Polarix (United States)

Present research in wide band-gap semiconductors is concentrated predominantly in CW applications. While their applicability for pulsed power is recognized, here, little work has been done in taking advantage of the individual characteristics of the candidate materials. We describe analysis of the relative merits of the key semiconductor technologies - Si, GaAs, SiC, and GaN - as limited in the pulsed power regime. The discussion includes limitations associated with majority carrier operation and thermal transients. We will also discuss a GaN photoconductor with a vertical topology. This is particularly well suited to higher current applications and also is geometrically more applicable for integration to transmission lines without degrading the high blocking field (~2MV/cm) now available. We will also discuss the relation between the blocking voltage and conduction current typical of majority carrier operation and how using optical carrier generation provides the much higher switching power associated with bipolar operation.

Previous work by this author has identified three key elements for optimizing the performance of NL lines. These include the superiority of resonant complementary lines[1][2] where i) both saturable inductances and saturable capacitances are used; ii) parasitic inductances and capacitances need to maintain a unique impedance relation with the individual stage impedances for highest efficiency; iii) there is an optimum number of stages for peak efficiency for any given power multiplication. Here we derive switch non-linearity performance parameter, α, which equals G*W, (the product of the power multiplication G by the energy compressed W per unit volume of switch material in one switching operation). When saturable materials are used as the power multiplying medium, it is shown that α equals the area under the B vs. H and the D vs. E curves. For semiconductor and photoconductors switches it is the power density of the switch times its blocking time before switching. We compare the various technologies based on this performance parameter to show the superiority of photoconductors using silicon as photoconductive off switches and GaN as on switches by many orders of magnitude over ferroelectric and ferromagnetic switches.

HPM systems fall into two general categories. The first uses moderately high power, quasi CW sources in the MW range with pulse duration around a millisecond and are generally of narrow bandwidth but with large average power. In the second category we have very high Peak power - in the GW range, but of very short pulse duration, typically in the 100ns range, and are of a large bandwidth. These sources, due to their pulse power technology are limited in average power and pulse repetition frequency. Some HPM applications require beam steering either by mechanical means or by phasing an array. Some applications, such as counter electronics, require the continuous sweeping of the beam over a large forward area. Sweeping arrays require phase shifters that are costly and difficult if they are required to accommodate a large bandwidth and Power.