RF hollow cathode discharges with tapered shape

A hollow cathode with tapered shape (HCT) is developed in order to expand the range of operating pressures. Although the plasma density produced by the HCT becomes slightly lower than that by an ordinary hollow cathode, it is demonstrated experimentally that the range of operating pressures for stable RF hollow cathode discharge is expanded. It is shown that the position of the negative glow moves inside the HCT for different operating pressures to sustain the hollow cathode discharge.