Stable, High Density Field Emission Cold Cathode

The practical application of the field emission electron source has heretofore been impeded by insufficient reliability. Instability (i.e., changes in emitted current at a fixed applied voltage) results from changes in the cold cathode surface associated with contamination and sputtering. The cold clean cathode is shown to be electrically stable at dc emission densities up to 107 amp/cm2. Techniques are discussed which permitted stable operation of a single needle tungsten cathode during 1000 hr at an average beam power of 35 w (corresponding to a beam power density of 35 billion w per unit cathode area). A simple method is described which permits reconditioning of the cathode surface when required, and apparently extends life indefinitely; operating periods in excess of 12 000 hr are reported. An explanation is suggested for the small, gradual residual changes observed in the emitted current.