Production of sheet electron beams with crossed-field secondary emission diodes

Summary form only given. Crossed-Field Secondary Emission (CFSE) diodes, which are based on a mechanism of self-sustained secondary electron emission, generate normally tubular electron beams with the current of up to several hundreds of Amperes for diode voltages of less than 40 kV (Saveliev et al., 1999). Linear current density of the output electron beam is in the range of 1-20 A/cm. A number of applications such as planar microwave devices (Agafonov et al., 1997) and large area plasma processing systems (Fernsler et al., 1999) do however require sheet electron beams rather than cylindrical beams. This work is concerned with a development of a CFSE planar diode that is capable of producing sheet electron beams. Several diode designs having cathode widths of 45-60 mm have been tested and characteristics of output electron beams were investigated. For diode voltages in the 25-40 kV range, the electron beams were generated with total currents of 15-40 A and linear current densities of 2-8A/cm depending on the diode voltage, magnetic field strength and the diode design. Due to the specific nature of the electron flow production in this CFSE diodes, two closely spaced electron sheets of /spl sim/1 mm thickness separated by 1-2 mm are produced. One of these can be easily suppressed, if desired, by the incorporation of a downstream reflecting electrode. A significant problem encountered in this research was the non-uniformity of the linear current density distribution j(x) along the diode width where the main contributory factor was found to be due to cathode edge effects. The influence of these edge effects has been reduced by an appropriate design of the cathode electrodes and, to date, a /spl plusmn/25% uniformity of the j(x) distribution has been achieved. Considerations relating to the further refinement of the electron beam characteristics and extension of-the beam width will be discussed.