Residual gas effect in LEBT on transverse emittance of multiply charged heavy ion beams extracted from ECR ion source

By utilizing a pepper-pot emittance meter, we have measured the four-dimensional transverse phase-space distribution for multiply charged argon ions generated by an 18-GHz superconducting electron cyclotron resonance ion source (18-GHz SC-ECRIS) at RIKEN for gas pressures of 10−5 to 10−3 Pa during low-energy beam transport (LEBT), in order to reveal the effects of residual gas. An advantage of the presence of residual gas is neutralization and moderation of the space-charge effect of the beam. At the beam-extraction point of the SC-ECRIS, a few milliamps ion beam produces a non-negligible space-charge effect, which is expected to influence the emittance, and to depend on the LEBT pressure. To evaluate the effects of charge exchange, natural argon or hydrogen gas was injected into an LEBT system through a variable leak valve to control the amount of residual gas. In the case of argon gas injection, the charge exchange between the argon beam and the injected argon gas clearly increased when the LEBT pressur...