ON THE USE OF BIASED MOVABLE B4C-LIMITER FOR PUMPING O-2 AND H2O DURING DISCHARGE CLEANING

The movable limiter, the head plate of which is formed with a boron ca rbide plate hot-pressed in vacuum, is used for studying plasma impurit y removal and the possibility of boronization during discharge cleanin g in Uragan-3M torsatron. Measurements of current-voltage characterist ics, boron and oxygen spectroscopies, residual-gas mass-spectrometry w ere carried out for different biased and unbiased limiter positions. I t is shown that at a negative limiter bias during pulsed discharges cl eaning the boron spectral signal from the plasma increases due to arci ng. At the same time the oxygen spectral line intensity decreases and it probably means desorbed oxygen and water effective trapping by boro nized surfaces and the limiter B4C-plate, since the main plasma parame ters do not change at this moment, The estimations of the limiter appl ication for impurity pumping and solid target boronization shows that the negatively biased movable B,C-limiter can be used to improve pulse d discharge cleaning in Uragan-3M torsatron.