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

Abstract

Design criteria for hydrogen thyratrons operating at fast rates of current rise ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</tex> ), high anode voltages (e <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">py</inf> ), and high peak currents (i <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</inf> ) have been theoretically and experimentally determined. The approach was to divide the investigation into two basic areas. The criteria for achieving high <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</tex> were first established at relatively low voltages. Then the information necessary to incorporate features promoting high <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</tex> into a high-voltage structure was determined. The principal factors affecting <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</tex> 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</tex> . Rise rates of the order of a few times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> A/s are considered feasible for properly designed tubes operating with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e_{py} = 50</tex> kV and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_{b} = 10</tex> kA. The criteria necessary for high di/dt are burdensome when high e <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">py</inf> and high i <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</inf> 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 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">py</inf> 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 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">py</inf> are discussed, and the boundaries of the state of the art are drawn.