Risetime characterisation of 3–5 MV oil Blumlein pulse generators at AWE

Summary form only given. AWE has a suite of Marx-folded Blumlein X-ray generators, which are used to drive focused electron-beam diodes with an output voltage between 1 and 10 MV. The EROS simulator, one of these machines, has recently been adapted for partial use as a to develop low-impedance, pinched e-beam diodes for flash radiography. However, the risetime of the voltage pulse of EROS Blumlein is twice that of these service machines and, as a consequence of the collapsing diode impedance of the low-impedance self-magnetic pinch diodes results in poor radiographic performance. A characterization of the self-breaking oil-Blumlein switch on EROS was made in the 2-4 MV range using a selection of Marx charge voltages between 30 and 60kVdc. Options to modify the pulse-shape for 3MV operation were investigated as a reduction of the Blumlein switch inductance, previously estimated at ~300nH, or its replacement is required. The methods to achieve this improvement are described. Comparison of predicted and measured Blumlein switch performance between EROS and the service machines at their operational voltages were made. Options to modify the EROS configuration to obtain a switch inductance below ~100nH were investigated but, the techniques to improve the output voltage risetime to less than 10 ns require unacceptable modifications to the machine geometry.