Ionization by bulk heating of electrons in capacitive radio frequency atmospheric pressure microplasmas
Ionization by bulk heating of electrons in capacitive radio frequency atmospheric pressure microplasmas
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DOI：
10.1088/0963-0252/22/1/015012
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发表时间：
2013-02-01
影响因子：
3.8
通讯作者：
Schulze, J.
中科院分区：
文献类型：
--
作者：
Hemke, T.;Eremin, D.;Schulze, J.
采用粒子模拟和半解析模型研究了氦中电容耦合射频微等离子体的电子加热和电离动力学。一个强大的加热的电子和电离的等离子体体由于高体积电场观察在不同的时间内的RF周期。基于该模型，电场被认为是一个漂移场所造成的低电导率，由于高电子-中性碰撞频率在大气压下。因此，电离主要是由欧姆加热在这个“Ω模式”。最强体电场和电离的相位受驱动电压幅值的影响。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。在鞘膨胀期间观察到异相和最大电离，在鞘边缘具有局部最大值。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，从而导致约4.因此，最大电离发生在RF周期内的后期，最大值在放电中心。显着的类比，以电负性低压宏观放电中的漂移双极模式中发现，类似的机制引起的高电负性，而不是高碰撞频率已被确定。
Electron heating and ionization dynamics in capacitively coupled radio frequency (RF) atmospheric pressure microplasmas operated in helium are investigated by particle-in-cell simulations and semi-analytical modeling. A strong heating of electrons and ionization in the plasma bulk due to high bulk electric fields are observed at distinct times within the RF period. Based on the model the electric field is identified to be a drift field caused by a low electrical conductivity due to the high electron-neutral collision frequency at atmospheric pressure. Thus, the ionization is mainly caused by ohmic heating in this 'Omega-mode'. The phase of strongest bulk electric field and ionization is affected by the driving voltage amplitude. At high amplitudes, the plasma density is high, so that the sheath impedance is comparable to the bulk resistance. Thus, voltage and current are about 45. out of phase and maximum ionization is observed during sheath expansion with local maxima at the sheath edges. At low driving voltages, the plasma density is low and the discharge becomes more resistive, resulting in a smaller phase shift of about 4.. Thus, maximum ionization occurs later within the RF period with a maximum at the discharge center. Significant analogies to electronegative low-pressure macroscopic discharges operated in the drift-ambipolar mode are found, where similar mechanisms induced by a high electronegativity instead of a high collision frequency have been identified.