Electrical Characteristics of a Penning Discharge

The uniform-space-charge theory of the high-vacuum, Penning discharge has been tested and supported in two experiments. In one experiment a measurement of ion energies verifies the existence of a large space-charge depression of potential along the axis of the anode cylinder. In another, the frequency of body rotation of the electron cloud is verified by allowing the cloud to interact with the structure of a split-anode magnetron. Spontaneous oscillation is obtained. The avalanche theory of the cold-cathode discharge is tested by a measurement of the noise spectrum of the discharge current. Partial confirmation is obtained, although it is finally concluded that the discharge may be dominated by other processes, such as plasma instabilities. Evidence for plasma instabilities is presented in the form of star-shaped, ion-sputtering patterns. Three possible instability mechanisms are discussed, by means of which such sputtering patterns could be formed. A useful by-product of this investigation is the discovery that a Penning "ion-gun" produces a naturally collimated, intense ion beam of sharply defined energy.