DC Characterization of High Gradient Multilayer Insulators

Abstract

We have developed a novel insulator concept that involves the use of alternating layers of conductors and insulators with periods less than 1 mm. We have demonstrated that these structures perform 2 to 5 times better than conventional insulators in long pulse, short pulse, and alternating polarity applications. We present new testing results showing exceptional behavior at DC, with gradients in excess of 110kV/cm in vacuum. I. IntroductionEmpirical scaling laws for insulators in a vacuum reveal that the threshold electric field for surface flashover is not directly proportional to the insulator length i.e. doubling the length of a simple, bulk (single material or composite) insulator does not double the voltage where surface flashover occurs. Literature suggests the most likely mechanism of flashover in a conventional insulator is due to a cascade effect of secondary electrons released from the insulator surface. The High Gradient Insulators (HGI's) developed at LLNL are fabricated using alternating layers of kapton and copper with periods on the order of 0.5mm. We have shown experimentally that these insulators perform significantly better than conventional insulators under a variety of conditions. One theory suggests that the HGI interrupts the process of cascading secondary electrons by placing conductors at periodic intervals along the insulator surface. Thus, the HGI appears to behave as an ensemble of independent insulator structures [1] as shown in figure 1.