Intense beam propagation at low pressure

Transport of an intense relativistic electron beam through a low pressure gas column is investigated. The electron beam has an energy of 700 keV and a pulse width of 100 ns. The diode electrodes consist of a 7.5 cm diameter carbon cathode and a 0.6 mil thick titanium anode foil. The authors desire a high quality beam with a low beam current of a few kiloamperes. Therefore positioned immediately downstream of the anode foil is a range thick carbon disk with a 2 cm diameter aperture. This carbon mask allows only electrons emitted from the central portion of the planar cathode to be injected into the drift tube. Also it reduces the beam current from 70 kA in the diode to approximately 3 kA at the entrance to the drift tube. The drift tube was either a 10 cm diameter stainless steel tube, or a 10 cm diameter acrylic tube with a copper screen insert which allows photographic diagnostics. A Rogowski coil was used to monitor the injected current and a Faraday cup to measure the transported current. Side-on open shutter photography was employed to observe the gross behavior of beam propagation. Emittance measurements were performed to obtain more quantitative results