Development of MeV Range Heavy Ion Beam Probe

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The purpose of this collaboration program is to establish foundations for the design of 6 MeV heavy ion beam probe to be installed on the Large Helical Device (LHD). The critical issues are summarized in the following three items.(1) Design of 6 MeV accelerator with low ripple(2) Design of control system for three dimensional beam trajectory(3) Design of energy analyzer with high resolution of DE/E < 10^<-5> We summarize below the results of the collaboration program.1. On Heavy Ion Beam AcceleratorA thermionic ion source and single ended accelerator has been used in the conventional heavy ion beam probe, but it should be too large for the LHD experimental hall. We have decided to utilize a negative ion source and tandem accelerator. It is based on the facts that development of a negative gold ion source with energy spread less than 10 eV is within range and that high voltages with ripple less than 10^<-5> can be achieved by a RF derived power supply as is used in JIPPT-IIU HIBP.2. On Beam trajectory controlBeam trajectories are completely three dimensional and data accuracy for two dimensional potential profile measurement can be degraded. We have designed a new arrangement of the beam line in which second sweep electrodes are placed on the analyzer side to control the secondary beam trajectory so that the energy analyzer can be placed away from the torus, which will be tested with CHS HIBP. This will require sophisticated computer-controlled system.3. An Energy AnalyzerWe have constructed a new type of parallel plate analyzer with shaped electrode without guard ring, which is free from electric field disturbance in the analyzer, and successfully tested with JIPPT-IIU HIBZP. Furthermore, a new method of error elimination for the potential profile measurements has been developed. However, This type of analyzer is not a realistic for 6 MeV HIBP for LHD. New idea is necessary to be introduced.