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FRC Introduction
An FRC (field reversed configuration) is an
elongated plasma ellipsoid conducting an azimuthal current which
reverses the direction of an externally applied magnetic field. The
resultant field provides for toroidal plasma confinement without
requiring a toroidal vacuum vessel or coil set. This type of magnetic
configuration is called a compact toroid, and has an ideal geometry
for a fusion reactor.
Following is the Executive Summary of a White Paper on FRC
Development prepared by the
world-wide FRC community. Click here for the
entire document in pdf format.
A WHITE PAPER ON FRC DEVELOPMENT
April 1998
EXECUTIVE SUMMARY
The ultimate objective of fusion research is the application of
fusion energy in a manner acceptable to society. This concerns not
only its economic benefit, but also safety and environmental issues.
The field reversed configuration (FRC) may be the ideal tool for
confining a fusion plasma, especially one with low-hazard advanced
fuels. This document expresses the views of a worldwide community of
fusion energy scientists on near-term directions for research on the
FRC.
The FRC is a variety of compact toroid that occupies a unique
position in the parameter space of magnetically confined plasmas. It
differs from other toroidal systems in possessing the following
attributes: no mechanical structure in the center of the torus; no
appreciable toroidal field; an engineering beta near unity; no
rotational transform; all the equilibrium current (except possibly a
seed current) maintained by classical diamagnetism; and a scrape-off
layer exhausting outside the coil system. FRCs range from small
gyro-orbit fluid-like plasmas to large-orbit ion ring-dominated
plasmas. Because of their peculiar attributes FRCs offer the
possibility of a step change in reactor attractiveness. In addition,
FRC research adds unique insight into the physics of other fusion
systems such as tokamaks, and offers a means of exploring fundamental
plasma physics questions unrelated to fusion.
Review panels have repeatedly called for fusion system
improvements in order to project economical fusion energy. However,
even improved tokamaks may not overcome the shortcomings of low power
density, high complexity, large unit size, and high development cost.
Among alternative concepts based on low-density magnetic confinement,
the FRC offers arguably the best reactor potential because of high
power density, simple structural and magnetic topology, simple heat
exhaust handling, and potential for advanced fuels. The unit size of
FRC reactors may be smaller than those based on the tokamak. Low
magnetic field and a simple structure also lead to lower costs. These
advantages might be accentuated if an innovative reactor design such
as a liquid wall vessel could be adopted. The enormous potential
payoff as a reactor justifies a broad and sustained program on FRC
sustainment, stability, and confinement.
Several FRC-related facilities are in operation around the world
as well as other small theory efforts. Favorable results from theory
and experiments have raised hopes for ultimate development into a
practical fusion system. Parameters achieved include densities
ranging from 5x10**13 to 5x10**15 cm3, temperatures up
to 3 keV (ions) and 500 eV (electrons); and
b ~ 0.75-0.95. Noteworthy
achievements include: formation by q-pinch,
counter-helicity spheromak merging, and by rotating magnetic fields;
simulation of large-orbit ion ring injection and trapping;
stabilization of rotational instability; detection of global internal
modes; tilting mode theory; global translation and acceleration along
a guide field; identification of transport anomalies; and
demonstration of the convective nature of energy loss.
In view of the foregoing, five action items are recommended. (1)
FRC research should be continued and expanded both as an adjunct to
mainline fusion research and as a stand-alone alternative fusion
concept. (2) Existing FRC-related resources should be effectively
utilized in an expanded program: including both facilities and the
intellectual capital established in institutions and individuals with
a strong commitment to FRCs. (3) New FRC facilities or upgrades of
existing facilities should be considered on the merits of how they
address the directions offered in this document. This should include
consideration of a jointly-operated international FRC research
facility. (4) Researchers and institutions with a history of activity
on the tokamak should be encouraged to broaden their research to
include FRC theory, diagnostic development, and systems studies. (5)
Vigorous international collaboration on FRC research should be
encouraged, including, at the least, annual workshops and long-term
exchange visits.
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