Radiographic results for the rod-pinch diode scaled up to 6 MV

The rod-pinch diode is evaluated as a pulsed radiographic source for diode voltages up to 6 MV on the ASTERIX generator. Peak currents of 105 to 135 kA are delivered to the diode for peak voltages of 5.2 to 6.3 MV. The diode couples efficiently to the generator for 1.6-, 2.0-, and 3.0-mm diameter tungsten (or gold) anode rods producing a 40-ns radiation pulse. The coupling is degraded if the anode-cathode gap (Rc - RA) is too small (7.5 mm), if the anode rod extension is too short (10 mm), or if the aspect ratio Rc/RA is too large (20). For the standard anodes considered here, the figure-of-merit (FOM) is largest [11 rad(air)/mm:] for a 1.6-mm diameter anode, corresponding to an on-axis (0/spl deg/) dose of 28 rad(air) at 1 meter from the source and a 1.55-mm source diameter (LANL measure). For a 2-mm diameter anode, the largest FOM [9.2 rad(air)/mm/sub 2/] is obtained for a 1.95-mm source diameter and a 35-rad(air) dose. Blunt-end anodes have larger on-axis source diameters and smaller FOMs than tapered-tip anodes. Measured angular distributions indicate that the dose increases monotonically from 0/spl deg/ to 80/spl deg/ by a factor of 1.6 to 1.8 and suggest that the electron distribution incident on the anode rod peaks at a large angle from the forward direction.