Conference Paper

Design and performance of the Z magnetically-insulated transmission lines

Sandia Nat. Labs., Albuquerque, NM
DOI: 10.1109/PPC.1997.679404 Conference: Pulsed Power Conference, 1997. Digest of Technical Papers. 1997 11th IEEE International, Volume: 1
Source: IEEE Xplore


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 ±1.6%. Power-flow measurements
indicate the vacuum section performs as expected until peak current.
Afterward, measurements and simulation results diverge

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    ABSTRACT: Circuit code simulations were used to predict the performance of and to assess design trade-offs for the vacuum section of PBFA-Z. PBFA-Z was designed to drive a plasma radiation source (PRS) within the PBFA-II facility by replacing its central water and vacuum sections. The insulator stack and vacuum feeds were patterned after those of the SATURN PRS configuration which has 4 separate sources combined in vacuum by a relatively small diameter double post hole convolute (DPHC). The design method for choosing the PBFA-Z MITL impedance profiles is described and represents a departure from the method used for PROTO-II and SATURN and was motivated by analysis of SATURN experimental data. Other trade studies included the effect of MITL impedance profile on anode dose along the MITL due to partial magnetic insulation at early times and during the load run-in, and the choice of load diameter and mass on the choice of MITL profiles. These simulations predicted peak load currents ranging from 16 to 23 MA and kinetic energies from 1 to 1.6 MJ for plasma radiation sources (PRS) with implosion times from 100 to 150 ns. PBFA-Z experimental data is compared with an "as built" circuit model for a wire array load with good agreement up to the time of peak load current. A significant disagreement between the data and the model then starts and increases until the time of implosion.
    Pulsed Power Conference, 1997. Digest of Technical Papers. 1997 11th IEEE International; 01/1997
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    ABSTRACT: The Z (formerly PBFA Z) vacuum insulator system consists of four stacks of Rexolite rings about 11 ft. in diameter, immersed in water, that insulate four biconic vacuum power-flow regions. The power flows are combined by a post-hole convolute just outside the imploding plasma load. Each ring stack is driven by nine similar water transmission lines connected around its perimeter. The different inductances between each stack of insulators and the load lead to a different voltage magnitude and waveform across each stack; therefore two stacks consist of five 2.25 inch high insulators, and two stacks consist of six such insulators. The design criteria for the insulator stacks were developed using the analysis described by I.D Smith (Proc. 10th IEEE Int. Pulsed Power Conf., 1995). This treats the case of multiple stack modules each composed of a number of series insulators and each having a large circumferential transit time. The analysis tries to take account of the fact that when one flashover occurs at a particular location in one insulator stage, or even a number of flashovers at various locations, effective breakdown may not have occurred, because it takes time for series stages to flash locally in the same stack, while other parts of the stack are transit-time-isolated. To develop criteria for Z the analysis was first applied to Saturn, and was normalized by assuming a safe level for Saturn based on experience; it was then applied to Z. The analysis is presented, and results to date for the Z stack are described
    Pulsed Power Conference, 1997. Digest of Technical Papers. 1997 11th IEEE International; 01/1997
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    ABSTRACT: Doubling the number of tungsten wires from 120 to 240, keeping the mass fixed, increased the radiated X-ray power relative to the electrical power at the insulator stack of the Z accelerator by (35±15)% for 8.75- and 20-mm radii Z-pinch wire arrays. One-dimensional radiation magneto hydrodynamic calculations suggest that the arrays were operating in a quasi “plasma-shed” regime, where the plasma generated by the individual wires partially merge prior to the inward implosion of the entire array
    IEEE Transactions on Plasma Science 09/1998; 26(4-26):1086 - 1093. DOI:10.1109/27.725136 · 1.10 Impact Factor
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