Development and testing of a mercury free switch for high current high coulomb applications

EEV Ltd. has recently undertaken the development of two novel types of pulsed power closing switch. These developments were intended to extend the switching performance available from established technologies such as ignitrons, gas filled spark gaps and hydrogen/deuterium thyratrons. In the case of the device described in this paper, which is intended to address high current high coulomb applications in which ignitrons would typically have been used, the use of an environmentally acceptable mercury free technology was an essential objective. The series of devices described here, denoted the HCS series, has been designed to give reliable performance as a stand-alone sealed switch for high current high coulomb applications. Testing has been performed at voltages of up to 22 kV, peak currents of up to 340 kA and coulomb transfers of up to 100 coulombs per pulse. A range of test results are described for the 2.5 inch, 6 inch and 10 inch diameter devices, denoted as HCS1, HCS2 and HCS3 respectively. The advantages of the HCS range of switches include high voltage hold-off, high peak current capability, large dynamic range, easy triggering, environmental acceptability and low standby power requirements. The wide operating range of the HCS series of devices makes them ideal for use as crowbar protection devices where triggerability at low voltages is essential. The HCS series is triggerable at anode voltages of 1 kV or above. The envisaged limitations of the range of devices are discussed.