Ion Extraction From Magnetically Driven Carbon Shunting Arc Plasma

Abstract

Shunting arc discharge is a pulsed plasma source of metals and semimetal materials and is ignited without any trigger sources at a wide range of gas pressures, from vacuum to atmospheric pressure under identical discharge conditions. In this paper, an ion extraction from magnetically driven carbon shunting arc discharge and a criterion of the arc ignition are described. A carbon rod with a diameter of 2 mm and a length of 40 mm was employed for arc ignition. The carbon rod was set in the vacuum and was initially heated up with a pulsed current supplied by a charged capacitor with a capacitance of 20 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$muhboxF$</tex> , followed by self-ignition. The heating energy is almost independent of the charging voltage of the capacitor and changes with the rod position on the rail. The ions are extracted from the arc plasma by applying a negative pulse voltage to a target. The target current has a sharp peak at the initial stage, followed by a stationary state. The stationary current decreases with increasing the distance to the target from a muzzle of the shunting arc plasma gun. Under the assumption of a collisionless ion sheath, the ion density at a 20-mm target–muzzle distance is estimated as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1 times 10^8$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2 times 10^7 hboxcm^-3$</tex> for the delay times of 250 and 1000 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$muhboxs$</tex> , respectively. The density at a 250- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$muhboxs$</tex> delay time decreases from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1 times 10^8$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.8 times 10^8 hboxcm^-3$</tex> by increasing the distance from 20 to 140 mm. The ion density increases as the charging voltage of the capacitor for arc generation is increased.