Although the tokamak is the leading magnetic fusion approach worldwide, its design embodiment and associated physics have not been attractive to the potential commercial users of magnetic fusion. Serious design concept development for a device to carry out ignition and burn physics and/or fusion engineering development in magnetic fusion has been in progress for several years. Prominent concepts and associated reference material include the following: Engineering Test Facility (ETF), ETF Design Center Team, Engineering Test Facility Mission Statement Document, ORNL/TM-6733, Oak Ridge National Laboratory (1980); International Tokamak Reactor (INTOR), INTOR Group, Nuclear Fusion 23, 1513 (1983); Fusion Engineering Device (FED), Fusion Engineering Device Design Description, ORNL/TM-7948, Oak Ridge National Laboratory (1981); and the Toroidal Fusion Core Experiment (TFCX), "The Toroidal Fusion Core Experiment (TFCX) Studies", paper IAEA-CN-44/H-I-3, presented at the Tenth International Conference on Plasma Physics and Controlled Nuclear Fusion Research, London, England, Sept. 12-19 (1984). The estimated, direct total cost of each of these systems is about $1 billion or more with perceived high risk in achieving the stated performance goals. Thus, continued progress of fusion can be enhanced if a design can be found which provides a more favorable cost risk-to-benefit ratio (i.e., an embodiment with small unit size and limited risk in reaching adequate plasma and fusion engineering performance).
Major factors that contribute to the larger size and higher cost of the aforementioned design studies can be traced to a combination of physics assumptions, engineering criteria, nnd conventional tokamak wisdom. The conventional wisdom of tokamak operation and prudent engineering suggests the inclusion of a solenoid for inductive current drive, nuclear shields inboard of the plasma torus for protection of inboard coils and insulators, and a separate first wall and vacuum boundary. These items tend to increase the major radius of the torus and aspect ratio (major radius divided by the minor radius of the torus), which, in turn, leads to modest values of average beta (the plasma pressure divided by the magnetic field pressure containing the plasma, typically up to about 5% for aspect ratios of about 3). In the physics area, the assumed plasma energy confinement efficiency at reactor conditions leads to large plasma major and minor radii (about 3 meters or more and 1 meter or so, respectively) and plasma current of 6 to 12 megamperes (MA) when intermediate values of magnetic field between 4 and 6 tesla (T) are employed. For ignition devices with significant burn, a typical design has about 100 cubic meters in plasma volume, 100 megajoules (MJ) in plasma thermal energy content, and produces about 200 megawatts (MW) of deuterium-tritium (D-T) fusion power. The latest cost estimate of such a device using copper toroidal field (TF) coils is about $1 billion. Therefore, it is readily apparent that there is a need for a fusion device with small unit size, and limited risk in reaching adequate plasma and engineering performance.