Pub Date : 2020-06-25DOI: 10.1103/physrevresearch.2.033226
V. Nosenko, F. Luoni, A. Kaouk, M. Rubin-Zuzic, H. Thomas
Active Janus particles suspended in a plasma were studied experimentally. The Janus particles were micron-size plastic microspheres, one half of which was coated with a thin layer of platinum. They were suspended in the plasma sheath of a radio-frequency discharge in argon at low pressure. The Janus particles moved in characteristic looped trajectories suggesting a combination of spinning and circling motion; their interactions led to the emergence of rich dynamics characterized by non-Maxwellian velocity distribution. The particle propulsion mechanism is discussed, the main force driving the particle motion is identified as photophoretic force.
{"title":"Active Janus particles in a complex plasma","authors":"V. Nosenko, F. Luoni, A. Kaouk, M. Rubin-Zuzic, H. Thomas","doi":"10.1103/physrevresearch.2.033226","DOIUrl":"https://doi.org/10.1103/physrevresearch.2.033226","url":null,"abstract":"Active Janus particles suspended in a plasma were studied experimentally. The Janus particles were micron-size plastic microspheres, one half of which was coated with a thin layer of platinum. They were suspended in the plasma sheath of a radio-frequency discharge in argon at low pressure. The Janus particles moved in characteristic looped trajectories suggesting a combination of spinning and circling motion; their interactions led to the emergence of rich dynamics characterized by non-Maxwellian velocity distribution. The particle propulsion mechanism is discussed, the main force driving the particle motion is identified as photophoretic force.","PeriodicalId":8461,"journal":{"name":"arXiv: Plasma Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83158609","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-06-23DOI: 10.1103/physrevaccelbeams.23.111304
Tianhong Wang, V. Khudik, G. Shvets
Propagation distances of intense laser pulses and high-charge electron beams through the plasma are, respectively, limited by diffraction and self-deceleration. This imposes severe constraints on the performance of the two major advanced accelerator concepts: laser and plasma wakefield accelerators. Using numerical simulations, we demonstrate that when the two beams co-propagate in the plasma, they can interact synergistically and extend each other's travel distances. The key interactions responsible for the synergy are found to be laser channeling by the electron bunch, and direct laser acceleration of the bunch electrons by the laser pulse. Remarkably, the amount of energy transferred from the laser pulse to the plasma can be increased by several times by the guiding electron bunch despite its small energy content. Implications of such synergistic interactions for the high-gradient acceleration of externally injected witness charges are discussed, and a new concept of a Laser-pulse and Electron-bunch Plasma Accelerator (LEPA) is formulated.
{"title":"Laser-pulse and electron-bunch plasma wakefield accelerator","authors":"Tianhong Wang, V. Khudik, G. Shvets","doi":"10.1103/physrevaccelbeams.23.111304","DOIUrl":"https://doi.org/10.1103/physrevaccelbeams.23.111304","url":null,"abstract":"Propagation distances of intense laser pulses and high-charge electron beams through the plasma are, respectively, limited by diffraction and self-deceleration. This imposes severe constraints on the performance of the two major advanced accelerator concepts: laser and plasma wakefield accelerators. Using numerical simulations, we demonstrate that when the two beams co-propagate in the plasma, they can interact synergistically and extend each other's travel distances. The key interactions responsible for the synergy are found to be laser channeling by the electron bunch, and direct laser acceleration of the bunch electrons by the laser pulse. Remarkably, the amount of energy transferred from the laser pulse to the plasma can be increased by several times by the guiding electron bunch despite its small energy content. Implications of such synergistic interactions for the high-gradient acceleration of externally injected witness charges are discussed, and a new concept of a Laser-pulse and Electron-bunch Plasma Accelerator (LEPA) is formulated.","PeriodicalId":8461,"journal":{"name":"arXiv: Plasma Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89821422","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Huijts, I. Andriyash, L. Rovige, A. Vernier, J. Faure
Driving laser wakefield acceleration with extremely short, near single-cycle laser pulses is crucial to the realisation of an electron source that can operate at kHz-repetition rate while relying on modest laser energy. It is also interesting from a fundamental point of view, as the ponderomotive approximation is no longer valid for such short pulses. Through particle-in-cell simulations, we show how the plasma response becomes asymmetric in the plane of laser polarization, and dependent on the carrier-envelope phase (CEP) of the laser pulse. For the case of self-injection, this in turn strongly affects the initial conditions of injected electrons, causing collective betatron oscillations of the electron beam. As a result, the beam pointing and electron energy spectrum become CEP-dependent. For injection in a density gradient these effects are reduced, as electron injection is mostly longitudinal and mainly determined by the density gradient. Our results highlight the importance of controlling the CEP in this regime for producing stable and reproducible relativistic electron beams. Mitigation of CEP effects can nevertheless be achieved using density gradient injection.
{"title":"Identifying observable carrier-envelope phase effects in laser wakefield acceleration with near-single-cycle pulses","authors":"J. Huijts, I. Andriyash, L. Rovige, A. Vernier, J. Faure","doi":"10.1063/5.0037925","DOIUrl":"https://doi.org/10.1063/5.0037925","url":null,"abstract":"Driving laser wakefield acceleration with extremely short, near single-cycle laser pulses is crucial to the realisation of an electron source that can operate at kHz-repetition rate while relying on modest laser energy. It is also interesting from a fundamental point of view, as the ponderomotive approximation is no longer valid for such short pulses. Through particle-in-cell simulations, we show how the plasma response becomes asymmetric in the plane of laser polarization, and dependent on the carrier-envelope phase (CEP) of the laser pulse. For the case of self-injection, this in turn strongly affects the initial conditions of injected electrons, causing collective betatron oscillations of the electron beam. As a result, the beam pointing and electron energy spectrum become CEP-dependent. For injection in a density gradient these effects are reduced, as electron injection is mostly longitudinal and mainly determined by the density gradient. Our results highlight the importance of controlling the CEP in this regime for producing stable and reproducible relativistic electron beams. Mitigation of CEP effects can nevertheless be achieved using density gradient injection.","PeriodicalId":8461,"journal":{"name":"arXiv: Plasma Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81170532","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Tochitsky, A. Pak, F. Fiuza, D. Haberberger, N. Lemos, A. Link, D. Froula, C. Joshi
This paper overviews experimental and numerical results on acceleration of narrow energy spread ion beams by an electrostatic collisionless shockwave driven by 1 um (Omega EP) and 10 um (UCLA Neptune Laboratory) lasers in near critical density CH and He plasmas, respectively. Shock waves in CH targets produced high-energy 50 MeV protons (energy spread of <30%) and 314 MeV C6+ ions (energy spread of <10%). Observation of acceleration of both protons and carbon ions to similar velocities is consistent with reflection of particles off the moving potential of a shock front. For shocks driven by CO2 laser in a gas jet, 30 MeV peak in He ion spectrum was detected. Particle-in-cell simulations indicate that regardless of the target further control over its density profile is needed for optimization of accelerated ion beams in part of energy spread, yield and maximum kinetic energy.
本文综述了在近临界密度CH和He等离子体中，由1 um (Omega EP)和10 um (UCLA Neptune Laboratory)激光器驱动的静电无碰撞冲击波对窄能量扩散离子束加速的实验和数值结果。CH靶中的激波产生50 MeV的高能质子(能量扩散<30%)和314 MeV的C6+离子(能量扩散<10%)。质子和碳离子加速到相似速度的观测结果与粒子在激波锋面运动势下的反射一致。对于气体射流中CO2激光驱动的冲击，在He离子谱中检测到30mev的峰值。细胞内粒子模拟表明，无论目标如何，加速离子束在能量扩散、产率和最大动能方面的优化都需要进一步控制其密度分布。
{"title":"Laser-driven collisionless shock acceleration of ions from near-critical plasmas","authors":"S. Tochitsky, A. Pak, F. Fiuza, D. Haberberger, N. Lemos, A. Link, D. Froula, C. Joshi","doi":"10.1063/1.5144446","DOIUrl":"https://doi.org/10.1063/1.5144446","url":null,"abstract":"This paper overviews experimental and numerical results on acceleration of narrow energy spread ion beams by an electrostatic collisionless shockwave driven by 1 um (Omega EP) and 10 um (UCLA Neptune Laboratory) lasers in near critical density CH and He plasmas, respectively. Shock waves in CH targets produced high-energy 50 MeV protons (energy spread of <30%) and 314 MeV C6+ ions (energy spread of <10%). Observation of acceleration of both protons and carbon ions to similar velocities is consistent with reflection of particles off the moving potential of a shock front. For shocks driven by CO2 laser in a gas jet, 30 MeV peak in He ion spectrum was detected. Particle-in-cell simulations indicate that regardless of the target further control over its density profile is needed for optimization of accelerated ion beams in part of energy spread, yield and maximum kinetic energy.","PeriodicalId":8461,"journal":{"name":"arXiv: Plasma Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81136242","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Analysis of driven dust vortex flow is presented in a weakly magnetized plasma. The 2D hydrodynamic model is applied to the confined dust cloud in a non-uniform magnetic field in order to recover the dust vortex flow driven in a conservative force field setup, in absence of any non-conservative fields or dust charge variation. Although the time independent electric and magnetic fields included in the analysis provide conservative forcing mechanisms, when the a drift based mechanism, recently observed in a dusty plasma experiment by [M. Puttscher and A. Melzer, Physics of Plasmas, 21,123704(2014)] is considered, the dust vortex flow solutions are shown to be recovered. We have examined the case where purely ambipolar electric field, generated by polarization produced by electron E*B drift, drives the dust flow. A sheared E*B drift flow is facilitated by the magnetic field gradient, driving the vortex flow in the absence of ion drag. The analytical stream-function solutions have been analyzed with varying magnetic field strength, its gradient and kinematic viscosity of the dust fluid. The effect of B field gradient is analyzed which contrasts that of E field gradient present in the plasma sheath.
对弱磁化等离子体中驱动尘埃涡旋流动进行了分析。将二维流体力学模型应用于非均匀磁场条件下的密闭尘云，在不存在非保守场和尘荷变化的情况下，恢复了在保守力场条件下驱动的尘涡流动。虽然分析中包含的与时间无关的电场和磁场提供了保守的强迫机制，但最近在尘埃等离子体实验中观察到的基于漂移的机制。Puttscher and A. Melzer，等离子体物理，21,123704(2014)]，尘埃涡旋流解被证明是可恢复的。我们研究了由电子E*B漂移产生的极化产生的纯双极电场驱动尘埃流的情况。在没有离子阻力的情况下，磁场梯度有利于剪切E*B漂移，驱动涡旋流动。分析了不同磁场强度、磁场梯度和粉尘流体运动粘度对流函数解析解的影响。分析了B场梯度的影响，并与等离子体鞘层中存在的E场梯度进行了对比。
{"title":"Dust vortex flow analysis in weakly magnetized plasma","authors":"Prince Kumar, D. Sharma","doi":"10.1063/5.0010850","DOIUrl":"https://doi.org/10.1063/5.0010850","url":null,"abstract":"Analysis of driven dust vortex flow is presented in a weakly magnetized plasma. The 2D hydrodynamic model is applied to the confined dust cloud in a non-uniform magnetic field in order to recover the dust vortex flow driven in a conservative force field setup, in absence of any non-conservative fields or dust charge variation. Although the time independent electric and magnetic fields included in the analysis provide conservative forcing mechanisms, when the a drift based mechanism, recently observed in a dusty plasma experiment by [M. Puttscher and A. Melzer, Physics of Plasmas, 21,123704(2014)] is considered, the dust vortex flow solutions are shown to be recovered. We have examined the case where purely ambipolar electric field, generated by polarization produced by electron E*B drift, drives the dust flow. A sheared E*B drift flow is facilitated by the magnetic field gradient, driving the vortex flow in the absence of ion drag. The analytical stream-function solutions have been analyzed with varying magnetic field strength, its gradient and kinematic viscosity of the dust fluid. The effect of B field gradient is analyzed which contrasts that of E field gradient present in the plasma sheath.","PeriodicalId":8461,"journal":{"name":"arXiv: Plasma Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88358876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-05-27DOI: 10.1088/1741-4326/aba9ec/meta
Yanzeng Zhang, S. Krasheninnikov, R. Masline, R. Smirnov
An impact of neutrals on anomalous edge plasma transport and zonal flow (ZF) is considered. As an example, it is assumed that edge plasma turbulence is driven by the resistive drift wave (RDW) instability. It is found that the actual effect of neutrals is not related to a suppression of the instability textit{per se}, but due to an impact on the ZF. Particularly, it is shown that, whereas the neutrals make very little impact on the linear growth rate of the RDW instability, they can largely reduce the zonal flow generation in the nonlinear stage, which results in an enhancement of the overall anomalous plasma transport. Even though only RDW instability is considered, it seems that such an impact of neutrals on anomalous edge plasma transport has a very generic feature. It is conceivable that such neutral induced enhancement of anomalous plasma transport is observed experimentally in a detached divertor regime, which is accompanied by a strong increase of neutral density.
{"title":"Anomalous edge plasma transport, neutrals, and divertor plasma detachment","authors":"Yanzeng Zhang, S. Krasheninnikov, R. Masline, R. Smirnov","doi":"10.1088/1741-4326/aba9ec/meta","DOIUrl":"https://doi.org/10.1088/1741-4326/aba9ec/meta","url":null,"abstract":"An impact of neutrals on anomalous edge plasma transport and zonal flow (ZF) is considered. As an example, it is assumed that edge plasma turbulence is driven by the resistive drift wave (RDW) instability. It is found that the actual effect of neutrals is not related to a suppression of the instability textit{per se}, but due to an impact on the ZF. Particularly, it is shown that, whereas the neutrals make very little impact on the linear growth rate of the RDW instability, they can largely reduce the zonal flow generation in the nonlinear stage, which results in an enhancement of the overall anomalous plasma transport. Even though only RDW instability is considered, it seems that such an impact of neutrals on anomalous edge plasma transport has a very generic feature. It is conceivable that such neutral induced enhancement of anomalous plasma transport is observed experimentally in a detached divertor regime, which is accompanied by a strong increase of neutral density.","PeriodicalId":8461,"journal":{"name":"arXiv: Plasma Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85808675","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
I. Vasko, I. Kuzichev, A. Artemyev, S. Bale, J. Bonnell, F. Mozer
The recent simulations showed that the whistler heat flux instability, which presumably produces the most of quasi-parallel coherent whistler waves in the solar wind, is not efficient in regulating the electron heat conduction. In addition, recent spacecraft measurements indicated that some fraction of coherent whistler waves in the solar wind may propagate anti-parallel to the electron heat flux, being produced due to a perpendicular temperature anisotropy of suprathermal electrons. We present analysis of properties of parallel and anti-parallel whistler waves unstable at electron heat fluxes and temperature anisotropies of suprathermal electrons typical of the pristine solar wind. Assuming the electron population consisting of counter-streaming dense thermal core and tenuous suprathermal halo populations, we perform a linear stability analysis to demonstrate that anti-parallel whistler waves are expected to have smaller frequencies, wave numbers and growth rates compared to parallel whistler waves. The stability analysis is performed over a wide range of parameters of core and halo electron populations. Using the quasi-linear scaling relation we show that anti-parallel whistler waves saturate at amplitudes of one order of magnitude smaller than parallel whistler waves, which is at about $10^{-3};B_0$ in the pristine solar wind. The analysis shows that the presence of anti-parallel whistler waves in the pristine solar wind is more likely to be obscured by turbulent magnetic field fluctuations, because of lower frequencies and smaller amplitudes compared to parallel whistler waves. The presented results will be also valuable for numerical simulations of the electron heat flux regulation in the solar wind.
{"title":"On quasi-parallel whistler waves in the solar wind","authors":"I. Vasko, I. Kuzichev, A. Artemyev, S. Bale, J. Bonnell, F. Mozer","doi":"10.1063/5.0003401","DOIUrl":"https://doi.org/10.1063/5.0003401","url":null,"abstract":"The recent simulations showed that the whistler heat flux instability, which presumably produces the most of quasi-parallel coherent whistler waves in the solar wind, is not efficient in regulating the electron heat conduction. In addition, recent spacecraft measurements indicated that some fraction of coherent whistler waves in the solar wind may propagate anti-parallel to the electron heat flux, being produced due to a perpendicular temperature anisotropy of suprathermal electrons. We present analysis of properties of parallel and anti-parallel whistler waves unstable at electron heat fluxes and temperature anisotropies of suprathermal electrons typical of the pristine solar wind. Assuming the electron population consisting of counter-streaming dense thermal core and tenuous suprathermal halo populations, we perform a linear stability analysis to demonstrate that anti-parallel whistler waves are expected to have smaller frequencies, wave numbers and growth rates compared to parallel whistler waves. The stability analysis is performed over a wide range of parameters of core and halo electron populations. Using the quasi-linear scaling relation we show that anti-parallel whistler waves saturate at amplitudes of one order of magnitude smaller than parallel whistler waves, which is at about $10^{-3};B_0$ in the pristine solar wind. The analysis shows that the presence of anti-parallel whistler waves in the pristine solar wind is more likely to be obscured by turbulent magnetic field fluctuations, because of lower frequencies and smaller amplitudes compared to parallel whistler waves. The presented results will be also valuable for numerical simulations of the electron heat flux regulation in the solar wind.","PeriodicalId":8461,"journal":{"name":"arXiv: Plasma Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85289457","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
One of the paradigm-shifting phenomena triggered in laser-plasma interactions at relativistic intensities is the so-called relativistic transparency. As the electrons become heated by the laser to relativistic energies, the plasma becomes transparent to the laser light even though the plasma density is sufficiently high to reflect the laser pulse in the non-relativistic case. This paper highlights the impact that relativistic transparency can have on laser-matter interactions by focusing on a collective phenomenon that is associated with the onset of relativistic transparency: plasma birefringence in thermally anisotropic relativistic plasmas. The optical properties of such a system become dependent on the polarization of light, and this can serve as the basis for plasma-based optical devices or novel diagnostic capabilities.
{"title":"Birefringence in thermally anisotropic relativistic plasmas and its impact on laser–plasma interactions","authors":"A. Arefiev, D. Stark, T. Toncian, M. Murakami","doi":"10.1063/5.0008018","DOIUrl":"https://doi.org/10.1063/5.0008018","url":null,"abstract":"One of the paradigm-shifting phenomena triggered in laser-plasma interactions at relativistic intensities is the so-called relativistic transparency. As the electrons become heated by the laser to relativistic energies, the plasma becomes transparent to the laser light even though the plasma density is sufficiently high to reflect the laser pulse in the non-relativistic case. This paper highlights the impact that relativistic transparency can have on laser-matter interactions by focusing on a collective phenomenon that is associated with the onset of relativistic transparency: plasma birefringence in thermally anisotropic relativistic plasmas. The optical properties of such a system become dependent on the polarization of light, and this can serve as the basis for plasma-based optical devices or novel diagnostic capabilities.","PeriodicalId":8461,"journal":{"name":"arXiv: Plasma Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81543071","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-05-23DOI: 10.13140/RG.2.2.17302.37445
E. Tsiper
A design principle is suggested to overcome obstacles that prevent positive net energy output in nuclear fusion devices based on electrostatically accelerated ions. Since Coulomb scattering cross-section dwarfs that of nuclear fusion, the focus is on re-capturing energy of elastically scattered ions before the energy is lost to heat. Device configuration to achieve efficient energy re-capturing is proposed and a favorable estimate of net energy gain is obtained.
{"title":"Feasibility of Net Energy Gain in Kinematic Nuclear Fusion Devices","authors":"E. Tsiper","doi":"10.13140/RG.2.2.17302.37445","DOIUrl":"https://doi.org/10.13140/RG.2.2.17302.37445","url":null,"abstract":"A design principle is suggested to overcome obstacles that prevent positive net energy output in nuclear fusion devices based on electrostatically accelerated ions. Since Coulomb scattering cross-section dwarfs that of nuclear fusion, the focus is on re-capturing energy of elastically scattered ions before the energy is lost to heat. Device configuration to achieve efficient energy re-capturing is proposed and a favorable estimate of net energy gain is obtained.","PeriodicalId":8461,"journal":{"name":"arXiv: Plasma Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90868304","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The design of a stellarator with acceptable confinement properties requires optimization of the magnetic field in the non-convex, high-dimensional spaces describing their geometry. Another major challenge facing the stellarator program is the sensitive dependence of confinement properties on electro-magnetic coil shapes, necessitating the construction of the coils under tight tolerances. In this Thesis, we address these challenges with the application of adjoint methods and shape sensitivity analysis. Adjoint methods enable the efficient computation of the gradient of a function that depends on the solution to a system of equations, such as linear or nonlinear PDEs. This enables gradient-based optimization in high-dimensional spaces and efficient sensitivity analysis. We present the first applications of adjoint methods for stellarator shape optimization. The first example we discuss is the optimization of coil shapes based on the generalization of a continuous current potential model. Understanding the sensitivity of coil metrics to perturbations of the winding surface allows us to understand features of configurations that enable simpler coils. We next consider solutions of the drift-kinetic equation. An adjoint drift-kinetic equation is derived based on the self-adjointness property of the Fokker-Planck collision operator, allowing us to compute the sensitivity of neoclassical quantities to perturbations of the magnetic field strength. Finally, we consider functions that depend on solutions of the MHD equilibrium equations. We generalize the self-adjointness property of the MHD force operator to include perturbations of the rotational transform and the currents outside the confinement region. This self-adjointness property is applied to develop an adjoint method for computing the derivatives of such functions with respect to perturbations of coil shapes or the plasma boundary.
{"title":"Adjoint methods for stellarator shape optimization and sensitivity analysis","authors":"E. Paul","doi":"10.13016/TNOZ-3MOV","DOIUrl":"https://doi.org/10.13016/TNOZ-3MOV","url":null,"abstract":"The design of a stellarator with acceptable confinement properties requires optimization of the magnetic field in the non-convex, high-dimensional spaces describing their geometry. Another major challenge facing the stellarator program is the sensitive dependence of confinement properties on electro-magnetic coil shapes, necessitating the construction of the coils under tight tolerances. In this Thesis, we address these challenges with the application of adjoint methods and shape sensitivity analysis. Adjoint methods enable the efficient computation of the gradient of a function that depends on the solution to a system of equations, such as linear or nonlinear PDEs. This enables gradient-based optimization in high-dimensional spaces and efficient sensitivity analysis. We present the first applications of adjoint methods for stellarator shape optimization. The first example we discuss is the optimization of coil shapes based on the generalization of a continuous current potential model. Understanding the sensitivity of coil metrics to perturbations of the winding surface allows us to understand features of configurations that enable simpler coils. We next consider solutions of the drift-kinetic equation. An adjoint drift-kinetic equation is derived based on the self-adjointness property of the Fokker-Planck collision operator, allowing us to compute the sensitivity of neoclassical quantities to perturbations of the magnetic field strength. Finally, we consider functions that depend on solutions of the MHD equilibrium equations. We generalize the self-adjointness property of the MHD force operator to include perturbations of the rotational transform and the currents outside the confinement region. This self-adjointness property is applied to develop an adjoint method for computing the derivatives of such functions with respect to perturbations of coil shapes or the plasma boundary.","PeriodicalId":8461,"journal":{"name":"arXiv: Plasma Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79908476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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