Progress in the Development of RF Driven Negative Ion Sources for ITER NBI

Abstract

The Neutral Beam Injection (NBI) system for ITER is at present based on arc sources which suffer up to now from a limited lifetime of the tungsten filaments and from unacceptable plasma non-uniformity. Inductively coupled radio frequency (RF) sources, which have successfully been developed at IPP Garching for positive ion based NBI, offer substantial advantages for ITER. Since December 2002 the development of a large area RF source for negative ions is supported through an official EFDA task agreement. This development is carried out at IPP on three different test facilities: "BATMAN" is devoted to the physical understanding of the underlying processes of the negative ion formation, but with small extraction areas (<100 cm2) and short pulses (<10 s). The calorimetric H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"/> and D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"/> current density has already exceeded ITER requirements. Source filling pressure and electron to ion ratio are compatible with ITER requirements. Test facility "MANITU" focuses mainly on long pulse operation (3600 s) and larger extraction areas (300 cm2). The system has been operational since spring 2005 but still requires improvements with respect to reliability. The "RADI" test bed is dedicated to demonstrate plasma uniformity and the modular concept of the RF source, by scaling up the size of the source to half the size of the ITER source. The new "Half-Size Source" with about the width and half the height of the ITER source will be delivered within the next weeks.