Emission of electron and ion pulses from porous tungsten partially covered with cesium

Abstract Cesiated tungsten at about 1700 K provides a low work function (∼ 2 eV) surface for the emission of high current density electron beams as well as for the generation of cesium ions by contact ionization at 1300 K. Tungsten with porosities up to 35% has been investigated, supplying the cesium coverage by diffusion through the body from a heated reservoir. A test diode has been designed by computer simulation, achieving extremely high current densities by a convex emission surface. In dc mode of operation, the obtained ion current density of 8 mA/cm 2 compares well with data from literature, whereas the electron emission was negligible. In pulsed operation, however, electron densities of up to 512 A/cm 2 have been obtained for pulses as long as 100 μs. Even more surprising is an increase of the emitted ion current density to 200 mA/cm 2 for up to 0.8 ms.