Sheath constraints on turbulent magnetised plasmas

IF 2.1 2区 物理与天体物理 Q2 PHYSICS, FLUIDS & PLASMAS
A Geraldini, S Brunner and F I Parra
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Abstract

A solid target in contact with a plasma charges (negatively) to reflect the more mobile species (electrons) and thus keep the bulk plasma quasineutral. To shield the bulk plasma from the charged target, there is an oppositely (positively) charged sheath with a sharp electrostatic potential variation on the Debye length scale . In magnetised plasmas where the magnetic field is inclined at an oblique angle α with the target, some of the sheath potential variation occurs also on the ion sound gyroradius length scale , caused by finite ion gyro-orbit distortion and losses. We consider a collisionless and steady-state magnetised plasma sheath whose thickness is smaller than the characteristic length scale L of spatial fluctuations in the bulk plasma, such that the limit is appropriate. Spatial structures are assumed to be magnetic field-aligned. In the case of small magnetic field angle , electric fields tangential to the target transport ions towards the target via E × B drifts at a rate comparable to the one from parallel streaming. A generalised form of the kinetic Bohm–Chodura criterion at the sheath entrance is derived by requiring that the sheath electric field have a monotonic spatial decay far from the target. The criterion depends on tangential gradients of potential and ion distribution function, with additional nontrivial conditions.
湍流磁化等离子体的鞘约束
与等离子体接触的固体目标会带电(负电),以反射移动性较强的物质(电子),从而保持等离子体的准中性。为了屏蔽带电目标对等离子体的影响,等离子体中存在一个带相反(正)电荷的鞘,其静电势在德拜长度尺度上有急剧的变化。在磁场与目标呈斜角 α 倾斜的磁化等离子体中,由于有限离子回旋轨道的扭曲和损耗,鞘势的部分变化也发生在离子声回旋长度尺度上。我们考虑的是一个无碰撞和稳态磁化等离子体鞘,其厚度小于体等离子体空间波动的特征长度尺度 L,因此极限是合适的。空间结构假定为磁场对齐。在磁场角较小的情况下,与目标相切的电场通过 E × B 漂移将离子输送到目标,其速率与平行流的速率相当。通过要求鞘电场在远离靶的地方有单调的空间衰减,得出了鞘入口处动力学博姆-乔杜拉准则的广义形式。该准则取决于电势和离子分布函数的切向梯度,以及附加的非难条件。
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来源期刊
Plasma Physics and Controlled Fusion
Plasma Physics and Controlled Fusion 物理-物理:核物理
CiteScore
4.50
自引率
13.60%
发文量
224
审稿时长
4.5 months
期刊介绍: Plasma Physics and Controlled Fusion covers all aspects of the physics of hot, highly ionised plasmas. This includes results of current experimental and theoretical research on all aspects of the physics of high-temperature plasmas and of controlled nuclear fusion, including the basic phenomena in highly-ionised gases in the laboratory, in the ionosphere and in space, in magnetic-confinement and inertial-confinement fusion as well as related diagnostic methods. Papers with a technological emphasis, for example in such topics as plasma control, fusion technology and diagnostics, are welcomed when the plasma physics is an integral part of the paper or when the technology is unique to plasma applications or new to the field of plasma physics. Papers on dusty plasma physics are welcome when there is a clear relevance to fusion.
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