Nuclear fusion using a plasma jet

[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.

Reference:
http://en.wikipedia.org/wiki/Cross_section_%28physics%29"
http://en.wikipedia.org/wiki/Lawson_criterion"
http://en.wikipedia.org/wiki/Nuclear_fusion"