Gradual Tuning of the Current Pulse Width Within 1-0.03 ns in Gas-Filled Diodes of Nanosecond Electron Accelerators

Abstract

The conditions for the generation of subnanosecond and picosecond electron beams with a tunable pulse width are studied on an SLEP-150 generator with a tubular cathode at a voltage pulse rise time of 0.3 ns. The width and shape of the beam current pulse are varied by varying the pressure and gas kind in the diode. It is shown that in the vacuum diode mode, the beam current rise time decreases from <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\sim}{0.5}$</tex></formula> to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{\rm 0.2}~{\rm ns}$</tex></formula> as the interelectrode gap is decreased from 12 to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{\rm 2}~{\rm mm}$</tex> </formula> . It is found that with a 3-mm interelectrode gap, increasing the air pressure in the diode of the SLEP-150 generator from 0.1 to 6 torr decreases the full width at half maximum (FWHM) of the current pulse from <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{1}$</tex></formula> to 0.18 ns, with the beam current amplitude greater than 400 A and the beam current rise time less delayed with respect to the voltage pulse rise time. It is confirmed that with a nanosecond voltage pulse, the residual pressure of helium, nitrogen, and air in the diode ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{0.1}$</tex></formula> torr or less) does not affect the beam current amplitude and pulse width. At low pressure of air in the gas diode, the attained beam current density at a beam current pulse FWHM of 0.18-1 and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{\rm 0.1}~{\rm ns}$</tex></formula> is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}{500}$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\sim}{100}~{\rm A}/{\rm cm}^{2}$</tex></formula> , respectively.