Calibration of the heavy ion beam probe parallel plate analyzer using the gas target and reference beam

The most important and difficult problem in heavy ion beam probe diagnostics is the absolute measurement of the plasma potential. The analyzer that measures the energy of the secondary ions must be perfectly calibrated. The accuracy necessary should be at least 10−4. We used two methods of calibration: in situ using the gas target, and in vitro using the reference beam. Calibration allows one to obtain the gain G and dynamic coefficient F of the analyzer. We developed a procedure of fast calibration that uses the dynamic curve Ub/Ua(δi), where Ub and Ua correspond to the accelerating voltage of the beam and the voltage on the analyzer, and δi is a normalized difference of currents on the plates. The analyzer used on the T-10 tokamak was calibrated by both methods. Results of both calibrations are in a reasonable agreement at the moderate values of the entrance angle. The nonideal effects caused by ionization of the gas target and asymmetric secondary electron exchange are considered.