Design and performance of the Z magnetically-insulated transmission lines
The authors have designed and tested a 10 nH, 1.5 m radius vacuum section for the Z accelerator. The vacuum section consists of four vacuum flares, four conical 1.3 m radius magnetically-insulated transmission lines (MITLs), a 7.6 cm radius 12-post double-post-hole convolute which connects the four outer MITLs in parallel, and a 5 cm long inner MITL which connects the output of the convolute to a z-pinch load. The authors have demonstrated they can deliver a 100 ns rise-time 20 MA current pulse to the baseline z-pinch load. They can reproduce the peak MITL current to within /spl plusmn/1.6%. Power-flow measurements indicate the vacuum section performs as expected until peak current. Afterward, measurements and simulation results diverge.
Precision electron flow measurements in a disk transmission line
There have been several models which have been successful in characterizing many aspects of the electron flow in simple self-insulated geometries. For complicated structures, which are typically found in actual systems, particle-in-cell (PIC) calculations are used. These simulation models have demonstrated a fundamental difficulty in resolving the electron flow in strongly insulated systems. When the electron flow is confined to a very small sheath size, relative to the transmission line gap, finer meshing must be applied near the cathode surface. This increase in cells can lead to inadequate resolution through a process known as “numerical heating”. Precise measurements of these electron flows, typically found in low-impedance driven loads, are essential in providing a benchmark for these widely used simulation techniques. Detailed measurements conducted on a low-impedance disk transmission line provide a useful comparison between the theoretical models and the simulation results. In addition a method for directly measuring the electron current at the load of a strongly insulated system is developed. This would circumvent the difficulty of typical diagnostic methods in resolving these electron flows which are usually minimized for optimal efficiency.
Imploding argon plasma experiments
The Pithon pulsed electron beam accelerator was used to implode an argon plasma at 4 TW. The plasma was prepared by microwave preionization of an annular column of gas injected between the output electrodes of the pulser. The electrodynamic behavior implied that most of the gas was involved in the pinch. The plasma conditions were inferred from hydrogenlike and heliumlike x‐ray emission spectra. Final pinch dimensions were determined from x‐ray pinhole photographs and laser shadowgraphs.