Source Properties of a Hollow Cathode Arc Plasma

Experiments have been carried out on the properties of a hollow cathode as an ion-source. The measured electron density, ion and neutral temperatures and drift velocities have been compared with predictions from the conservation laws for matter, momentum and energy. Very large exit drift velocities of ions and neutrals are observed. The magnitude and direction, against the electric field, can be explained on the basis of the momentum balance. At weak magnetic field strengths even supersonic drift velocities are found. The charge flux carried by the ions is about five percent of the net arc current. For small flows, the ionized fraction of the gas supply approaches 100%. The neutral particle density outside the cathode consist of a fraction drifting with a large velocity out of the cathode and a fraction of cool background atoms. The change of the ratio of these fractions with increasing distance to the cathode causes the average neutral particle drift to decrease very rapidly. Finally, an analysis of the overall cathode power balance is given.