Current flow in a high-voltage diode subjected to a crossed magnetic field

The space-charge limited electron current (approx. =50 kA) flowing in a pulsed, high voltage (approx.200 kV) vacuum diode is studied as a function of magnetic field applied at right angles to the diode electric field. The observations compare favorably with predictions from self-consistent theory which takes account of space-charge and allows for the presence of the magnetic field. Time-resolved measurements of the diode current and voltage lead to a determination of the expansion velocity of the cathode and anode plasmas. It is shown that a magnetic field of approx.5 kG suffices to stop plasma motion, in agreement with magnetohydrodynamic computations. Thus, diode closure is inhibited, at least over the 40 nsec time span of the voltage pulse