Abstract
Many papers have been published on the theory of magnetic insulation and the use of Zflow analysis of magnetically insulated transmission lines (MITLs). We describe herein a novel design process using the circuit code SCREAMER for a real-world MITL for z-pinch loads based on the Zflow model of magnetic insulation. In particular, we design a 15-TW, 10-MA, 100-ns double-disk transmission line using only circuit modeling tools and Zflow analysis of the MITL. Critical issues such as current loss to the anode during the setup of magnetic insulation and the transition from a non-emitting vacuum power feed to an MITL play a large role in the MITL design. This very rapid design process allows us for the first time to explore innovative MITL designs such as variable-impedance MITLs that provide a significantly lower total inductance and improved energy delivery to the load. The tedious process of modeling the final MITL design with highly resolved 2D and 3D electromagnetic particle-in-cell codes occurs as a validation step, not as part of the design process.
Highlights
The designers of magnetically insulated transmission lines (MITLs) have traditionally used analytic approaches and simple, experimentally validated design concepts as the basis for new MITL designs
The fraction of the current in vacuum flow is insignificant even at peak voltage and, even if all of that vacuum-electron-flow current is lost at the post-hole convolute (PHC), it is not a significant current loss. [Note that the magnitude of electron losses at the PHC depends on the convolute voltage, and those losses increase dramatically with peak driver current (PHC voltage), as was seen going from Z to ZR.] These MITL behaviors are typical with z-pinch loads that are effectively a short circuit until peak current, after which the dL/dt voltage makes magnetic insulation more perilous
The electron losses seen at each MITL segment are a strong function of local impedance and local electric field
Summary
The designers of magnetically insulated transmission lines (MITLs) have traditionally used analytic approaches and simple, experimentally validated design concepts as the basis for new MITL designs. We describe an MITL design process that is more theoretically based than that used in earlier MITL designs This MITL design process is supported by extensive theoretical and computational work on magnetic insulation by Creedon, Mendel et al., VanDevender et al., Di Capua, and Ottinger et al.. This MITL design process is supported by extensive theoretical and computational work on magnetic insulation by Creedon, Mendel et al., VanDevender et al., Di Capua, and Ottinger et al.29,31,32 While this early work gave an excellent detailed theoretical description of magnetic insulation and MITL power flow, the application of MITL theory to actual MITL designs was lacking. MITL designs should have the lowest-overall-inductance MITL that has a smooth transition region between nonemissive and emissive transmission lines; they should be consistent with the thresholds for anode plasma formation resulting from electron losses; and they should have a geometry that has smooth transitions in flow impedance (vacuum impedance, gap, etc.). While we present an MITL design for a specific driver and a specific load, the approach presented can be readily adapted to any driver and any load
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