Title of Document: STUDIES OF HIGH FREQUENCY WAVE EXCITATION IN FAST AND SLOW WAVE VACUUM DEVICES

THz and millimeter-wave length radiation is widely used in imaging, detection and plasma heating. Vacuum electronic devices are the most efficient sources of high power radiation in the THz and millimeter range. Efforts to increase power by increasing current, are hampered by self-field effects and instabilities. Two examples of these effects are considered: the reduction in bunching efficiency in orotrons (a slow wave device), and the excitation of backward wave instabilities, in gyrotrons (a fast wave device). The goal of producing THz radiation from miniature electron beam devices has refocused interest in orotrons. The efficiency of these devices improves with increasing current density. However, with increasing current density, self-fields become more important. Here, the theory of self-fields in a planar orotron is developed. We find that the parameters of the grating, which provides the slow wave fields that interact with the beam, also affect the self-fields, which give rise to the slow space charge wave. Thus, optimization of the grating parameters requires consideration of their impact on the dispersive properties of the slow space charg