Pressure dependences of electron energy distribution and power dissipation in symmetrical RF helium discharges

The electron energy distribution function (EEDF) is measured with a Langmuir probe in a symmetrically capacitively-coupled RF (13.56 MHz) helium discharge over a range of gas pressures from 0.1 to 1.0 Torr while keeping the discharge current constant at 100 mA. The bulk electrons are Maxwellian over this range, while the average electron energy decreases with increasing pressure, together with an increase in electron density. The power dissipation calculated from the EEDF and the discharge current-voltage relation agrees with that measured.