Optimizing drive parameters of a nanosecond, repetitively pulsed microdischarge high power 121.6 nm source

Abstract

Utilizing nanosecond high voltage pulses to drive microdischarges (MDs) at repetition rates in the vicinity of 1 MHz previously enabled increased time-averaged power deposition, peak vacuum ultraviolet (VUV) power yield, as well as time-averaged VUV power yield. Here, various pulse widths (30-250 ns), and pulse repetition rates (100 kHz-5 MHz) are utilized, and the resulting VUV yield is reported. It was observed that the use of a 50 ns pulse width, at a repetition rate of 100 kHz, provided 62 W peak VUV power and 310 mW time-averaged VUV power, with a time-averaged VUV generation efficiency of ∼1.1%. Optimization of the driving parameters resulted in 1-2 orders of magnitude increase in peak and time-averaged power when compared to low power, dc-driven MDs.

Electric field determination in transient plasmas: in situ & non-invasive methods

“…Such justification of the hydrodynamic approximation can be done, for example, by comparing the collision frequencies for momentum and energy dissipation as well as the mean free path and the energy dissipation length with the frequency and length of the electric field variation, respectively. More precisely, the spatial and temporal relaxation of the electron gas temperature in the expected electric field strength range can be investigated using Monte-Carlo simulation or solving the time dependent Boltzmann equation [20,21,[32][33][34][35].…”

“…An important aspect is that electron collisional processes typically take place in picosecond time scales at elevated pressures or background medium densities. The large collisionality of atmospheric pressure discharges (see the marked range of electron-neutral collision frequency ν e-n ∼ THz in figure 1) also leads to short energy relaxation times [20][21][22][23][24]. These short times tend to drive the electron kinetics in equilibrium with the instantaneous electric field.…”

“…The energy relaxation time is orders of magnitude smaller than typical periods of the applied voltage waveform, even for microwave sustained discharges (see the bottom part of figure 1). The EEDF relaxes typically in a few picoseconds in atmospheric pressure air [20,21]. Discharge inception, dissociation reactions and wave-ionization processes proceed at hundreds of picoseconds and nanosecond time scales.…”

VUV irradiance measurement of a 2.45 GHz microwave-driven hydrogen discharge

“…Vacuum ultraviolet (VUV) emission of plasmas is rarely applied, but increasingly important tool in applications and diagnostics of plasma sources. VUV-radiation can, for example, significantly affect material processing ( [1,2,3] and references therein), and it can be utilized in photolithography for decreasing the length scale of semiconductor components [4,5]. Furthermore, VUV-emission could play an important role in plasma dynamics via photoelectron emission [6] or cleaning of plasma chamber walls [7].…”