PIM - A Test-Bed for Determining Accelerator Requirements for Flash Radiography at 1 TO 3 MV

The PIM pulsed power machine, originally a prototype for a 14 MV Inductive Voltage Adder (IVA), is now being used as a test-bed to determine the requirements of future radiographic accelerators in the 1 to 3 MV range. A 1.5 MV, 100 ns duration pulse is generated by a 10 ohm water Blumlein A prepulse reduction system designed and built by Titan PSD has been fitted, reducing the prepulse to less than 3 kV, sufficiently low to successfully drive a number of different types of e-beam diode. In the configuration used for recent experiments the output of the blumlein is split into two in an oil insulated co-axial feed sharing the current between two induction cells which add the voltage generated along a magnetically insulated transmission line (MITL) feeding the diode. The machine is therefore potentially capable of driving a 40 Ohm load at up to 3 MV. Three types of diode have been tested on PIM in this configuration. These are the paraxial, a relatively high impedance diode usually used at higher voltages, and the lower impedance self magnetic pinch and rod pinch diodes. The low impedance diodes load down the machine as configured reducing the available voltage. Some possible modifications to the PIM machine will be discussed that may improve its ability to drive them. The machine is now being reconfigured to drive only one induction cell and therefore provide a 10 Ohm 1.5 MV capability. This will be used to drive a plasma filled rod pinch diode with a view to developing higher brightness X-ray sources with the softer spectrum obtained by operating at ~ 1 MV. The data obtained in this work is being used to improve our ability to model such machines and assess concepts for future accelerators operating in the voltage range mentioned.