Development of a plasma gun for application in MTF: the LICA (linearly injected coaxial accelerator)

Abstract

Summary form only given. This research project only concerns itself with the aspects of the plasma gun required for the MTF, namely a plasma gun capable of reproducible results of 0.2 mg of high velocity hydrogen plasma at a frequency of 10 Hz. A unique coaxial plasma gun that linearly injects a neutral gas pulse (the LICA - linearly injected coaxial accelerator) has been developed. A piezoelectric valve is used to introduce a neutral hydrogen gas pulse into the plasma gun. The LICA consists of a coaxial accelerator 10 cm in diameter and 30 cm in length, with the cathode supported in the centre of the accelerator by four insulated struts, which also serve the purpose of supplying voltage to the cathode. Positioned 40 cm behind the coaxial accelerator separated by a skimmer is a high vacuum chamber containing the piezoelectric valve which is aligned with the axis of the plasma accelerator. In front of the plasma gun is a 2 m flight chamber with a background pressure of 2 uTorr that contains diagnostic equipment - this plasma gun system has a high vacuum compatibility. In LICA, plasma formation is a two stage process, firstly a gas pulse is produced from the piezoelectric valve, then a delayed 650 V pulse applied to a grid causes gas breakdown at a position close to the valve. The electrons produced by the ionising pulse are accelerated towards the accelerator. These electrons through collisions ionises the neutral gas pulse in the plasma gun. At this stage the capacitor discharges and the resulting plasma is accelerated by the action of the Lorentz force down the plasma gun. We report on the initial series of experiments with this unique apparatus.