29 Appendix on TFTR and JET results (Fusion)
Description
This article is from the Fusion FAQ, by Robert F. Heeter heeter1@llnl.gov with numerous contributions by others.
29 Appendix on TFTR and JET results (Fusion)
TFTR results vs JET results from 1991:
(Written by Stephen R. Cooper at JET, with comments [like this]
by R.F. Heeter.)
>From src@jet.uk Tue Dec 14 11:14:34 EST 1993
Newsgroups: sci.physics.fusion
Subject: Re: Laymen Q: Was Princeton's Fusion a 'breakthrough?'
Organization: Joint European Torus
References: <2ebdvg$44e@Mercury.mcs.com> <2ei3vk$o7o@mailer.fsu.edu>
Date: Tue, 14 Dec 1993 12:01:28 GMT
In <2ei3vk$o7o@mailer.fsu.edu> jac@ds8.scri.fsu.edu (Jim Carr)
writes:
>As I recall, the reports from JET in November 1991 indicated a Q of
>about 1/9 for the light load of T, with plans to increase the T
>to 50% by 1996. I think their extrapolation to 50% indicated
>they would be very close to breakeven at that point, but do not
>recall the details.
>Could some JET person fill us in?
[ Note by rfheeter: Q is the ratio of power produced in the
machine by fusion to power put into the machine to heat
the plasma. Q = 1 means fusion yield is equal to power
input. Economical fusion will require Q significantly
greater than 1. See the glossary (Section 10) for more details.]
Results quoted from "The JET Preliminary Tritium Experiment",
invited talk given to the 1992 International Conference on
Plasma Physics by P-H Rebut, Innsbruck, Austria, 29th June-3rd
July 1992).
"Two Deuterium plasmas were heated by high power deuterium
neutral beams from fourteen sources and fuelled by two neutral
beam sources injecting tritium. In the best of the two D-T
discharges, the tritium concentration was about 11% of bulk plasma
at peak performance, when the total neutron emmision rate was
6.0E17 per second, with 1.7MW of fusion power. The fusion
amplification factor Q(DT) was 0.15. With an optimum tritium
concentration, this pulse would have produced a fusion power
of ~ 5MW and nominal Q(DT) of 0.46. The same extrapolation for
the best pure deuterium discharge of the PTE series gives about
11MW and a nominal Q(DT) of 1.14.
[ Note by rfheeter: neutral beams are made by accelerating
deuterium ions, and then neutralizing the ions so that they
can fly into the magnetic field of the tokamak without being
deflected. As they enter the plasma, they are re-ionized
and their energy is subsequently shared with the other
ions in the plasma. Thus this is a method for simultaneously
heating and refueling the plasma. See glossary for more info...]
The total integrated total neutron yield was 7.2E17 with an
accuracy of +/- 7% and the total fusion energy was about 2MJ.
The tritium injections last just 2 seconds out of a 10 second,
3MA flat top. The amount of tritium injected and the limited
number of shots were deliberatly restricted for operational
convenience."
[ Note by rfheeter: 2 MJ = 2 million joules = 1 million
watts for a duration of 2 seconds, or 2 million watts for
a duration of one second. 1 Joule = 1 watt * 1 second.
A "10 second, 3 MA flat top" refers to the relatively stable
flat peak of a current-vs-time graph, indicating that
the plasma current is stable at about 3 million amps
(3 MA) for 10 seconds. "Operational convenience" should
probably be interpreted as "because we didn't want to
make our reactor too radioactive, and tritium handling
is a pain." - that's an editorial comment. ]
--> Personal remarks start
[this Cooper writing now, and not quoting others.]
The above seems to indicate that if JET had gone into it's full
D-T phase at this time and with this configuration, we certainly
should have got to 50% of breakeven. As to if we could have
matched our best deuterium pulse, I guess we would have come
close especially as the TFTR results show no pathological
problems with a 50/50 D-T mix. But this is all hypothetical,
we no longer have anything like the configuration we had in
1991, we're just about to finish a major shutdown incorporating
a pumped divertor to look at impurity control and ash removal.
The old H mode shots that the 1991 experiment were based on
are a thing of the past and we'll have to wait and see how she
performs with the new configuration.
[ Note by rfheeter: a "divertor" is a magnetic or physical
way of channeling particles from the edge of the plasma
out of the way, and helps to improve confinement of the plasma
as well as remove impurities. "H mode" is a relatively
stable operational mode of the tokamak, as contrasted with
"L mode", which is less stable. I believe H = High and
L = Low, referring to high and low confinement.]
[[ The rest of the article was about TFTR and not JET,
and I have omitted it to save some space. ]]
Stephen R Cooper Physics Operations Group
src@jet.uk Operations Division, JET.
- Disclaimer: Please note that the above is a personal view and
should not be construed as an official comment from the JET project.
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