The Influence of Anode-Plasma Location on Total Current in Self-Magnetically-Limited Electron-Beam Diodes

Cooperstein, G.; Ottinger, P.P.; Schumer, J.W.; Swanekamp, S.B.; Alien, R.J.; Commisso, R.J.; Hinshelwood, D.D.; Mosher, D.; Stephanakis, S. J.; Weber, B.V.; Young, F.C.

doi:10.1063/1.1530838

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“…Recent research shows that depends on ion space-charge, electron kinetics, and 2-D effects [28]- [30]. PIC simulations show that the factor is also sensitive to the position from which ion emission is enabled along the anode [31]. Proton emission from the anode rod is allowed in the simulations from a position extending from one A-K gap upstream of the cathode aperture to the end of the rod.…”

Section: B Magnetically Limited Regimementioning

confidence: 99%

Evaluation of Self-Magnetically Pinched Diodes up to 10 MV as High-Resolution Flash X-Ray Sources

Swanekamp

Cooperstein

Schumer

et al. 2004

IEEE Trans. Plasma Sci.

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The merits of several high-resolution, pulsed-powerdriven, flash X-ray sources are examined with numerical simulation for voltages up to 10 MV. The charged particle dynamics in these self-magnetically pinched diodes (SMPDs), as well as electron scattering and energy loss in the high-atomic-number target, are treated with the partic by coupling the output from LSP with the two-dimensional component of the integrated tiger series of Monte Carlo electron/photon transport codes, CYLTRAN. The LSP/CYLTRAN model agrees well with angular dose-rate measurements from positive-polarity rod-pinch-diode experiments, where peak voltages ranged from 5.2-6.3 MV. This analysis indicates that, in this voltage range, the dose increases with angle and is a maximum in the direction headed back into the generator. This suggests that high-voltage rod-pinch experiments should be performed in negative polarity to maximize the extracted dose. The benchmarked LSP/CYLTRAN model is then used to examine three attractive negative-polarity diode geometry concepts as possible high-resolution radiography sources for voltages up to 10 MV. For a 2-mm-diameter reentrant rod-pinch diode (RPD), a forward-directed dose of 740 rad(LiF) at 1 m in a 50-ns full-width at half-maximum radiation pulse is predicted. For a 2-mm-diameter nonreentrant RPD, a forward-directed dose of 1270 rad(LiF) is predicted. For both RPDs, the on-axis X-ray spot size is comparable to the rod diameter. A self-similar hydrodynamic model for rod expansion indicates that spot-size growth from hydrodynamic effects should be minimal. For the planar SMPD, a forward-directed dose of 1370 rad(LiF) and a similar X-ray spot size are predicted. These results show that the nonreentrant RPD and the planar SMPD are very attractive candidates for negative-polarity high-resolution X-ray sources for voltages of up to 10 MV.Index Terms-Bremsstrahlung, coupled electron-photon transport, electron beams, flash X-radiography, high-power diodes, ion beams, Monte Carlo, particle-in-cell.

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Section: B Magnetically Limited Regimementioning

confidence: 99%