+ 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.
+ 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
+ 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
