Abstract
Quasiequilibrium power flow in two radial magnetically insulated transmission lines (MITLs) coupled to a vacuum post-hole convolute is studied at $50\text{ }\text{ }\mathrm{TW}--200\text{ }\text{ }\mathrm{TW}$ using three-dimensional particle-in-cell simulations. The key physical dimensions in the model are based on the ZR accelerator [D. H. McDaniel, et al., Proceedings of 5th International Conference on Dense Z-Pinches, edited by J. Davis (AIP, New York, 2002), p. 23]. The voltages assumed for this study result in electron emission from all cathode surfaces. Electrons emitted from the MITL cathodes upstream of the convolute cause a portion of the MITL current to be carried by an electron sheath. Under the simplifying assumptions made by the simulations, it is found that the transition from the two MITLs to the convolute results in the loss of most of the sheath current to anode structures. The loss is quantified as a function of radius and correlated with Poynting vector stream lines which would be followed by individual electrons. For a fixed MITL-convolute geometry, the current loss, defined to be the difference between the total (i.e. anode) current in the system upstream of the convolute and the current delivered to the load, increases with both operating voltage and load impedance. It is also found that in the absence of ion emission, the convolute is efficient when the load impedance is much less than the impedance of the two parallel MITLs. The effects of space-charge-limited (SCL) ion emission from anode surfaces are considered for several specific cases. Ion emission from anode surfaces in the convolute is found to increase the current loss by a factor of 2--3. When SCL ion emission is allowed from anode surfaces in the MITLs upstream of the convolute, substantially higher current losses are obtained. Note that the results reported here are valid given the spatial resolution used for the simulations.
Highlights
A system of magnetically insulated vacuum transmission lines (MITLs) is a key element in a number of present and future pulsed-power systems
The optimal design of these complex MITL systems must satisfy a number of often competing system-design criteria, including low inductance and minimal current losses [1,2]
The PIC code LSP [45] is used to carry out fully kinetic, EM, relativistic 3D ðr; ; zÞ simulations to examine electron current losses in an idealized coupled MITL-convolute system
Summary
A system of magnetically insulated vacuum transmission lines (MITLs) is a key element in a number of present and future pulsed-power systems. Jennings et al [37] carried out a detailed circuit analysis of Z shot data for wire array loads They inferred losses from a variety of sources, which included electron MITL current flow, resistive electrode plasma expansion in the convolute, and deposition in the final transmission line between the convolute and load. Using these techniques, an estimate of current loss in the convolute can be obtained for individual shots.
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