Pulsed-power driver for a 100 to 200 T single-turn-coil cluster fusion experiment

Recent experiments have shown that interactions of intense ultrafast lasers with targets of small DD clusters with hundreds to thousands of atoms can produce very high ion temperature plasmas and produce DD fusion neutrons. Because ion temperatures exceeding 10 keV are achievable it is possible to produce high fusion yields even with laser pulses of a few joules to a few hundred joules. The fusion yield in these experiments is limited by the fast disassembly time (<100 ps) of the small, hot laser-produced deuterium plasma. Enhancement of fusion neutron yield might be achieved if plasma confinement could be improved by the introduction of an external magnetic field, even if for only a few nanoseconds. At the densities of these plasmas (~10¹⁹/cm³), magnetic fields of 100 to 200 T are needed to slow plasma expansion sufficiently to enhance neutron yield. Because magnetic pressures exceed the yield strength of almost materials at these field levels it is necessary to design a system based on disposable, single-use, single-turn coils. The current required to drive these coils ranges from 1 to 2 MA, depending on coil diameter. Such parameters are similar to a driver at the National High Magnetic Field Laboratory. However, a driver for this application must be transportable with a sufficiently small footprint that it can be placed near the output of the laser. In this paper we describe the conceptual design of a compact pulsed-power driver that can deliver 2 MA in 1.7 mus into a 50 nH load using available hardware. Two design options are considered: a design with multiple capacitors connected in parallel to a single biplate transmission line, switched with a rail-gap switch, and a design with each capacitor having its own switch and connected in parallel with other capacitor/switch modules to a load transmission line through multiple parallel coaxial cables. Mainly for convenience and safety considerations, we have focused on the second option, a- d will present testing results on prototype modules.