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 3.1×10-19m2. 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.