Evolution of ionization waves in a multi-pulsed plasma jet: the role of memory charges

In this paper, we discuss the properties of ionization waves (IWs) in a multi-pulsed plasma jet while using the two-dimensional computational approach. The IWs are generated by application of three short negative pulses with a repetition frequency 12.5 MHz. The simulations are performed continuously during a single run while accounting for charges accumulated inside (surface charges) and outside (space charges) the tube. The plasma forming gas mixture (He/O-2 = 99.8%/0.2%) is injected through the discharge tube into the surrounding humid air. We show that an IW can emerge from the tube exit at a pulse rising edge (as a negative IW) and at a falling edge of the same pulse (as a positive IW). It is demonstrated that remnants of the negative and positive charges play an essential role in the discharge evolution. The first pulse travels the shortest distance as it propagates through the initially non-ionized environment. The IWs developing during the second pulse essentially enlarge the plasma plume length. At the same time, the IWs generated by the third pulse eventually decay due to the remnants of charges accumulated during the previous pulses. Accumulated memory charges can lead to the IW extinction.

Automated summary

In this study, the properties of ionization waves (IWs) in a multi-pulsed plasma jet were investigated using a two-dimensional computational approach. The IWs were generated by applying three short negative pulses with a repetition frequency of 12.5 MHz. The simulations accounted for both surface charges and space charges accumulated inside and outside the tube. It was found that IWs could emerge from the tube exit at both the rising and falling edges of the pulses, and the remnants of charges played a crucial role in the discharge evolution. The IWs generated by the second pulse significantly increased the plasma plume length, while those generated by the third pulse eventually decayed due to the accumulated charges from previous pulses, which could lead to the extinction of IWs.