Re: SF Cold Fusion
- From: "Carey Sublette" <careysub@xxxxxxxxx>
- Date: Tue, 8 Jul 2008 22:00:52 -0700
"Luke Campbell" <lwcamp@xxxxxxxxx> wrote in message
news:87d54d12-75de-4e0f-b39a-3c68c8e16fce@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Jul 7, 7:09 pm, MacFrag...@xxxxxxxxxxxxxx wrote:
Let's assume that at some point in the future, they get myonic cold
fusion to work efficiently.
I am going to assume you mean "muons" rather than "myons" for my
response.
What's the real-world problem? As is, myonic cold fusion kind of
works, but cannot be exploited as power source because it takes more
energy to generate a myon than the myon-catalyzed D-T fusion cycles
release before the myon gets stuck on a core.
Or just decays on its own, even if not stuck to anything.
It takes 3 GeV to generate a myon, each D-T fusion releases 17,6MeV,
and the myon is lost after an average 167 cycles, resulting in a 2,9
GeV subtotal. Figures.
Do you have a cite for that? I find it doubtful that these values are
so close, or else we would see a lot more research in this field.
I think the figures are about right.
Regarding research in the field - there is some, but remember the specifics
of muon catalyzed fusion were worked out fairly completely by 1957 and other
than the possibility of getting "cheaper" muons not much has changed since.
After 50 years of non-success interests typically flags, probably for good
reason.
Also (like thermal fusion avenues) "break-even" is not of much use unless
you can push well beyond it (say, a factor of 5 or 10 would be good).
Break-even (energy released compared to the direct input energy) does not
take into account efficiencies of energy conversion to useful form (take a
factor of 2.5 at a minimum) and other energy costs of whole system (you
discuss these issues below of course).
Thermal fusion offers a reasonable promise that if you can get to
break-even, then you can get to break-even times 10. Muon catalyzed fusion
is up against fundamental physical processes that don't quite cooperate.
Pushing MCF to break-even or a little beyond accomplishes nothing in a
practical-producing-energy sense.
MCF, like many seemingly useful physical processes, would be a whole lot
more attractive if Nature would alter the physical parameters by a factor of
3 or so in favor of our desires.
The theoretical minimum energy for producing a muon is 0.106 GeV - the
rest mass of the muon. Clearly we are nowhere near that. For beam-
target interactions that are typically used to generate muons, the
minimum energy is a little over twice that because much of the energy
is carried away by the center-of-mass motion of the reactant particles
(assuming protons are used - for electrons it is over 200 times as
much minimum energy per muon). Another source of loss is that proton-
target reactions do not produce muons directly. They produce pions,
which decay to muons. The minimum energy for pion production is 0.28
GeV. About 2/5 of the pions produced will be pi^0 mesons, which decay
to gamma rays rather than muons. Another 2/5 will be pi^+ mesons,
which decay to positively charged muons that cannot participate in
fusion catalysis. The remaining 1/5 or so will be pi^- mesons which
will decay to negatively charged muons that can catalyze fusion. This
bumps the minimum energy per negative muon up to about 1.4 GeV. (You
can increase the number of negative muons slightly by using target
nuclei richer in neutrons. Even with a pure neutron target
(impossible to achieve since neutrons by themselves are unstable) you
would get only 1/3 of the pions with a negative charge). Then there
are losses due to all the other interaction channels with the target -
nuclear knock-out, ionization of target atoms, elastic scattering that
removes your protons from the beam. This is all difficult to estimate
without knowing the cross sections for various interactions but if you
tune the energy of your beam to the pion production resonance at 0.28
GeV you will maximize your pion production, and thus the number of
negative muons you get. This is also nice because it is the slowest
you can get your pions (and thus muons), and you don't have to work so
hard to slow them down (they'll be going about 30% the speed of light
at this minimum speed).
As you mention, there is also the inefficiency at turning AC
electrical energy into the kinetic energy of the proton beam - modern
accelerators get somewhere around 30% efficiency in this regard. This
gives on the order of 4.7 GeV per muon times the ratio of total proton
reactions with your target to the number of reactions that produce
muons (that ratio is always greater than 1).
Then, you need to turn the heat produced by the fusion into
electricity. If the reactor is limited by the ability of its
materials to withstand high temperatures, you can probably get around
40% efficiency at turning fusion heat into electricity. With each
fusion producing 17.6 MeV, you would need each muon to produce
(4700/17.6) * (1/0.4) = 668
fusions for electrical breakeven.
This is not even counting muons lost due to collection inefficiencies.
How could an SF-Tech improve this?
Possibly a colliding-beam muon generator. Use electrons and positrons
tuned to the mu^+ - mu^- production resonance, at 0.106 MeV of kinetic
energy for both the positron and electron beam. Your rate of
production will go way down, and you will have to bite the energy cost
to make the positrons, but you don't waste any energy on the center of
mass motion of the reaction products and you don't have to slow the
muons down (they are created at rest, or close to it). Half of your
muons will be the negative muons you want. Again, a big difficulty
with estimating the total energy cost is knowing the rate of competing
reactions relative to that of muon production.
I suppose there is simply no way to
prevent sticking. However, maybe future tech may be able to generate
myons more efficiently. Some breakthroughs in the fields of
superconducting and particle acceleration,
Turning RF energy into kinetic energy of the beam particles is already
very close to 100% efficient. The losses that I've been able to find
in the literature come mainly in the form of compressors for your
refrigerators that keep your superconductors at comfortably cryogenic
temperatures, running the injector (which gets you your beam
particles), and overhead like lighting and computing and monitoring
instruments for the lab. Running the klystrons that generate the RF
energy may be another source of inefficiency.
BTW there's still a potentially ugly product of cold fusion, one
neutron per fusion. I didn't find any solid data on this but if the
fusion energy yield (17,6MeV) is distributed evenly among the
products, this neutron might have a kinetic energy of 2,5MeV - not
quite a "cold" neutron anymore, but definitely on the lower end of
thermic neutrons.
Actually, it is much worse than that - the neutron ends up with most
of the energy. each deuterium-tritium fusion yields a 14.1 MeV
neutron and a 3.5 MeV helium-4 nucleus. And this is definitely not
thermal. Thermal neutrons have around 0.05 eV of energy, much less
than MeV particles.
However, I'm not sure about one thing: how is that energy released,
and how can you tap it? How can the energy best be converted to
electrity, and alternatively, how can it be used to power a starship
drive?
The energy imparted to the helium nucleus is deposited almost
immediately in the surrounding material, heating it. The neutron
escapes the immediate vicinity, but will eventually be captured in the
shielding. A reactor could be designed to use lithium-6 as the
neutron shielding, which gives an additional 4.8 MeV per captured
neutron and produces additional tritium to use as fuel via the
reaction n + 6Li -> 4He + T. This heats the lithium. Use the lithium
to cool the rest of the reactor as well. Now use a heat exchanger to
remove the heat from the lithium, boiling water into high pressure
steam to run a turbine that turns a generator which produces
electricity.
Luke
.
- References:
- SF Cold Fusion
- From: MacFraggin
- Re: SF Cold Fusion
- From: Luke Campbell
- SF Cold Fusion
- Prev by Date: Re: SF Cold Fusion
- Next by Date: Re: Beam Weapon Targeting / Aiming
- Previous by thread: Re: SF Cold Fusion
- Next by thread: SF Cold Fusion
- Index(es):
Relevant Pages
|
