The performance of the pulse bias hairpin resonator probe for negative ion diagnostic

The pulsed bias hairpin resonator probe (HP) is a novel concept which has been applied to measure negative ion density and temperature in electronegative discharges. The underlying concept relies on the response of negative ions and electrons to the rapidly changing sheath width around the cylindrical pins of the hairpin resonator. Pulsed bias HP has advantages of spatial resolution and less sophistication over the conventional pulsed laser photo-detachment (LPD) technique, where the spatial resolution is limited to in-line laser beam measurements. In this presentation, pulsed bias HP has been characterised in detail for a range of positive values of pulse bias and working pressures in a 13.56 MHz CCRF oxygen discharge. It is seen that with the increase in positive bias, negative ion density also increases, and it attains saturation when biased above the plasma potential. On the other hand, the negative ion diffusion time scale reduces when biased above the plasma potential. Furthermore, the results have been validated with the LPD technique.