MEQALAC, a MeV multi-channel RF-accelerator for light ions

The next generation of fusion devices will require neutral particle beams for diagnosis, current drive and/or heating. The particle energy has to be at least a few hundred keV in order to penetrate the plasma. The objective of MEQALAC (Multiple Electrostatic Quadrupole Array Linear Accelerator) is to accelerate a number of highcurrent ion beams to an energy in the MeV range, by means of a radio-frequency (rf) electric field. In general, the space-charge induced blow-up of a particle beam sets severe limits to the current which can be accelerated. With the MEQALAC concept this problem is circumvented by dividing the beam in a number of parallel beamlets. An advantage of this set-up is that the total current can be increased via the number of beamlets. The space charge dominated beams are focussed by arrays of miniaturized electrostatic quadrupoles, arranged in an F0d0 lattice; the channel radius is 2.5 mm. In a proof-of-principle experiment we accelerated four 2.2 mA He+beams from 40 keV to 120 keV. The objective for the next stage, which is presently under construction, is to accelerate a total Li-current of 5 mA to an energy of 0.5 MeV, for diagnostic purposes. Initial performance test will be done with N+beams, accelerated from 40 keV to 1 MeV.Performance test on various components are presented.(author). 6 refs.; 8 figs.; 1 tab