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The MAGPIE Generator

MAGPIE (Mega Ampere Generator for Plasma Implosion Experiments) is a TeraWatt (1012 W) pulsed power generator used for dense z-pinch experiments in the Plasma Physics group at Imperial College, London.
The generator consists of four 100kV Marx banks which store a total of 336 kJ, and generate an output potential of 2.4 MV. Each Marx bank is connected to a 5 Ohm, 100 ns, water filled transmission line and then to a trigatron switch. After the switches, the four lines join to a single, 1.25 Ohm water filled transfer line. This line is vertical and has a single transit time of 65 ns. At the top of the transfer line, the vacuum section is located. This consists of a conventional diode stack as the water-vacuum interface, a magnetically insulated transmission line and the experimental load.

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Left: The MAGPIE generator Right: Circuit diagram of a Marx bank

The generator has been used for experiments at charges of up to 80% of maximum charging voltage (100kV). Load current waveforms for 60% and 80% charging voltage are shown below for a ‘short circuit’ load.img00002

Wire array experiments typically use 60% charge and measured load currents are ~1.04 MA. MAGPIE is a relatively high impedence “stiff” generator. Load current does not depend significantly on load impedence and this allows many array configurations to be fired without reducing drive current levels.