Particle-in-cell and global simulations of α to γ transition in atmospheric pressure Penning-dominated capacitive discharges
Particle-in-cell and global simulations of α to γ transition in atmospheric pressure Penning-dominated capacitive discharges
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DOI：
10.1088/0963-0252/23/3/035014
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发表时间：
2014-06-01
影响因子：
3.8
通讯作者：
Lazzaroni, C.
中科院分区：
文献类型：
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作者：
Kawamura, E.;Lieberman, M. A.;Lazzaroni, C.
大气压射频容性微放电因其新兴的应用而备受关注，特别是在生物医学领域。以前的全球模型没有考虑高功率的现象，如鞘倍增，从而限制了其适用性较低的功率范围。为了克服这一点，我们使用一维粒子在细胞（PIC）模拟大气He/0.1%N-2电容放电在很宽的电流和频率范围内，以指导更一般的全球模型，这也是有效的，在更高的功率的发展。新模型包括鞘倍增和两类电子：与鞘相关的高温“热”电子和与体相关联的较冷“暖”电子。电场和电子功率平衡解析求解，以确定随时间变化的热和暖温度和有效速率系数。粒子平衡方程的数值积分，以确定物种密度。模型和PIC的结果进行了比较，显示出合理的协议的范围内的电流和频率的研究。它们指示从低功率下的模式的过渡，其特征在于相对高的电子温度T-e，具有接近均匀的轮廓，到高功率下的伽马模式，其中T-e轮廓在体等离子体中被强烈抑制。这种转变伴随着密度的增加和鞘层宽度的减小。通过PIC仿真验证了模型的电流和频率定标性。
Atmospheric pressure radio-frequency (rf) capacitive micro-discharges are of interest due to emerging applications, especially in the bio-medical field. A previous global model did not consider high-power phenomena such as sheath multiplication, thus limiting its applicability to the lower power range. To overcome this, we use one-dimensional particle-in-cell (PIC) simulations of atmospheric He/0.1%N-2 capacitive discharges over a wide range of currents and frequencies to guide the development of a more general global model which is also valid at higher powers. The new model includes sheath multiplication and two classes of electrons: the higher temperature 'hot' electrons associated with the sheaths, and the cooler 'warm' electrons associated with the bulk. The electric field and the electron power balance are solved analytically to determine the time-varying hot and warm temperatures and the effective rate coefficients. The particle balance equations are integrated numerically to determine the species densities. The model and PIC results are compared, showing reasonable agreement over the range of currents and frequencies studied. They indicate a transition from an a mode at low power characterized by relatively high electron temperature T-e with a near uniform profile to a gamma mode at high power with a T-e profile strongly depressed in the bulk plasma. The transition is accompanied by an increase in density and a decrease in sheath widths. The current and frequency scalings of the model are confirmed by the PIC simulations.