BORONIZATION WITH TRIMETHYLBORON IN THE REVERSED-FIELD PINCH RFX

The first wall and the vessel of the Reversed Field Pinch RFX has been in situ coated with a B/C:H film by glow discharge cleaning with a mi xture of 12.5% of trimethylboron ((CH3)(3)B) in He. The film has been analysed and the effects on the plasma discharges of the boronized wal l are reported for a plasma current of 520 kA. The main effects on the plasma are a reduction in the oxygen content by a factor of 5 to 10 a nd a decrease in the carbon content by a factor of two. The Z(eff) has been reduced from 2-2.5 to 1.4-1.5. A slight reduction of the loop vo ltage is observed. The radiation power decreases by a factor of 2, enh ancing the high density operation limit with a consequent increase of the poloidal beta beta(theta) and of the energy confinement time tau(E ).