Investigation of light weight permanent magnet focusing schemes for millimeter wave tubes

Electron tubes operating in the millimeter wave regime are characterized by their small, fragile r.f. circuits which are usually machined into relatively massive supporting structures. This imposes two restrictions on the beam focusing problem, 1) the electron beam needs to be focused through such structures with minimal interception, and 2) the magnetic focusing scheme must provide enough room to accommodate the r.f. circuit and its supporting structure. Because of these restrictions, only uniform magnetic fields produced by either solenoids or large permanent magnets have hitherto been used to focus the electron beams. The recently developed magnet material Samarium-Cobalt now provides other means of meeting both the focusing field and mechanical requirements needed for milimeter wave tubes.