Beam interaction measurements with a Retarding Field Analyzer in a high-current high-vacuum positively charged particle accelerator

A Retarding Field Analyzer (RFA) was inserted in a drift region of the magnetic transport section of the High-Current Experiment (HCX), that is at high-vacuum, to measure ions and electrons resulting from beam interaction with background gas and walls. The ions are expelled during the beam pulse by the space-charge potential and the electrons are expelled mainly at the end of the beam, when the beam potential decays. The ion energy distribution shows the beam potential of ∼2100V and the beam-background gas total cross-section of 3.1x10-19m2. The electron energy distribution reveals that the expelled electrons are mainly desorbed from the walls and gain ∼22eV from the beam potential decaying with time before entering the RFA. Details of the RFA design and of the measured energy distributions are presented and discussed