Wall Potential in Crossed-Field Devices

The effect of a magnetic field on the two stable potentials of the glass wall in high-vacuum devices is investigated; it is shown that a transition is possible from one stable potential to another under the effect of a magnetic field. The physical conditions are formulated for the stabilization of the wall potential at either of two values. The applicability of the expression given by James and Carter for the lower stable potential is discussed. The influence on the higher stable potential of the ion and electron currents reaching the wall and of the secondary-emission multiplication process is also investigated. The experimental results on the variation of the wall potential as a function of the magnetic field in a plane-parallel crossed-field device with glass walls are compared with those obtained in similar devices with walls provided with a conducting coating.