CALIBRATION OF THE HEAVY-ION BEAM PROBE PARALLEL-PLATE ANALYZER USINGTHE GAS-TARGET AND REFERENCE BEAM

The most important and difficult problem in heavy ion beam probe diagn ostics is the absolute measurement of the plasma potential. The analyz er that measures the energy of the secondary ions must be perfectly ca librated. The accuracy necessary should be at least 10(-4). We used tw o methods of calibration: in situ using the gas target, and in vitro u sing the reference beam. Calibration allows one to obtain the gain G a nd dynamic coefficient F of the analyzer. We developed a procedure of fast calibration that uses the dynamic curve U-b/U-a(delta i), where U -b and U-a correspond to the accelerating voltage of the beam and the voltage on the analyzer, and Si is a normalized difference of currents on the plates. The analyzer used on the T-10 tokamak was calibrated b y both methods. Results of both calibrations are in a reasonable agree ment at the moderate values of the entrance angle. The nonideal effect s caused by ionization of the gas target and asymmetric secondary elec tron exchange are considered. (C) 1997 American Institute of Physics.