Energy Loss Investigation On Low Energy Ions Interacting With Plasma Target

Investigation of ion beam interacting with plasma is of ke y importance in the frontiers of “high energy density matter driven by heavy ion beams", “energy transportation in the thermal nuclear fusion reactor”, “α-heating and fast ignition in inertial confinement fusion”. However, it is still lack of experimental studies, especially for ion beam in low energy region, the discrepancy between the experiments and theoretical models or simulations is more than 30%, sometime even in different orders. High precision experimental data are badly needed.In this paper, the experimental studies of low-energy ion beam-plasma interaction on the 320 k V physics research platform in the Institute of Modern Physics（IMP） are reported. The experimental data for proton with initial energy of 100 ke V and for He2+ with initial energy of 400 ke V were analyzed. The plasma target is created by electric discharge in the hydrogen gas. The time evolution of the discharging current was monitored by means of the Rogowsky coil, and the state of the plasma was diagnosed using the laser interferometer method. In the experiments, the discharging voltage and the initial hydrogen pressure were varied from 3 to 5 k V and from 1 to 8 mbar, respectively. Under these condition, the free electron density is up to 10¹6 cm^-3 and the temperature was about 1-2 e V. We measured the energy loss of proton and He²⁺ at different delay times.It was found that the free electron density and the energy loss of ions in the plasma first increased from zero to a maximum value before they started to drop, which have a similar behavior with the temporal evolution of the discharging current. In the proton experiment, according to the experiment and diagnostic results, we calculate the energy loss and stopping power enhancement factor of free electron over bound electron in gas. Then we compare our result to the previous results. Finally we calculate the coulomb logarithms of free electron and compare to the theoretical prediction; In the He²⁺ experimental, we investigate the effect of different voltage and different hydrogen pressure on energy loss. It is found that both have great influence on energy loss. We also calculate the effective charge of He and found that the effective charge is lower than 2 but larger than that in cold gas.