A Compact 70MW, 250KV Modulator Using Thyratrons

A compact oil immersed modulator is described suitable for driving a 30MW output klystron and using two 70KV 2,500 Amp hydrogen thyratrons as switches. The design is a development of an earlier modulator using a 70KV triggered spark gap. This earlier model was limited to a maximum repetition rate of about 250 p.p.s. but the thyratron switches permit operation to over 1000 p.p.s. and a maximum duty cycle of .001. Complete oil immersion in a single tank results in compactness, economy, reliability and facilitates the use of a high charging voltage which, in turn, leads to a simplification in the pulse circuit, particularly in relation to pulse flattening and pulse length selection. A high current silicon clipper is described which is used to reduce the inverse voltage and which still permits rapid thyratron recovery time.