25 Recent Results on TFTR: D-T Experiments (Fusion)
Description
This article is from the Fusion FAQ, by Robert F. Heeter heeter1@llnl.gov with numerous contributions by others.
25 Recent Results on TFTR: D-T Experiments (Fusion)
* (a) What was done?
The Tokamak Fusion Test Reactor (TFTR) here at Princeton
switched from pure-deuterium fuel to a deuterium-tritium
(D-T) fuel mixture in December 1993. As discussed in
Section 1, the D-T fuel is easier to fuse, but the neutrons
produced in the reaction D + T -> 4He + n will slowly make
the reactor radioactive, so this set of experiments will
be the last for TFTR. In these reactions, over 6 million
watts (MW) of fusion power were produced for about a second.
This is four times more power than any previous controlled
fusion experiment. The value of 6 MW should be compared to
the roughly 30 MW of input power used, which indicates that
fusion in TFTR remains short of breakeven. (See glossary for
explanations of unfamiliar terminology.)
(There was an article on this in _Time_, Dec 20, 1993, p. 54,
at least in the American edition; there are of course other
articles out there too. See Section 9, Part A (the bibliography
on recent literature) for more references.)
>>Update May 31 (mostly from TFTR News Updates by Rich Hawryluk):
Over 9 megawatts were generated in late May.
This is 90 million times what could be generated in 1974
when TFTR was proposed.
Input power was up to 33.7 MW -> Q = 0.27.
This means we are making almost as much fusion power as
is used to heat the plasma now.
Two articles on the December experiments were published in
the May 30 issue of Physical Review Letters.
Recent TFTR shots have exhibited exceptionally high performance,
with preliminary indications that energy confinement is
enhanced by 20-30 percent in D-T relative to D-D fuel.
Plasma disruptions possibly caused by TAE mode activity have
been observed. Fusion performance is limited by the MHD
activity, not by heating power or confinement.
Central fusion power density has been increased from 1.25 MW m-3
to 1.8 MW m-3.
>>Update August 7
Work is ongoing to try to stabilize the power-limiting modes.
>>Update September 13
Funding to continue D-T experiments throughout FY 1995 has
been granted. (see below)
>>Update October 16
Though TFTR has not literally achieved "breakeven" (fusion power
output equals plasma heating power input), we are very close
now, and in addition we have achieved plasma conditions very
close to those needed in a real fusion powerplant. The
scientific results achieved suggest that D-T plasmas have
better confinement than their D-D counterparts. A number of
crucial scientific issues have been resolved and the sense
of the scientists here is that we can be fairly confident
that we can build a fusion reactor which will generate
gigawatts of surplus energy. The trick now is to find ways
to do this an an environmental and cost-effective manner.
* (b) Why does it matter?
The generation of multi-megawatt levels of fusion power is a major
achievement for the controlled fusion program. Sustaining the
power output for a second is also significant, because most
known plasma instabilities occur much more quickly. Also, use
of tritium to achieve high power levels enables researchers to
study plasmas under conditions closer to those of a working
fusion reactor. There are effects due to the heavier tritium
ions, and due to the presence of highly energetic helium ions
produced in the fusion reaction. In particular, scientists
were worried that the energetic He ions might trigger new plasma
instabilities. (Plasmas are notorious for finding new ways to
misbehave whenever scientists manage to improve the operating
conditions.) Fortunately, no major instabilities were observed,
and in fact early reports are that plasma performance actually
improves in high-power D-T conditions. These results enhance
the prospects for future experiments which will try to achieve
even higher power outputs in nearly steady-state conditions.
(See Section 8 for more information on future experiments.)
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