Measurement of ac ion current from a corona ionizer using a Faraday cage

The use of ac ionizers operating at high frequency has become common in the semiconductor industry. The mechanism by which equipment neutralizes charge, however, is not well understood, because ac induction interferes with the measurement of extremely small ion currents. In this work, we use a Faraday cage that is directly connected to an ac ionizer. At frequencies of 1 and 10 Hz, we measure distinct pulses of ion current. The amount of transported charges increases with both applied voltage and ambient pressure. The effect of pressure is more significant than the effect of voltage. At the higher chosen frequency, the current changes from pulses to a sinusoidal shape. By noting the delay time at 1 kHz, the average air velocity between the needle and the Faraday cage was calculated. From dc corona measurements inside the ionizer outlet, we determine that the fraction of charge transported to the Faraday cage is small compared to the total amount of charge generated by corona.