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.
2-D PIC Simulations of Electron Flow in the Magnetically Insulated Transmission Lines of Z and ZR
The ZR project [1] to refurbish the Z accelerator at Sandia National Laboratories [2] is scheduled for completion in FY06. An important factor for the success of ZR is limiting current losses in the vacuum section. On Z today, late-time losses of 5 - 10% are observed, which are known to occur in the post-hole convolute region. The most direct way to mitigate these losses is to limit the electron flow into the convolute from the magnetically insulated transmission lines (MITLs). The key design consideration is the radial profile of the MITL gap. The MITL gap profile is a compromise between two competing constraints - limiting both the electron flow into the convolute and the MITL inductance. Larger gaps reduce the flow, while smaller gaps reduce the inductance. 2-D particle-in-cell (PIC) simulations suggest that the current Z A-level MITL profile is close to optimum, in the sense of minimizing the flow for its total inductance. For ZR, operating at ~40% higher voltage and ~30% higher current, the decision was made to limit the flow into the convolute to be no larger than on Z today. Time-accurate simulations, with a Z-pinch load, show that profiles based on Z, but with 20% larger gaps meet this condition. It does not appear to be possible to meet the flow limitation without this increase in inductance.
Electrothermal Measurements of Bridgewires Used in Electroexplosive Devices
The bridgewire of an electroexplosive device is evaluated for its thermal response to impulse energy and to square-wave power. Thermal time constant and basic electrothermal parameters can be measured from the response. These parameters are useful in the study and characterization of electroexplosive devices.