The Discharge Mechanism in the High-Vacuum Cold-Cathode Pulsed X-ray Tube

The existing theory of the discharge mechanism in the cold-cathode pulsed X-ray tube based on ionization of residual gas and plasma formation is reviewed and is shown to fail for a high-vacuum tube. A new theory is presented which is based on the production at the cathode of a vapour jet having a velocity of approximately 10 6 cm sec -1 . This results in an expanding region of low voltage discharge, and leaves most of the applied voltage across a rapidly contracting vacuum region adjacent to the anode. It is shown that the tube current and voltage as functions of time and the X-ray pulse duration can be predicted from a knowledge of the voltage supply and tube parameters, and the results are verified experimentally.