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Status of plasma neutralizer development

V. Kulygin, I. Moskalenko, A. Spitsyn, A. Skovoroda, S. Yanchenkov, V. Zhiltsov

Kurchatov Institute, Moscow, Russia

Abstract: Neutral beam injection based on negative ions acceleration with further additional electron detachment became necessary in plasma experiments when the fusion devices have been grown up to sizes large enough to need beam energies in range of the 200-1000 keV/nucleon. In that range the accelerated positive ion charge exchange on gas or vapor targets becomes ineffective and negative ion stripping proves to be the only possible choice. The electron detachment can be provided with using several ways. Gas cell is the simplest neutralizer. If we would like to increase overall NNBI efficiency and decrease a gas load, we should use Plasma Neutralizer (PN). PN can provide the neutral fraction of initial deuterium negative ion beam up to 86% instead of 60% at the gas one.
The following PN concept was chosen: it is proposed to use a multipole magnetic trap of large volume with closed ∇B drift of electrons,. The steady state plasma should be produced by electrodeless microwave discharge at gas pressure less than 10-4 torr at mainly collisionless character of microwave energy absorption.

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