CRISP: a Compact RF Ion Source Prototype for emittance scanner testing

SPIDER is the prototype beam source of the ITER Heating Neutral Beam Injector, and it recently started beam acceleration, up to a voltage of 30 kV. A movable Allison type emittance scanner is being developed to characterize the phase-space distribution of its beamlets. To test the device, a Compact RF Ion Source Prototype (CRISP) has been set up at Consorzio RFX, capable to accelerate 0.5 mA of helium ions up to a voltage of 2 kV. A commercial 100 W RF generator creates a plasma inside a Pyrex tube, with a density between 1015 and 1016 m-3 and an electron temperature of a few eV. Three multi-aperture grids in accel-decel configuration extract and accelerate the ions, which impinge on a copper plate beam stopper, acting as a Faraday cup. We present in this paper the numerical simulations performed with SLACCAD and OPERA to dimension the grids and the calculation of the pressure profile inside the vessel made with the AVOCADO code. Measurements of beam current and profile are presented and compared with the simulations. Plasma density and temperature estimations obtained with a Langmuir probe are also reported.