Development of the plasma generator for a long pulse 10×40 neutral beam

Abstract

Users of fusion devices have identified heating requirements for positive ion based neutral beams to include energies of 80 or 120 kV with pulse length up to 30 s. Additional requirements are low beam divergence (0.3°×1.0°; 1/e half angles), low impurity (less than 1%), high species (over 80% atomic), and cathode lifetime exceeding 5 h of beam operation. Accelerator design remains as an engineering problem, whereas most of the performance goals have required development of the plasma generator. Problems of concern which relate to the performance goals are the heat dissipation, magnetic field configuration, and cathode placement. The plasma generator was tested on TS IIA (the plasma generator testing facility) which does not have beam extraction capability but is used to evaluate efficiency, operating conditions, arc notching characteristics, species, plasma uniformity, and cathode conditioning. The source, consisting of the plasma generator mounted on the long pulse accelerator was mounted on NBETF (Neutral Beam Engineering Test Facility) for beam testing. During beam operation the back-streaming electrons add power to the source and affect the arc operation. Source durability and stability were studied at 80 kV and 40 A of accelerator current (deuterium). The arc efficiency was higher than the value used for the design. Power loading from back-streaming electrons was much less than the design level. With feedback control, plasma density and accel current were constant to ±2% during 30-s shots. The beam atomic fraction of 84%–88% (deuterium) was slightly higher than measured on TS IIA. Cathode durability was tested by operating over 500, 30-s full shots at 80 kV and 40 A of deuterium. Arc conditioning was found to be an important phase to avoid filament damage.

H−Formation in a Barium-Seeded Hydrogen Discharge

“…5 In the past, attempts have also been made to extract H ~ ions directly from the plasma of a multicusp source equipped with a permanent magnet filter. 1,6~8 The highest H ~~ current density achieved was about 250 mA/cm 2 and was obtained from a small multicusp source operated in a pulsed mode with relatively high gas pressure and high discharge power.…”

Report on the engineering test of the LBL 30 second neutral beam source for the MFTF-B project

“…Development of the LPS for 30 second operation was done in the spring of 1983. 5 In this Report, measured beam properties, such as, perveance and divergence are discussed, as well as source reliability. An Operating Manual for the LPA/LPS has also been prepared as a separate document.!…”