A particle-in-cell (PIC) simulation study is performed to investigate the discharge asymmetry, higher harmonic generations and electron heating mechanism in a low pressure very high frequency capacitively coupled plasma (CCP) excited by a saw-tooth like current waveform. Two current densities, 50 A/m2 and 100 A/m2 are chosen for a constant gas pressure of 5 mTorr in argon plasma. The driving frequency is varied from 13.56 MHz to 54.24 MHz. At a lower driving frequency, high frequency modulations on the instantaneous sheath edge position at the grounded electrode are observed. These high frequency oscillations create multiple ionization beam like structures near to the sheath edge that drives the plasma density in the discharge and responsible for discharge/ionization asymmetry at lower driving frequency. Conversely, the electrode voltage shows higher harmonics generation at higher driving frequencies and corresponding electric field transients are observed into the bulk plasma. At lower driving frequency, the electron heating is maximum near to the sheath edge followed by electron cooling within plasma bulk, however, alternate heating and cooling i.e. burst like structures are obtained at higher driving frequencies. These results suggest that electron heating in these discharges will not be described accurately by simple analytical models.

中文翻译：

---

锯齿波激发的低压甚高频电容耦合等离子体中的高频鞘层调制和高次谐波产生

进行了电池内粒子 (PIC) 模拟研究，以研究由锯齿状电流波形激发的低压甚高频电容耦合等离子体 (CCP) 中的放电不对称性、高次谐波产生和电子加热机制。选择了两种电流密度，50 A/m2 和 100 A/m2，以在氩等离子体中保持 5 mTorr 的恒定气压。驱动频率从 13.56 MHz 到 54.24 MHz 不等。在较低的驱动频率下，可以观察到接地电极处瞬时护套边缘位置的高频调制。这些高频振荡在鞘边缘附近产生多个电离束状结构，驱动放电中的等离子体密度，并导致较低驱动频率下的放电/电离不对称。反过来，电极电压显示在较高驱动频率下产生高次谐波，并且在体等离子体中观察到相应的电场瞬变。在较低的驱动频率下，电子加热在鞘边缘附近最大，然后是等离子体体内的电子冷却，然而，在较高的驱动频率下获得交替的加热和冷却，即爆裂状结构。这些结果表明，这些放电中的电子加热将无法通过简单的分析模型准确描述。在更高的驱动频率下获得突发状结构。这些结果表明，这些放电中的电子加热将无法通过简单的分析模型准确描述。在更高的驱动频率下获得突发状结构。这些结果表明，这些放电中的电子加热将无法通过简单的分析模型准确描述。