Solenoidal transport of low-voltage sheet beams for millimeter wave amplifiers

The stable transport of high-perveance, low-voltage sheet electron beams is a key requirement for the successful development of compact, high-power sheet beam amplifiers. Here, we examine the transport of such beams in a solenoidal magnetic field and compare and contrast this transport with that produced by a periodic permanent magnet array. It is shown that a solenoid can stably transport a sheet beam of significantly higher current density than a periodic array and that diocotron effects, which are usually cited as a reason for not considering solenoidal transport, can be effectively suppressed over propagation distances needed for MMW amplifiers. Based on these considerations, we have designed a sheet beam gun and permanent magnet solenoid, which are now being fabricated as a beam stick for a W-band extended interaction klystron.