub>O<sub>3</sub>. The underlying mechanism is still unclear. This study focuses on the influence of irradiation-induced point defects on the dissolution and diffusion of H in γ-Al<sub>2</sub>O<sub>3</sub> using first-principles theory. Our results show that the irradiation-induced point defect exhibit a strong ability to capture dissolved H atoms, leading to higher hydrogen retention. When dissolved H atoms are captured by vacancy-type defects, the diffusion barrier becomes so high that isolated vacancy-type irradiation-induced point defects can hinder the diffusion of H atoms. This in turn enhances the effectiveness of TPB in preventing H permeation. Furthermore, the impediment effect of Al vacancies on H diffusion in γ-Al<sub>2</sub>O<sub>3</sub> is higher than that in α-Al<sub>2</sub>O<sub>3</sub>, whereas O vacancies have the opposite effect, impeding H diffusion in γ-Al<sub>2</sub>O<sub>3</sub> less than in α-Al<sub>2</sub>O<sub>3</sub>. However, the diffusion barrier of O interstitial atoms and H as a bound entity is only 0.11 eV, which is even far lower than that in α-Al<sub>2</sub>O<sub>3</sub> (0.44 eV). Therefore, O interstitial atoms can accelerate the diffusion process of H, which can reduce the efficiency of protection against H permeation through γ-Al<sub>2</sub>O<sub>3</sub> TPB. The accelerating effect in γ-Al<sub>2</sub>O<sub>3</sub> is higher than that in α-Al<sub>2</sub>O<sub>3</sub>. These findings provide valuable insights into the influence of irradiation-induced point defects on H behavior in γ-Al<sub>2</sub>O<sub>3</sub>, which is essential for improving the efficiency of FeAl/Al<sub>2</sub>O<sub>3</sub> tritium permeation barriers.</div></div>","PeriodicalId":56004,"journal":{"name":"Nuclear Materials and Energy","volume":"42 ","pages":"Article 101890"},"PeriodicalIF":2.3,"publicationDate":"2025-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143173087","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-28DOI: 10.1016/j.nme.2025.101880
J. Karhunen , B. Lomanowski , S. Aleiferis , P. Carvalho , M. Groth , A. Holm , K.D. Lawson , A.G. Meigs , A. Shaw , V. Solokha , JET Contributors , EUROfusion Tokamak Exploitation Team
The impact of re-absorption of the deuterium Lyman series emission was addressed in inferring divertor plasma conditions from Balmer series emission with 2D spectroscopic camera analysis during detachment in JET L-mode plasmas. The previously presented methodology was amended by modifying the standard photon emission coefficients and ionization and recombination rate coefficients of the ADAS database to consider the re-population of excited states due to Lyman opacity. This resulted in the estimate for the atomic density near the outer strike point to decrease by up to 75% at the onset of detachment at strike point temperatures of 1.0–3.0 eV with respect to the strongly overestimated previously obtained values, whereas the estimated electron temperature and density were unaffected by the opacity correction within the scatter of the data and only a moderate reduction by up to 20% was observed in the estimate for the molecularly induced fraction of the Balmer emission. No noticeable change was seen in the ionization rate, calculated from the estimated outer strike point conditions, due to the decrease in the atomic density estimate compensating for the increased values of the opacity-corrected ADAS rate coefficients for ionization. In detached conditions at 0.5–1.0 eV, 25%–35% lower recombination rates were provided by the opacity-corrected model. The observed effects on the experimental analysis were supported by a corresponding synthetic analysis based on EDGE2D-EIRENE simulations.
{"title":"Addressing the impact of Lyman opacity in inference of divertor plasma conditions with 2D spectroscopic camera analysis of Balmer emission during detachment in JET L-mode plasmas","authors":"J. Karhunen , B. Lomanowski , S. Aleiferis , P. Carvalho , M. Groth , A. Holm , K.D. Lawson , A.G. Meigs , A. Shaw , V. Solokha , JET Contributors , EUROfusion Tokamak Exploitation Team","doi":"10.1016/j.nme.2025.101880","DOIUrl":"10.1016/j.nme.2025.101880","url":null,"abstract":"<div><div>The impact of re-absorption of the deuterium Lyman series emission was addressed in inferring divertor plasma conditions from Balmer series emission with 2D spectroscopic camera analysis during detachment in JET L-mode plasmas. The previously presented methodology was amended by modifying the standard photon emission coefficients and ionization and recombination rate coefficients of the ADAS database to consider the re-population of excited states due to Lyman opacity. This resulted in the estimate for the atomic density near the outer strike point to decrease by up to 75% at the onset of detachment at strike point temperatures of <span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mi>e,osp</mi></mrow></msub><mo>≈</mo></mrow></math></span> 1.0–3.0 eV with respect to the strongly overestimated previously obtained values, whereas the estimated electron temperature and density were unaffected by the opacity correction within the scatter of the data and only a moderate reduction by up to 20% was observed in the estimate for the molecularly induced fraction of the Balmer emission. No noticeable change was seen in the ionization rate, calculated from the estimated outer strike point conditions, due to the decrease in the atomic density estimate compensating for the increased values of the opacity-corrected ADAS rate coefficients for ionization. In detached conditions at <span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mi>e,osp</mi></mrow></msub><mo>≈</mo></mrow></math></span> 0.5–1.0 eV, 25%–35% lower recombination rates were provided by the opacity-corrected model. The observed effects on the experimental analysis were supported by a corresponding synthetic analysis based on EDGE2D-EIRENE simulations.</div></div>","PeriodicalId":56004,"journal":{"name":"Nuclear Materials and Energy","volume":"42 ","pages":"Article 101880"},"PeriodicalIF":2.3,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143174244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-26DOI: 10.1016/j.nme.2025.101884
G. Sinclair , T. Abrams , M.S. Parsons , S.H. Messer , J. Mateja , S.A. Zamperini , D.M. Thomas , J.D. Elder , R. Maurizio , T. Odstrcil , R.S. Wilcox , J.L. Herfindal , D.D. Truong , J.G. Watkins , A.G. McLean , D.L. Rudakov , J. Ren , D. Donovan
A series of L-mode plasma discharges was performed in the DIII-D tokamak to assess the impact of outer strike point (OSP) position and toroidal magnetic field direction on erosion and core contamination potential of the recently-installed, tungsten-coated Small Angle Slot (SAS-VW) divertor. In one discharge, in-slot emission spectroscopy measured an < 48 % increase in the W gross erosion rate when the OSP was moved 3 cm outwards, away from the V-shaped vertex of the slot divertor. However, the effective W yield (erosion rate divided by the incident D flux) was, overall, insensitive to changes in OSP location. Consistently low estimates of the effective W yield based on measurements taken a few cm outwards from the vertex suggest potentially significant C surface contamination. No W emission signal was detected when orienting the toroidal magnetic field such that the ion B×∇B drift direction is pointed away from the X-point. However, measurements of W content in the plasma core for both toroidal magnetic field directions suggest the presence of additional, unmeasured sources of erosion. The difference in the measured core W density with OSP position is much greater than the difference in the measured erosion rates, which may suggest that the leakage of eroded impurities out of the divertor is governed primarily through the parallel ion temperature gradient and friction forces.
{"title":"Tungsten erosion during L-mode discharges in the DIII-D SAS-VW divertor","authors":"G. Sinclair , T. Abrams , M.S. Parsons , S.H. Messer , J. Mateja , S.A. Zamperini , D.M. Thomas , J.D. Elder , R. Maurizio , T. Odstrcil , R.S. Wilcox , J.L. Herfindal , D.D. Truong , J.G. Watkins , A.G. McLean , D.L. Rudakov , J. Ren , D. Donovan","doi":"10.1016/j.nme.2025.101884","DOIUrl":"10.1016/j.nme.2025.101884","url":null,"abstract":"<div><div>A series of L-mode plasma discharges was performed in the DIII-D tokamak to assess the impact of outer strike point (OSP) position and toroidal magnetic field direction on erosion and core contamination potential of the recently-installed, tungsten-coated Small Angle Slot (SAS-VW) divertor. In one discharge, in-slot emission spectroscopy measured an < 48 % increase in the W gross erosion rate when the OSP was moved 3 cm outwards, away from the V-shaped vertex of the slot divertor. However, the effective W yield (erosion rate divided by the incident D flux) was, overall, insensitive to changes in OSP location. Consistently low estimates of the effective W yield based on measurements taken a few cm outwards from the vertex suggest potentially significant C surface contamination. No W emission signal was detected when orienting the toroidal magnetic field such that the ion B×∇B drift direction is pointed away from the X-point. However, measurements of W content in the plasma core for both toroidal magnetic field directions suggest the presence of additional, unmeasured sources of erosion. The difference in the measured core W density with OSP position is much greater than the difference in the measured erosion rates, which may suggest that the leakage of eroded impurities out of the divertor is governed primarily through the parallel ion temperature gradient and friction forces.</div></div>","PeriodicalId":56004,"journal":{"name":"Nuclear Materials and Energy","volume":"42 ","pages":"Article 101884"},"PeriodicalIF":2.3,"publicationDate":"2025-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143343830","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-25DOI: 10.1016/j.nme.2025.101881
Z.X. Wen , Z.H. Gao , B. Liu , Z. Zhou , Z.C. Lin , Y. Feng , S.Y. Dai
The edge transport and core accumulation of lithium (Li) impurity under a liquid Li divertor on EAST have been investigated by the EMC3-EIRENE and STRAHL codes, respectively. At the edge region, the Li density distribution and power dissipation derived from divertor targets have been simulated by EMC3-EIRENE modeling. At the core region, the ONETWO and TGYRO codes are used to calculate the Li transport coefficients for STRAHL modeling, which is implemented through the OMFIT framework. At the core–edge transition region ( = 0.95 ∼ 1.02, is the normalized poloidal flux coordinate), the representative distribution of ion density is used for the comparison between EMC3-EIRENE and STRAHL modellings, which can achieve a reasonable agreement between two codes. On this basis, the Li-ion core density and radiation distributions have been analyzed by STRAHL modeling, which indicates there exist two radiation peaks located at the magnetic axis and = 1.01. The impacts of Li radiation on H-L back transition have been studied by Martin’s threshold power scaling law (Martin et al 2008J Phys Conf Ser 123 012033). The core radiation of lithium has a limited impact on the operation regime of EAST. Even for the maximum lithium effective sputtering coefficient of 0.1 used in the current study, it is still insufficient to cause H-L back transition.
{"title":"Integrated modelling of lithium transport and radiation under a liquid lithium divertor on EAST","authors":"Z.X. Wen , Z.H. Gao , B. Liu , Z. Zhou , Z.C. Lin , Y. Feng , S.Y. Dai","doi":"10.1016/j.nme.2025.101881","DOIUrl":"10.1016/j.nme.2025.101881","url":null,"abstract":"<div><div>The edge transport and core accumulation of lithium (Li) impurity under a liquid Li divertor on EAST have been investigated by the EMC3-EIRENE and STRAHL codes, respectively. At the edge region, the Li density distribution and power dissipation derived from divertor targets have been simulated by EMC3-EIRENE modeling. At the core region, the ONETWO and TGYRO codes are used to calculate the Li transport coefficients for STRAHL modeling, which is implemented through the OMFIT framework. At the core–edge transition region (<span><math><mrow><msub><mi>Ψ</mi><mi>N</mi></msub><mspace></mspace></mrow></math></span> = 0.95 ∼ 1.02, <span><math><mrow><msub><mi>Ψ</mi><mi>N</mi></msub></mrow></math></span> is the normalized poloidal flux coordinate), the representative distribution of <span><math><mrow><msup><mrow><mi>L</mi><mi>i</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></mrow></math></span> ion density is used for the comparison between EMC3-EIRENE and STRAHL modellings, which can achieve a reasonable agreement between two codes. On this basis, the Li-ion core density and radiation distributions have been analyzed by STRAHL modeling, which indicates there exist two radiation peaks located at the magnetic axis and <span><math><mrow><msub><mi>Ψ</mi><mi>N</mi></msub></mrow></math></span> = 1.01. The impacts of Li radiation on H-L back transition have been studied by Martin’s threshold power scaling law (Martin <em>et al</em> 2008<em>J Phys Conf Ser</em> 123 012033). The core radiation of lithium has a limited impact on the operation regime of EAST. Even for the maximum lithium effective sputtering coefficient of 0.1 used in the current study, it is still insufficient to cause H-L back transition.</div></div>","PeriodicalId":56004,"journal":{"name":"Nuclear Materials and Energy","volume":"42 ","pages":"Article 101881"},"PeriodicalIF":2.3,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143173569","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-23DOI: 10.1016/j.nme.2025.101879
Chengcheng Liu , Hang Su
In the field of materials science, accurately predicting the swelling rate of materials in irradiated environments is crucial for ensuring safety and reliability. This study aims to enhance the predictive accuracy of the swelling rate of irradiated 316L stainless steel, particularly in high-tech applications such as nuclear energy. By comparing various machine learning models, it was found that the Extreme Trees Regression (ETR) model performed best on the test set, achieving an R2 of 0.79 and a Root Mean Square Error (RMSE) of 1.65 %. Although it demonstrated strong generalization capabilities, the limited data volume restricted its predictive accuracy. To address this issue, the study employed Variational Autoencoders (VAEs) for data augmentation, generating an additional 400 synthetic data points to expand the original dataset. This enhancement increased the R2 on the test set to 0.91 and reduced the RMSE to 1.11 %. Following data augmentation, feature selection was conducted, resulting in Si, C, IrF, T, and Dd being identified as the optimal feature combination. SHapley Additive exPlanations (SHAP) was then utilized for interpretability analysis, revealing the significant effects of these features on the swelling rate. The findings provide essential insights for understanding and optimizing the swelling behavior of materials following irradiation.
{"title":"Prediction of post-irradiation swelling rate of 316L stainless steel based on Variational Autoencoders and interpretable machine learning","authors":"Chengcheng Liu , Hang Su","doi":"10.1016/j.nme.2025.101879","DOIUrl":"10.1016/j.nme.2025.101879","url":null,"abstract":"<div><div>In the field of materials science, accurately predicting the swelling rate of materials in irradiated environments is crucial for ensuring safety and reliability. This study aims to enhance the predictive accuracy of the swelling rate of irradiated 316L stainless steel, particularly in high-tech applications such as nuclear energy. By comparing various machine learning models, it was found that the Extreme Trees Regression (ETR) model performed best on the test set, achieving an R<sup>2</sup> of 0.79 and a Root Mean Square Error (RMSE) of 1.65 %. Although it demonstrated strong generalization capabilities, the limited data volume restricted its predictive accuracy. To address this issue, the study employed Variational Autoencoders (VAEs) for data augmentation, generating an additional 400 synthetic data points to expand the original dataset. This enhancement increased the R<sup>2</sup> on the test set to 0.91 and reduced the RMSE to 1.11 %. Following data augmentation, feature selection was conducted, resulting in Si, C, IrF, T, and Dd being identified as the optimal feature combination. SHapley Additive exPlanations (SHAP) was then utilized for interpretability analysis, revealing the significant effects of these features on the swelling rate. The findings provide essential insights for understanding and optimizing the swelling behavior of materials following irradiation.</div></div>","PeriodicalId":56004,"journal":{"name":"Nuclear Materials and Energy","volume":"42 ","pages":"Article 101879"},"PeriodicalIF":2.3,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143173567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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