Magnetic confinement

Fig. 3. Schematics of magnetic confinement geometries (a) planar and (b) cylindrical geometries for magnetron sputtering sources (24) (c) open-ended...

High temperature is an important requirement for the attainment of fusion reactions in a plasma. The conditions necessary for extracting as much energy from the plasma as went into it is the Lawson criterion, which states that the product of the ion density and the confinement or reaction time must exceed 10 s/cm in the most favorable cases (173). If the coUisions are sufficiently violent, the Lawson criterion specifies how many of them must occur to break even. Conventional magnetic confinement involves fields of as much as 10 T (10 G) with large (1 m ) plasmas of low densities (<10 particles/cm ) and volumes and reaction times of about 1 s. If the magnetic flux can be compressed to values above 100 T (10 G), then a few cm ... 

Much of the driver energy goes into ablation, or blowing-off the surface of the sphere of fuel to force the compression (implosion) by the rocket effect. As a result, the ntT needed for scientific break-even for inertial confinement is around twenty times higher than for magnetic confinement. 

Schematic representation of the magnetic structure of the Tokamak magnetic confinement device. The lines on the shells represent the direction of the total magnetic field, most of which comes from external coils. The portion that gives the twist, however, comes from current inside the hot plasma itself. The twisting is necessary for stable confinement.

Also in 1950 Sakliarov and Tamm proposed an idea for a controlled thermonuclear fusion reactor, the TOKAMAK (acronym for the Russian phrase for toroidal chamber with magnetic coiF ), which achieved the highest ratio of output power to input power of any fusion device of the twentieth centuiy. This reactor grew out of interest in a controlled nuclear fusion reaction, since 1950. Sakharov first considered electrostatic confinement, but soon came to the idea of magnetic confinement. Tamm joined the effort with his work on particle motion in a magnetic field, including cyclotron motion, drifts, and magnetic surfaces. Sakharov and Tamm realized that... 

Another approach to nuclear fusion is shown in Figure 19.6. Tiny glass pellets (about 0.1 nun in diameter) filled with frozen deuterium and tritium serve as a target. The pellets are illuminated by a powerful laser beam, which delivers 1012 kilowatts of power in one nanosecond (10 9 s). The reaction is the same as with magnetic confinement unfortunately, at this point energy breakeven seems many years away. 

Gruen, D. M., Vepfek, S., and Wright, R. B. Plasma-Materials Interactions and Impurity Control in Magnetically Confined Thermonuclear Fusion Machines. 89, 45-105 (1980). 

Forth. It.P. "Magnetic Confinement Fusion." -Silence. 1522 (September 28. I990i. Graham. D. "Quesi for Fusion." Technolinty Review fSHTi. 14 (July 1992). 

Fig. 1.9. Apparatus for the production of a magnetically confined positron beam in operation at University College London.

Plasma-Materials Interactions and Impurity Control in Magnetically Confined Thermonuclear Fusion Machines ... 

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