Evolution of the electron distribution function during gas ionization by a sub-nanosecond microwave pulse of hundreds MW power

TL;DR

This paper investigates how the electron velocity distribution evolves during gas ionization caused by a high-power, sub-nanosecond microwave pulse, combining theoretical, simulation, and experimental approaches.

Contribution

It provides new insights into the evolution of the electron distribution function during intense microwave-induced gas ionization, supported by theoretical, numerical, and experimental evidence.

Findings

Electron distribution follows a decreasing power-law during the pulse.

Energetic electrons persist long after the microwave pulse, continuing ionization.

Experimental results confirm the presence of high-energy electrons post-pulse.

Abstract

The electron velocity distribution function in the plasma, formed by gas ionization with a sub-nanosecond, hundreds of megawatts power level microwave pulse, is studied by a theoretical model and by numerical 3D simulations, the results of which agree well and show that the distribution varies along the pulse as a decreasing power-law function at the rear of the pulse. Experiments performed in a waveguide filled with helium gas confirm that energetic (from several keV to several tens of keV) electrons remain in plasma long after the pulse has crossed the experimental volume. These electrons continue the gas ionization over extended times up to tens of nanoseconds.