Fusion with help of accelerators?

[mheslep]

Electrons are ubiquitous and easily accelerated to say 100 keV. Building ion sources of deuterium or tritium is very difficult. Accelerating these ions to 100 keV while controlling the defocusing space charge forces is extremely challenging.

For a colinear beam, sure, but that is not the case for one of these fusors as the poster has in mind, which are essentially anode - cathode tubes. Add D or T gas with a high E field and it is quickly ionized. They appear to quite simple to construct.

 

[mheslep]

I read claims in a scientific magazine that if you direct D and T beams straight at each other and make them collide, then if their density will be higher then 10^14 ions per cm^-3, then fusion will become practical and give some surplus energy.To achieve such ion densities you need ion beams with current over few tens of Ampers.They also claim that modern high-current ion drivers allow to achieve currents over 1 million of Ampers.With energy of ions over 1 MeV.Could it be made that simple?

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.
https://www.physicsforums.com/showpost.php?p=2450588&postcount=20

 

[Drakkith]

I don't think that claim has validity without public release of the WB-6 results.

I think I remember reading the results, but I don't have the link anymore.

 

[mheslep]

I think I remember reading the results, but I don't have the link anymore.

I fairly sure I recall that the results were *not* released, though there has been a lot of informal inference to read about based on some continued funding.

 

[Stanley514]

What is principal difference between inertial fusion and accelerator/plasma focus fusion?
Why you cannot easily achieve conditions in former similar to the first?
Could you create some local thermonuclear explosions with beam fusion?

 

[Drakkith]

What is principal difference between inertial fusion and accelerator/plasma focus fusion?
Why you cannot easily achieve conditions in former similar to the first?
Could you create some local thermonuclear explosions with beam fusion?

I'm not sure this can be explained if you don't already know the basics of nuclear fusion power.

 

[cdotter]

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]

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]

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]

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]

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]

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]

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 traveling toward the D-T fuel. They will then proceed to conveniently fuse with deuterons in the fuel. DD Fusion!

 

[Drakkith]

Yes but like Beam-Beam fusion, the reactions are much too sparse compared to scattering events.

 

[Stanley514]

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]

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]

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]

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]

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/v42/i13/p5884_s1?isAuthorized=no
http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=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]

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]

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]

One would have to heat it from all sides equally. It is not easy.

Why?The very idea of fast fusion is to achieve 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]

Why?The very idea of fast fusion is to achieve 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]

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/Inertial_confinement_fusion#Fast_ignition

 

[Drakkith]

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/Inertial_confinement_fusion#Fast_ignition

Interesting. I hadn't read about this development before.

 

[ZapperZ]

In case people missed it, NIF did not achieve ignition last year and missed their stated milestone.

So, are we still trying to achieve fusion with accelerators here? I still find it amusing that people think we can get a net energy out of such a thing. The whole issue with fusion is not just creating the process, but generating energy out of the whole process, i.e. it generates more energy that it uses.

So for people who are proposing this concept of using accelerators, have you ever looked at the wall-plug efficiency of a typical particle accelerator? And what kind of luminosity do you need to actually get more energy than you are consuming? After all, this IS in the "engineering" forum, isn't it? Such issue must be considered and is part of an engineering design concept.

Zz.

 

[Joseph Chikva]

Typical particle accelerator's efficiency is rather high - has 90% order.
Unlike lasers having 1-2 orders lower efficiency.

luminosity?
Ion diods, ion diods with inductive voltage adders give very high currents - tens thousands and even millions amperes in short pulses.
As well as induction linacs.

You can direct two ion beams at the same direction but with different velocities and along the same axis but oppositely you can direct relativistic electron beam with 3 orders of magnitude lower current. As result in some conditions you will get the combined self-focusing beam (high density), in which fast ions will collide slowly moving ions.
Fusion in beams is possible!

 

[Velikovsky]

The general train of thought seems to be "smashing" atoms together to achieve fusion, This is certainly possible but the greatest challenge would be the containment of said fusion. I wonder is it possible to make "compressive clusters" of atoms to achieve fusion around a high gravity core? Such a fusion reactor would be self containing around the core that would in fact act as a "cluster resistor" with the atoms "squeezing" themselves together at the point of highest resistance. Any thoughts or ideas on this? Is it a possibility?

 

[Joseph Chikva]

The general train of thought seems to be "smashing" atoms together to achieve fusion, This is certainly possible but the greatest challenge would be the containment of said fusion. I wonder is it possible to make "compressive clusters" of atoms to achieve fusion around a high gravity core? Such a fusion reactor would be self containing around the core that would in fact act as a "cluster resistor" with the atoms "squeezing" themselves together at the point of highest resistance. Any thoughts or ideas on this? Is it a possibility?

Yes, gravitational confinement is in existence in the stars. But in Earth conditions that is impossible because for starting fusion impracticable large gas quantities of gas have to be combined together.

 

[Stanley514]

You can direct two ion beams at the same direction but with different velocities and along the same axis but oppositely you can direct relativistic electron beam with 3 orders of magnitude lower current. As result in some conditions you will get the combined self-focusing beam (high density), in which fast ions will collide slowly moving ions.
Fusion in beams is possible!

If this is for real why is not used to generate power?Could you give some ref. on such experiments?