Generation of Powerful Sub-Nanosecond E-Beams and X-Rays in Gas Discharges Under Atmospheric Pressure

Abstract

Summary form only given. This paper reports on experimental studies the generation of sub-nanosecond electron beams and X-rays in gas discharges under atmospheric pressure (Tarasenko et al., 2005). The properties of runaway electrons and X-ray radiation produced using a nanosecond volume discharge are examined. An electron beam with amplitude of ~100 A has been obtained. Pulse duration of the fast electrons beam current formed in an atmospheric gases diode is ~ 100 ps at FWHM behind the foil. Three groups of fast electrons form in a gas diode filled in with atmospheric air pressure applied with nanosecond voltage pulses with amplitude of hundreds of kilovolts. The first group electrons have the energies of units-tens of keV (fast electrons), the second -tens-hundreds of keV, and the third group electrons have the energies above the gap voltage (the electrons with anomalous energies). For formation sub-nanosecond electron beams with the maximal amplitudes, it is needed to have small-sized gas diodes with low inductance, having also no protrusions or grooves on their internal metallic surfaces. Besides that, the time of sub-nanosecond electron beams formation should coincide with the gap peak voltage. X-ray radiation at a pulse repetition rate of 3 kHz was obtained in a gas diode filled with air at atmospheric pressure. Based on beam temporal characteristics and discharge spatial characteristics, the critical fields were supposed to be reached at plasma approach to anode. Simultaneously, the sharp high-energy pulse of e-beam current is generated. Of critical importance is the cathode type and occurrence on the cathode of plasma protrusions. After beam current ends, the discharge is usually continued in quasi-stationary mode being of a volume character. Within 2-5 ns during voltage pulse at the gap the anode current density reaches ~6 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , specific input energy in gas is ~1 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and specific input power is ~800 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . A volume discharge has been obtained in a non-uniform electric field at helium pressure of up to 6 atm, and in nitrogen up to 3 atm, gap voltage from 10 to 200 kV. Properties of plasma produced in volume nanosecond high-pressure discharge and its formation conditions under elevated pressure in air, nitrogen, krypton, argon, neon, helium, and gas mixtures Ar-N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , Ar-Xe, CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -He in the gap with the cathode having small curvature radius have been investigated. Time-amplitude characteristics and radiation spectra of plasma in different gases in the range of 120-800 nm were defined. Lasing in the gas mixture Ar-Xe has been achieved by excitation through volume nanosecond high-pressure discharge.