Pub Date : 2024-03-01DOI: 10.1088/1361-6587/ad2b91
M V Umansky, B I Cohen, I Joseph
A new simulation model for tokamak boundary plasma, SOLT3D, is implemented in the BOUT++ framework (Dudson et al 2009 Comput. Phys. Commun.180 1467). The simulation model includes a set of dynamic equations describing collisional boundary plasma and neutral gas in the tokamak scrape-off layer and divertor region. The model is verified against standard linear plasma instabilities and available nonlinear results. For L-mode like conditions, SOLT3D reproduces characteristics of boundary plasma turbulent fluctuations that are similar to published experimental data, in terms of the amplitude and spatial dependence of the fluctuations. It also reproduces realistic plasma fluxes on material surfaces and expected Bohm-like effective radial transport. Plasma fluctuations inferred from the simulations imply inevitably a significant level of intrinsic ‘noise’ for axisymmetric tokamak plasma transport modeling, introducing errors on the order of unity. In particular, the toroidally averaged atomic rates below 5–10 eV are strongly modified by turbulent plasma fluctuations, which should significantly affect the standard axisymmetric modeling of the tokamak edge plasma and divertor.
托卡马克边界等离子体的新模拟模型 SOLT3D 是在 BOUT++ 框架中实现的（Dudson 等人，2009 年，Comput.）该模拟模型包括一组动态方程，描述了碰撞边界等离子体以及托卡马克刮除层和分流器区域的中性气体。该模型根据标准线性等离子体不稳定性和现有非线性结果进行了验证。在类似 L 模式的条件下，SOLT3D 重现了边界等离子体湍流波动的特征，在波动的幅度和空间依赖性方面与已公布的实验数据相似。它还再现了材料表面上真实的等离子通量和预期的类似玻姆的有效径向传输。从模拟中推断出的等离子体波动意味着轴对称托卡马克等离子体输运建模不可避免地会有很大程度的内在 "噪声"，会带来单位数量级的误差。特别是，5-10 eV 以下的环状平均原子速率受到湍流等离子体波动的强烈影响，这将对托卡马克边缘等离子体和分流器的标准轴对称建模产生重大影响。
{"title":"Simulations of tokamak edge plasma turbulent fluctuations based on a minimal 3D model","authors":"M V Umansky, B I Cohen, I Joseph","doi":"10.1088/1361-6587/ad2b91","DOIUrl":"https://doi.org/10.1088/1361-6587/ad2b91","url":null,"abstract":"A new simulation model for tokamak boundary plasma, SOLT3D, is implemented in the BOUT++ framework (Dudson <italic toggle=\"yes\">et al</italic> 2009 <italic toggle=\"yes\">Comput. Phys. Commun.</italic>\u0000<bold>180</bold> 1467). The simulation model includes a set of dynamic equations describing collisional boundary plasma and neutral gas in the tokamak scrape-off layer and divertor region. The model is verified against standard linear plasma instabilities and available nonlinear results. For L-mode like conditions, SOLT3D reproduces characteristics of boundary plasma turbulent fluctuations that are similar to published experimental data, in terms of the amplitude and spatial dependence of the fluctuations. It also reproduces realistic plasma fluxes on material surfaces and expected Bohm-like effective radial transport. Plasma fluctuations inferred from the simulations imply inevitably a significant level of intrinsic ‘noise’ for axisymmetric tokamak plasma transport modeling, introducing errors on the order of unity. In particular, the toroidally averaged atomic rates below 5–10 eV are strongly modified by turbulent plasma fluctuations, which should significantly affect the standard axisymmetric modeling of the tokamak edge plasma and divertor.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"54 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140315356","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-29DOI: 10.1088/1361-6587/ad2a83
A V Chankin, G Corrigan, A Huber, JET Contributors4
Predictions of the Huber–Chankin (HC) scaling for the upstream impurity fraction were verified in a series of EDGE2D-EIRENE (‘code’) runs for highly radiating plasmas with nitrogen injection. The main quantity extracted from the code was poloidally averaged, from X-point to X-point, separatrix impurity fraction cZ in the main scrape-off layer (SOL). Variation of the main working gas (H, D and T) revealed a qualitative agreement between the model and code results owing to the very large isotope difference in the predicted cZ values caused primarily by the inverse isotope mass dependence of the H-mode power threshold assumed in the HC model and implemented in the code. At the same time, the variation of the toroidal field and safety factor in deuterium cases yielded no correlation between the model predictions and code results. The code showed much higher local impurity fractions (fZ) in the divertor compared to the main SOL, as well as large case-to-case variations in the divertor to the main SOL ratio of impurity fractions. The analysis of code results has wide-ranging consequences not only for the HC model, but also for other similar 1D models which use simple geometry ignoring strong neutral recycling in the divertor/ Different topology makes plasma parameters in the divertor and main SOL very different, resulting in different impurity charge state composition. Missing mechanisms in 1D codes (e.g. friction and thermo-forces exerted on impurity ions by main working gas ions) lead to impurity density redistribution. Neglecting all above factors, 1D models assume a constant impurity fraction along field lines.
对注入氮气的高辐射等离子体进行了一系列 EDGE2D-EIRENE（"代码"）运行，对上游杂质分数的休伯-钱金（HC）比例预测进行了验证。从代码中提取的主要数量是从 X 点到 X 点的极平均值，即主刮除层（SOL）中的分离基质杂质分数 cZ。主要工作气体（H、D 和 T）的变化表明，由于 HC 模型中假设并在代码中实施的 H 模式功率阈值的反同位素质量依赖性，导致预测的 cZ 值存在很大的同位素差异，因此模型和代码结果在质量上是一致的。同时，氘情况下环形场和安全系数的变化导致模型预测和代码结果之间没有关联。代码显示，与主 SOL 相比，岔流器中的局部杂质分数（fZ）要高得多，而且岔流器与主 SOL 的杂质分数比在不同情况下变化很大。对代码结果的分析不仅对 HC 模型有广泛的影响，而且对其他类似的一维模型也有影响，因为这些模型使用简单的几何结构，忽略了岔流器中的强中性循环。1D 代码中缺失的机制（如主工作气体离子对杂质离子施加的摩擦力和热力）导致杂质密度重新分布。忽略上述所有因素，1D 模型假定沿场线的杂质分数恒定不变。
{"title":"Testing validity of 1D models for impurity fraction scaling for divertor detachment with EDGE2D-EIRENE","authors":"A V Chankin, G Corrigan, A Huber, JET Contributors4","doi":"10.1088/1361-6587/ad2a83","DOIUrl":"https://doi.org/10.1088/1361-6587/ad2a83","url":null,"abstract":"Predictions of the Huber–Chankin (HC) scaling for the upstream impurity fraction were verified in a series of EDGE2D-EIRENE (‘code’) runs for highly radiating plasmas with nitrogen injection. The main quantity extracted from the code was poloidally averaged, from X-point to X-point, separatrix impurity fraction <italic toggle=\"yes\">c<sub>Z</sub>\u0000</italic> in the main scrape-off layer (SOL). Variation of the main working gas (H, D and T) revealed a qualitative agreement between the model and code results owing to the very large isotope difference in the predicted <italic toggle=\"yes\">c<sub>Z</sub>\u0000</italic> values caused primarily by the inverse isotope mass dependence of the H-mode power threshold assumed in the HC model and implemented in the code. At the same time, the variation of the toroidal field and safety factor in deuterium cases yielded no correlation between the model predictions and code results. The code showed much higher local impurity fractions (<italic toggle=\"yes\">f<sub>Z</sub>\u0000</italic>) in the divertor compared to the main SOL, as well as large case-to-case variations in the divertor to the main SOL ratio of impurity fractions. The analysis of code results has wide-ranging consequences not only for the HC model, but also for other similar 1D models which use simple geometry ignoring strong neutral recycling in the divertor/ Different topology makes plasma parameters in the divertor and main SOL very different, resulting in different impurity charge state composition. Missing mechanisms in 1D codes (e.g. friction and thermo-forces exerted on impurity ions by main working gas ions) lead to impurity density redistribution. Neglecting all above factors, 1D models assume a constant impurity fraction along field lines.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"71 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-02-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140315204","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-23DOI: 10.1088/1361-6587/ad2975
Óscar Amaro, Marija Vranic
The new generation of multi-PetaWatt laser facilities will allow tests of strong field quantum electrodynamics (QED), as well as provide an opportunity for novel photon and lepton sources. The first experiments are planned to study the (nearly) head-on scattering of intense, focused laser pulses with either relativistic electron beams or high-energy photon sources. In this work, we present a numerical framework that can provide fast predictions of the asymptotic particle and photon distributions after the scattering. The method detailed in this manuscript can include multiple features such as spatial and temporal misalignment between the laser and the scattering beam, broadband electron beams, and beam divergence. The expected mean energy, energy spread, divergence or other observables are calculated by combining an analytical description and numerical integration. This method can provide results within minutes on a personal computer, which would otherwise require full-scale 3D QED-PIC simulations using thousands of cores. The model, which has been compiled into an open-source code QScatter, may be used to support the analysis of large-size data sets from high-repetition rate experiments, leveraging its speed for optimization or reconstruction of experimental parameters.
{"title":"QScatter: numerical framework for fast prediction of particle distributions in electron-laser scattering","authors":"Óscar Amaro, Marija Vranic","doi":"10.1088/1361-6587/ad2975","DOIUrl":"https://doi.org/10.1088/1361-6587/ad2975","url":null,"abstract":"The new generation of multi-PetaWatt laser facilities will allow tests of strong field quantum electrodynamics (QED), as well as provide an opportunity for novel photon and lepton sources. The first experiments are planned to study the (nearly) head-on scattering of intense, focused laser pulses with either relativistic electron beams or high-energy photon sources. In this work, we present a numerical framework that can provide fast predictions of the asymptotic particle and photon distributions after the scattering. The method detailed in this manuscript can include multiple features such as spatial and temporal misalignment between the laser and the scattering beam, broadband electron beams, and beam divergence. The expected mean energy, energy spread, divergence or other observables are calculated by combining an analytical description and numerical integration. This method can provide results within minutes on a personal computer, which would otherwise require full-scale 3D QED-PIC simulations using thousands of cores. The model, which has been compiled into an open-source code <monospace>QScatter</monospace>, may be used to support the analysis of large-size data sets from high-repetition rate experiments, leveraging its speed for optimization or reconstruction of experimental parameters.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"19 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140010939","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-13DOI: 10.1088/1361-6587/ad2428
A Pidatella, D Mascali, A Galatà, B Mishra, E Naselli, L Celona, R Lang, F Maimone, G S Mauro, D Santonocito, G Torrisi
We present a numerical study of metals dynamics evaporated through resistively heated ovens in electron cyclotron resonance (ECR) plasma traps, used as metal ion beam injectors for accelerators and multi-disciplinary research in plasma physics. We use complementary numerical methods to perform calculations in the framework of the PANDORA trap. The diffusion and deposition of metal vapours at the plasma chamber’s surface are explored under molecular flow regime, with stationary and time-dependent particle fluid calculations via COMSOL Multiphysics®. The ionisation of vapours is then studied in the strongly energised ECR plasma. We have developed a Monte Carlo (MC) code to simulate the in-plasma metal ions’ dynamics, coupled to particle-in-cell simulations of the plasma physics in the trap. The presence of strongly inhomogeneous plasmas leads to charge-exchange and electron-impact ionisations of metals, in turn affecting the deposition rate/pattern of the metal on the walls of the trap. Results show how vapours dynamics depends both on evaporated metals and the plasma target. The 134Cs, 176Lu, and 48Ca isotopes were investigated, the first two being radioisotopes interesting for the PANDORA project, and the third as one of the most required rare isotope by the nuclear physics community. We present an application of the study: MC computing the γ activity due to the deposited radioactive neutral nuclei during the measurement time, we quantitatively estimated the overall γ-detection system’s efficiency using GEANT4, including the poisoning γ-signal from the walls of the trap, relevant for the γ-tagging of short-lived nuclei’s decay rate in the PANDORA experiment. This work can give valuable support both to the evaporation technique and plasma source optimisation, for improving the metal ion beam production, avoiding huge deposit/waste of metals known to affect the long-term source stability, as well as for radio-safety aspects and reducing material waste in case of rare isotopes.
{"title":"Metal evaporation dynamics in electron cyclotron resonance ion sources: plasma role in the atom diffusion, ionisation, and transport","authors":"A Pidatella, D Mascali, A Galatà, B Mishra, E Naselli, L Celona, R Lang, F Maimone, G S Mauro, D Santonocito, G Torrisi","doi":"10.1088/1361-6587/ad2428","DOIUrl":"https://doi.org/10.1088/1361-6587/ad2428","url":null,"abstract":"We present a numerical study of metals dynamics evaporated through resistively heated ovens in electron cyclotron resonance (ECR) plasma traps, used as metal ion beam injectors for accelerators and multi-disciplinary research in plasma physics. We use complementary numerical methods to perform calculations in the framework of the PANDORA trap. The diffusion and deposition of metal vapours at the plasma chamber’s surface are explored under molecular flow regime, with stationary and time-dependent particle fluid calculations via COMSOL Multiphysics®. The ionisation of vapours is then studied in the strongly energised ECR plasma. We have developed a Monte Carlo (MC) code to simulate the in-plasma metal ions’ dynamics, coupled to particle-in-cell simulations of the plasma physics in the trap. The presence of strongly inhomogeneous plasmas leads to charge-exchange and electron-impact ionisations of metals, in turn affecting the deposition rate/pattern of the metal on the walls of the trap. Results show how vapours dynamics depends both on evaporated metals and the plasma target. The <sup>134</sup>Cs, <sup>176</sup>Lu, and <sup>48</sup>Ca isotopes were investigated, the first two being radioisotopes interesting for the PANDORA project, and the third as one of the most required rare isotope by the nuclear physics community. We present an application of the study: MC computing the <italic toggle=\"yes\">γ</italic> activity due to the deposited radioactive neutral nuclei during the measurement time, we quantitatively estimated the overall <italic toggle=\"yes\">γ</italic>-detection system’s efficiency using GEANT4, including the poisoning <italic toggle=\"yes\">γ</italic>-signal from the walls of the trap, relevant for the <italic toggle=\"yes\">γ</italic>-tagging of short-lived nuclei’s decay rate in the PANDORA experiment. This work can give valuable support both to the evaporation technique and plasma source optimisation, for improving the metal ion beam production, avoiding huge deposit/waste of metals known to affect the long-term source stability, as well as for radio-safety aspects and reducing material waste in case of rare isotopes.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"64 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140010938","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-13DOI: 10.1088/1361-6587/ad238f
A P L Robinson
It is argued that the electronic stopping power in a plasma should be expected to exhibit significant differences in the presence of effects that shift the electron distribution function away from a Maxwellian. This is potentially important for nuclear reactions produced by laser-driven ion beams, where non-Maxwellian effects may have to be considered. We have calculated the electronic stopping power for a number of model distributions. Importantly, comparisons with the Maxwellian are done under the condition of energy density parity. ‘Hollow’ electron distribution functions (e.g. f∝vnfmax) could be expected to show a reduced stopping power (when vi/vt<1). We show that this is indeed the case and that the difference can become a factor of 70. The super-Gaussian electron distribution function, on the other hand, will always show a higher stopping power than the Maxwellian for orders greater than 2.
{"title":"Reduction of fast ion drag in the presence of ‘hollow’ non-Maxwellian electron distributions","authors":"A P L Robinson","doi":"10.1088/1361-6587/ad238f","DOIUrl":"https://doi.org/10.1088/1361-6587/ad238f","url":null,"abstract":"It is argued that the electronic stopping power in a plasma should be expected to exhibit significant differences in the presence of effects that shift the electron distribution function away from a Maxwellian. This is potentially important for nuclear reactions produced by laser-driven ion beams, where non-Maxwellian effects may have to be considered. We have calculated the electronic stopping power for a number of model distributions. Importantly, comparisons with the Maxwellian are done under the condition of energy density parity. ‘Hollow’ electron distribution functions (e.g. <inline-formula>\u0000<tex-math><?CDATA $f propto v^nf_{text{max}}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mi>f</mml:mi><mml:mo>∝</mml:mo><mml:msup><mml:mi>v</mml:mi><mml:mi>n</mml:mi></mml:msup><mml:msub><mml:mi>f</mml:mi><mml:mrow><mml:mtext>max</mml:mtext></mml:mrow></mml:msub></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad238fieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>) could be expected to show a reduced stopping power (when <inline-formula>\u0000<tex-math><?CDATA $v_mathrm{i}/v_mathrm{t} lt 1$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:msub><mml:mi>v</mml:mi><mml:mrow><mml:mi mathvariant=\"normal\">i</mml:mi></mml:mrow></mml:msub><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:msub><mml:mi>v</mml:mi><mml:mrow><mml:mi mathvariant=\"normal\">t</mml:mi></mml:mrow></mml:msub><mml:mo><</mml:mo><mml:mn>1</mml:mn></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad238fieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>). We show that this is indeed the case and that the difference can become a factor of 70. The super-Gaussian electron distribution function, on the other hand, will always show a higher stopping power than the Maxwellian for orders greater than 2.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"5 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140011042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-07DOI: 10.1088/1361-6587/ad238e
Srimanta Maity, Alamgir Mondal, Eugene Vishnyakov, Alexander Molodozhentsev
Laser wakefield acceleration (LWFA) in a gas cell target separating injection and acceleration section has been investigated to produce high-quality electron beams. A detailed study has been performed on controlling the quality of accelerated electron beams using a combination of truncated ionization and density downramp injection mechanisms. For this purpose, extensive two-dimensional particle-in-cell simulations have been carried out considering a gas cell target consisting of a hydrogen and nitrogen mixture in the first part and pure hydrogen in the second part. Such a configuration can be realized experimentally using a specially designed capillary setup. Using the parameters already available in the existing experimental setups, we show the generation of an electron beam with a peak energy of 500–600 MeV, relative energy spread less than 5%, normalized beam emittance around 1.5 mm-mrad, and beam charge of 2–5 pC/µm. Our study reveals that the quality of the accelerated electron beam can be independently controlled and manipulated through the beam loading effect by tuning the parameters, e.g. laser focusing position, nitrogen concentration, and gas target profile. These simulation results will be useful for future experimental campaigns on LWFA, particularly at ELI Beamlines.
{"title":"Parametric analysis of electron beam quality in laser wakefield acceleration based on the truncated ionization injection mechanism","authors":"Srimanta Maity, Alamgir Mondal, Eugene Vishnyakov, Alexander Molodozhentsev","doi":"10.1088/1361-6587/ad238e","DOIUrl":"https://doi.org/10.1088/1361-6587/ad238e","url":null,"abstract":"Laser wakefield acceleration (LWFA) in a gas cell target separating injection and acceleration section has been investigated to produce high-quality electron beams. A detailed study has been performed on controlling the quality of accelerated electron beams using a combination of truncated ionization and density downramp injection mechanisms. For this purpose, extensive two-dimensional particle-in-cell simulations have been carried out considering a gas cell target consisting of a hydrogen and nitrogen mixture in the first part and pure hydrogen in the second part. Such a configuration can be realized experimentally using a specially designed capillary setup. Using the parameters already available in the existing experimental setups, we show the generation of an electron beam with a peak energy of 500–600 MeV, relative energy spread less than <inline-formula>\u0000<tex-math><?CDATA $5%$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mn>5</mml:mn><mml:mi mathvariant=\"normal\">%</mml:mi></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad238eieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>, normalized beam emittance around 1.5 mm-mrad, and beam charge of 2–5 pC/<italic toggle=\"yes\">µ</italic>m. Our study reveals that the quality of the accelerated electron beam can be independently controlled and manipulated through the beam loading effect by tuning the parameters, e.g. laser focusing position, nitrogen concentration, and gas target profile. These simulation results will be useful for future experimental campaigns on LWFA, particularly at ELI Beamlines.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"16 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139770639","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-19DOI: 10.1088/1361-6587/ad1b89
K Dolgova, E Vekshina, V Rozhansky
Formation of a high-field-side high-density (HFSHD) regime and the role of the high-field-side (HFS) poloidal electric field in the scrape-off layer of the spherical tokamak Globus-M2 are analyzed using SOLPS-ITER edge plasma simulations. The dependence of the HFS poloidal electric field sign and, consequently, radial drift fluxes on the discharge density is discussed. It is demonstrated that the HFS poloidal electric field is the key element in the formation of a HFSHD regime in the Globus-M2 tokamak as in ASDEX Upgrade. It is demonstrated that the physics of HFSHD formation in a small spherical tokamak is similar to that suggested by Kaveeva et al (2009 36th EPS Conf. on Plasma Physics) and is in line with experimental observations and modeling, performed later on ASDEX Upgrade.
{"title":"Modeling of high-field-side high-density regime in the Globus-M2 tokamak","authors":"K Dolgova, E Vekshina, V Rozhansky","doi":"10.1088/1361-6587/ad1b89","DOIUrl":"https://doi.org/10.1088/1361-6587/ad1b89","url":null,"abstract":"Formation of a high-field-side high-density (HFSHD) regime and the role of the high-field-side (HFS) poloidal electric field in the scrape-off layer of the spherical tokamak Globus-M2 are analyzed using SOLPS-ITER edge plasma simulations. The dependence of the HFS poloidal electric field sign and, consequently, radial drift fluxes on the discharge density is discussed. It is demonstrated that the HFS poloidal electric field is the key element in the formation of a HFSHD regime in the Globus-M2 tokamak as in ASDEX Upgrade. It is demonstrated that the physics of HFSHD formation in a small spherical tokamak is similar to that suggested by Kaveeva <italic toggle=\"yes\">et al</italic> (2009 <italic toggle=\"yes\">36th EPS Conf. on Plasma Physics</italic>) and is in line with experimental observations and modeling, performed later on ASDEX Upgrade.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"3 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139509547","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-18DOI: 10.1088/1361-6587/ad1a3e
John Kappel, Matt Landreman, Dhairya Malhotra
The separation between the last closed flux surface of a plasma and the external coils that magnetically confine it is a limiting factor in the construction of fusion-capable plasma devices. This plasma-coil separation must be large enough so that components such as a breeding blanket and neutron shielding can fit between the plasma and the coils. Plasma-coil separation affects reactor size, engineering complexity, and particle loss due to field ripple. For some plasmas it can be difficult to produce the desired flux surface shaping with distant coils, and for other plasmas it is infeasible altogether. Here, we seek to understand the underlying physics that limits plasma-coil separation and explain why some configurations require close external coils. In this paper, we explore the hypothesis that the limiting plasma-coil separation is set by the shortest scale length of the magnetic field as expressed by the ∇B tensor. We tested this hypothesis on a database of >40 stellarator and tokamak configurations. Within this database, the coil-to-plasma distance compared to the minor radius varies by over an order of magnitude. The magnetic scale length is well correlated to the coil-to-plasma distance of actual coil designs generated using the REGCOIL method (Landreman 2017 Nucl. Fusion57 046003). Additionally, this correlation reveals a general trend that larger plasma-coil separation is possible with a small number of field periods.
{"title":"The magnetic gradient scale length explains why certain plasmas require close external magnetic coils","authors":"John Kappel, Matt Landreman, Dhairya Malhotra","doi":"10.1088/1361-6587/ad1a3e","DOIUrl":"https://doi.org/10.1088/1361-6587/ad1a3e","url":null,"abstract":"The separation between the last closed flux surface of a plasma and the external coils that magnetically confine it is a limiting factor in the construction of fusion-capable plasma devices. This plasma-coil separation must be large enough so that components such as a breeding blanket and neutron shielding can fit between the plasma and the coils. Plasma-coil separation affects reactor size, engineering complexity, and particle loss due to field ripple. For some plasmas it can be difficult to produce the desired flux surface shaping with distant coils, and for other plasmas it is infeasible altogether. Here, we seek to understand the underlying physics that limits plasma-coil separation and explain why some configurations require close external coils. In this paper, we explore the hypothesis that the limiting plasma-coil separation is set by the shortest scale length of the magnetic field as expressed by the <inline-formula>\u0000<tex-math><?CDATA $nabla mathbf{B}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mi mathvariant=\"normal\">∇</mml:mi><mml:mrow><mml:mi mathvariant=\"bold\">B</mml:mi></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad1a3eieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> tensor. We tested this hypothesis on a database of <inline-formula>\u0000<tex-math><?CDATA $gt$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mo>></mml:mo></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad1a3eieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>40 stellarator and tokamak configurations. Within this database, the coil-to-plasma distance compared to the minor radius varies by over an order of magnitude. The magnetic scale length is well correlated to the coil-to-plasma distance of actual coil designs generated using the <monospace>REGCOIL</monospace> method (Landreman 2017 <italic toggle=\"yes\">Nucl. Fusion</italic>\u0000<bold>57</bold> 046003). Additionally, this correlation reveals a general trend that larger plasma-coil separation is possible with a small number of field periods.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"38 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139509546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-12DOI: 10.1088/1361-6587/ad1ae4
C Zhang, D Storey, P San Miguel Claveria, Z Nie, K A Marsh, M Hogan, W B Mori, E Adli, W An, R Ariniello, G J Cao, C Clarke, S Corde, T Dalichaouch, C E Doss, C Emma, H Ekerfelt, E Gerstmayr, S Gessner, C Hansel, A Knetsch, V Lee, F Li, M Litos, B O’Shea, G White, G Yocky, V Zakharova, C Joshi
High repetition rates and efficient energy transfer to the accelerating beam are important for a future linear collider based on the beam-driven plasma wakefield acceleration scheme (PWFA-LC). This paper reports the first results from the Plasma Wakefield Acceleration Collaboration (E300) that are beginning to address both of these issues using the recently commissioned FACET-II facility at SLAC national accelerator laboratory. We have generated meter-scale hydrogen plasmas using time-structured 10 GeV electron bunches from FACET-II, which hold the promise of dramatically increasing the repetition rate of PWFA by rapidly replenishing the gas between each shot compared to the hitherto used lithium plasmas that operate at 1–10 Hz. Furthermore, we have excited wakes in such plasmas that are suitable for high gradient particle acceleration with high drive-bunch to wake energy transfer efficiency- a first step in achieving a high overall energy transfer efficiency. We have done this by using time-structured electron drive bunches that typically have one or more ultra-high current (>30 kA) femtosecond spike(s) superimposed on a longer (∼0.4 ps) lower current (<10 kA) bunch structure. The first spike effectively field-ionizes the gas and produces a meter-scale (30–160 cm) plasma, whereas the subsequent beam charge creates a wake. The length and amplitude of the wake depends on the longitudinal current profile of the bunch and plasma density. We find that the onset of pump depletion, when some of the drive beam electrons are nearly fully depleted of their energy, occurs for hydrogen pressure ⩾1.5 Torr. We also show that some electrons in the rear of the bunch can gain several GeV energies from the wake. These results are reproduced by particle-in-cell simulations using the QPAD code. At a pressure of ∼2 Torr, simulation results and experimental data show that the beam transfers about 60% of its energy to the wake.
{"title":"Generation of meter-scale hydrogen plasmas and efficient, pump-depletion-limited wakefield excitation using 10 GeV electron bunches","authors":"C Zhang, D Storey, P San Miguel Claveria, Z Nie, K A Marsh, M Hogan, W B Mori, E Adli, W An, R Ariniello, G J Cao, C Clarke, S Corde, T Dalichaouch, C E Doss, C Emma, H Ekerfelt, E Gerstmayr, S Gessner, C Hansel, A Knetsch, V Lee, F Li, M Litos, B O’Shea, G White, G Yocky, V Zakharova, C Joshi","doi":"10.1088/1361-6587/ad1ae4","DOIUrl":"https://doi.org/10.1088/1361-6587/ad1ae4","url":null,"abstract":"High repetition rates and efficient energy transfer to the accelerating beam are important for a future linear collider based on the beam-driven plasma wakefield acceleration scheme (PWFA-LC). This paper reports the first results from the Plasma Wakefield Acceleration Collaboration (E300) that are beginning to address both of these issues using the recently commissioned FACET-II facility at SLAC national accelerator laboratory. We have generated meter-scale hydrogen plasmas using time-structured 10 GeV electron bunches from FACET-II, which hold the promise of dramatically increasing the repetition rate of PWFA by rapidly replenishing the gas between each shot compared to the hitherto used lithium plasmas that operate at 1–10 Hz. Furthermore, we have excited wakes in such plasmas that are suitable for high gradient particle acceleration with high drive-bunch to wake energy transfer efficiency- a first step in achieving a high overall energy transfer efficiency. We have done this by using time-structured electron drive bunches that typically have one or more ultra-high current (<inline-formula>\u0000<tex-math><?CDATA $gt$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mo>></mml:mo></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad1ae4ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>30 kA) femtosecond spike(s) superimposed on a longer (∼0.4 ps) lower current (<inline-formula>\u0000<tex-math><?CDATA $lt$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mo><</mml:mo></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad1ae4ieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>10 kA) bunch structure. The first spike effectively field-ionizes the gas and produces a meter-scale (30–160 cm) plasma, whereas the subsequent beam charge creates a wake. The length and amplitude of the wake depends on the longitudinal current profile of the bunch and plasma density. We find that the onset of pump depletion, when some of the drive beam electrons are nearly fully depleted of their energy, occurs for hydrogen pressure <inline-formula>\u0000<tex-math><?CDATA $unicode{x2A7E}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mtext>⩾</mml:mtext></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad1ae4ieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>1.5 Torr. We also show that some electrons in the rear of the bunch can gain several GeV energies from the wake. These results are reproduced by particle-in-cell simulations using the QPAD code. At a pressure of ∼2 Torr, simulation results and experimental data show that the beam transfers about 60% of its energy to the wake.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"251 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139509544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-03DOI: 10.1088/1361-6587/ad1a3d
V. Neverov, R. Pitts, R. I. Khusnutdinov, Andrey G Alekseev, Evgeny Andreenko, Matthew Carr, Martin Kocan, Maarten De Bock, A. V. Gorshkov, Andrey M Kozlov, A. B. Kukushkin, J. Lovell, A. Meakins, Anton A Morozov, E. Veshchev
A new method for estimating the global erosion of beryllium (Be) in ITER is proposed. The method uses ray tracing-aided tomography to reconstruct the three-dimensional (3D) profile of beryllium visible-light emissivity in boundary plasma from images captured with filtered cameras of VIS/IR wide angle viewing system, H-alpha (and Visible) Spectroscopy diagnostics and signals collected with divertor impurity monitor. The light reflected into the detectors from metallic plasma-facing components (PFCs) is filtered out in the process. The reconstructed Be emissivity is then used to assess the Be influx density distribution along all Be PFCs by integrating the product of the emissivity and the S/XB coefficient along the normal to the PFC surface. The accuracy of this method is evaluated by a comparison with synthetic emissivity data produced by recent simulation of global Be erosion and migration in ITER using the ERO2.0 code. The impact of the uncertainty of PFC light reflection properties on the error in reconstructing the 3D Be emissivity profile and Be influx density is analyzed. The method allows to recover with good accuracy the Be influx density in plasma-wetted areas under the conditions of H-mode fusion power operation with high plasma density in far scrape-off layer (SOL). Under the conditions of lower far-SOL plasma density and L-mode operation, only the total Be influx integrated over the area of the first wall panels with relatively high Be erosion can be reconstructed with a high accuracy. It is shown that neglecting the effects of light reflection may lead to a twofold overestimation of the total Be influx.
提出了一种估算热核实验堆中铍 (Be) 全球侵蚀情况的新方法。该方法利用射线追踪辅助断层扫描技术，从 VIS/IR 广角观察系统的滤波相机捕获的图像、H-alpha（和可见光）光谱诊断以及分流器杂质监测器收集的信号中，重建边界等离子体中铍可见光发射率的三维（3D）轮廓。在此过程中，从面向等离子体的金属部件（PFC）反射到探测器的光被过滤掉。然后，利用重建的 Be 发射率，通过沿 PFC 表面法线积分发射率与 S/XB 系数的乘积，评估沿所有 Be PFC 的 Be 流入密度分布。通过与最近使用ERO2.0代码模拟ITER中全球Be侵蚀和迁移所产生的合成发射率数据进行比较，对该方法的准确性进行了评估。分析了 PFC 光反射特性的不确定性对重建三维 Be 发射率曲线和 Be 流入密度误差的影响。在远刮除层（SOL）等离子体密度较高的 H 模式核聚变功率运行条件下，该方法可以很准确地恢复等离子体浸润区的 Be 流入密度。在较低的远SOL等离子体密度和L模式运行条件下，只能高精度地重建Be侵蚀相对较高的第一壁板区域的Be流入总量。结果表明，忽略光反射的影响可能会导致 Be 总流入量被高估两倍。
{"title":"Assessing global beryllium erosion via tomographic reconstruction of 3D beryllium emission profiles in ITER","authors":"V. Neverov, R. Pitts, R. I. Khusnutdinov, Andrey G Alekseev, Evgeny Andreenko, Matthew Carr, Martin Kocan, Maarten De Bock, A. V. Gorshkov, Andrey M Kozlov, A. B. Kukushkin, J. Lovell, A. Meakins, Anton A Morozov, E. Veshchev","doi":"10.1088/1361-6587/ad1a3d","DOIUrl":"https://doi.org/10.1088/1361-6587/ad1a3d","url":null,"abstract":"A new method for estimating the global erosion of beryllium (Be) in ITER is proposed. The method uses ray tracing-aided tomography to reconstruct the three-dimensional (3D) profile of beryllium visible-light emissivity in boundary plasma from images captured with filtered cameras of VIS/IR wide angle viewing system, H-alpha (and Visible) Spectroscopy diagnostics and signals collected with divertor impurity monitor. The light reflected into the detectors from metallic plasma-facing components (PFCs) is filtered out in the process. The reconstructed Be emissivity is then used to assess the Be influx density distribution along all Be PFCs by integrating the product of the emissivity and the S/XB coefficient along the normal to the PFC surface. The accuracy of this method is evaluated by a comparison with synthetic emissivity data produced by recent simulation of global Be erosion and migration in ITER using the ERO2.0 code. The impact of the uncertainty of PFC light reflection properties on the error in reconstructing the 3D Be emissivity profile and Be influx density is analyzed. The method allows to recover with good accuracy the Be influx density in plasma-wetted areas under the conditions of H-mode fusion power operation with high plasma density in far scrape-off layer (SOL). Under the conditions of lower far-SOL plasma density and L-mode operation, only the total Be influx integrated over the area of the first wall panels with relatively high Be erosion can be reconstructed with a high accuracy. It is shown that neglecting the effects of light reflection may lead to a twofold overestimation of the total Be influx.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"25 3","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139451568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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