We investigate the electron heating dynamics in electropositive argon and helium capacitively coupled RF discharges driven at 13.56 MHz by Particle in Cell simulations and by an analytical model. The model allows to calculate the electric field outside the electrode sheaths, space and time resolved within the RF period. Electrons are found to be heated by strong ambipolar electric fields outside the sheath during the phase of sheath expansion in addition to classical sheath expansion heating. By tracing individual electrons we also show that ionization is primarily caused by electrons that collide with the expanding sheath edge multiple times during one phase of sheath expansion due to backscattering towards the sheath by collisions. A synergistic combination of these different heating events during one phase of sheath expansion is required to accelerate an electron to energies above the threshold for ionization. The ambipolar electric field outside the sheath is found to be time modulated due to a time modulation of the electron mean energy caused by the presence of sheath expansion heating only during one half of the RF period at a given electrode. This time modulation results in more electron heating than cooling inside the region of high electric field outside the sheath on time average. If an electric field reversal is present during sheath collapse, this time modulation and, thus, the asymmetry between the phases of sheath expansion and collapse will be enhanced. We propose that the ambipolar electron heating should be included in models describing electron heating in capacitive RF plasmas.
Ionization by bulk heating of electrons in capacitive radio frequency atmospheric pressure microplasmas
采用Particle in Cell模拟和半解析模型研究了氦气中大气压下电容耦合射频微等离子体的电子加热和电离动力学。在RF周期内的不同时间观察到由于高体积电场导致的等离子体体积中的电子和电离的强烈加热。基于该模型，确定了该电场是由大气压下高电子-中性粒子碰撞频率导致的低电导率引起的漂移场。因此，在这种“Ω模式”中，电离主要由欧姆加热引起。驱动电压幅值影响最强体电场和电离的相位。在高振幅下，等离子体密度高，使得鞘层阻抗与体电阻相当。因此，电压和电流约为45 °异相，在鞘膨胀期间观察到最大电离，在鞘边缘处具有局部最大值。在低驱动电压下，等离子体密度低并且放电变得更具电阻性，导致约4 °的较小相移。因此，最大电离发生在RF周期内的后期，在放电中心具有最大值。显着的类比电负性低压宏观放电中的漂移双极模式下工作，其中类似的机制引起的高电负性，而不是高碰撞频率已被确定。
Revisiting Electron Heating in Capacitively Coupled Plasma (CCP) Discharges: A Nonlinear Dynamics Perspective
Institute for Plasma Research（等离子体研究所）；Homi Bhabha National Institute（霍米·巴巴国立研究所）；School of Physical Sciences, UM-DAE Centre for Excellence in Basic Sciences, University of Mumbai（孟买大学物理科学学院，UM-DAE基础科学卓越中心）
High frequency sheath modulation and higher harmonic generation in a low pressure very high frequency capacitively coupled plasma excited by sawtooth waveform
Investigation of the effects of customized electrodes on capacitively coupled radio frequency microplasma jets using emission spectroscopy and laser diagnostics
The Ambipolar electric field in multispecies plasma atmospheres: effects of alpha particles and stochastic heating
LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台，巴黎文理研究大学，索邦大学，巴黎西岱大学，塞吉-蓬图瓦兹大学，法国国家科学研究中心）；Mullard Space Science Laboratory, University College London（穆拉德空间科学实验室，伦敦大学学院）
Collisionless Bulk Electron Heating in Resonant Low-Voltage Capacitively Coupled Plasmas
Institute for Plasma Research（等离子体研究所）；Homi Bhabha National Institute（霍米·巴巴国立研究所）；Princeton Plasma Physics Laboratory（普林斯顿等离子体物理实验室）；Department of Physics, Indian Institute of Science（印度科学学院物理系）；School of Physical Sciences, UM-DAE Centre for Excellence in Basic Sciences, University of Mumbai（孟买大学基础科学卓越中心物理科学学院）
The effect of the driving frequency on the confinement of beam electrons and plasma density in low pressure capacitive discharges
采用Particle in Cell/Monte Carlo碰撞模拟和解析模型，研究了在几Pa的低压下工作的电容式射频氩等离子体中，改变驱动频率对等离子体密度和电子动力学的影响。与先前的假设相反，在这种非局部无碰撞的情况下，等离子体密度不遵循对驱动频率的二次依赖。相反，观察到在不同的驱动频率下的阶梯状增加。基于分析的功率平衡模型，结合电子动力学的详细分析，密度跳跃被发现是由电子加热模式从经典的$α$模式转变成低密度谐振加热模式，其特征在于在每个电极每个鞘层膨胀阶段产生两个高能电子束。这些电子束在没有碰撞的情况下通过主体传播，并与相对的鞘层相互作用。在低密度模式中，发现第二束在其塌陷期间撞击相对鞘。因此，大量的高能电子在电极处损失，导致与在较高驱动频率下观察到的经典$α$模式相比，束电子的约束较差。基于分析模型，这种调制的约束质量和相关的调制的能量损失的每电子在电极上被证明是导致等离子体密度的阶梯状变化。根据模拟结果分析了电极间隙、中性气体压力、电极的电子粘附系数和次级电子发射系数的变化对等离子体密度阶梯状增加的影响。
Magnetothermal evolution of neutron star cores in the `weak-coupling' regime: implications of ambipolar diffusion for the quiescent X-ray luminosity of magnetars
Investigating the effects of electron bounce-cyclotron resonance on plasma dynamics in capacitive discharges operated in the presence of a weak transverse magnetic field
Simulation Studies of Resonant Excitation of Electron Bernstein Waves in Capacitive Discharges
School of Physical Sciences, UM-DAE Centre for Excellence in Basic Sciences, University of Mumbai（孟买大学基础科学卓越中心物理学院）；Institute for Plasma Research（等离子体研究所）；Homi Bhabha National Institute（霍米·巴巴国立研究所）；Princeton Plasma Physics Laboratory（普林斯顿等离子体物理实验室）
Electron dynamics in planar radio frequency magnetron plasmas: II. Heating and energization mechanisms studied via a 2d3v particle-in-cell/Monte Carlo code
Phasor-particle-in-cell algorithm for bidirectional external-circuit coupling of inductively coupled plasma
State Key Laboratory of Advanced Electromagnetic Technology, International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology（华中科技大学电气与电子工程学院）；School of Physics and Mechanics, Wuhan University of Technology（武汉理工大学物理与力学学院）；School of Physics, Huazhong University of Science and Technology（华中科技大学物理学院）
