Z-pinch wire-contact resistance reduction using clamped and soft metal contacts

The contact resistance in a wire array z-pinch has a significant affect on both the level and uniformity of energy deposition in the wires. Typically wires are held taut against the electrodes by wire weights (-1-10 g depending on wire material and diameter). This can lead to contact resistance values of -90-99% of the load resistance. Previous techniques to reduce the contact resistance (i.e. soldering) do not scale to large wire number arrays (such as Z-Machine). UM contact resistance experiments used 13 micron diameter Al 5056 wires. Bench measurements of the load resistance for double-ended weighted contact (similar to the method used on the Z-Machine) gave values in the range of 100-3000 ohms per wire. The actual wire resistance was 6.5 ohms. A second set of measurements in which the z-pinch wire was clamped to the electrodes using an indium gasket showed a reduction in load resistance to -10 ohms. Using a silver gasket further reduced the load resistance to 7 ohms. This clamping technique reduced the contact resistance by 2-3 orders of magnitude. Additionally, the contact resistance for clamped contact is significantly less than the resistance of the wire itself. Experiments performed on a 20 kA, 100 kV, 150 ns risetime Marx bank showed that the energy deposition and uniformity of the plasma expansion profile was significantly affected by the contact resistance. An open pinhole camera was used to observe a time integrated image of the plasma emission, and dark-field laser Schlieren photos were used to monitor the expansion profile of the plasma. The cases with clamped contact had more intense wire-plasma emission and more uniform expansion profiles. The weighted cases exhibited distinct, bright emission regions at the electrodes, indicative of contact arcing. Additional experiments are being conducted using 11.5 micron diameter W wire. Three cases are being examined: baseline weighted case, clamped contact case, and weighted case with soft metal (In or Ag) electrode gaskets. Preliminary results show that the electrode material may have a significant impact on contact resistance.