Modelling the effects of an electron beam on the potential distribution in a low pressure parallel electrode discharge

The effect of an electron beam on the potential distribution in a one-dimensional model of a steady parallel electrode discharge is investigated theoretically. Taking the electrodes to be well separated, it is shown that the potential across the sheath of the emitting electrode is decreased by the electron beam. At the absorbing electrode the potential across the sheath is increased. For the latter electrode the potential must be less than a certain maximum value if the beam electrons are to traverse the discharge. Coupling the electrodes by an external current I ext , a characteristic is derived relating I ext and the applied voltage V a . Assuming the beam current at the absorber is some fraction of the beam current at the emitter, then the maximum slope of the characteristic can be used to determine the electron temperature, or . Finally, the properties of the special case of coupled electrodes with I ext = 0, one electrode being earthed, is discussed.