High current, annular e-beam generation and transport experiments

Summary form only given, as follows. High current, annular electron beams are important for the Twobetron accelerator and axis-encircling-beam microwave devices, such as the large orbit gyrotron and the peniotron. Experiments are underway to characterize the properties of annular e-beams generated by the Michigan Electron Long Beam Accelerator (MELBA) at parameters: V=-0.8 MV, I=1-10 kA, and pulselength =0.5 /spl mu/seconds. Transport experiments have been performed to measure the e-beam current through annular slots in a microwave cavity. Computer simulations have been performed on E-Gun code to test the effect of different cathode shapes on e-beam alpha (Vperp/Vpar). Transported beam current was measured after passing through slots centered at 2.15 cm radius with a solenoidal magnetic field of 2.0-2.5 kGauss. Initial experimental results show maximum transported current through slots with a 0.5 cm width (/spl Delta/r) to be between 0.5-0.8 kA using an annular cathode tip of radius 4.5 cm. Qualitative results using the E-Gun code compared favourably with these experiments. Further experiments are in progress to measure transported current through a pillbox microwave cavity at higher fields (>3.5 kGauss).