Nuclear fusion using a plasma jet

[timbot]

As per a previous thread, if you fire two plasma jets of deuterium at each other at high enough relative velocity, the deuterons would collide and fuse into helium.

Does anyone know what is the relative velocity in kilometers per hour necessary for deuterons hitting each other head on to fuse into helium?

How is this calculated?

 

[hamster143]

As calculated in the previous thread, you're looking at velocities of ~500 km/s, whether for hydrogen or deuterium (square root of two or 40% lower for deuterium, which does not help all that much) and we don't know how to accelerate macroscopic objects to this kind of speed ... Note that there's no minimum fusion "threshold", but probability of fusion between two nuclei goes up quickly as you add more energy.

There's an easy way to accelerate individual ions, you basically strip the deuterium atom of electrons and stick it into strong electric field, tens of kilovolts ... if you create a vacuum chamber with two concentric electrodes, apply 10 kV between electrodes, and put a small quantity of deuterium gas into the chamber, you _will_ see fusion events, but, to the best of our knowledge, this process can't be optimized to result in net production of energy.

 

[timbot]

Hi Hamster143,

The reason i keep hammering this point is that I have thought of a method to accelerate plasma jets to a very high speeds, using an accelerating magnetic field.

The figure you mentioned is in the realm of feasibilty.

Half of 500 km/s for each plasma jet is 250 km/s (directed against each other). Times 60% for deuterium is 150 km/s. That is 540,000 km per hour.

Now if you want only 1% of the plasma jet to fuse, a statistician friend told me you can reduce the averge velocity to 25% of 540,000 km/hour, or 135,000 km/hour, assuming a normal distribution of particle velocities.

A plasma accelerator which can accelerate plasma to an average speed of 135,000 km/hour is well within the realms of feasibility.

I think continuous commercial plasma fusion is quite feasible if you direct two high speed plasma jets of deuterium againast each other.

 

[Bob_for_short]

Thirty years ago, when I was a young researcher, I was told that one of our colleagues (Leopold Skripnik) had already proposed (theoretically) a “solid-state/beam thermonuclear reactor”. Indeed, he took a solid target and a fast beam of deuterons or so, I do not remember now. He calculated the efficiency of such a system. In a solid body the charged projectile loses its energy but can provoke an energy release due to fusion. He found that starting from some energy the losses are smaller than the gain but nobody believed it. In fact, it is a question of efficiency. Theoretically it is possible in a solid target. I do not know how about two colliding jets, where there is a region of their velocities to make the fusion energy release superior to projectile energy losses.

 

[Bob S]

The reason i keep hammering this point is that I have thought of a method to accelerate plasma jets to a very high speeds, using an accelerating magnetic field...I think continuous commercial plasma fusion is quite feasible if you direct two high speed plasma jets of deuterium againast each other.

I have never seen or read of magnetic acceleration of any charged particles except electrons. Are you talking about a "betatron" accelerator for deuterons? See
http://en.wikipedia.org/wiki/Betatron
I have seen and used 14.1 MeV neutrons from (I think) 300 KeV deuterons hitting a tritiated tantalum (or tungsten) target yielding D-T fusion, but it was extremely inefficient, like maybe 1 neutron per million deuterons or worse.

 

[Bob_for_short]

I have seen and used 14.1 MeV neutrons from (I think) 300 KeV deuterons hitting a tritiated tantalum (or tungsten) target yielding D-T fusion, but it was extremely inefficient, like maybe 1 neutron per million deuterons or worse.

300 KeV is too small energy for the projectile to get a reasonable efficiency. It should be increased by a factor of 100 or even more.

 

[Bob S]

300 KeV is too small energy for the projectile to get a reasonable efficiency. It should be increased by a factor of 100 or even more.

So you're saying 30 MeV. Is this per beam in the center of mass, or deuterons on a fixed (stationary) target? What is the fusion cross section there? Considering that the energy release including neutrons in D-T fusion is only about 17 MeV, it is hard to visualize break-even power output with 30 MeV beams.

 

[Astronuc]

300 KeV is too small energy for the projectile to get a reasonable efficiency. It should be increased by a factor of 100 or even more.

Not for fusion. Look at the kinetic energies of the reactants for the Q values of the reaction and those are in the low MeV range, so it is impractical to accelerate deuterons much beyond 1 MeV in order to induce fusion. The optimal temperature for d+d fusion is around 500 keV - 1 MeV, and with diminishing returns one would probably want a temperature on the order of 300-400 keV.

d + d -> T (1 MeV) + p (3 MeV), or 3He (0.82 MeV) + n (2.45 MeV)

Colliding beams have been considered. With losses due to scattering, I believe the concept was found to be impractical.

Another consideration is the neutrality of plasma. Usually injected deuterons are neutralized, otherwise the local positive charge can induce plasma instability as well as dispersion of the deutron beam. So either one collides neutral deutron beams or one has to add similar current so electron beams to the reation volume.

 

[Bob_for_short]

So you're saying 30 MeV. Is this per beam in the center of mass, or deuterons on a fixed (stationary) target? What is the fusion cross section there? Considering that the energy release including neutrons in D-T fusion is only about 17 MeV, it is hard to visualize break-even power output with 30 MeV beams.

I really do not know all the numbers - I never did it myself. But what is necessary to reach is to obtain the thermo-nuclear reaction for sure and recuperate as much of lost energy as possible. I do not know details of his calculations. Anyway, all energy release is then used in a heat machine with a known efficiency so there may be some positive output.

 

[hamster143]

300 KeV is too small energy for the projectile to get a reasonable efficiency. It should be increased by a factor of 100 or even more.

DT fusion cross section peaks at ~60 KeV CM:

http://media.photobucket.com/image/...on6808/FusionCrossSections-grid-81pct-l-1.jpg

 

[Bob_for_short]

DT fusion cross section peaks at ~60 KeV CM

Yes but one has to diminish the losses too. The loss cross section may decrease faster with E than the reaction cross section. Besides, I do not know what target and what projectile Leopold used in his calculations.

 

[Bob S]

DT fusion cross section peaks at ~60 KeV CM:

http://media.photobucket.com/image/...on6808/FusionCrossSections-grid-81pct-l-1.jpg

Hi Hamster
Yes, but the integrated cross section. from incident deuteron beam energy of ~300 KeV to zero energy in a tritiated target, has the greatest probability of producing a D-T fusion reaction.
Bob S

 

[timbot]

For more information about the plasma acceleration device I have designed, go to my blog
http://collidingplasmafusion.blogspot.com

 

[dswill]

Would the d-d cross section graph be the same for magnetic confinement as for inertial confinement? What about cold fusion? In fact I'm struggling a bit with the concept of cross-section. It doesn't seem to mean just the physical measurement of the area of a 'cross-section'. Correct?

It seems from some things I've been reading that the cross-section is dependent on the process, or derived from the experimental reaction rate rather than the physical dimensions of the deuteron. (E.g. http://hyperphysics.phy-astr.gsu.edu/Hbase/nuclear/nucrea.html#c3; http://www.iupac.org/goldbook/R05169.pdf; http://fds.oup.com/www.oup.co.uk/pdf/0-19-856264-0.pdf at p.3)

DT fusion cross section peaks at ~60 KeV CM:

http://media.photobucket.com/image/...on6808/FusionCrossSections-grid-81pct-l-1.jpg

 

[Bob_for_short]

...In fact I'm struggling a bit with the concept of cross-section.

We speak of scattering cross sections or of reaction cross sections. It is not an atomic size squared. It is a process-dependent thing and is determined as a ratio of the reaction output within a certain solid angle to the incident particle (projectile) flux.

 

[Bob S]

Lawrence Berkeley Lab, in conjunction with Lawrence Livermore Lab, at one time built a rotating target neutron source (RTNS) that produced a 5 milliamp beam of deuterons at 400 KeV hitting a tritiated target.
RTNS rotating target 5 ma 399 KeV euerium
http://www.nuc.berkeley.edu/research/fusion/belgr1.pdf
see also
http://accelconf.web.cern.ch/accelconf/p79/PDF/PAC1979_3058.PDF

Bob S

 

[dswill]

So the cross-section of d-d would be different for a tokamak than for the NIF or cold fusion? I'd like to try to compare these. Does anyone know of good sources online or a primer of sorts? Or a source that explains why cross-section is not atomic radius squared? Thank you greatly.

We speak of scattering cross sections or of reaction cross sections. It is not an atomic size squared. It is a process-dependent thing and is determined as a ratio of the reaction output within a certain solid angle to the incident particle (projectile) flux.

 

[Bob S]

So the cross-section of d-d would be different for a tokamak than for the NIF or cold fusion? I'd like to try to compare these. Does anyone know of good sources online or a primer of sorts? Or a source that explains why cross-section is not atomic radius squared? Thank you greatly.

See Fig 1.4 on pdf page 6/9 in for cross section plots of D-D and D-T reactions.
http://www.tdr.cesca.es/TESIS_UPC/AVAILABLE/TDX-0114104-103202//05CAPITOL1.pdf
10^-28 m² is 10^-24 cm² = 1 barn is more than geometric for a proton (~ 60 millibarns).

(It is very difficult to find appropriate physics papers that are not pay per view)

Bob S

 

[Astronuc]

So the cross-section of d-d would be different for a tokamak than for the NIF or cold fusion? I'd like to try to compare these. Does anyone know of good sources online or a primer of sorts? Or a source that explains why cross-section is not atomic radius squared? Thank you greatly.

One would have to compute the temperatures of the d-d plasma under NIF or cold fusion conditions.

One thought on cold fusion was that the palladium atoms, or rather the electron field around the palladium nucleus, somehow allowed the deutrons to approach each other so that the fusion reaction could occur at lower temperature.

 

[mheslep]

http://books.google.com/books?id=7k...age&q=deuterium coulomb cross section&f=true"

The fusion scheme described by the OP is typically called beam-beam or accelerator based fusion. These approaches can produce fusion, but they are hopelessly inefficient. The problem is that the coulomb (or Rutherford) scattering cross section is 1000x, maybe 10000x greater than the fusion cross section for a given beam/plasma energy, as indicated in Figure 11.3 of the reference. This means for every collision that succeeds in producing fusion, another 1000 will 'bounce' away. These bounced ions have begun to 'thermalize', or trend towards the average energy (temperature) of all the particles in the system, at which point we no longer have a beam with which to smash into something.

Say the beam energy per ion is 50 keV, well up towards the sweet spot for D+T fusion cross sections. Then every successful D+T fusion releases 17 meV, but on average it required ~1000 x 50keV, or 50meV to be wasted.

 

[dswill]

That's what I suspected. What I'm looking for is a book or article to help me study those calculations for cross sections specifically for cold fusion or beam-target studies (perhaps focusing on Oppenheimer-Phillips or electron screening). But I don't have access to college libraries or online pay journals, only the NY public library. I guess I should first ask what physics journals are available online and then search those myself?

One would have to compute the temperatures of the d-d plasma under NIF or cold fusion conditions.

One thought on cold fusion was that the palladium atoms, or rather the electron field around the palladium nucleus, somehow allowed the deutrons to approach each other so that the fusion reaction could occur at lower temperature.

http://books.google.com/books?id=7k...age&q=deuterium coulomb cross section&f=true" * * *

 

[mheslep]

That's what I suspected. What I'm looking for is a book or article to help me study those calculations for cross sections specifically for cold fusion or beam-target studies (perhaps focusing on Oppenheimer-Phillips or electron screening). But I don't have access to college libraries or online pay journals, only the NY public library. I guess I should first ask what physics journals are available online and then search those myself?

Tom Dolan's University of Illinois 421 class:
http://npre421.ne.uiuc.edu/

MIT also has their undergrad physics curriculum online.

 

[timbot]

http://books.google.com/books?id=7k...age&q=deuterium coulomb cross section&f=true"

The fusion scheme described by the OP is typically called beam-beam or accelerator based fusion. These approaches can produce fusion, but they are hopelessly inefficient. The problem is that the coulomb (or Rutherford) scattering cross section is 1000x, maybe 10000x greater than the fusion cross section for a given beam/plasma energy, as indicated in Figure 11.3 of the reference. This means for every collision that succeeds in producing fusion, another 1000 will 'bounce' away. These bounced ions have begun to 'thermalize', or trend towards the average energy (temperature) of all the particles in the system, at which point we no longer have a beam with which to smash into something.

Say the beam energy per ion is 50 keV, well up towards the sweet spot for D+T fusion cross sections. Then every successful D+T fusion releases 17 meV, but on average it required ~1000 x 50keV, or 50meV to be wasted.

I have noted the comments of 'mhslep' above. Mhslep says that beam-beam based fusion is hopelessly inefficient because every collision that succeeds in producing fusion, another 1000 will 'bounce' away.

It appears that the basis of this misunderstanding is the use of the term 'beam-beam'. Obviously in the past physicists have been used to only beam collision experiments and this has constrained their thinking.

What I am talking about is the collision of dense plasmas. If this happens, even if only one in 1000 collisions succeed in producing fusion, you will still succeed in producing usable fusion.

Now the core of the hslep's argument is in his second pargraph. Yes, D+T fusion appears to be hopelessly inefficient according to these calculations. Deuterium needs to be accelerated to very high velocities to achieve fusion.

However Hydrogen has a coulomb barrier of of one thirtieth of Deuterium, I believe. So the beam energy per ion required is one thirtieth of 50 kev, or 1.6 kev. Massively smaller. The energy output tips in favour of hydrogen collisions.

Yes, the hydrogen fusion reaction is a p + p reaction, and this requires several steps to complete the fusion process. [reference to personal theory deleted]

So a step by step fusion reaction dies out under low plasma densities because of the improbability of collision of the various required particles. However you can increase the probababilty of a sustained hydrogen fusion reaction if you increase the density of the plasma. INCREASING THE DENSITY OF THE PLASMA IS THE KEY TO THE FUSION OF HYDROGEN.

And this is why those experiments fixated on low density particle beams got nowhere. (Indeed Tockamacs cannot sustain very high densites for a useful period of time).

However high density head-on hydrogen plasma beams will fuse! High density plasma beams supplying the plasma density which exists at the centre of the sun are certainly feasible. And this can produce continuous energy output.

[reference to personal theory deleted]

 

[mheslep]

...

However Hydrogen has a coulomb barrier of of one thirtieth of Deuterium, I believe. So the beam energy per ion required is one thirtieth of 50 kev, or 1.6 kev. Massively smaller. The energy output tips in favour of hydrogen collisions.

No, see the definition of the coulomb barrier here
http://en.wikipedia.org/wiki/Coulomb_barrier
The energy barrier depends on charge and distance, not mass, so protons and deuterium have the same coulomb barrier at a given distance. The fusion cross section, i.e., the likelihood of fusion given an encounter, depends on other factors besides besides this barrier, and it turns out proton-proton fusion is dramatically less likely to occur at a given energy level than is d-d or d-t fusion.

However you can increase the probababilty of a sustained hydrogen fusion reaction if you increase the density of the plasma. [...]

Yes, that's true. But the the 1000:1 ratio given above does not depend on density. As the fusion rate goes up with density, so does the scattering loss.

 

[Vanadium 50]

I have removed the references to personal theories here. Please, let's try and keep this within PF guidelines.

Timbot, your argument that Tokamak scientists got it all wrong would be bolstered if you would devote more effort into studying what they have actually done. Or at least studied it enough to spell Tokamak correctly.

 

[Astronuc]

However Hydrogen has a coulomb barrier of of one thirtieth of Deuterium, I believe. So the beam energy per ion required is one thirtieth of 50 kev, or 1.6 kev. Massively smaller. The energy output tips in favour of hydrogen collisions.

Incorrect. A deutron and proton have the same charge. The Coloumb barrier is essentially the same - particularly at the atomic scale.

Yes, the hydrogen fusion reaction is a p + p reaction, and this requires several steps to complete the fusion process. [reference to personal theory deleted]

Yes - one can see this in the pp-cycle of stars.

So a step by step fusion reaction dies out under low plasma densities because of the improbability of collision of the various required particles. However you can increase the probababilty of a sustained hydrogen fusion reaction if you increase the density of the plasma. INCREASING THE DENSITY OF THE PLASMA IS THE KEY TO THE FUSION OF HYDROGEN.

Step by step processes occur in stars, e.g., the Sun where the core pressures are about 200-340 billion atmospheres. The best we can possibly do on Earth is about 70 atm in a confined magetic field. In the Suns core, the plasma density is about 150 grams per cubic centimeter, nearly 15 times the density of lead, and even with that, the probability of pp fusion is quite low.
Ref: http://www.nasa.gov/worldbook/sun_worldbook.html
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/procyc.html

And this is why those experiments fixated on low density particle beams got nowhere. (Indeed Tockamacs cannot sustain very high densites for a useful period of time).

However high density head-on hydrogen plasma beams will fuse! High density plasma beams supplying the plasma density which exists at the centre of the sun are certainly feasible. And this can produce continuous energy output.

Quite incorrect, and technically unfeasible!

 

[timbot]

OK. However given what is now the immediate necessity of finding a way to create usable hydrogen fusion, I would have thought it is worth a try. Tokamacs (see I have spelt it right!) have not worked, and without wanting to sound nasty, have over the past 50 years provided little more than a pension to the participants. And building bigger ones will fare no better.

With all due respect to these obviously knowledgeable physicists, proving something 'mathematically' that it will not work is falling into the same trap as Lord Kelvin, who proved mathematically that the sun will expire in one million years and mechanical flight was impossible. What is needed now is experiment to see if there is something in this idea, as all alternatives have proved a dead end. On the density issue, I am pretty sure that if you accelerate the plasma at a high enough rate, you will momentarily achieve half the density required for fusion. (Remember you are talking about a head-on collision).

 

[Astronuc]

OK. However given what is now the immediate necessity of finding a way to create usable hydrogen fusion, I would have thought it is worth a try. Tokamacs (see I have spelt it right!) have not worked, and without wanting to sound nasty, have over the past 50 years provided little more than a pension to the participants. And building bigger ones will fare no better.

With all due respect to these obviously knowledgeable physicists, proving something 'mathematically' that it will not work is falling into the same trap as Lord Kelvin, who proved mathematically that the sun will expire in one million years and mechanical flight was impossible. What is needed now is experiment to see if there is something in this idea, as all alternatives have proved a dead end. On the density issue, I am pretty sure that if you accelerate the plasma at a high enough rate, you will momentarily achieve half the density required for fusion. (Remember you are talking about a head-on collision).

One cannot direct individual particles in a beam with dead-on accuracy for a head-on collision. One is inherently constrained by the physics of particle collision and the technical constraints of the materials with which one has at hand.

The physics
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/impar.html#c1

The technical contraints relate to the maximum pressure one can achieve with the maximum magnetic field or the material strength of the magnet/supporting structure, whichever is limiting.

Even under the most ideal conditions in the sun - which we cannot reproduce by any man made object (while we can accelerate protons to necessary energy (100 keV), but we cannot reproduce the particle densities of the sun) - protons cannot exist for something like millions of years and not fuse by p-p, which is the rate limiting step in the pp-chain.

 

[mheslep]

With all due respect to these obviously knowledgeable physicists,

To be clear I am not a physicist, I'm an electrical engineer by training.

 

[timbot]

I apologize to everyone for my outburst.

However I feel that if an experiment is conducted to collide dense plasmas (not beams), I am sure that fusion will be detected at even quite low velocities i.e. gamma rays etc. The question is, as you increase the speed of collision will the rate of fusion increase faster than the speed? If so, all this stuff about "cross-sections" will have neglected some very important points.

Given the importance of the subject, and yes, the complete failure of the Tokamacs for all practical purposes, (except maybe some experimental results), I strongly suggest that experiments should be conducted along the lines proposed.

A final warning. This site is US of A centric. But I am not from the USA. Other readers, such as the Chinese, are on to this site also. Somebody (some country) is going to get in first. Now I personally would have no objection. The result would benefit the world. But this result would be egg on the face of the Lawrence Livermore labs, Los Alamos, Chicago, etc. Wouldn't it?

 

[takeTwo]

Maybe this has already been discussed. I have read the thread, but it didn't stand out. It is fairly easy to fuse some fraction of the fuel in two beams. But all current designs for either magnetic confinement fusion energy (MFE) or inertial confinement fusion (ICF) ask that the fusion products be used to help burn some more of the fuel. For D-T, the "alpha" particles (He ions) must not escape so fast that they don't contribute to the heating of the fuel. If they can be contained, then the fusion burn will be efficient. For ICF, the alphas must heat the unburned fuel prior to escaping the small, compressed pellet (stopping power = compressed-density * radius > x grams/cm^2, x ~ 5-10). Similar for MFE. The alphas heat the plasma faster than the total heat loss, be it via particles or radiation. I've forgotten the details, but think of density*temperature as proportional the probability per unit time that fusion will occur. Add confinement time (for the heat); density*temperature*time. This then is proportional to the fraction of fuel that will burn; i.e. efficiency.

Both approaches have produced fusion energy, but neither has yet met the so-called Lawson criterion which deals with the requirement that the energy deposition of the (initial) fusion products either substantially completes the burn (ICF) or sustains the burn (substains the required plasma temperature) for literally many seconds (MFE).

see. http://en.wikipedia.org/wiki/Lawson_criterion

For beams, I would guess that the problem is in recycling the un-burnt fuel back to a chamber that can extract the heat for boiling water. Somebody mentioned that these beams should be neutral, and probably so if the current is high. So, how does one recycle these beams such that the collision point occurs in an (expensive) central piece of a power plant... where the "heat" is used to boil water?

By the way, word has it that NIF will achieve scientific break-even earlier than expected, perhaps by mid 2010.

 

[mheslep]

...
By the way, word has it that NIF will achieve scientific break-even earlier than expected, perhaps by mid 2010.

Well good luck to them, but given NIF has not fired the first full power shot at a live target yet, and the efficiency of the lasers and optics, I can't see such a claim as anything but the loosest of hand waving.

 

[mheslep]

For beams, I would guess that the problem is in recycling the un-burnt fuel back to a chamber that can extract the heat for boiling water. Somebody mentioned that these beams should be neutral, and probably so if the current is high. So, how does one recycle these beams such that the collision point occurs in an (expensive) central piece of a power plant... where the "heat" is used to boil water?

Yes, but the problem is that the 'recirculating power', the power to hurd the un-burnt fuel, has been shown via standard thermodynamic heat cycle analysis to be 5x to 50x times the fusion power.
See, e.g., slide 16 here:
http://www.fusor.net/board/getfile.php?bn=fusor_future&att_id=3718

 

[timbot]

Everyone is fixated (naturally enough) on existing designs, whether Tokamacs. pellets etc.

What is need is a simple and effective alternative.

While I have described my design elsewhere, conceptually it is very simple.

Imagine two hydrogen plasmas directed at high speed at each other head on. Fusion occurs where they collide. A third gas, helium, water vapour, oxygen, is directed at the intersection of the plasmas. This absorbs the energy created by the fusion. If the fusion energy exceeds the energy cost of generation there is a net advantage. The third intersecting gas stream can be directly used for electricity generation. No boiling of water is required.

That is the concept. Very simple. No major problems of physics are involved, as I am pretty certain that fusion will take place at even relatively slow speeds. There are of course engineering problems, but compared to Tokamacs, not major ones.

So there is the solution to fusion power generation. Simple. Effective. Practical. Why did not anybody think of it before? Well, I can't answer that.

 

[timbot]

Why am I pretty sure fusion will take place at relatively low speeds?

Because everyone has forgotten that central tenet of nuclear physics - the effect of quantum physics probabilities.

Even at relatively low plasma speeds a small amount of fusion will take place due to quantum effects. A minute proportion of the hydrogen or deuterium plasma will fuse. And in this situation quantum effects are your friend.

As fusion is the direct conversion of mass into energy, even small amounts of fusion release large quantities of energy.

So all you need to do is the raise the speed of the hydrogen or deuterium plasmas until a sufficient proportion of the plasma fuses and you obtain a net gain in energy production. As the proportion of the plasma which needs to be fused is very small so as to obtain a net gain in energy, the speed of the plasmas similarly needs to be relatively small.

What speeds? Well that is a matter for experiment. But as I said in a previous thread you are likely to detect fusion quite early, and its rate of increase relative to the speed of the plasma would give a good handle regarding when the reaction becomes sustainable.

PS I suggest for safety reasons that it is necessary to 'burn' the 'waste' hydrogen or deuterium by injecting a stream of oxygen at the point of collision. However when fusion starts occurring I suggest the extra heat be taken up by also injecting water vapor. The steam produced could be used to directly power turbines.

 

[takeTwo]

Well good luck to them, but given NIF has not fired the first full power shot at a live target yet, and the efficiency of the lasers and optics, I can't see such a claim as anything but the loosest of hand waving.

(I know this is a tiny bit off the original question, but I sense a bit of doubt towards the potential of "traditional" approaches to fusion in this thread. Fusion is a passion of mine (along with lasers) so I offer my learning, thoughts and opinions to the Physics Forum regarding what seems to be a truly historical moment coming within the next year).

Correct. "Full power" and "live target"; not together (yet). There are good reasons for this. (a) The laser is still being commissioned and this is going well. They are shooting targets with almost 0.9 MJ at 1/3 micron wavelength. They will be close to 1.2-1.4 MJ very soon. 1.8 MJ is the design energy, but this must be approached slowly. The source and type of damage to the optics is an active topic or research at NIF as it was for Livermore's 60 year history. (b) The fact that they are in a startup phase (doing physics experiments to understand what will happen, not attempting world records for neutrons) and people will have to access the target chamber, they are purposely keeping all hazards to a minimum. For example, the hohlraum (the "container" for the x-rays that actually implode the pellet) is gold rather than depleted uranium. The outer shell of the pellet (the rocket) is plastic doped with Ge rather than Be. A weak DD mix in the fuel is used for diagnostics rather than full-on DT, etc.

Nevertheless, the x-rays in the hohlraum that implode the capsule have a "radiation temperature" of nearly 290 eV now (a pleasant surprise, by the way) and they expect >300 eV with the higher laser-drive energy. This will cause the capsule to implode with sufficient velocity to achieve the high compression ratio (initial fuel radius over final fuel radius) of their design and thus a sufficiently high density of the assembled fuel.

If the converging shock waves in the core of the imploded pellet are timed correctly, then they expect a "spark" of fusion at the center. The density of the assemble fuel is sufficient to absorb some of the energy from the fusion alphas, further heating the fuel and, hopefully, achieve "scientific breakeven"; more fusion energy out than laser power in. The expected "target gain" of about 10 should occur in the next 6 months or so, even with the non-ideal (technician-friendly) fuel capsules and hohlraums and without the full 1.8 MJ (1.2 may be enough).

So where is the hand waving? Of course any press release on this project is glossing over potential problems. I would ask, can they get the shocks to converge and produce the spark? How can they know the density of the assembled fuel? Will the optics allow for a 30% increase in fluence?

But I'm an optimist. These folks at LLNL have never oversold themselves (unlike magnetic fusion) because (I believe) that the physics is relatively more tractable in ICF. The possibility that NIF will achieve breakeven (scientific, that is) at less-than-all-out conditions is a result of the 60 years of research (closer to 30 years if we start with Shiva) on the same damn thing. This can't be said for tokamaks. There, the physics seems to change from machine to machine in a way. With aspect ratio, with heating method, with field geometry, etc.

As far as efficiency and high rep rate goes, this is not going unnoticed. The efficiency of NIF-scale lasers can be improved 10-50 times. The Europeans are working on a concept called HiPER to put all the pieces together for a demonstration ICF plant with "engineering breakeven"; enough electrical power produced to run the facility while still supplying power to the grid. See the video at http://physicsworld.com/blog/2009/12/laser_fusion_gets_hiperactive.html

 

[Vanadium 50]

With all due respect to these obviously knowledgeable physicists, proving something 'mathematically' that it will not work is falling into the same trap as Lord Kelvin, who proved mathematically that the sun will expire in one million years

Timbot, like I said before, it helps to do some research up-front. (You still can't even spell "Tokamak" correctly - despite being corrected). Kelvin was not the idiot that you take him for. He was absolutely correct that processes known in his day could not keep the sun burning long enough to explain the age of features on the earth, and correctly concluded that there needed to be some other energy source. He even went as far as to propose one - meteoric impacts on the solar surface. He then calculated the rate of impacts necessary and then - again correctly - concluded that the present rate of impacts was too small, and for his idea to work, there needs to be periods of much higher rates.

In short, you got it wrong, and Kelvin knew far more about the subject than you think.

Thus far, the only evidence you have given for your outlandfish claims is that "I am sure" and "everyone has forgotten that central tenet of nuclear physics ". It's time for you to put forward some real evidence for your position.

 

[mheslep]

So where is the hand waving?

Here,

...
By the way, word has it that NIF will achieve scientific break-even earlier than expected, perhaps by mid 2010.

here,

But I'm an optimist. These folks at LLNL have never oversold themselves

and here

The efficiency of NIF-scale lasers can be improved 10-50 times. The Europeans are working on a concept

highlights mine

 

[takeTwo]

So where is the hand waving? (quoting myself)

.

The list below is the hand waving regarding the physics and technology issues that worry me, again quoting from myself.

Of course any press release on this project is glossing over potential problems. I would ask, can they get the shocks to converge and produce the spark? How can they know the density of the assembled fuel? Will the optics allow for a 30% increase in fluence?

mheslep; you have picked some more "hand waving" inherent in my two posts. I don't disagree with anything you pointed out. But those seem to me to be more political than, for example, the three physics/technology concerns I have expressed. Indeed, the (newly) bolded text above regarding press releases applies to the politics, too. Am I being duped. Not on everything. I've followed this since 1977 and I feel that my "learning, thoughts and opinions" are more grounded now than ever--for NIF.

The future is less clear. Will the Europeans actually build a MJ, 5 Hz laser with ~ 40% efficiency in the next 20-30 years? Pure politics. I can be done. If they do, can they load a target with microns accuracy at 5 Hz in such an environment? Maybe. Requires many future inventions. And so on.

Yet, I still urge this forum to be prepared for "a truly historical moment coming within the next year", at NIF! Apart from the implications on the Nuclear Test Ban Treaty, I believe it will spark other countries to take a more positive look at fusion as a *viable* future energy source.

 

[Astronuc]

Everyone is fixated (naturally enough) on existing designs, whether Tokamacs. pellets etc.

What is need is a simple and effective alternative.

While I have described my design elsewhere, conceptually it is very simple.

Imagine two hydrogen plasmas directed at high speed at each other head on. Fusion occurs where they collide. A third gas, helium, water vapour, oxygen, is directed at the intersection of the plasmas. This absorbs the energy created by the fusion. If the fusion energy exceeds the energy cost of generation there is a net advantage. The third intersecting gas stream can be directly used for electricity generation. No boiling of water is required.

That is the concept. Very simple. No major problems of physics are involved, as I am pretty certain that fusion will take place at even relatively slow speeds. There are of course engineering problems, but compared to Tokamacs, not major ones.

So there is the solution to fusion power generation. Simple. Effective. Practical. Why did not anybody think of it before? Well, I can't answer that.

This idea is not effective or practical. It simply will not work. One has ignored the fact that particle beams and fusion plasmas operate in what is essentially a vacuum. Plasma particle densities are on the order of 10¹⁴ particles/cc or 10²⁰ particles/m³, and even with these low densities, the plasma pressure at optimal ignition temperature reaches a limit for magnetic confinement systems.

A gas such as gas, helium, water vapour, oxygen, would quench the plasma formed by colliding beams. A third gas would scatter beams, not to mention flood the vacuum chamber. One hasn't described the thermodynamic cycle or system to generate electricity.

Furthermore, one seems to have ignored matters like the fact a beam of ions (nuclei) would diverge if fully ionized.

With respect to:

as I am pretty certain that fusion will take place at even relatively slow speeds.

on what basis does one make such a claim?

This?

Because everyone has forgotten that central tenet of nuclear physics - the effect of quantum physics probabilities.

Even at relatively low plasma speeds a small amount of fusion will take place due to quantum effects. A minute proportion of the hydrogen or deuterium plasma will fuse. And in this situation quantum effects are your friend.

One is quite incorrect! We are well familiar with the process, and the scientists and engineers in fusion research haven't forgotten their fundamentals. The problem so far is the 'minute' fusion energy production is a small fraction of the energy input to establish the conditions for fusion.

 

[timbot]

The two issues discussed together in the above thread are:
1. the engineering
2. the physics.

On the issue of 'flooding' the device, there will of course be an exit to a turbine for the heated vapor to generate electicity. The question whether 'excess' vapor will interfere with the fusion reaction is a matter for experiment. I say it will not, because due to the device's design, the fusion will take place before the contact with the extraneousness vapor takes place. You dispute that? Well, try it and see.

On the issue of the physics, 'it won't work', due to various calculations and the interference of the vapor, I can only suggest again, 'try it and see'. On a previous thread regarding Lord Kelvin's work, the respondent seems to have lost the basic point, that Lord Kelvin was wrong because his ASSUMPTIONS were wrong. I do not criticize the mathematical ability of Lord Kelvin, but that the (wrong) mathematical results depended directly on the assumptions made.

Now calculations based implicitly on experiments with beams, Tokamaks (see I got the spelling right this time), and current experiments, have implicit assumptions (such as vacuum, attenuated beams, and stationary plasma) which are often not taken into account explicitly. 'The physics works because it has always worked' is not necessarily true. There is no reason that you MUST have these pre-conditions (especially as these experiments are not successful in producing useful fusion).

I am just pointing out (repeatedly) that given the very strong need for useful nuclear fusion, and the very limited success achieved so far, it is worthwhile to conduct one or more experiments along the lines I have suggested above. In the end, scientific advance is based on experiment, not on mathematical 'proofs', and it is very worthwhile conducting these experiments as the potential cost-benefit ratio of the suggested experiments are very high.

 

[Vanadium 50]

You dispute that? Well, try it and see.

That's not how science works. You made the claim, you need to be the one to back it up.

On a previous thread regarding Lord Kelvin's work, the respondent seems to have lost the basic point, that Lord Kelvin was wrong because his ASSUMPTIONS were wrong.

No, the point is that your scholarship was sloppy and Kelvin did not make the claim that you said he did.

 

[takeTwo]

As per a previous thread, if you fire two plasma jets of deuterium at each other at high enough relative velocity, the deuterons would collide and fuse into helium.

Does anyone know what is the relative velocity in kilometers per hour necessary for deuterons hitting each other head on to fuse into helium?

How is this calculated?

I am sure this has been considered. I did a google search ["neutral beams" head on fusion] and found the following Invention (1981, I think). The inventor mentions the problems with head-on collisions leading to de-confinement (see end of this post), but found a way around this (he claims) by letting the D and T go in the same direction in a "racetrack" accelerator/storage ring. With the same momentum, D goes faster than T. So, it is a "overtake collision" rather than head-on.

The relative velocity needed is 4 x 10^8 cm/sec.

Abstract and link follow.

From the Abstract of the Invention:
This invention discloses apparatus and methods to produce nuclear fusion utilizing fusible material in the form of high energy ion beams confined in magnetic fields. For example, beams of deuterons and tritons are injected in the same direction relative to the machine axis, but the deuteron velocity is sufficiently greater than the triton velocity so that the deuterons overtake the tritons at a relative velocity which produces a high fusion reaction cross section. The momentum of the deuterons is approximately equal to the momentum of the tritons so that both types of ions follow essentially the same path. Thus, the deuteron and triton beams, together with electrons for space charge neutralization, constitute a "moving-plasma", in which fusion reactions occur. Various alternative magnetic field configurations are described for confinement of the high energy ion beams. Methods are given for the starting and steady state operation of the invention, based on change-of charge-state trapping of injected material.

http://www.google.com/patents?id=m_MyAAAAEBAJ&zoom=4&dq=%22neutral%20beams%22%20head%20on%20fusion&pg=PA1#v=onepage&q=&f=false

Regarding head on, the inventor says...
In fusion literature to date, the concept of "colliding beams" has been based on configurations such that the beams are oppositely directed, causing "head-on" collisions. Claims have been published that for such oppositely-directed beams, Coulomb collisions (i.e., the interaction of two ions having the same sign of electric charge) would cause loss of beam particles and loss of beam energy (carried by the ions) before appreciable nuclear fusion reactions would occur. However, the concepts that are disclosed in this patent application are new, and are not subject to the limitations ascribed to "head-on" colliding beams.

 

[mheslep]

...

Regarding head on, the inventor says...
In fusion literature to date, the concept of "colliding beams" has been based on configurations such that the beams are oppositely directed, causing "head-on" collisions. Claims have been published that for such oppositely-directed beams, Coulomb collisions (i.e., the interaction of two ions having the same sign of electric charge) would cause loss of beam particles and loss of beam energy (carried by the ions) before appreciable nuclear fusion reactions would occur. However, the concepts that are disclosed in this patent application are new, and are not subject to the limitations ascribed to "head-on" colliding beams.

I fail to see how this matters. All this idea does is change to a moving reference frame. It doesn't change the fusion cross section to collision cross section ratio.

 

[timbot]

Beams. Beams. Yes I have read some of these similar claims myself. Colliding beams have not worked. Stationary plasmas (Tokamaks) have not worked. Plasma impacted pellets have not worked.

Yes, with all three, you do get momentary fusion. But there is no practical method of extracting continuous power.

Colliding plasmas are different from beams, because of the sheer quantity of the atoms colliding. Yes you get all these inefficiencies, but you do get continuous fusion. And that is what you need, and even a small amount of fusion releases a tremendous amount of energy. Continuously.

 

[Orion1]

Timbot, I recommend studying fusion cross sections and collision cross sections and the concept of particle scattering and also the Lawson criterion.

In nuclear and particle physics, the concept of a cross section is used to express the likelihood of interaction between particles.

Also, none of your references cite a published scientific paper regarding your topic.
[/Color]
Reference:
http://en.wikipedia.org/wiki/Cross_section_%28physics%29"
http://en.wikipedia.org/wiki/Lawson_criterion"
http://en.wikipedia.org/wiki/Nuclear_fusion"