GB959150A - Plasma generator - Google Patents

Abstract

959,150. Discharge apparatus. UNITED STATES ATOMIC ENERGY COMMISSION. Oct. 12, 1962 [Dec. 7, 1961], No. 38687/62. Heading H1D. In a plasma generator, the plasma is created at a point remote from electrodes and other structures, and is produced within a containing magnetic field by the initiation of a travelling ionizing wavefront in a gas disposed within the field. As shown, a plasma generator comprises a cylindrical shell 6 with a first end closure 7 and a second end closure 8 having openings for connection to a vacuum pump 17 and a gas source 18, an electrode 11 supported by an insulator 14 within an aperture 13 in the closure 7, a conductive sleeve 12 spaced apart from and coaxial with the electrode 11, and magnet coils 21, 22, 23 for producing a magnetic mirrortype field of the configuration indicated by dashed lines 25. To generate the plasma a charge of deuterium or the like is first admitted to the chamber 9 and then a high energy pulse, derived from a circuit including a high voltage power supply 26, a pulse line 28, an ignitron 32 and a trigger pulse generator 37, is applied to the electrode 11; a discharge is thereby produced between the electrode 11 and the grounded sleeve 12 creating a hydromagnetic ionization wavefront which follows the magnetic field and proceeds axially through the chamber 9, leaving behind a fully ionized gas. Before the wavefront reaches the end closure 8, electrode 11 and sleeve 12 are short-circuited by an ignitron 39 which is fired, at a definite interval after the ignitron 32 starts to conduct, by a portion of the triggering pulse from the unit 37, which portion is passed through a delay circuit 43 for such interval. This short-circuiting has a braking effect on the wavefront which is thus stopped before it reaches the end closure 8. The ionized plasma within the containing magnetic field is thus substantially free from contaminants as it has not contacted the various structural elements of the generator. In a modification (Fig. 2, not shown), initial break down of the gas in chamber 9 is facilitated by providing a spark gap at the centre of electrode 11.