DEVELOPMENT OF NEUTRAL BEAM INJECTORS FOR JET AT FaR

A rectangular version of the periplasmatron ion source capable of illuminating with a homogeneous plasma a 40 × 18 cm2 extraction area has been constructed at FAR for the need of JET [1]’. Intense ion beams up to 40 A, 80 KeV energy, 240 mA/cm2 extracted ion current density, 0,1 sec pulse length have been produced with this source by using an extraction area of 12 × 38 cm2 and a three electrodes multi-aperture extraction system. The full size JET ion source will be an extrapolated version with an extraction area of 18 × 45 cm2 The line is now in operation with an electrostatic beam dump, which is under test. Experiments have been carried out, to investigate some phenomena which affects the injector operation like the thermal load of the grids by the acceleration of charged particules created in the accelerating gaps of the beam-forming electrodes and the transmission losses due to the beam divergence.