The development of a negative ion beam plasma neutralizer for ITER NBI

A plasma neutralizer (PN) could be an attractive upgrade for the NBI system of ITER. A multicusp magnetic trap with microwave discharge plasma generation has been proposed as a scheme for a PN. The experimental investigation of the scheme is being undertaken in the Kurchatov Institute. The preliminary experiments were done at a small (70 L of plasma volume, 2.45 GHz, 1.5 kW) installation, PNX-1, slightly modified during the experiments to PNX-2. The achieved plasma density of 5x1011 cm-3 exceeded the cut-off density by a factor of 7. The next step in this experimental activity is PNX-U (500 L, 7 GHz, 50 kW). Some results of the PNX-U experiments are presented. (author)