ENERGY RECOVERY EXPERIMENTS WITH A POWERFUL 100 KEV D- BASED NEUTRAL BEAM INJECTOR

Energy recovery experiments have been conducted for the first time with a negative ion based neutral beam injector. A new type of energy recovery system was utilized, which: (i) separates electrostatically the neutrals and charged components of the beam at the exit of the neutraliser; (ii) decelerates the residual unneutralised negative ions; (iii) prevents secondary emission of electrons from the negative ion collector by means of electrostatic trapping. With 102 keV, 1.2 A D- beams, the residual negative ions have been decelerated with high efficiency down to 8 keV: even when the additional power consumption of the electrostatic deflector is taken into account, the efficiency of recovery of the residual negative ion power was as good as 81%. The energy recovery system operation has been shown to be rather insensitive to the background ps pressure in a range of values relevant for the injector operation.