Experiments on a High-Vacuum, High-Electric Field Stress Pulsed Power Interface

Improving the materials used in a vacuum interface between a pulsed power system and the vacuum region has been a goal for many years. The interface problem is difficult because of the electrical, mechanical and vacuum issues that must be satisfied simultaneously. Traditionally the pulsed power community has made use of acrylics for the interface, and has found applying a light coating of oil is needed for reliable operation. However, the oil coating typically limits use for tens to hundreds of pulses and must be re-applied periodically. The acrylic material limits the base vacuum obtainable; the vapor pressure of acrylic is in the low 10"7 Torr vacuum. The opposite end of interface spectrum is conventional vacuum tube industry that uses ceramics to obtain ultra-high vacuums. The goal has been to obtain the base vacuums obtainable by ceramic interfaces without the associated high cost relative to acrylic interfaces. Several years earlier, a pulsed power system (500 kV, 100 Omega, 1 musec, 1 pulse/sec) was assembled using a high-density polyethylene vacuum interface. The base vacuum was observed to reach the low 10
^-9
Torr level. We present results on experiments comparing the performance of an acrylic and high-density polyethylene interface. We also discuss a ceramic interface that was designed and built.