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December 16, 2010

Plasma-Jet driven Magneto-Inertial Fusion (PJMIF)

The Icarus project blog covers Plasma-Jet driven Magneto-Inertial Fusion (PJMIF)

PJMIF can be called a hybrid approach, trying to take the best of both MCF (Magnetic Confinement Fusion/ Tokamaks / ITER) and ICF (Inertial Confinement Fusion / National Ignition Facility, high-energy laser pulses to compress a solid-state target).



In PJMIF, a magnetized plasma target is confined inertially (like ICF) by imploding plasma jets, and electron thermal conduction is suppressed by internal, usually closed field, lines. The suppression of thermal conduction is important because this way we prevent the precious energy from flowing away from the reaction domain. There is no material shell close to the plasma, so PJMIF provides an elegant solution for the stand-off problem (stand-off problem is referring to the issues of surrounding equipment being damaged during the fusion process). The time-scale of the whole process is supposed to be on the order of several microseconds, where the confinement time is proportional to the jet velocity over jet length ratio. The parameter space, which illustrates a range of operational parameters (primarily density), is intermediate, between ICF and MCF. The higher densities of fuel compared with MCF mean that reacting volumes are smaller by orders of magnitude (because of the Lawson criteria), and the magnetized target permits lower power drivers for implosion and confinement compared with ICF, resulting in a potentially low cost development path to fusion.

Target magnetization can be achieved in several ways, of which probably the easiest one is so called “field-reversed configuration” (FRC) and this is a well-known topology, with many techniques for forming such plasmas, for all those which are in the field of pulsed plasma thrusters or nuclear fusion.

Preliminary analytical and numerical studies (Thio, Lindemuth, Siemon, Cassibry et. al.) show that the parameters at which PJMIF should operate are almost literally halfway between MCF and ICF, which is a parameter space no fusion concept has yet explored. By introducing a magnetic field in the target, the requirements on the initial jet energy can be significantly lowered, because thermal losses are cut during the compression and so better overall efficiency is achieved. Lower initial jet energy requires less power capacitors and this results in a more compact system. If proven, PJMIF would require vastly lighter and smaller facilities than those needed for MCF and ICF.

PJMIF facility should only cost around fifty million dollars. This is primarily due to the lower input energy and the fact that the rail-guns are far simpler than lasers or tokamaks. The very idea of PJMIF, as it exists now, has been formed merely ten years ago and it wasn’t until last year that the funding for some mid-scale experiment was actually granted. The project is called PLX (Plasma Liner Experiment) and it is a collaborative project among several universities and companies, with Los Alamos lab at its top



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