High-perveance electron beams for high-power, slow-wave microwave devices

Summary form only given. One of the problems in the scaling of high-power vacuum microwave sources to higher frequencies is the need to transport beams with high space charge density, since the RF circuit transverse dimensions tend to decrease with wavelength. Research results establish that novel periodic magnetic focusing optics offer the opportunity to propagate much higher beam currents than previously achievable in slow-wave vacuum microwave devices. Theory and simulations establish that stable, edge focused transport of linear sheet electron beams can be realized with periodically-cusped magnetic (PCM) focusing for very high current density beams (>200 A/cm/sup 2/) at low beam voltages (10 kV). Edge focusing options include offsetting the poles of the planar PCM array or using periodic permanent quadrupole magnetic (PPQM) edge focusing. Both options provide stable edge focusing with the former method requiring fewer magnet pieces and the latter method providing superior beam matching capability. Using quadrupole magnetic optics to produce very large aspect ratio elliptical sheet electron beams is well suited for laboratory experiments. Simulation and experimental results with a 10 kV, 2 A electron beam confirm the feasibility of this approach. Round beam focusing by short period PPQM arrays was also studied.