A 70 keV neutral hydrogen beam injector with energy recovery for an MSE diagnostic application in fusion research

A 70 keV 40 A hydrogen beam injector has been developed at Cadarache for a plasma diagnostic (MSE: Motional Stark Effect) to provide a measurement of the plasma current distribution in the Tore-Supra Tokamak. We present in this paper, the principle and the first experimental results of the injector, where a new type, and advantageous, energy recovery system, based on a magnetic neutraliser plasma confinement, has been developed. The hydrogen ion beam is accelerated to 70 keV with a three-grid multi-aperture system (aperture diameter /spl Phi/=11 mm) with an ion current density of /spl ap/160 mA/cm/sup 2/. An ion source with a shape (height 1.2 m, width 80 mm) specifically adapted to the recovery system has been developed to meet the injector requirements: uniformity, high proton fraction (>80%) and high current density, /spl ap/160 mA/cm/sup 2/ over the whole extraction surface (900 cm/sup 2/). A neutral beam power (H/sup 0/) of 500 kW has been achieved with a divergence of /spl ap/0.6/spl deg/ at 70 keV.