Re: Tokomak fusion (some question)
- From: nanjasad@xxxxxxxxx
- Date: 27 Aug 2006 10:45:57 -0700
Allright, from this website
http://www.jet.efda.org/pages/content/fusion4.html
it said that the current tokomak(JET) already using all combined
heating method,
but still unable to achieve energy output greater then energy input.
Boss not in wrote:
"Bruce Scott TOK" <Use-Author-Supplied-Address-Header@[127.1]> wrote in
message news:200608141235.k7ECZJJa019966@xxxxxxxxxxxxx
Boss not in asked:
|> In Tokomak fusion, people is trying to control the current (flow of
electron
|> in the hot plasma)
|> with another current (electron flow in the supercondutive coil).
That's right... the current in the external coil produces the toroidal
magnetic field, while the current flowing in the plasma produces the
poloidal current.
|> What is the magnitud of current in the hot plasma?
Typically about 1 MA in current tokamaks, more in the planned ITER.
See www.iter.org for the latter.
|> and what is the magnitud of current in the superconductive coil?
I don't know but here's an estimate: the toroidal magnetic field in our
experiment is about 2 or 2.5 Tesla and the minor radius of the plasma is
about 0.5 m. The plasma is elongated by about 1.6 to 1, so for rough
estimate purposes we take a circle of about 1 m, and let a solenoidal
current flow to make the magnetic field.
http://en.wikipedia.org/wiki/Solenoid
http://farside.ph.utexas.edu/teaching/302l/lectures/node61.html
The magnetic field inside a solenoid is B = mu_0 N I, where N is the
number of coil turns per meter and I is the current... hence this is a
current density of I N amperes per meter. The length is 2 pi times the
toroidal radius of 1.6 meters, or about 10 meters. So for a B of 2.5
Tesla, you need a current density of I N = 2 MA per meter. That's as
far as I can go because I don't know the technical detail of how tightly
our coils are wound.
The toroidal current inside the plasma is typically 1 MA or so and the
poloidal/toroidal pitch of the magnetic field at the plasma edge is
about 0.1 or so.
Another example is given here:
ATLAS Solenoid Magnetic Field Simulation
http://www.hep.man.ac.uk/u/miyagawa/work/bfield/
In his case the current is 7.6 kA and the number of coil turns per
length is 1154 in 5.291 m and the radius is 1.246 m (the radius is only
important because in a realistic model the finite aspect ratio changes
the result). Putting these numbers into the above formula gives a
magnetic field of 2.08 Tesla, and he says 7.6 kA is the nominal current
at 2 Tesla.
|> I am not scientist so I don't know, anyone know?
|>
|> An how is it possible for the current to heat-up the plasma to
temparature
|> hoter sun,
|> while the current in the superconductive coil will not heat-up the
coil.
Current heats the stuff it is flowing in by means of resistive
dissipation. The plasma has much much lower energy density than the
metal making up the coil, so it heats up faster by that consideration
alone. The plasma makes resistivity via collisions between charged
particles. The metal makes resistivity according to its solid state
phonon properties, and these are quite different. In a superconducting
coil the resistivity is effectively zero, so the discharge current flows
for a long time. In a normal metal coil the metal does heat up, and
this puts a limit on how many discharges can be run during a typical
day.
Heating of the plasma by current and resistivity is called Ohmic
heating. Ohmic plasmas only get up to a few hundred electron volts
worth of temperature. A fusion plasma has to be in the range of 20 keV
which is about 220 million degrees K.
--
ciao,
Bruce
drift wave turbulence: http://www.rzg.mpg.de/~bds/
Thanks for the the detail answer, and information.
We now know that large scale energy output from fusion of hydrogen/duetrium
is still impossible by just using electric discharge + magnetic confinement.
But how about if we combined all the heating method together.
Say if we have a basketfull hydrogen/duetrium at the center of the "fusion
reactor".
In very short period of time, we discharge few million Amp through it +
laser beam from all direction +
magnetic compression.+...some other method (which I don't know)
will that be able to acheive higher energy output? maybe only experiment
will tell?
(Note: I am talking about controlled fusion and the possible of a fusion
power plan for electricity generation.
I am not talking about the possibillity of such fusion reactor being
converted to some other use)
Allright, from this website
http://www.jet.efda.org/pages/content/fusion4.html
it said that the current tokomak(JET) already using all combined
heating method,
but still unable to achieve energy output greater then energy input.
----------------
from Boss not in
.
- Follow-Ups:
- Re: Tokomak fusion (some question)
- From: Bruce Scott TOK
- Re: Tokomak fusion (some question)
- References:
- Tokomak fusion (some question)
- From: Boss_not_in
- Re: Tokomak fusion (some question)
- From: Bruce Scott TOK
- Re: Tokomak fusion (some question)
- From: Boss not in
- Tokomak fusion (some question)
- Prev by Date: Re: Can someone answer these simple questions for a layman re. fusion?
- Next by Date: Re: Say finally we have the fusion reactor
- Previous by thread: Re: Tokomak fusion (some question)
- Next by thread: Re: Tokomak fusion (some question)
- Index(es):
Relevant Pages
|
