Double-ended hydrogen thyratrons for crowbar protection of high-power TWT systems

Abstract

The doubt-ended multigap ceramic thyratron is a versatile switch for crowbar applications. It will provide protection over a very wide range of HT voltages and will operate within a submicrosecond time delay. Since the tube operates in a normal nondestructive "thyratron mode" it will fire reliably for many millions of shots. Practical crowbar conditions can be complex, in particular with floating-deck modulators where stray capacitance and inductance can cause the HT voltage to ring and sometimes completely reverse. In the event of voltage reversal, the double-ended thyratron conducts smoothly in the reverse direction as the circuit requires. The paper describes a new range of compact double-ended thyratrons specifically designed for crowbar use up to 100 kV with an auxiliary power consumption of only 75 W. A dynamic test arrangement is described which demonstrates the tube's capability of discharging 0.75µF charged to 60 kV, the current rising to 5000 A at a rate of 50 kA/µs, with an anode delay time of 200 ns. The test equipment simulates either grounded cathode or floating-deck operation under conditions where a flash arc fault occurs. The efficiency of the protection is evaluated by monitoring the "let-through current" ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</tex> ), charge ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</tex> ), and energy ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_{2}t</tex> ). Coincidence counters register faulty operations. A compact auxiliary supply module makes these tubes especially attractive to aerospace systems engineers.