An ionisation device was developed and tested as part of a supersonic
electron-beam-sustained cw laser. This device was a wide-aperture elec
tron accelerator with extended but discrete thermionic emitters. The d
ensity of the current extracted from this accelerator was up to 75 mu
A/cm(2). Experimental and theoretical investigations were made of the
characteristics and of the thermal conditions of the operation of this
ionisation device.