Centauri Dreams covered the recent Advanced Space Propulsion Workshop. The ASPW is focused on low Technology Readiness Level (TRL) concepts ranging from TRL 1 to 3. John Slough gave a presentation on his research at the University of Washington on Inductively Driven Liner Compression of Fusion Plasmoids. His was the only team at the conference working on pulse propulsion concepts. Initial systems should be able to achieve 200 km/second speed and more advanced versions 1000+ km/second.
The basic concept involves pulsing fusion fuel plasma at high rates into a reaction chamber where it would undergo fusion via use of metal liners to accomplish compression of a magnetized plasmoid. Although remarkable, the only purpose of the fusion would be to drive the next round of plasmoid firing. Propulsion would be achieved through momentum transfer occurring between the electromagnetic gun and the accelerating plasmoid. In other words, all the fusion gain would be put back into driving the next cycle. This differs markedly from the idea behind Daedalus, where a large fraction of the exploding fusion material itself transfers the momentum.
Update- A Deuterium-Helium 3 version of FRC plasmoid propulsion could achieve 1,000,000 ISP. Exhaust velocity would be 3% of lightspeed.
A presentation of the state of Field Reversed Configuration propulsion is summarized at this link
Propagating Magnetic Wave Accelerator (PMWAC) for Manned Deep Space Missions by John Slough (1999)
Propagating Magnetic Wave Plasmoid Accelerator poster from 2005
A high-velocity plasma accelerator utilizing a Propagating Magnet Wave
(PMW) has been designed and constructed that is directly applicable to space
propulsion as well as to new innovative high energy density approaches
towards fusion. The PMW plasmoid accelerator also has possible applications
as a fueler for future fusion reactors such as the international fusion reactor,
ITER, as well as current tokamak experiments for adding rotational momentum
and velocity shear for enhanced stability and transport control.
The natural application for the PMW accelerator is for high power electric
propulsion in space. For this purpose the PMW is employed as a pulsed
thruster that operates naturally at both high power and efficiency with no need
for electrodes or grids. Operational parameters can be varied over a wide
range in both exhaust velocity and propellant mass. To efficiently accelerate
plasmoids to high velocities an acceleration method other than the simple
tapered coil must be employed. In these experiments, the rapid acceleration of
a compact plasmoid is realized through the application of an externally applied
propagating magnetic field. Here, the large axial JxB force is generated from
the induced azimuthal current inside the plasmoid and the radial component of
the external, axially propagating magnetic field. This accelerating force is
sustained as long as the plasmoid remains in phase with the wave field. Exit
velocities greater than 200 km/sec for plasmoid masses on the order of 0.1 mg
are anticipated from the device that is currently being tested, and the results
from the initial experiments will be presented. With a 10kHz repetition rate an output of 30MW could be achieved
John Slough is working on applying the same principles to a nuclear fusion generator. They have built a one third of commercial scale system.
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