Plasma Confinement / Tokamak 478

Tokamak - use magnetic fields to cage hot plasma (ionized gas) in a donut shaped veseel. Princeton U Tokamak Fusion Test Reactor (TFTR) 1994 Record fusion-power outputs. Success! Main problem before : taming plasma instabilities that rattle and tear the fragile magnetic cage, allowing particles to leak out and limit tokamak's performance. Tailoring B field : Increased central density of plasma by threefold reduced particle leakage by a factor of 50. | / | / | / | _/ central | _/ reversed shear mode electron | _/ pressure | / | / | __/ | /................. typical discharge | __/ |______/ | +------------------------- Time Deuterium - low power grade of fusion fuel could double TFTR power output. Deuterium-tritium mix will likely fuel a working reactor. Cost : Improved confinement and power could slash size and cost of a working fusion reactor by 50% Plasma instabilities : charged particle gyrate tightly around magnetic field lines but travel easily along them, like rings sliding along a wire. Physicists reasoned they could trap a plasma by creating a hoop-shaped field lines- by bending a cylindrical coil of current-carrying wires, producing field lines paralleling its axis, into a donut. The particles should be able to cross the field lines only when they collided and suddenly changed direction. Since outer hoops are longer - thus weaker than inner ones, particles can drift out of this cage. To solve this problem, early fusion researchers found that they had to give the curving field lines a slight twist, causing them to spiral through the donut. That way the particle drifts on opposite sides of each spiral cancel out. In a tokamak, this twist is applied by an electrical current running the long way around the donut, through the plasma itself. When the current is strongest in the center of the plasma - as it usually is, that being the easiest arrangement to produce - the spirals wrap most tightly in the center and gradually loosen toward the tokamak's walls. Because of the more complicated orbits of particles in this geometry, they take larger steps when they collide, and the minimum leakage rate across the field lines is 100times higher than in a straight field (where particles leak out along field lines ). Problem : Infinite variety of wave modes roil the hot, high-pressure plasma. These instabilities boost the particle leakage by a factor of 100. Plasma current which were "hollow" = a trick to create barrier to this partial diffusion (Kessel et al). This hollow or pipelike in cross section instead of peaked in the center. Pressure gradients within the plasma naturally generate such hollow currents Hollow current also force magnetic spirals to tighten from the center out to the edge of the plasma - the reverse of the usual pattern. The region of tightening spirals , or "reversed magnetic shear" is stable enough to reduce the anomalous diffusion. TFTR's plasma reacted to the reversed shear created by the hollow current profiles, its central pressure shot up! Diffusion of particles dropped by a factor of 50 and leakage of heat fell below absolute minimum. S +

Bacterial Genome Sequence Bagged

explore genome <---- sequence or partial -------> comparison w/ -------> understand evolutionary organization? sequence other genomes giology from any organism | || +---------> Identify new genes || \/ search for gene complete DNA sequence and regulating <----- exact location of similar H. elements influenzae gene || || \/ \/ understand gene make primers and clone gene control // || \\ // || \\ \/ \/ \/ overexpress knock out add gene to gene gene defective bacteria || /\ /\ /\ \/ \\ || // antibiotics, \\ || // vaccines, understand role of protein and gene industrial enzymes S +

Japan picks first centers of excellence

------------------------------------+-------------------------------- Groundbreaking Groups | lead institution ------------------------------------+-------------------------------- Research Theme | hitotsubashi U. Compilation of integrated long-term | economic statistical database | for the trans-Asian region | ------------------------------------+-------------------------------- | university of tokyo Probing the early universe | ------------------------------------+-------------------------------- | Tokyo institute of tech Ultraparallel optoelectronics | ------------------------------------+-------------------------------- | Nagoya u Molecular chirality | ------------------------------------+-------------------------------- | Kyoto U Regulation of higher order | biological systems | ------------------------------------+-------------------------------- | Osaka U Signal transduction in cell growth, | Medical school differentiation and death | ------------------------------------+-------------------------------- --fin