Chemical & Engineering
NEWS FEBRUARY 13, 1967
The Chemical World This Week Magnetic bottle quiets plasma Containment and control of plasma has been achieved in a magnetic bottle at the University of Wisconsin by graduate student research workers John A. Schmidt, J. Clint Sprott, and Donald E. Lencioni, working under the direction of physicist Donald W. Kerst. The apparatus used generates an octupole toroidal furnace, a magnetic field formed by four current-carrying hoops. The device was designed and built at the university and has now been perfected to a point where a quiet and stable plasma is contained in a closed system. Work by former graduate students also contributed to the achievement, Dr. Kerst said at the annual meeting of the American Physical Society, held in New York City. The encouraging development, Dr. Kerst notes, has opened the door to research on methods to control and capture the energy released by thermonuclear reactions. The Wisconsin workers ran their first experiments in 1964. Scientists at General Atomic division of General Dynamics then built a similar device and corroborated the Wisconsin results (C&EN, Nov. 14, 1966, page 4 7 ) . A quiescent plasma was also observed in a stellerator by West German scientists. At Wisconsin, Dr. Harold K. Forsen cooperated in modifying the octupole device to give a system similar to a stellerator. In the Wisconsin system, a plasma cloud was injected through the multipole magnetic field from the outside at a point where lines of force were concave toward the oncoming plasma. Two actions caused penetrations of the field by plasma: Ions are deflected in the magnetic field in one direction while the electron component in the plasma bends in the opposite direction. This charge separation produces opposite charges on the opposing boundaries of the particle cloud. Polarization thus cancels the magnetic force on the moving ions, permitting the cloud to drift across the magnetic field, Dr. Kerst says. In operation, the apparatus injects plasma of about 100-e.v. ion energy into the octupole magnetic field. A zero field locus is near the middle of
Graduate students and plasma confinement system A quiet and stable plasma the region, and fields of 1000 to 8000 gauss exist along the wall and around the current-carrying loops forming the multipole field. Probes and microwave observations show that the electron component has 10-e.v. (about 120,000° K.) temperature and remains for 2.5 milliseconds. The energetic ions were extracted from the plasma to determine the energy and lifetime of the ions for the same period of time. There were no sudden or catastrophic losses or fluctuations in either the central or extracted plasma which would indicate instability, according to Dr. Kerst. After 100 microseconds, the large electric fields present during filling died away and the plasma apparently acquired a boundary with small electric potential differences, compared to the 100-e.v. energies of contained ions. This quiescent condition, according to the Wisconsin scientist, continued while the plasma was gradually being lost on probes and supports. The development of plasma confinement apparatus is paralleled by research on techniques for improving plasma injection devices. Such devices are needed before the full potential of experimental (and eventually practical) plasma reactors can be re-
alized. Research on the Madison campus is now under way to devise techniques for efficient continuous plasma creation and injection. One source currently being used is the E X B (or rotating plasma) source, characterized by two inherent problems: limited gyromotion conversion and impurity control. These have yet to be overcome, although some progress has been made. Still other work under way at Wisconsin, under the direction of nuclear engineer Forsen, is the attempt to devise a method of converting the rotating system into a plasma gun, which might offer easier gyromotion conversion and effect impurity control.
Clinical fluorometry grows Changes in fluorescence caused by enzyme systems are finding use in clinical laboratories. The diminishing of the native fluorescence of nicotinamide adenine dinucleotide (NAD) from its reduced form (NADH) has been used as a basis for assaying serum lactic acid dehydrogenase and other enzyme systems, according to Dr. Martin Rubin, director of the clinical chemistry laboratory at Georgetown FEB.
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