Fusion with help of accelerators?


by Stanley514
Tags: accelerators, fusion
cdotter
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#37
May8-12, 08:53 PM
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Quote Quote by Drakkith View Post
I'm not sure this can be explained if you don't already know the basics of nuclear fusion power.
I conceptually understand how laser-driven ICF works, basically imparting a massive amount of energy into a small object which causes the object to heat up and implode. How does magnetic confinement work, though? From my understanding, a tokamak's magnetic fields confine the plasma which is at a (very) high temperature. But what gives the plasma its high temperature?
Drakkith
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#38
May8-12, 09:04 PM
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Quote Quote by cdotter View Post
I conceptually understand how laser-driven ICF works, basically imparting a massive amount of energy into a small object which causes the object to heat up and implode. How does magnetic confinement work, though? From my understanding, a tokamak's magnetic fields confine the plasma which is at a (very) high temperature. But what gives the plasma its high temperature?
Here you go: http://en.wikipedia.org/wiki/Tokamak#Plasma_heating
Rive
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#39
May9-12, 09:56 AM
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Quote Quote by mheslep View Post
The problem is a 'bounce' off collision is much more likely than a fusion event, regardless of density, so that beam-beam attempts inevitably waste more energy than they can generate.
I wonder if it is possible to form beams right form and in the plasma. Some MHD pumps, maybe? I don't really know the available 'tools' for this, but if it's possible then we won't waste the energy of the beam: it would just heat up the plasma which we are working from.
Drakkith
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#40
May9-12, 03:12 PM
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Quote Quote by Rive View Post
I wonder if it is possible to form beams right form and in the plasma. Some MHD pumps, maybe? I don't really know the available 'tools' for this, but if it's possible then we won't waste the energy of the beam: it would just heat up the plasma which we are working from.
I'd guess it's about as likely to happen as pumping multiple "beams" of water at supersonic speeds in my swimming pool.
Rive
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#41
May9-12, 03:26 PM
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Quote Quote by Drakkith View Post
I'd guess it's about as likely to happen as pumping multiple "beams" of water at supersonic speeds in my swimming pool.
Well... On small scale and for water it's on the edge but more or less possible... Cavitation? Steady (longitudial) waves?
Drakkith
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#42
May9-12, 03:40 PM
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Quote Quote by Rive View Post
Well... On small scale and for water it's on the edge but more or less possible... Cavitation? Steady (longitudial) waves?
The problem is how you would create these beams inside the plasma AND keep the other plasma away from plasma in the beams. The hotter you heat the plasma outside the beams, the harder it is to contain.
EulersFormula
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#43
May10-12, 08:05 PM
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Another inertial confinement scheme involves using tabletop lasers to accelerate ions from a solid target into another target of D-T fuel. If you shoot an ultra intense laser pulse at a thin solid target, you can accelerate ions from the rear-side of the target via a process called Target Normal Sheath Acceleration. The laser pulse immediately ionizes the target into plasma. As the laser pulse propagates through the target, electromagnetic fields from the laser pulse drive electrons toward the back of the target which then form a sheath. The resulting charge segregation region between the electron sheath and the rest of the target set up a strong electric field which accelerates the ions.

If this target happens to contain, say some deuteron atoms, then you'll get MeV-KeV deuterons travelling toward the D-T fuel. They will then proceed to conveniently fuse with deuterons in the fuel. DD Fusion!
Drakkith
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#44
May10-12, 08:10 PM
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Yes but like Beam-Beam fusion, the reactions are much too sparse compared to scattering events.
Stanley514
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#45
May15-12, 10:58 PM
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What is progress with fast ignition approach in which fuel is compressed with light ion beams and ignited with picosecond laser?Is it far from a positive net gain?
EulersFormula
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#46
May16-12, 07:22 AM
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The parameters for the ion beam have been met in individual experiments but not in the same experiment as far as I know.

The Sandia website has some good information regarding progress on the topic.
Stanley514
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#47
May16-12, 04:12 PM
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Is it possible to combine dense plasma focus and fast ignition approaches?
They claim that plasma focus is very dense.If so, it could be easily ignited with
picosecond laser and thermonuclear explosion should happen?
EulersFormula
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#48
Feb6-13, 09:38 PM
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In a dense plasma focus, you essentially have a coaxial electrode system. One end is insulated and a huge amount of current is released in a microsecond from a marx generator. The plasma sheath propagates up like a plasma gun (lorentz force) and at the top of the electrode system, some hydrodynamic shock effects occur which result in the formation of an extremely dense plasma column. Fusion occurs, although the lifetime is of the order of nanoseconds due to instabilities.

The dense plasma focus is useful as a neutron source. It would be difficult to focus the laser pulse into the exact location of the plasma column at the correct time.
Stanley514
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#49
Feb15-13, 07:18 PM
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It would be difficult to focus the laser pulse into the exact location of the plasma column at the correct time.
Why so?I read that they trying to heat plasma focus with external electron beam.Is it more difficult to aim it with laser than with electron beam?
Also at least some experiments with heating of plasma focus with laser seem already been conducted and quite successful.
http://jap.aip.org/resource/1/japiau...sAuthorized=no
http://oai.dtic.mil/oai/oai?verb=get...fier=AD0910345
So it seem to be principally possible back in 1970-es.
Another question: if it is assumed that entire plasma focus device is filled with ambient
deuterium gas how they suppose to prevent reactor walls melting through convection and gas heating?
Drakkith
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#50
Feb15-13, 08:40 PM
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Quote Quote by Stanley514 View Post
Is it possible to combine dense plasma focus and fast ignition approaches?
They claim that plasma focus is very dense.If so, it could be easily ignited with
picosecond laser and thermonuclear explosion should happen?
One would have to heat it from all sides equally. It is not easy.
Drakkith
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#51
Feb15-13, 08:45 PM
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Quote Quote by Stanley514 View Post
Another question: if it is assumed that entire plasma focus device is filled with ambient
deuterium gas how they suppose to prevent reactor walls melting through convection and gas heating?
I'd guess that the gas wouldn't be heated high enough to melt the walls. The pinch area is very small, and heat transfer through the walls would keep the small amount of gas inside the chamber cool. Plus, depending on the type of fuel you use, most of the energy may be taken away as neutrons, which wouldn't heat the gas.
Stanley514
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#52
Feb15-13, 09:46 PM
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One would have to heat it from all sides equally. It is not easy.
Why?The very idea of fast fusion is to acheive ignition of target with only one ultrashot impulse.In variant with deuterium capsules it is assumed that few lasers compess target from all the sides while one ultrashort laser ignites it.In case with plasma focus there is no need in precompression since plasma coloumn is already dense enough to start some fusion process.
Drakkith
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#53
Feb15-13, 11:32 PM
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Quote Quote by Stanley514 View Post
Why?The very idea of fast fusion is to acheive ignition of target with only one ultrashot impulse.In variant with deuterium capsules it is assumed that few lasers compess target from all the sides while one ultrashort laser ignites it.In case with plasma focus there is no need in precompression since plasma coloumn is already dense enough to start some fusion process.
Ah I see what you're saying. Well, I think the problem isn't that we can't heat it high enough, it's that containment of the plasma at sufficient density is very difficult. I know much of the work involved in practically every fusion device is figuring out how to keep the plasma contained and compressed as well as heated. I don't know the details on laser heating of pre-heated plasma, but I would guess that it's simply an unnecessary complication at this stage. Consider that the containment method of dense plasma focus is the current moving through the plasma itself. Heating the plasma up with a laser may simply be detrimental to the plasma, or at the very least it might do nothing at all if the magnetic field generated by the current simply isn't strong enough to contain the plasma as it's heated. Plus, if I'm reading the info right, there isn't just one spot that the plasma is pinched, it's multiple spots. And these spots are REALLY small. Perhaps too small to effectively heat with a laser. Especially if we can't accurately predict where the pinch will occur at beforehand.
Stanley514
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#54
Feb16-13, 07:04 AM
P: 292
Heating the plasma up with a laser may simply be detrimental to the plasma, or at the very least it might do nothing at all if the magnetic field generated by the current simply isn't strong enough to contain the plasma as it's heated.
In the best scenario the ultrashort laser pulse would not just heat plasma coloumn,it suppose to cause thermonuclear explosion of the coloumn instantly.If dense focus exist couple of nanosecond it is quite sufficient time for picosecond pulse to explode it.
Picosecond is much smaller piece of time than nanosecond.
http://en.wikipedia.org/wiki/Inertia...#Fast_ignition


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