On peak current in atmospheric pulse-modulated microwave discharges by the PIC-MCC model

Abstract

Pulse modulation provides a new way to tailor the electron density, electron energy and gas temperature in atmospheric radio-frequency (rf) discharges. In this paper, by increasing the rf frequency to several hundreds of MHz, or even much higher to the range of GHz, a very strong peak current in the first period (PCFP) with much larger electron energy can be formed during the power-on phase, which is not observed in the common pulse modulation discharges at a rf frequency of 13.56 MHz. The PIC-MCC model is explored to unveil the generation mechanism of PCFP, and based on the simulation data a larger voltage increasing rate over a quarter of a period and the distribution of electron density just before the power-on phase are believed to play key roles; the PCFP is usually produced in the microplasma regime driven by the pulsed power supply. The effects of duty cycle and pulse modulation frequency on the evolution of PCFP are also discussed from the computational data. Therefore, the duty cycle and pulse modulation frequency can be used to optimize the generation of PCFP and high-energy electrons.

Comparing Study on Formation of Large Discharge Currents in Atmospheric Pulse-Modulated Radio Frequency Discharges

“…It is indicated that the pulsed discharge effectively enhances the ignition intensity of RF discharge, especially during the first few cycles of the RF discharge, which also has been demonstrated by the experimental investigations [38], [39]. In addition, high-energy electrons generated in the LDCs are expected to have implications for many applications [42], [48], and the underpinning physics should be further clarified by computational data.…”

“…The peak values of LDCs are 16.6 and 16.3 A/cm 2 , respectively, which are nearly 13% stronger than those in the stable state of 14.6 A/cm 2 . Compared to the counterpart without dielectric barriers that only one positive LDC can be generated in [42], [49], and [44], double LDCs indicate that the high-energy electrons could be produced two times during the positive and negative half-cycles, which makes this kind of discharge have great potential and advantages in numerous applications. But the mechanisms on the production of LDCs have not yet been fully investigated.…”

“…Nevertheless, the underpinning interaction mechanism between the short pulsed discharge and RF discharge is still far from clear. On the other hand, when the pulse modulation is introduced into microplasmas maintained by the dielectric barrier discharges (DBDs) with the driving frequency in the range of UHF, LDCs will also occur in the first positive and negative half-cycle during the power-on phase, respectively [42]- [44]. Detailed computational results by particle-in-cell/Monte Carlo collision (PIC-MCC) model have illustrated that quantities of energetic electrons larger than 50 eV can also be generated in an effective way [45]- [47], which are supposed to be crucial to break chemical bonds in the plasma biomedicine applications [20], [42], [48], [49].…”

“…On the other hand, when the pulse modulation is introduced into microplasmas maintained by the dielectric barrier discharges (DBDs) with the driving frequency in the range of UHF, LDCs will also occur in the first positive and negative half-cycle during the power-on phase, respectively [42]- [44]. Detailed computational results by particle-in-cell/Monte Carlo collision (PIC-MCC) model have illustrated that quantities of energetic electrons larger than 50 eV can also be generated in an effective way [45]- [47], which are supposed to be crucial to break chemical bonds in the plasma biomedicine applications [20], [42], [48], [49]. In this study, it is proposed that the underpinning physics of the production of LDCs in two types of discharge structures, especially their distinctive sheath structure may be helpful to further understand the corresponding discharge mechanisms and find the methods for optimizing the LDCs for plasma applications at atmospheric pressure.…”

Numerical study on discharge modes in atmospheric dielectric barrier discharges and their transition excited by the medium frequencies

“…然而, 随着输入 功率的增加, 放电比较容易转化成为体积较小、发光 明亮的热等离子体, 电流密度增加而总电流减小, 这 就进入了所谓的γ模式 [18,19] . 为了有效地抑制这种模 式转换, 人们已经发展了一些行之有效的方法, 比如 降低放电间隙、提高放电频率, 对放电进行脉冲调制 等 [18,20,24,25] .…”