An investigation of trigatron breakdown by two different mechanisms

An investigation has been carried out into the mechanisms controlling high voltage trigatron operation. This paper describes the experimental work identifying the two different sequences of triggered breakdown. The operating conditions required for each of these breakdown mechanisms to take place are described and discussed. One mechanism (mode 1) is when the trigger pulse is applied to the trigger pin resulting in breakdown across the gas between the pin and earthed electrode. The resulting intense UV radiation is believed to produce free electrons through either photo-ionisation or photo-detachment in the gas which in turn leads to the initiation of an electron avalanche followed by breakdown of the main gap. The second mechanism (mode 2) is when the trigger pulse initiates breakdown between the pin and HV electrode first. After the main gap voltage has collapsed to the trigger pin, this produces a high degree of over-voltage between the pin and the adjacent earthed electrode and consequently, the voltage collapse time is very short. This mode of operation is desirable and can be ensured by careful design of the trigger/earthed electrode configuration. The jitter performance of the trigatron when operating in each of the above modes has been measured at operating voltages of 200 kV for mode 1 and 500 kV for mode 2. The results from this study indicate that the smaller jitter is obtained when the trigatron is operating mode 2, as expected.