Operation Modes of Hollow Cathode Arcs with Reduced Gas Flow

In 1971 the first research work on hollow cathode arcs (abbreviated HCA) started at Giessen University. Emphasis has been put on the operation of this hollow cathode arc for the ion beam neutralization of the electric propulsion unit RIT 10. In this application the HCA works as an electron source delivering electrons for main discharge starting and beam neutralization. But beside this, diagnostics have been performed dealing with the physical phenomena of HCA's. Different measurements including Langmuir probe analysis led to a simplified discharge model. The determination of the discharge current parts carried by the cathode and the electron emitter inside the cathode gave us hints to explain the observed operation modes, the plum mode, and the spot mode by assuming an electrical double sheath.