Fusion with help of accelerators?

[Stanley514]

Is it possible to use neutral beam accelerators to smash deuterium atoms at each other to achieve practical fusion?

 

[wizwom]

This was actually one of the first fusion experiment. The latest attempt was SIGFE at the University of Wisconsin, Madison. It was a failure; the results indicated that the neutron production was from Fe(D,2n) spallation rather than fusion. Plenty of Neutrons, though - best neutrons/Watt from any device.

 

[Stanley514]

This was actually one of the first fusion experiment. The latest attempt was SIGFE at the University of Wisconsin, Madison.

In this experiment they mention ion beams.If they use ions, then I do not see how could they get away from space-charge problems and similar.I meant rather to use neutral beam.
It means just neutral atoms.Neutral beam injectors are used as plasma heaters in TOKAMAK devices.Could we make something that works like MHD generator in reverse?
We could slightly ionize deuterium vapour just to make it conductive.And after speed it up with help of electrostatic accelerator. What speeds could we attain in this way?

 

[Rive]

In this experiment they mention ion beams.
...
We could slightly ionize deuterium vapour just to make it conductive.And after speed it up with help of electrostatic accelerator.

If you ionize your neutral atoms for acceleration then what you get is an ion beam.
If you don't ionize them then they don't accelerate...

 

[Stanley514]

If you don't ionize them then they don't accelerate...

Is it really necessary to ionize each atom?How then reilgun
works without any ionization?Maybe small ionization is sufficient?

 

[Drakkith]

Is it really necessary to ionize each atom?How then reilgun
works without any ionization?Maybe small ionization is sufficient?

A railgun uses the magnetic field created in the device and projectile to launch it. That requires an electromagnet which requires an electric current, which is electrons moving along the wires. You cannot accelerate individual ions using the same technique. Instead you have to use electric charge to accelerate them, which requires ionization of the atom, otherwise it is neutral and won't be accelerated.

 

[Stanley514]

Instead you have to use electric charge to accelerate them, which requires ionization of the atom, otherwise it is neutral and won't be accelerated.

What would you say about electrohydrodynamic generator http://en.wikipedia.org/wiki/ElectrohydrodynamicsIn which electrically charged particles used to flow and generate electricity?It is not necessary to ionize all the atoms or molecules in it.Creating some small charge is quite sufficient.Do you think it wouldn`t work in reverse?Principally we could use electromagnets too.But in this case we whould need to pare deuterium with something magnetic.Maybe some Iron hydride molecules.
There already exist some storage rings which designed for neutral atoms.
http://accessscience.com/content/Neutral-atom-storage-ring/YB050460
I guess if it could be stored then it could be accelerated too.

 

[Drakkith]

What would you say about electrohydrodynamic generator http://en.wikipedia.org/wiki/ElectrohydrodynamicsIn which electrically charged particles used to flow and generate electricity?It is not necessary to ionize all the atoms or molecules in it.Creating some small charge is quite sufficient.Do you think it wouldn`t work in reverse?Principally we could use electromagnets too.But in this case we whould need to pare deuterium with something magnetic.Maybe some Iron hydride molecules.
There already exist some storage rings which designed for neutral atoms.
http://accessscience.com/content/Neutral-atom-storage-ring/YB050460
I guess if it could be stored then it could be accelerated too.

None of these are effective options for fusion. Each ion still needs to be accelerated, which requires electric fields.

 

[Bob S]

If you ionize your neutral atoms for acceleration then what you get is an ion beam.
If you don't ionize them then they don't accelerate...

If you add an extra electron to the hydrogen atom, you have a negatively charged atom. You can accelerate this, and if you then strip off the second electron with a very thin foil, you will have a neutral beam.

See http://lss.fnal.gov/archive/2005/pub/fermilab-pub-05-094-ad.pdf

Bob S

 

[Stanley514]

If you add an extra electron to the hydrogen atom, you have a negatively charged atom. You can accelerate this, and if you then strip off the second electron with a very thin foil, you will have a neutral beam.

Unfortunatly it will create the same space-charge problems as in case with positive ions.Problem with beam density.To get it really dense it should be constantly almost neutral.I guess.

 

[Astronuc]

In order to magnetically confine a gas, one needs ions, either + or -. Usually this entails a fully ionized gas or plasma. In fusion plasmas, one has mixtures of ions (deuterons, tritons, ³He²⁺, . . . .) and electrons. Fusion reactions occur among the bare nuclei (ions), while the electrons scatter about wasting energy (brehmsstrahlung, cyclotron radiation, recombination, etc). Neutral atoms leak through magnetic fields.

Neutral beams are used to feed and heat a plasma because neutral atoms move through magentic fields. Once in a plasma, neutrals collide with other neutrals, ions or electrons and become ionized.

Nature favors neutrality, and plasmas are quasi-steady-state, because without energy input, they would tend to become a neutral gas.

Ideally, a fusion plasma develops enough fusion energy to maintain the plasma AND generate surplus energy that can be extracted as thermal energy or electric current IF the charges can be separated and recombined across a load (direct conversion).

 

[Stanley514]

What do you think the most perspective direction in fusion power research up to date?
Something that is cheap to implement and quite simple?

 

[Drakkith]

What do you think the most perspective direction in fusion power research up to date?

The most "perspective" direction? What does that mean?

Something that is cheap to implement and quite simple?

There is nothing that is cheap and simple. The closest thing in my opinion is the Polywell WB-6 device.

 

[Stanley514]

The closest thing in my opinion is the Polywell WB-6 device.

Do you think Polywell could be treated seriously?
And why it going to be cheap?As I know it would still require to have superconducting magnets to create strong enough magnetic field.And vacuum.So why is it going to be cheap?

 

[Drakkith]

Do you think Polywell could be treated seriously?

The Polywell is a new concept that hasn't had 30+ years of development behind it, so it might be a little to early to really say either way. The WB-6 showed very good results. Good enough that the US Navy gave them an 8 million dollar contract that they are currently under. Reports from the website aren't detailed, but say that they WB-7 and WB-8 have been working well and they are currently testing scalability factors and such. We'll have to wait and see what happens over the next few years with it.

And why it going to be cheap?As I know it would still require to have superconducting magnets to create strong enough magnetic field.And vacuum.So why is it going to be cheap?

I didn't say it was going to be cheap. Just cheaper than other options such as Tokamaks.

 

[Stanley514]

Why Polywell is going to be cheaper than Tokamak?

 

[Drakkith]

Why Polywell is going to be cheaper than Tokamak?

As far as I know it's much less complex. The coils are simple and easy to build and you don't need to use complicated ways of helping to stabilize the plasma like you do with other designs.

 

[wizwom]

Why Polywell is going to be cheaper than Tokamak?

Bussard's explanation:

Tests made on a large variety of machines, over a wide range
of drive and operating parameters have shown that the loss
power scales as the square of the drive voltage, the square
root of the surface electron density and inversely as the 3/4
power of the B fields. At the desirable beta = one condition,
this reduces to power loss scaling as the 3/2 power of the
drive voltage, the 1/4 power of the B field, and the square of
the system size (radius). Since the fusion power scales as
the cube of the size, the fourth power of the B field, and a
power of the E drive energy equal to the E-dependence of
the fusion cross-section (cross-section proportional to E to
the s power), minus 3/2. For DD, s = 2-4, while for DT, s =
3-6 in useful ranges of drive energy. For pB11, the cross
section scales about as s = 3-4 over the system-useful range.
Thus, the ratio of MG power loss to fusion power production
will always decrease with increasing drive voltage,
increasing B field, and increasing size. ... This is not the case in Maxwellian,
equilibrium fusion devices...

This is why the DoD is interested in testing the scaling - this is the huge claim that Bussard put forth.

A Tokomak's losses mount as the plasma gets more dense - and any increase in the magnetic confinement field makes the plasma more dense. A polywell can increase the well depth by multiple paths.

 

[Stanley514]

Could somebody calculate how dense should be deuterium ion beams that directing them at each other would produce some net energy?

 

[wizwom]

Could somebody calculate how dense should be deuterium ion beams that directing them at each other would produce some net energy?

The SIGFE, even calling every neutron a fusion, and calling their ion guns 100% efficient, was still producing on the order of Q=3*10^-8, that is, for each watt out they would have had to use 26 MW.

 

[Stanley514]

There seem to be such devices as Mercury-arc valve which able to produce
quite dense flow of ions.Could be the same principle used for fusion?

 

[beatlemaniacj]

The Farnsworth Fusor is an example of this. It takes 2-4 linacs (basically TV tubes with the fronts taken off) And accelerates them to high energies into a small, spherical, metal, "cage" that is electrically charged and fuses them to produce helium³ and a steady supply of neutrons. I am currently making one with the help of a physicist. Obviously the theory of operation is much more complex than this, but that is just an overview.

 

[Stanley514]

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?

 

[Bob S]

The Farnsworth Fusor is an example of this. It takes 2-4 linacs (basically TV tubes with the fronts taken off) And accelerates them to high energies into a small, spherical, metal, "cage" that is electrically charged and fuses them to produce helium³ and a steady supply of neutrons. I am currently making one with the help of a physicist. Obviously the theory of operation is much more complex than this, but that is just an overview.

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.

 

[Drakkith]

Could it be made that simple?

If it were that simple we would have fusion power already. Beam-beam fusion does not work well enough to generate power.

 

[Stanley514]

What is news on dense plasma focus devices?
Could they ever become practical working on D-D fuel?
How they think to reduce Bremsstrahlung looses?

 

[Drakkith]

Could they ever become practical working on D-D fuel?

Unknown. I guess we will know when it happens, or we go 200 years without it working after we achieve fusion another way.

 

[Stanley514]

Why DPF produces lots of X-ray?Is there no such problem with other types of fusion?

 

[Drakkith]

Why DPF produces lots of X-ray?Is there no such problem with other types of fusion?

I believe DPF is both hotter and denser than some other types of fusion, thus creating x-rays.

 

[mheslep]

The Polywell is a new concept that hasn't had 30+ years of development behind it, so it might be a little to early to really say either way. The WB-6 showed very good results. ...

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

 

[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.