Patent Number: 044252951
Section: summary

The present invention relates to systems for achieving nuclear fusion. A number of writings are listed in this paragraph to serve as background for the explanation hereinafter, the writings listed here being merely representative: "Confining a Tokamak Plasma with rf-Driven Currents" (Fisch), Physical Review Letters, Vol. 41, Sept. 25, 1978, p. 873 (called Fisch (1978) herein); "System and Method for Generating Steady State Confining Current for a Toroidal Plasma Fusion Reactor" (Fisch), U.S. patent application, Ser. No. 935,222, filed Aug. 21, 1978 (called Fisch (1978b) herein); "Methods of Driving Current by Heating a Toroidal Plasma" (Fisch), Proceedings of the Second Joint Varenna-Grenoble International Symposium on Heating in Toroidal Plasma, Como, Italy, Sept. 3, 1980 (called Fisch (1980) herein); "Creating an Asymmetric Plasma Resistivity with Waves" (Fisch et al.), Physical Review Letters, Vol. 45, Sept. 1, 1980, p. 720 (called Fisch et al. (1980) herein); "Current Generation in a Relativistic Plasma" (Fisch), Princeton University Plasma Physics Laboratory Report PPPL-1763, January, 1981 (called "Fisch (1981)" herein); "Tokamak Research" (Furth), Nuclear Fusion Vol. 15 (1975) p. 487 (called "Furth (1975)" herein); "Theory of Electron Cyclotron Resonance Heating of Tokamak Plasmas" (Ott et al.), Physics of Fluids Vol. 23, May, 1980, p. 1031 (called Ott et al. (1980) herein); "New Methods of Driving Current in Fusion Devices" (Ohkawa), Nuclear Fusion, Vol. 10, (1970), p. 185 (called "Ohkawa (1970)" herein); "Steady-State Operation of Tokamaks by r-f Heating" (Ohkawa), General Atomic Report GA-A13847, Feb. 23, 1976 (called "Ohkawa (1976)" herein); "The Peristaltic Tokamak" (Wort), Plasma Physics, Vol. 13, 1971, p. 258 (called "Wort (1971)" herein). See, also, Coppi et al. U.S. Pat. No. 3,778,343. The operation of a tokamak is dependent upon the maintenance of a toroidal electric current to confine the plasma. For a fusion reactor based upon the tokamak concept to become an economic reality, this toroidal current must be produced both cheaply and in long pulses. Long pulses are required in order to limit the metal fatigue arising from the heat stress to which the structural components of the tokamak are subjected in a pulsed device. The method originally envisioned for driving this toroidal current is by means of a time-varying magnetic field which induces a toroidal electric field. This method suffers, however, in that it is inherently a pulsed method. In contrast, the invention described herein provides means of generating this current continuously. Moreover, to sustain this current in the manner prescribed by the present invention requires an amount of power that is small enough for the system to be extremely attractive in fusion applications. Accordingly, it is an object of the present invention to provide a system of steady-state toroidal electric currents in the plasma of a fusion device serving to confine the plasma. The present invention exploits in a novel manner the principle that the rate of coulomb collisions between charged particles is a sensitive function of the relative speed of the colliding particles. Means are provided to selectively heat electrons traveling in one toroidal direction in order to assure that these (heated) electrons collide less with the plasma ions than do the unheated electrons traveling in the opposite direction. Consequently, the ions drag preferentially on the more collisional electrons, with the result that a current is generated with electrons, on average, flowing in the direction of the heated electrons and with ions, on average flowing in the opposite direction. This mechanism for generating current is especially attractive because it does not rely upon an external source of momentum in the direction that the current flows. For example, consider a plasma immersed in a steady magnetic field. To generate a current in the direction of the magnetic field (herein denoted as the parallel direction), it suffices merely to increase the cyclotron motion of selected electrons in this plasma. This cyclotron heating can be accomplished by launching various radio frequency (rf) waves into the plasma. That the waves need not have substantial parallel momentum allows the advantageous use of waves with parallel phase velocity greater than the speed of light, c. Such waves may be brought to the plasma by means of waveguides and injected into the plasma through conveniently small apertures. Waveguides are a particularly appealing construction for bringing energy into a tokamak; they can easily be interspersed between the toroidal magnets due to their relatively small apertures and they may be bent to suit engineering requirements.