Beam characterization measurement of a duoplasmatron ion source for the Nanjing Proton Source

Abstract

The beam characterization studies in terms of beam current, beam profile and RMS normalized emittance have been carried out in a duoplasmatron ion source developed for the Nanjing Proton Source (NPS). A test chamber installed a Faraday cup, a beam profile monitor and an Allision type scanner have been developed to perform the beam current, beam profile and beam emittance measurement, respectively. To solve the sparking problem of the ion source, we have used physical vapor deposition (PVD) to coat a zirconia film with a thickness of 3μm on the full surface of the extraction electrodes. The beam parameters have been measured at two locations (1) after beam extraction at the ion source end, (2) after focusing the beam using two solenoid magnets of low energy beam transport (LEBT). The relationship between arc current and gas pressure has been studied and the optimal operating point of gas pressure is found to be 1.0 × 10−3 Pa with corresponding hydrogen flow rate is 0.5 SCCM. At the ion source end, the results show that the measured beam current is 40.3 mA, the beam diameter is less than 5 cm and the RMS normalized emittance is less than 0.2 π mm-mrad. In addition, The variation of beam current has been studied as a function of the extraction voltage, gas pressure, and arc current. The variation of RMS normalized emittance of the proton beam has been studied as a function of extraction voltage and arc current. In addition, the results show that the measured beam current is 28.5 mA, the beam diameter is around 0.7 cm and the RMS normalized emittance is 0.31π mm-mrad after focusing at the LEBT end.