No abstract

The luminous region of the plasma cloud surrounding deuterium pellets injected into a tokamak is studied spectroscopically. At the time of peak luminosity the electron density is 2.4x 10 17 cm -3 to within 30% and the temperature is at most 2.0 eV. The intensity ratio of the Balmer-alpha and -beta light from the pellets, the total number of emitted photons, and the apparent size of the radiating region are consistent with local thermodynamic equilibrium at this temperature and density.PACS numbers: 52.40. Hf, 52.70.Kz In the past decade experiments have been performed in which pellets of solid hydrogen or deuterium with dimensions of 0.070-4.0 mm and velocities of 90-1300 m/s were injected into tokamak plasmas.

A threebarrel repeating pneumatic pellet injector for plasma fueling of the Joint European Torus A repeating pneumatic pellet injector has been developed for plasma fueling applications. The repetitive device extends pneumatic injector operation to steady state. The active mechanism consists of an extruder and a gun assembly that are cooled by flowing liquid-helium refrigerant. The extruder provides a continuous supply of solid hydrogen to the gun assembly, where a reciprocating gun barrel forms and chambers cylindrical pellet from the extrusion; pellets are then accelerated with compressed hydrogen gas (pressures up to 125 bar) to velocities ..; 1.9 km/s (1.6 km/s for deuterium pellets). The gun assembly design can accommodate different pellet sizes and barrel lengths. Steady-state rates of 2 S-1 have been obtained with 2.1-, 3.4-, and 4.D-mmdiameter peHets. The present apparatus operates at higher firing rates in short bursts; for example, a rate of 6 s -1 for 2 s with the larger pellets. These pellet parameters are in the range applicable for fueling large present-day fusion devices such as the Tokamak Fusion Test Reactor (TFfR). Experimental results are presented, including effects of propellant pressure and barrel length on gun performance.

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