Influence of Working Pressure on Ion Sensitive Probe Measurement in Microwave ECR Plasmas

In order to precisely measure the ion parameters in a microwave electron cyclotron resonance plasma using an ion sensitive probe, the dependences of the current-voltage (I-V ) characteristics on the shielding height (h) and the potential difference between inner and outer electrodes (V _B ) have been investigated at different working pressures of 0.03 Pa and 0.8 Pa. Results show that the I-V curves at higher pressure are more sensitive to the variation of h than those at lower pressure. The influence of V _B on ion temperature (T _i ) measurement becomes more prominent when the pressure is increased from 0.03 Pa to 0.8 Pa. Under both pressures, the optimized h is obtained at the condition where the current reaches zero in the positive voltage region with a suitable V _B of −1.5 V because of effective shielding of the electron E×B drift.