Experimental Study of a Triode Reflex Geometry Vircator
  Triode reflex geometry vircator operating within 3.0 - 4.2 GHz range with efficiency up to 6% is developed and experimentally investigated. Shiftable reflectors are shown to enable frequency tuning and output power control. Radiation frequency and power are analyzed for different cathode-anode gap values and varied reflector positions. 
Vladimir Baryshevsky, Alexandra Gurinovich, Evgeny Gurnevich and Pavel   Molchanov
physics.acc-ph physics.plasm-ph