New developments in super-fast, high-power, hydrogen thyratron switching

Design criteria for hydrogen thyratrons operating at fast rates of current rise (
di/dt
), high anode voltages (e
py
), and high peak currents (i
b
) have been theoretically and experimentally determined. The approach was to divide the investigation into two basic areas. The criteria for achieving high
di/dt
were first established at relatively low voltages. Then the information necessary to incorporate features promoting high
di/dt
into a high-voltage structure was determined. The principal factors affecting
di/dt
are the tube's effective inductance, the nature and rate of the plasma growth, and the manner in which commutation is effected. The inductance depends on the tube's geometry and dimensions. Plasma growth is a function of geometry and gas pressure, and must be controlled in a way such that the tube is triggered and then commutates in the optimum manner for highest
di/dt
. Rise rates of the order of a few times 10
¹²
A/s are considered feasible for properly designed tubes operating with
e_{py} = 50
kV and
i_{b} = 10
kA. The criteria necessary for high di/dt are burdensome when high e
py
and high i
b
are also required. A low-inductance, multigap structure is required, and command pulse charging must be used. The applied voltage is then distributed across the various gaps in a manner determined by the interstage capacitance and the stray capacitance to ground. Very high voltages are thus applied to the upper gaps and their corresponding insulators, and even higher voltages are impressed as the cascading process proceeds up the tube. Since low inductance requires short insulators, it is necessary that they be stressed well beyond the limits common to conventionally designed tubes. Values of e
py
in excess of several hundred kilovolts are shown to be feasible for tubes having inductances well below 100 nH. Theoretical and experimental results pertaining to both high di/dt and high e
py
are discussed, and the boundaries of the state of the art are drawn.