Angular dose variations from 4- to 6-MV rod-pinch diode experiments on the ASTERIX pulsed-power generator

The angular distribution of radiation from a rod-pinch diode is examined with coupled PIC-Monte-Carlo simulations using the LSP code (D.R. Welch, et al., 2001) and compared with angular dose measurements on the ASTERIX pulsed-power generator. For the 4- to 6-MV voltage range accessible in the experiments, both the measured and simulated doses at 1 m were 25 to 38 rad-LiF in the forward direction (0/spl deg/). The calculated dose at 90/spl deg/ is 1.2-1.8 times larger than the forward-directed dose depending on both the voltage and rod diameter. This is also in agreement with the measured angular variation (F.C. Young, et al.,). At 6 MV, the simulations show that the dose near 180/spl deg/ is more than twice the forward-directed dose. At these high voltages, electrons approach the anode rod primarily at angles close to 180/spl deg/ resulting in peak radiation in the backward direction. This suggests that negative polarity should be considered for voltages at or above 6 MV to maximize the extracted dose. Simulations show that the 0/spl deg/ dose is higher with tapered rods and increases with rod diameter. Simulations at 10 MV show that the dose near 180/spl deg/ is more than ten times higher than the 0/spl deg/ dose. At 10 MV, the dose near 180/spl deg/ at 1 m from a 2-mm diameter, blunt rod is calculated to be /spl sim/800 Rad (LiF).