fusion

Fusion News
Asdex Tokamak
Results Look
Promising
Researchers at the Institute for
Plasma Physics in Garching, West Germany,
report very promising results
on the Axial Symmetrical Divertor Experiment,
known as Asdex.
The Asdex, Europe's largest fusion
facility, has the same goal as the PDX
tokamak at the Princeton Plasma
Physics Laboratory: to produce the
purest possible plasma using poloidal
divertor fields. The first experiments
with the Asdex divertor at the beginning
of May showed a clear decrease
in plasma radiation and achieved an
exceptionally long plasma discharge
confinement time of 3 seconds. The
discharge confinement time, an improvement
of a factor of 3 over the
Princeton Large Torus tokamak, apparently
is the result of a lowered
level of impurity in the plasma.
The divertor concept is to construct
the usually closed magnetic field lines
that confine the fusion plasma with a
"hole," so that nonhydrogen elements
can be diverted out of the
plasma. Even minute quantities of
these impurities can cause a major
energy loss in the plasma. The impurities,
partially ionized heavy elements,
come from the materials on the wall
of the vacuum chamber. They have a
much greater nuclear electrical
charge than the hydrogen, and the
electromagnetic radiation they generate
cools down the plasma.
The Asdex is operating solely with
ohmic heating now. In order to test
the performance of the divertor at
high temperatures, neutral beam injection
will be installed in 1981. An
initial heat level of 2.5 megawatts is
planned, with a second-stage heating
capacity of 8 megawatts to attain reactor-relevant
temperatures.
Photo courtesy of Max Planck Institute
The Asdex, Europe's largest tokamak, achieved a discharge confinement
time three times greater than that of the PIT.
Dean: Now Is the Time
To Push Fusion Engineering
"The scientific basis now exists to
start fusion engineering," Dr. Stephen
Dean, president of Fusion Power Associates
and a past director of the
Office of Fusion Energy's magnetic
confinement program, told a May 1
session of the American Physical Society's
spring meeting in Washington.
Dean chaired the panel on "The Pace
of Fusion Energy Development."
"Engineers have now been given
the scientific information they need
to begin work on the development of
a fusion power demonstration plant,"
Dean asserted. The future of the fusion
program will no longer depend
on "good results," but on the political
commitment to get this engineering
started.
Although Dean's remarks were not
a scheduled part of the proceedings,
they were the most important and
most provocative part of the meeting.
The APS did not schedule any presentations
that discussed the magnetic
confinement program in tokamaks,
mirrors, or other large-scale fusion
projects.
Dean challenged the physicists in
the audience to consider a concrete,
two-phase program to achieve a commercial
demonstration fusion reactor
by the turn of the century, "as proposed
by Congressman Mike Mc-
Cormack." (McCormack's bill, HR
6308, calls for an "Apollo-style" crash
program to meet that goal.)
The first phase, extending over the
next eight years in Dean's proposed
timetable, would develop the engineering
needed to take fusion from
the "stage of scientific development
to the point where its commerical
viability can be assessed. Then, assuming
a positive result, the second phase
of national commitment would begin
in 1988, and lead to the operation of
a demonstration plant approximately
10 years later."
Dean made it clear that moving the
fusion program ahead into the engineering
stage in the tokamak program
does not imply downgrading either
basic science or alternate concepts
like laser or tandem mirror programs.
On the contrary, by developing a tokamak
engineering test facility, he
said, scientists will be gaining knowledge
and technology applicable to all
approaches in concept and design,
thereby enhancing research into basic
scientific questions.
72 FUSION August 1980