Secondary Electrons Problem Study for Beam Energy Recovery for Fusion: Experimental apparatus
In the ITER fusion project two deuterium Neutral Beam (NB) injectors of 40 MW will be used to further heating the TOKAMAK plasma up to the ignition temperature. The neutralization method of the two D- beams, the gas cells, has an efficiency of about 60%, then residual charged beams of about 40% have to be deflected and dumped before the injection in the plasma. In order to improve the electrical efficiency of the NB production, a beam recovery system of the residual charged particles can be studied. Since a scaled ITER type negative ion source, NIO1 (Negative Ion Optimization 1), has been developed at RFX (Padua) in collaboration with INFN-LNL for studying and improving the ion extraction efficiency of the future NB an experimental test on beam energy recovery of the NIO1 beam has been recently proposed. One important issue related to the beam energy recovery and mostly to the beam dumping are the secondary electrons generated by the interaction of the ions with the collector walls. They may escape from the collector electrodes causing damages and, at least, reduce energy recovery efficiency. A Proposal of an experimental test on the secondary electrons production in the beam energy recovery has been done to study that problem. In this contribution, the experimental apparatus set up for the test along with the simulations of the measurements are presented and discussed.