70 keV neutral hydrogen beam injector with energy recovery for application in thermonuclear fusion research

A 70 keV 40 A hydrogen beam injector has been developed at Cadarache for a plasma diagnostic [motional Stark effect (MSE)] to provide a measurement of the plasma current distribution in the Tore–Supra tokamak. We present in this article the principle and the first experimental results of the injector, where a new type, and advantageous, energy recovery system, based on a magnetic neutralizer plasma confinement, has been developed. The hydrogen ion beam is accelerated to 70 keV with a three-grid multiaperture system (aperture diameter Φ=11 mm) with an ion current density of ≈160 mA/cm2. 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, ≈160 mA/cm2 over the whole extraction surface (900 cm2). A neutral (H0) beam power of 500 kW has been achieved with a divergence of ≈0.6° at 70 keV.