Historical research guide · 0941 · 2001
A Physics Exploratory Experiment on Plasma Liner Formation
Y. C. Francis Thio · Charles E. Knapp · Ronald C. Kirkpatrick · Richard E. Siemon · Peter J. Turchi
In one minute
Magnetized target fusion sits between the two mainstream routes: make a ball of magnetised plasma, then crush it with an imploding shell. The hard part is the shell — anything solid has to be built, aimed and destroyed on every shot. Francis Thio, then at NASA Marshall, with Charles Knapp, Ronald Kirkpatrick and Richard Siemon of Los Alamos and Peter Turchi of the Air Force Research Laboratory, propose making the shell out of plasma instead: fire a ring of plasma guns inwards and let the jets merge in flight into a converging liner, so the driver stands well off from the target. This paper designs the first experiment of that programme and shows its arithmetic. Twelve coaxial guns of the Marshall type arranged in a circle, each launching two to four tenths of a milligram of plasma at two hundred kilometres a second, timed to better than a hundred nanoseconds. The authors size the capacitor bank that would do it, name the four phases that lead from this experiment to breakeven, and list the spin-offs on the way.
Connection
Chapter 9 is about plasma made to hold a shape, and a liner assembled in mid-flight from a dozen separate jets is that idea at its most demanding. Chapter 12 keeps the ledger of fusion routes, and this is the standoff-driver design the US government’s own non-electric applications panel later singled out as the compact, pulsed approach most suited to propulsion rather than to a power station.
From the source
The momentum flux that implodes a magnetized target can be delivered by an array of plasma guns whose separate jets merge in flight into a converging plasma shell, so the driver stands off from the target and nothing solid has to survive near it. The experiment described, PLX, is Phase 1 of a four-phase programme intended to carry the approach to fusion breakeven.Abstract; Section 1, Introduction; Section 6, Summary
The driver efficiency is the argument for the approach. Plasma guns may convert wall-plug electricity to directed plasma energy at up to about fifty per cent, against under two per cent for a laser driver once beam production and hydrodynamic coupling are both counted — so laser-driven inertial fusion may need a gain at least twenty-five times greater just to recover what its driver loses.Section 1, Introduction, second page
The gun is a power amplifier as well as an accelerator: kinetic energy is accumulated slowly, over about a metre of barrel and more than five microseconds, then delivered in under a tenth of a microsecond across less than a centimetre, which amplifies the imploding power flux density by three to four orders of magnitude.Section 1, Introduction; Figure 1 caption
The design point is quantitative. Twelve coaxial Marshall-type guns in a circle form a two-dimensional cylindrical liner; each jet carries 0.2 to 0.4 milligrams at two hundred kilometres per second from a gun no longer than one metre with a muzzle under 0.2 metres, launched with a timing precision better than a hundred nanoseconds. The full three-dimensional version uses as many as sixty guns, a total liner energy of about 0.4 megajoules and a liner mass of twenty milligrams, at about a third of a milligram per jet.Section 2, Experimental Goals and Parameters; Section 3, The Physics and Technology Requirements; Section 6, Summary
The pulsed power was sized by simulation rather than assumed: a two-section pulse forming network per gun with capacitors of 17.5 microfarads charged to forty kilovolts, an output-stage inductance held under sixty nanohenries and a second-stage inductance under fifty, with the current per capacitor limited to about five hundred kiloamps. The analytic starting point gives a net electric-to-kinetic efficiency near thirty-two per cent, consistent with experience from pulsed plasma thrusters.Section 4, The Plasma Accelerator; Table 1, the fifteen-case parametric scan; Section 6, Summary
What to watch: three-dimensional smoothed-particle-hydrodynamics modelling with the Los Alamos SPHINX code already shows the jets merging into cylindrical and spherical shells capable of compressing a target to thermonuclear conditions, and a zero-dimensional model indicates gains above seventy; an Air Force Research Laboratory experiment at Kirtland in the late 1980s, following earlier work at Sandia, formed an imploding cylindrical plasma from a circular array of twelve and twenty-four radial discharges. What nobody had done, and what PLX exists to measure, is forming a liner from detached jets carried more than a metre from their electrodes at the momentum flux density this programme needs.Section 3, closing paragraphs and Figure 3(c); Section 2, opening
The way in
https://doi.org/10.1023/a:1019813528507How to cite it
Y. C. Francis Thio, Charles E. Knapp, Ronald C. Kirkpatrick, Richard E. Siemon, Peter J. Turchi (2001) A Physics Exploratory Experiment on Plasma Liner Formation doi:10.1023/a:1019813528507