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.
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