Cathode-current dependence on pulse width for hydrogen thyratrons

It is well known that the oxide-coated cathode in a well-activated hydrogen thyratron is capable of sustaining a current density in excess of 20 amp/cm² (amperes per square centimeter) for pulse durations of 1 μsec (microsecond) or less. It is also known that, as the pulse length increases, the emission density at which arcing occurs decreases. The current capabilities of oxide-coated cathodes in hydrogen thyratrons were experimentally evaluated at pulse lengths of 5, 30, 110, and 1,000 μsec, and a number of different tube sizes were used. At a constant pulse width, it was found that the current density at which arcing occurred was related to the cathode-coating resistance and that the limiting factor was a maximum power-dissipation density; the power density at which arcing occurred was related to the pulse length. The use of this dependence to determine the cathode current capability at any pulse width is discussed.