First tests and commissioning of the emittance scanner for SPIDER

SPIDER is the prototype ion source for ITER Heating Neutral Beam. To investigate the phase-space distribution of its beamlets, an Allison type emittance scanner was developed. A slit in front of the device selects a part of the beam. A uniform electric field perpendicular to the beam, generated polarizing two parallel metallic plates, then deflects the particles. Only those with a well-defined entrance angle pass through another slit, aligned with the first one. The emittance profile of the beam is obtained by moving the device perpendicularly to the beam during the pulses, while sweeping the electric field between the plates and collecting the current reaching the Faraday cup placed after the second slit. This kind of diagnostic is widely used in ion sources for high-energy accelerators, but has not yet been extensively employed in fusion-relevant ion sources. We present in this paper the experimental setup of the diagnostic, together with the proposed operating procedure and the expected operating space. Tests carried on to assess the performance of the device, both with the Faraday cup and with the entire detector are described. The emittance measurements obtained in a dedicated test facility are also reported.