Pub Date : 2024-07-02DOI: 10.1088/1361-6587/ad5b85
A Jardin, D Mazon, J Bielecki, D Dworak, D Guibert, K Król, Y Savoye-Peysson, M Scholz, J Walkowiak and the WEST Team
X-ray tomography is a precious tool in tokamaks that provides rich information about the core plasma, such as local impurity concentration, electron temperature and density as well as magnetic equilibrium (ME) and magnetohydrodynamic activity. Nevertheless, inferring the local plasma emissivity from a sparse set of line-integrated measurements is an ill-posed problem that requires dedicated regularization and validation methods. Besides, speeding up the inversion algorithm in order to be compatible with real-time control systems is a challenging task with traditional approaches. In this contribution, in a first part we introduce tools aiming at validating and speeding up the x-ray tomographic inversions based on Tikhonov regularization, including ME constraint and parameter optimization, taking the WEST geometry as an example. In a second part, an alternative approach compatible with real-time, based on a set of neural networks is proposed and compared with the Tikhonov approach for an experimental case.
X 射线层析成像技术是托卡马克中的一项宝贵工具，可提供有关核心等离子体的丰富信息，如局部杂质浓度、电子温度和密度以及磁平衡（ME）和磁流体动力活动。然而，从一组稀疏的线积分测量值推断局部等离子体发射率是一个难以解决的问题，需要专门的正则化和验证方法。此外，加快反演算法的速度以便与实时控制系统兼容，对于传统方法来说也是一项具有挑战性的任务。在本文的第一部分，我们以 WEST 几何为例，介绍了旨在验证和加快基于 Tikhonov 正则化的 X 射线断层反演的工具，包括 ME 约束和参数优化。在第二部分中，我们提出了一种基于神经网络的与实时性兼容的替代方法，并在一个实验案例中与 Tikhonov 方法进行了比较。
{"title":"Validating and speeding up x-ray tomographic inversions in tokamak plasmas","authors":"A Jardin, D Mazon, J Bielecki, D Dworak, D Guibert, K Król, Y Savoye-Peysson, M Scholz, J Walkowiak and the WEST Team","doi":"10.1088/1361-6587/ad5b85","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5b85","url":null,"abstract":"X-ray tomography is a precious tool in tokamaks that provides rich information about the core plasma, such as local impurity concentration, electron temperature and density as well as magnetic equilibrium (ME) and magnetohydrodynamic activity. Nevertheless, inferring the local plasma emissivity from a sparse set of line-integrated measurements is an ill-posed problem that requires dedicated regularization and validation methods. Besides, speeding up the inversion algorithm in order to be compatible with real-time control systems is a challenging task with traditional approaches. In this contribution, in a first part we introduce tools aiming at validating and speeding up the x-ray tomographic inversions based on Tikhonov regularization, including ME constraint and parameter optimization, taking the WEST geometry as an example. In a second part, an alternative approach compatible with real-time, based on a set of neural networks is proposed and compared with the Tikhonov approach for an experimental case.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"39 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141502547","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 : 2024-06-27DOI: 10.1088/1361-6587/ad5a3a
T E Benedett, J Chen, D L Brower and W X Ding
Sawtooth crashes on tokamak plasmas exhibit relaxation much faster than resistive time scales via a mechanism not fully understood. Using core magnetic measurements from the Radial Interferometer-Polarimeter (RIP) diagnostic on the DIII-D tokamak, Grad–Shafranov equilibria constrained by internal magnetic measurements that have high time resolution ( µs) can be computed, allowing analysis of how equilibrium parameters such as safety factor q, current density J, and parallel electric field , particularly on-axis, evolve. At the sawtooth crash, on-axis safety factor q0 is observed to rise by 5% but remain below 1 throughout the cycle, and on-axis current density J0 is observed to drop by 5%. On-axis parallel electric field is found to be balanced by (resistivity times on-axis current density) except during the 200 µs crash period, where reaches 22 V m−1, exceeding by a factor of more than 2000. These first measurements in tokamak plasmas verify that generalized Ohm’s law is not balanced during the crash by resistive effects alone; this is a finding expected due to the relaxation being much faster than resistive timescales. Measurement of the electric field during the tokamak sawtooth serves to illuminate the physical mechanisms at work.
{"title":"Core inductive electric field during sawtooth crashes on DIII-D","authors":"T E Benedett, J Chen, D L Brower and W X Ding","doi":"10.1088/1361-6587/ad5a3a","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5a3a","url":null,"abstract":"Sawtooth crashes on tokamak plasmas exhibit relaxation much faster than resistive time scales via a mechanism not fully understood. Using core magnetic measurements from the Radial Interferometer-Polarimeter (RIP) diagnostic on the DIII-D tokamak, Grad–Shafranov equilibria constrained by internal magnetic measurements that have high time resolution ( µs) can be computed, allowing analysis of how equilibrium parameters such as safety factor q, current density J, and parallel electric field , particularly on-axis, evolve. At the sawtooth crash, on-axis safety factor q0 is observed to rise by 5% but remain below 1 throughout the cycle, and on-axis current density J0 is observed to drop by 5%. On-axis parallel electric field is found to be balanced by (resistivity times on-axis current density) except during the 200 µs crash period, where reaches 22 V m−1, exceeding by a factor of more than 2000. These first measurements in tokamak plasmas verify that generalized Ohm’s law is not balanced during the crash by resistive effects alone; this is a finding expected due to the relaxation being much faster than resistive timescales. Measurement of the electric field during the tokamak sawtooth serves to illuminate the physical mechanisms at work.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"19 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141502548","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 : 2024-06-26DOI: 10.1088/1361-6587/ad5586
M Madeira and R Jorge
With the advances in the optimization of magnetic field equilibria, stellarators have become a serious alternative to the tokamak, bringing this concept to the forefront of the pursuit of fusion energy. In order to be successful in experimentally demonstrating the viability of optimized stellarators, we must overcome any potential hurdles in the construction of its electromagnetic coils. Finding cost-effective ways of increasing the number of operating optimized stellarators could be key in cementing this magnetic confinement concept as a contender for a reactor. In this work, an alternative to modular coils, permanent magnets, are studied and are shown to enable the possibility of converting a tokamak into a stellarator. This is then applied to the case of ISTTOK tokamak, where an engineering design study is conducted.
{"title":"Tokamak to stellarator conversion using permanent magnets","authors":"M Madeira and R Jorge","doi":"10.1088/1361-6587/ad5586","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5586","url":null,"abstract":"With the advances in the optimization of magnetic field equilibria, stellarators have become a serious alternative to the tokamak, bringing this concept to the forefront of the pursuit of fusion energy. In order to be successful in experimentally demonstrating the viability of optimized stellarators, we must overcome any potential hurdles in the construction of its electromagnetic coils. Finding cost-effective ways of increasing the number of operating optimized stellarators could be key in cementing this magnetic confinement concept as a contender for a reactor. In this work, an alternative to modular coils, permanent magnets, are studied and are shown to enable the possibility of converting a tokamak into a stellarator. This is then applied to the case of ISTTOK tokamak, where an engineering design study is conducted.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"46 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141502549","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 : 2024-06-26DOI: 10.1088/1361-6587/ad5933
L Piron, S Jachmich, L Baylor, M Baruzzo, M Lehnen, P Carvalho, M Kong, P Martin, T Lo Presti Piccolo, S Silburn, D Terranova, D Valcarcel, JET Contributors and Eurofusion Tokamak Exploitation Team
In ITER, to mitigate the deleterious effects of plasma disruptions, massive quantities of radiating impurities will be injected into the disrupting plasma by shattered pellet injectors (SPI) to pre-emptively radiate away the stored thermal and magnetic energy (Lehnen et al Proc. 27th IAEA Fusion Energy Conf. (FEC 2018) (Gandhinagar, India) EX/P7-12). However, asymmetries in the radiation pattern could result in intense photon flashes during the thermal quench that could locally damage or erode the stainless steel plasma-facing surface of the diagnostic port plugs (Pitts et al 2015 J. Nucl. Mater.463 748–75). Experiments have been undertaken at JET to assess the potential dependence of the radiated power asymmetry on plasma energy during SPI mitigated disruptions. Calculations of the toroidal asymmetry in the radiated power indicate that the toroidal peaking factor is largest near the SPI position and decreases with the plasma stored energy, which is a promising result in view of radiation heat loads during mitigated disruptions in ITER.
{"title":"Radiation asymmetry in JET disruption mitigation experiments with shattered pellet injection","authors":"L Piron, S Jachmich, L Baylor, M Baruzzo, M Lehnen, P Carvalho, M Kong, P Martin, T Lo Presti Piccolo, S Silburn, D Terranova, D Valcarcel, JET Contributors and Eurofusion Tokamak Exploitation Team","doi":"10.1088/1361-6587/ad5933","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5933","url":null,"abstract":"In ITER, to mitigate the deleterious effects of plasma disruptions, massive quantities of radiating impurities will be injected into the disrupting plasma by shattered pellet injectors (SPI) to pre-emptively radiate away the stored thermal and magnetic energy (Lehnen et al Proc. 27th IAEA Fusion Energy Conf. (FEC 2018) (Gandhinagar, India) EX/P7-12). However, asymmetries in the radiation pattern could result in intense photon flashes during the thermal quench that could locally damage or erode the stainless steel plasma-facing surface of the diagnostic port plugs (Pitts et al 2015 J. Nucl. Mater.463 748–75). Experiments have been undertaken at JET to assess the potential dependence of the radiated power asymmetry on plasma energy during SPI mitigated disruptions. Calculations of the toroidal asymmetry in the radiated power indicate that the toroidal peaking factor is largest near the SPI position and decreases with the plasma stored energy, which is a promising result in view of radiation heat loads during mitigated disruptions in ITER.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"8 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141502550","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 : 2024-06-26DOI: 10.1088/1361-6587/ad59c4
Jielin Shi, Hideki Kaizawa, Yuta Uematsu, Hirohiko Tanaka, Shin Kajita, Noriyasu Ohno, Keiji Sawada and Hongbin Ding
The detachment processes of the hydrogen (H) and deuterium (D) plasmas are comparatively investigated in the linear plasma device NAGDIS-II. The laser Thomson scattering measurements demonstrate that the recombination rate of the H plasma is greater than that of the D plasma as the neutral pressure increases in the molecular activated recombination (MAR) dominant detachment phase. As the recombination process by MAR is strongly dependent on the vibrational and rotationally excited states of the molecule, the rovibrational quantum state populations of the H and D molecules are measured using the Fulcher-α band spectroscopy. The results indicate that the vibrational temperature in the electronic ground state is considerably higher than the rotational temperature during detachment. The reaction rate coefficients for MARs due to charge exchange chains (CX-MAR) and dissociative attachment chains (DA-MAR) are calculated by the collision-radiation model under the measured temperature conditions. It can be observed that the CX-MAR is larger than the DA-MAR for both H and D, and that the CX-MAR of H is larger than the CX-MAR of D at electron temperatures Te above 1 eV. In consideration of the experimentally observed vibrational and rotational excitation temperatures, the reaction rate coefficients of CX-MAR and DA-MAR are increasing in the low Te region. These calculations are in accordance with the experimental results, which indicate that recombination processes due to MAR are more predominant in the H plasma compared to the D plasma. Furthermore, a transition from MAR to electron–ion recombination processes is observed in the D plasma at Te below 0.5 eV.
在线性等离子体装置 NAGDIS-II 中，对氢（H）和氘（D）等离子体的分离过程进行了比较研究。激光汤姆逊散射测量结果表明，在分子活化重组（MAR）占主导地位的脱离阶段，随着中性压力的增加，氢等离子体的重组速率大于氘等离子体。由于 MAR 的重组过程与分子的振动态和旋转激发态密切相关，因此使用富彻-α 波段光谱法测量了 H 和 D 分子的旋转振动量子态种群。结果表明，在脱离过程中，电子基态的振动温度大大高于旋转温度。在测得的温度条件下，通过碰撞辐射模型计算了电荷交换链（CX-MAR）和分离附着链（DA-MAR）引起的 MAR 的反应速率系数。可以发现，H 和 D 的 CX-MAR 均大于 DA-MAR，而且在电子温度 Te 超过 1 eV 时，H 的 CX-MAR 大于 D 的 CX-MAR。考虑到实验观测到的振动和旋转激发温度，在低 Te 区域，CX-MAR 和 DA-MAR 的反应速率系数都在增加。这些计算与实验结果相符，实验结果表明，与 D 等离子体相比，MAR 导致的重组过程在 H 等离子体中更占优势。此外，在 Te 低于 0.5 eV 的 D 等离子体中，可以观察到从 MAR 向电子-离子重组过程的过渡。
{"title":"Hydrogen isotope effects on recombination dominant plasmas in NAGDIS-II","authors":"Jielin Shi, Hideki Kaizawa, Yuta Uematsu, Hirohiko Tanaka, Shin Kajita, Noriyasu Ohno, Keiji Sawada and Hongbin Ding","doi":"10.1088/1361-6587/ad59c4","DOIUrl":"https://doi.org/10.1088/1361-6587/ad59c4","url":null,"abstract":"The detachment processes of the hydrogen (H) and deuterium (D) plasmas are comparatively investigated in the linear plasma device NAGDIS-II. The laser Thomson scattering measurements demonstrate that the recombination rate of the H plasma is greater than that of the D plasma as the neutral pressure increases in the molecular activated recombination (MAR) dominant detachment phase. As the recombination process by MAR is strongly dependent on the vibrational and rotationally excited states of the molecule, the rovibrational quantum state populations of the H and D molecules are measured using the Fulcher-α band spectroscopy. The results indicate that the vibrational temperature in the electronic ground state is considerably higher than the rotational temperature during detachment. The reaction rate coefficients for MARs due to charge exchange chains (CX-MAR) and dissociative attachment chains (DA-MAR) are calculated by the collision-radiation model under the measured temperature conditions. It can be observed that the CX-MAR is larger than the DA-MAR for both H and D, and that the CX-MAR of H is larger than the CX-MAR of D at electron temperatures Te above 1 eV. In consideration of the experimentally observed vibrational and rotational excitation temperatures, the reaction rate coefficients of CX-MAR and DA-MAR are increasing in the low Te region. These calculations are in accordance with the experimental results, which indicate that recombination processes due to MAR are more predominant in the H plasma compared to the D plasma. Furthermore, a transition from MAR to electron–ion recombination processes is observed in the D plasma at Te below 0.5 eV.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"21 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141502551","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 : 2024-06-12DOI: 10.1088/1361-6587/ad5379
Arghya Mukherjee and Daniel Seipt
In this paper, we have studied the influence of laser polarization on the dynamics of the ionization-injected electron beams, and subsequently, the properties of the emitted betatron radiation in laser wakefield accelerators (LWFAs). While ionizing by strong field laser radiation, the generated photo-electrons carry a residual transverse momentum in excess of the ionization potential via the above threshold ionization (ATI) process. This ATI momentum explicitly depends on the polarization state of the ionizing laser and eventually governs the dynamics of the electron beam trapped inside the wake potential. In order to systematically investigate the effect of the laser polarization, here, we have employed complete three-dimensional particle-in-cell simulations in the nonlinear bubble regime of the LWFAs. We focus, in particular, on the effects the laser polarization has on the ionization injection mechanism, and how these features affect the final beam properties, such as beam charge, energy, energy spread, and transverse emittance. We have also found that as the laser polarization gradually changes from linear to circular, the helicity of the electron trajectory, and hence the angular momentum carried by the beam, increases significantly. Studies have been further extended to reveal the effect of laser polarization on the radiation emitted by the accelerated electrons. The far-field radiation spectra have been calculated for the linear and circular polarization states of the laser. It has been shown that the spatial distributions and the polarization properties (Stokes parameters) of the emitted radiation in the above two cases are substantially different. Therefore, our study provides a facile and efficient alternative to regulate the properties of the accelerated electron beams and x-ray radiation in LWFAs, utilizing ionization injection mechanism.
在本文中，我们研究了激光偏振对电离注入电子束动力学的影响，以及随后激光汪场加速器（LWFA）中发射的倍他辐射的特性。在强场激光辐射电离时，产生的光电子通过阈值以上电离（ATI）过程携带超过电离势的剩余横向动量。这种 ATI 动量明确取决于电离激光的偏振态，并最终控制着唤醒势内电子束的动态。为了系统地研究激光偏振的影响，我们在此采用了完整的三维粒子在胞模拟，模拟了 LWFAs 的非线性气泡机制。我们尤其关注激光偏振对电离注入机制的影响，以及这些特征如何影响最终光束的特性，如光束电荷、能量、能量扩散和横向幅射。我们还发现，当激光偏振从线性逐渐变为圆形时，电子轨迹的螺旋度以及光束携带的角动量会显著增加。研究进一步扩展到揭示激光偏振对加速电子辐射的影响。我们计算了激光线性和圆极化状态下的远场辐射光谱。结果表明，上述两种情况下发射辐射的空间分布和偏振特性（斯托克斯参数）大不相同。因此，我们的研究为利用电离注入机制调节 LWFA 中的加速电子束和 X 射线辐射特性提供了一种简便而有效的替代方法。
{"title":"Laser polarization control of ionization-injected electron beams and x-ray radiation in laser wakefield accelerators","authors":"Arghya Mukherjee and Daniel Seipt","doi":"10.1088/1361-6587/ad5379","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5379","url":null,"abstract":"In this paper, we have studied the influence of laser polarization on the dynamics of the ionization-injected electron beams, and subsequently, the properties of the emitted betatron radiation in laser wakefield accelerators (LWFAs). While ionizing by strong field laser radiation, the generated photo-electrons carry a residual transverse momentum in excess of the ionization potential via the above threshold ionization (ATI) process. This ATI momentum explicitly depends on the polarization state of the ionizing laser and eventually governs the dynamics of the electron beam trapped inside the wake potential. In order to systematically investigate the effect of the laser polarization, here, we have employed complete three-dimensional particle-in-cell simulations in the nonlinear bubble regime of the LWFAs. We focus, in particular, on the effects the laser polarization has on the ionization injection mechanism, and how these features affect the final beam properties, such as beam charge, energy, energy spread, and transverse emittance. We have also found that as the laser polarization gradually changes from linear to circular, the helicity of the electron trajectory, and hence the angular momentum carried by the beam, increases significantly. Studies have been further extended to reveal the effect of laser polarization on the radiation emitted by the accelerated electrons. The far-field radiation spectra have been calculated for the linear and circular polarization states of the laser. It has been shown that the spatial distributions and the polarization properties (Stokes parameters) of the emitted radiation in the above two cases are substantially different. Therefore, our study provides a facile and efficient alternative to regulate the properties of the accelerated electron beams and x-ray radiation in LWFAs, utilizing ionization injection mechanism.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"31 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141502664","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 : 2024-06-11DOI: 10.1088/1361-6587/ad5104
Vojtech Munzar, George Dowhan, Daniel Klir, Jan Novotny, Karel Rezac, Joe Chen, Jakub Cikhardt, Balzima Cikhardtova, Vojtech Juras, Nicholas Jordan, Pavel Kubes, Jakub Malir, Landon Tafoya, Karel Turek, Ryan McBride
We report on the results of point-projection ion deflectometry measurements from a mid-size university z-pinch experiment. A 1 MA 8 kJ LTD generator at the University of Michigan (called MAIZE) drove a hybrid x-pinch (HXP) with a deuterated polyethylene fiber load to produce a point-like source of MeV ions for backlighting. In these experiments, 2.7 MeV protons were generated by DD beam-target fusion reactions. Due to the kinematics of beam-target fusion, the proton energies were down-shifted from the more standard 3.02 MeV proton energy that is released from the center-of-mass rest frame of a DD reaction. In addition to the 2.7 MeV protons, strongly anisotropic beams of 3 MeV accelerated deuterons were detected by ion diagnostics placed at a radial distance of 90 mm from the x-pinch. Numerical reconstruction of experimental data generated by deflected hydrogen ion trajectories evaluated the total current in the vacuum load region. Numerical ion-tracking simulations show that accelerated deuteron beams exited the ion source region at large angles with respect to the pinch current direction.
{"title":"Self-driven ion deflectometry measurements using MeV fusion-driven protons and accelerated deuterons in the deuterated hybrid x-pinch on the MAIZE LTD generator","authors":"Vojtech Munzar, George Dowhan, Daniel Klir, Jan Novotny, Karel Rezac, Joe Chen, Jakub Cikhardt, Balzima Cikhardtova, Vojtech Juras, Nicholas Jordan, Pavel Kubes, Jakub Malir, Landon Tafoya, Karel Turek, Ryan McBride","doi":"10.1088/1361-6587/ad5104","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5104","url":null,"abstract":"We report on the results of point-projection ion deflectometry measurements from a mid-size university z-pinch experiment. A 1 MA 8 kJ LTD generator at the University of Michigan (called MAIZE) drove a hybrid x-pinch (HXP) with a deuterated polyethylene fiber load to produce a point-like source of MeV ions for backlighting. In these experiments, 2.7 MeV protons were generated by DD beam-target fusion reactions. Due to the kinematics of beam-target fusion, the proton energies were down-shifted from the more standard 3.02 MeV proton energy that is released from the center-of-mass rest frame of a DD reaction. In addition to the 2.7 MeV protons, strongly anisotropic beams of 3 MeV accelerated <italic toggle=\"yes\">deuterons</italic> were detected by ion diagnostics placed at a radial distance of 90 mm from the x-pinch. Numerical reconstruction of experimental data generated by deflected hydrogen ion trajectories evaluated the total current in the vacuum load region. Numerical ion-tracking simulations show that accelerated deuteron beams exited the ion source region at large angles with respect to the pinch current direction.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"4 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141502665","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 : 2024-06-10DOI: 10.1088/1361-6587/ad4f10
Qiusun Zeng, Igor Kotelnikov
MHD stabilization of flute and ballooning modes in an axisymmetric mirror trap is studied under the assumption of strong finite Larmor radius effect that suppresses all perturbations with azimuthal numbers <inline-formula> <tex-math><?CDATA $municode{x2A7E}2$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mi>m</mml:mi><mml:mtext>⩾</mml:mtext><mml:mn>2</mml:mn></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad4f10ieqn1.gif" xlink:type="simple"></inline-graphic> </inline-formula> and makes the <italic toggle="yes">m</italic> = 1 mode ‘rigid’. The rigid mode can be effectively suppressed using perfectly conducting lateral wall without any additional means of stabilization or in combination with end MHD anchors. Numerical calculations were carried out for an anisotropic plasma produced in the course of neutral beam injection into the minimum of the magnetic field at the right angle to the trap axis. The stabilizing effect of the conducting shell made of a straightened cylinder is compared with a proportional chamber, which, on an enlarged scale, repeats the shape of the plasma column. It is confirmed that for convincing wall stabilization of the rigid modes, the plasma beta (<italic toggle="yes">β</italic>, the ratio of the plasma pressure to the magnetic field pressure) must exceed some critical value <inline-formula> <tex-math><?CDATA $beta_{text{cr}2}$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:msub><mml:mi>β</mml:mi><mml:mrow><mml:mtext>cr</mml:mtext><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad4f10ieqn2.gif" xlink:type="simple"></inline-graphic> </inline-formula>. When conducting lateral wall is combined with conducting end plates imitating MHD end anchors, there are two critical betas and, respectively, two stability zones <inline-formula> <tex-math><?CDATA $beta lt beta_{text{cr}1}$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mi>β</mml:mi><mml:mo><</mml:mo><mml:msub><mml:mi>β</mml:mi><mml:mrow><mml:mtext>cr</mml:mtext><mml:mn>1</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad4f10ieqn3.gif" xlink:type="simple"></inline-graphic> </inline-formula> and <inline-formula> <tex-math><?CDATA $beta gt beta_{text{cr}2}$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mi>β</mml:mi><mml:mo>></mml:mo><mml:msub><mml:mi>β</mml:mi><mml:mrow><mml:mtext>cr</mml:mtext><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad4f10ieqn4.gif" xlink:type="simple"></inline-graphic> </inline-formula> that can merge, making the entire range <inline-formula> <tex-math><?CDATA $0 lt beta lt 1$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mn>0</mml:mn><mml:mo><</mml:mo><mml:mi>β</mml:mi><mml:mo><</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad4f10ieqn5.gif" xlink:type="simple"></inline-graphic> </inline-formula> of betas allowable for stab
{"title":"Influence of the shape of a conducting chamber on the stability of rigid ballooning modes in a mirror trap","authors":"Qiusun Zeng, Igor Kotelnikov","doi":"10.1088/1361-6587/ad4f10","DOIUrl":"https://doi.org/10.1088/1361-6587/ad4f10","url":null,"abstract":"MHD stabilization of flute and ballooning modes in an axisymmetric mirror trap is studied under the assumption of strong finite Larmor radius effect that suppresses all perturbations with azimuthal numbers <inline-formula>\u0000<tex-math><?CDATA $municode{x2A7E}2$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>m</mml:mi><mml:mtext>⩾</mml:mtext><mml:mn>2</mml:mn></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad4f10ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> and makes the <italic toggle=\"yes\">m</italic> = 1 mode ‘rigid’. The rigid mode can be effectively suppressed using perfectly conducting lateral wall without any additional means of stabilization or in combination with end MHD anchors. Numerical calculations were carried out for an anisotropic plasma produced in the course of neutral beam injection into the minimum of the magnetic field at the right angle to the trap axis. The stabilizing effect of the conducting shell made of a straightened cylinder is compared with a proportional chamber, which, on an enlarged scale, repeats the shape of the plasma column. It is confirmed that for convincing wall stabilization of the rigid modes, the plasma beta (<italic toggle=\"yes\">β</italic>, the ratio of the plasma pressure to the magnetic field pressure) must exceed some critical value <inline-formula>\u0000<tex-math><?CDATA $beta_{text{cr}2}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:msub><mml:mi>β</mml:mi><mml:mrow><mml:mtext>cr</mml:mtext><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad4f10ieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>. When conducting lateral wall is combined with conducting end plates imitating MHD end anchors, there are two critical betas and, respectively, two stability zones <inline-formula>\u0000<tex-math><?CDATA $beta lt beta_{text{cr}1}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>β</mml:mi><mml:mo><</mml:mo><mml:msub><mml:mi>β</mml:mi><mml:mrow><mml:mtext>cr</mml:mtext><mml:mn>1</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad4f10ieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> and <inline-formula>\u0000<tex-math><?CDATA $beta gt beta_{text{cr}2}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>β</mml:mi><mml:mo>></mml:mo><mml:msub><mml:mi>β</mml:mi><mml:mrow><mml:mtext>cr</mml:mtext><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad4f10ieqn4.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> that can merge, making the entire range <inline-formula>\u0000<tex-math><?CDATA $0 lt beta lt 1$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mn>0</mml:mn><mml:mo><</mml:mo><mml:mi>β</mml:mi><mml:mo><</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad4f10ieqn5.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> of betas allowable for stab","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"52 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141502668","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 : 2024-06-07DOI: 10.1088/1361-6587/ad5229
F Bagnato, B P Duval, O Sauter, S Coda, A Karpushov, A Merle, B Labit, O Fevrier, A Pau, D Mykytchuk, L Porte, J Ball
Carbon impurity transport is studied in the TCV tokamak using a charge exchange recombination diagnostic. TCVs flexible shaping capabilities were exploited to extend previous impurity transport studies to negative triangularity (<italic toggle="yes">δ</italic> < 0). A practical way of studying light impurity transport (like C, TCVs main impurity species due to graphite tiled walls) is to investigate the correlations between the impurity ion gradients that, in this study, highlighted significant differences between positive (PT) and negative <italic toggle="yes">δ</italic> (NT) plasma configurations. <italic toggle="yes">δ</italic> scans (<inline-formula> <tex-math><?CDATA $-0.6ltdeltalt +0.6$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mo>−</mml:mo><mml:mn>0.6</mml:mn><mml:mo><</mml:mo><mml:mi>δ</mml:mi><mml:mo><</mml:mo><mml:mo>+</mml:mo><mml:mn>0.6</mml:mn></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad5229ieqn1.gif" xlink:type="simple"></inline-graphic> </inline-formula>) were performed in limited configurations, but displayed little correlation between C temperature, rotation and density gradients for positive <italic toggle="yes">δ</italic>. This stiff response for <italic toggle="yes">δ</italic> > 0 changes for negative <italic toggle="yes">δ</italic>, where the evolution of <inline-formula> <tex-math><?CDATA $nabla v_mathrm{tor}$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mi mathvariant="normal">∇</mml:mi><mml:msub><mml:mi>v</mml:mi><mml:mrow><mml:mi>tor</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad5229ieqn2.gif" xlink:type="simple"></inline-graphic> </inline-formula> was accompanied by variations of <inline-formula> <tex-math><?CDATA $nabla n_mathrm{C}$?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mi mathvariant="normal">∇</mml:mi><mml:msub><mml:mi>n</mml:mi><mml:mrow><mml:mi mathvariant="normal">C</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad5229ieqn3.gif" xlink:type="simple"></inline-graphic> </inline-formula> over a range of negative <italic toggle="yes">δ</italic>, showing that transport, in NT, is affected by velocity gradients. Similar <italic toggle="yes">δ</italic> scans were performed with additional NBH (Neutral Beam Heating), with power steps ranging from 0.25 MW to 1.25 MW, highlighting increased momentum confinement in negative <italic toggle="yes">δ</italic>. Finally, the evolution of intrinsic plasma toroidal rotation across linear to saturated ohmic confinement regime (LOC/SOC) transitions was explored at <italic toggle="yes">δ</italic> < 0, expanding previous studies performed in TCV for <inline-formula> <tex-math><?CDATA $delta gt $?></tex-math> <mml:math overflow="scroll"><mml:mrow><mml:mi>δ</mml:mi><mml:mo>></mml:mo></mml:mrow></mml:math> <inline-graphic xlink:href="ppcfad5229ieqn4.gif" xlink:type="simple"></inline-graphic> </inline-formula> 0 (Bagnato <italic toggle="yes">
{"title":"Study of impurity C transport and plasma rotation in negative triangularity on the TCV tokamak","authors":"F Bagnato, B P Duval, O Sauter, S Coda, A Karpushov, A Merle, B Labit, O Fevrier, A Pau, D Mykytchuk, L Porte, J Ball","doi":"10.1088/1361-6587/ad5229","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5229","url":null,"abstract":"Carbon impurity transport is studied in the TCV tokamak using a charge exchange recombination diagnostic. TCVs flexible shaping capabilities were exploited to extend previous impurity transport studies to negative triangularity (<italic toggle=\"yes\">δ</italic> < 0). A practical way of studying light impurity transport (like C, TCVs main impurity species due to graphite tiled walls) is to investigate the correlations between the impurity ion gradients that, in this study, highlighted significant differences between positive (PT) and negative <italic toggle=\"yes\">δ</italic> (NT) plasma configurations. <italic toggle=\"yes\">δ</italic> scans (<inline-formula>\u0000<tex-math><?CDATA $-0.6ltdeltalt +0.6$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mo>−</mml:mo><mml:mn>0.6</mml:mn><mml:mo><</mml:mo><mml:mi>δ</mml:mi><mml:mo><</mml:mo><mml:mo>+</mml:mo><mml:mn>0.6</mml:mn></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad5229ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>) were performed in limited configurations, but displayed little correlation between C temperature, rotation and density gradients for positive <italic toggle=\"yes\">δ</italic>. This stiff response for <italic toggle=\"yes\">δ</italic> > 0 changes for negative <italic toggle=\"yes\">δ</italic>, where the evolution of <inline-formula>\u0000<tex-math><?CDATA $nabla v_mathrm{tor}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi mathvariant=\"normal\">∇</mml:mi><mml:msub><mml:mi>v</mml:mi><mml:mrow><mml:mi>tor</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad5229ieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> was accompanied by variations of <inline-formula>\u0000<tex-math><?CDATA $nabla n_mathrm{C}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi mathvariant=\"normal\">∇</mml:mi><mml:msub><mml:mi>n</mml:mi><mml:mrow><mml:mi mathvariant=\"normal\">C</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad5229ieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> over a range of negative <italic toggle=\"yes\">δ</italic>, showing that transport, in NT, is affected by velocity gradients. Similar <italic toggle=\"yes\">δ</italic> scans were performed with additional NBH (Neutral Beam Heating), with power steps ranging from 0.25 MW to 1.25 MW, highlighting increased momentum confinement in negative <italic toggle=\"yes\">δ</italic>. Finally, the evolution of intrinsic plasma toroidal rotation across linear to saturated ohmic confinement regime (LOC/SOC) transitions was explored at <italic toggle=\"yes\">δ</italic> < 0, expanding previous studies performed in TCV for <inline-formula>\u0000<tex-math><?CDATA $delta gt $?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi>δ</mml:mi><mml:mo>></mml:mo></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"ppcfad5229ieqn4.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> 0 (Bagnato <italic toggle=\"yes\">","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"21 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141502666","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 : 2024-06-06DOI: 10.1088/1361-6587/ad5105
Y Kosuga, J Bourgeois, M Lesur, I Oyama
A theory is presented to describe fluctuation dynamics in magnetized plasmas with impurities. In particular, it is shown that impurities can significantly facilitate an abrupt transient increase of fluctuation amplitude. To demonstrate this, a fluid model is derived to describe how impurities enter fluctuation dynamics. At the linear level, a wave similar to a drift wave can be excited in the presence of impurities. The nonlinear dynamics of this wave is formulated via modulational analysis, and it is demonstrated that drift waves with impurities can develop into a breather, a nonlinear wave that exhibits transient increase of amplitude. Our model indicates that nonlinear breathers become easier to be excited as impurity concentration increases. Breathers transiently increase fluctuation amplitude, and hence may be important to expel impurities. Implications on basic experiments and magnetic fusion are discussed as well.
{"title":"Breathing impure plasmas","authors":"Y Kosuga, J Bourgeois, M Lesur, I Oyama","doi":"10.1088/1361-6587/ad5105","DOIUrl":"https://doi.org/10.1088/1361-6587/ad5105","url":null,"abstract":"A theory is presented to describe fluctuation dynamics in magnetized plasmas with impurities. In particular, it is shown that impurities can significantly facilitate an abrupt transient increase of fluctuation amplitude. To demonstrate this, a fluid model is derived to describe how impurities enter fluctuation dynamics. At the linear level, a wave similar to a drift wave can be excited in the presence of impurities. The nonlinear dynamics of this wave is formulated via modulational analysis, and it is demonstrated that drift waves with impurities can develop into a breather, a nonlinear wave that exhibits transient increase of amplitude. Our model indicates that nonlinear breathers become easier to be excited as impurity concentration increases. Breathers transiently increase fluctuation amplitude, and hence may be important to expel impurities. Implications on basic experiments and magnetic fusion are discussed as well.","PeriodicalId":20239,"journal":{"name":"Plasma Physics and Controlled Fusion","volume":"25 1","pages":""},"PeriodicalIF":2.2,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141502667","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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