Temporal Control of Radiation Pulse Using Gas Filled Drift Cells on Hermes Ill

Significant erosion of the front of the HERMES-III electron beam in drift cells filled with N2 gas is measured for pressures greater than 100 Torr as much as 10 ns 3m of beam length at 630 Torr for 11-m length cells. Little rise time RT sharpening or pulse width reduction of the subsequent radiation pulse generated at bremsstrahlung targets terminating the cells, however, is measured. Three-dimensional numerical simulations show that the increased virulence of the resistive-hose instability with increased pressure degrades the spatial coherence of the leading edge of the beam, degrading in turn the RT of the radiation pulse. Transport in the lower-pressure ion-focused regime, on the other hand, does permit intense radiation fields to be produced near the beam axis at the target, with RTs and pulse widths that can be controlled with pressure. Over the range 5 to 50 mTorr, the RT and full-width half-maximum FWHM of the on-axis radiation pulse are inversely related to pressure and can be varied from 5 to 2 ns and -8 to 3 ns, respectively. At 10mTorr, for example, the RT and FWHM are 4.2 -1.7 ns and 6.1 - 1.3 ns, and the corresponding peak dose, peak-dose rate, and useful area of exposure are 25 krad CaF2, 4 Trad CaF2s, and 300 cm2, respectively.