PERIODIC MAGNETIC FOCUSING OF SHEET ELECTRON-BEAMS

Sheet electron beams focused by periodically cusped magnetic (PCM) fie lds are stable against low-frequency velocity-shear instabilities (suc h as the diocotron mode). This is in contrast to the more familiar uns table behavior in uniform solenoidal magnetic fields. A period-average d analytic model shows that a PCM-focused beam is stabilized by ponder omotive forces for short PCM periods. Numerical particle simulations f or a semi-infinite sheet beam verify this prediction and also indicate diocotron stability for long PCM periods is less constraining than pr oviding for space-charge confinement and trajectory stability in the P CM focusing system. In this article the issue of beam matching and sid e focusing for sheet beams of finite width is also discussed. A review of past and present theoretical and experimental investigations of sh eet-beam transport is presented.