Improvement of energy confinement time by continuous pellet fuelling in beam-heated Doublet III limiter discharges

Abstract

A centrifuge injector that repetitively fires 1.3 mm deuterium pellets (1 torr • L per pellet) at a rate of 32 pellets per second was used to build up and maintain a Doublet III 2.4 MW neutral-beam-heated limiter discharge at a line-averaged density of 1 X 10 14 cm" 3 . When compared to a conventional gas-fuelled plasma at similar density, the pelletfuelled plasma was characterized by a factor-of-three reduction in edge neutral density and limiter recycling, a centrally peaked profile, a 70% increase in global energy confinement, and a tenfold increase in the fusion reaction rate.

Development of pellet fuelling system in HL-2A tokamak

“…The HL-2A device is a medium size tokamak with a closed divertor [5]. And it is operated in the following parameter range: plasma current I p = 200-400 kA, toroidal magnetic field B t = 2.2-2.6 T, line- * Corresponding author.…”

Tritium Proof-of-Principle Injector Experiment

“…High-pressure gai>, generally hydrogen at 10 MPa (1500 psi), is then used to accelerate the solid tritium pellet down the 1-m-long barrel of the gun. The total gas used for each shot will be -160 Pam 3 (typically 1200 torr-L). In a fusion reactor, the pellet would be shot through a vacuum system into the plasma.…”

“…Gas will be supplied initially from a cylinder. A three-way valve (SV1) separates the hydrogen storage cylinder from the experiment so that the volume of gas that can be released into the glovebox is limited to approximately 100 cm 3 . Releasing this amount of gas into the box at 3-1 MPa would cause a 23-Pa (0.17-psi) pressure rise, not enough to cause a failure of the glovebox, even if all pressure control systems were to fail.…”

“…Helium-3 must be removed periodically from the tritium in the storage reservoir by using the 3 He separator. The separator is a copper countercurrent heat exchanger '.vith liquid helium cooling and a large volume for tritium condensation and 3 He accumulation. The tritium/ 3 He mixture is cryopumped into the 3 He separator at less than 12 K. At this temperature, the tritium will solidify and the 3 He will remain as a gas.…”

“…Souers 9 reported that low concentrations of helium can block the cryopumping action of systems with dimensions similar ti> the pipe gun. Souers further reported that the best, 3 He level that can he achieved with uranium bed purification is 0.12%. For this work, levels of 0.001% may be required.…”