Patent Number: 040653501
Section: summary

BACKGROUND OF THE INVENTION In the field of plasma physics, a need exists for magnetically confining a toroidal plasma column along an endless equilibrium axis in a vacuum containment means. Various means and methods have been proposed and used for this purpose, comprising the tokamak of U.S. Pat. No. 3,663,361, wherein poloidal field coil means are combined with a toroidal field and a plasma current stably to confine the plasma column in a circular cross-section. While these arrangements have been useful and have accomplished the desired confinement, they have been expensive, since they have required large diameter plasma cross-sections. Also, it has been difficult to increase the plasma volume in an equilibrium by using elliptical plasma columns, without decreasing the vertical stability of the plasma column. SUMMARY OF THE INVENTION This invention overcomes the difficulties and shortcomings of the heretofore known devices by adding a specific multipole forming a poloidal coil means, which is referred to herein as an octupole, to the outside of a round cross-section toroidal current carrying plasma column in a tokamak to change the plasma column into a rectangular cross-section characterized by an external separatrix. For purposes of this invention, an octupole is defined as the number of poles present at the center of the plasma vacuum space by taking away the current carrying toroidal plasma column. By taking away the plasma, the magnetic field wouldn't be square in cross-section, as understood in more detail hereinafter, and the field lines would form loops having eight poles, as understood from the Gulf General Atomic octupole shown in "Survey of the USAEC Program in Controlled Thermo-nuclear Research" June 1971. By elongating the spacing between the octupole coil means, which comprises at least four poloidal current carrying rings that are co-axial with the plasma column equilibrium axis, the plasma column cross-section is vertically elongated while the rectangular cross-section is maintained. This maintains vertical stability efficiently to increase the poloidal flux in the plasma column in linear proportion to the plasma cross-section height to achieve a much greater plasma volume than could be achieved with the heretofore known round cross-section plasma columns. Also, plasma column stability against vertical displacement is enhanced at larger volumes over elliptical cross-section plasma columns. Additionally, in another aspect, this invention provides poloidal magnetic divertors. In one embodiment, this invention provides in a tokamak of the type having a toroidal containment means and toroidal and poloidal current carrying magnetic field producing coil means for producing a nested set of concentric, circular cross-section, toroidal magnetic surfaces confining a plasma current carrying toroidal plasma column in the containment means so that the plasma column is stably located on a vertical axis and has equal radial axes defining an endless circular equilibrium axis around an axis of rotation in the annulus of the containment means, the improvement comprising: octupole means along the equilibrium axis and around the outside of the plasma column in the space between the equilibrium axis and the axis of rotation for producing poloidal separatrices external to the plasma column having stagnation points that define the four corners of a rectangular magnetic surface for confining and shaping the circular cross-section magnetic surface into a rectangular cross-sectional shape inside the rectangular surface. With the proper selection of elements and steps, as described in more detail hereinafter, the desired vertical stability and elongated cross-section in a tokamak are achieved. it is an object of this invention, therefore, to provide an elongated cross-section toroidal plasma column in an equilibrium having vertical stability. The above and further novel features and objects of this invention will appear more fully from the following detailed description when read in connection with the attached drawings, and the novel features will be particularly pointed out in the appended claims.