Whats the holdup with Fusion Power?

[Dropout]

You got temperature and/or pressure, and one simple atom to play with. What's the big deal?

 

[MaWM]

Unfortunately, it takes many many atoms to produce useful amounts of energy. Now you have a volume of superheated plasma. Now the problems begin.

 

[Astronuc]

You got temperature and/or pressure, and one simple atom to play with. What's the big deal?

As MaWM indicated it's many ionized atoms (free nuclei and electrons) magnetically confined in a plasma. The plasma is loosing energy very rapidly due to phenomena like brehmsstrahlung and cyclotron radiation, while nuclei scatter more often than they fuse.

The plasma densities are on the order of 10¹⁴ (nuclei and electrons)/cm³. The densities are limited by pressure which is constrained by the achievable magnetic fields and strength of the structure supporting the magnets.

 

[Morbius]

You got temperature and/or pressure, and one simple atom to play with. What's the big deal?

Dropout,

"You got temperature and/or pressure". Unfortunately you need BOTH simultaneously, AND for
a long enough time.

Additionally, as was pointed out; you have to do this for a LOT of atoms. When you try to do that -
you get some very wicked instabilities that wreak havoc with your attempts at fusion.

As Astronuc pointed out, the densities that have been realized so far within the constraints of present
magnetic confinement technology are on the order of 10¹⁴ atoms per cc.

In any other field - something with that density would be considered a very good VACUUM!

Controlled thermonuclear fusion is NOT an easy problem to solve AT ALL

Dr. Gregory Greenman
Physicist

 

[D H]

You got temperature and/or pressure, and one simple atom to play with. What's the big deal?

You can say just about the same for any complex and hard-to-solve technical or social challenge we as a society confront. Example: What's the holdup with solar energy? You got photons streaming in for free and lots of ways of harnessing them. What's the big deal?

What you did in your initial post was to trivialize the problem by whitewashing over all of the huge challenges noted by Astronuc and Morbius.

 

[mheslep]

"..., AND for a long enough time.

Confinement time ala Larsen would apply to confinement approaches, inertial or magnetic. Confinement time does not seem to apply to any of the several beam - beam approaches (e.g. IEC). That is, there's no intention to do ignition; they are purely 'driven' schemes. - Not that IEC has shown any possibility of power production

 

[Morbius]

Confinement time does not seem to apply to any of the several beam - beam approaches (e.g. IEC). That is, there's no intention to do ignition; they are purely 'driven' schemes.

mheslep,

The designs for the NIF - the National Ignition Facility are intended to "do ignition".

LLNL has developed the "Fast Ignitor" concept, and it is also being explored by
the University of Rochester on the Omega laser:

http://fusion-energy.llnl.gov/ife/llnl_papers/236640.pdf

http://www.llnl.gov/str/Petawatt.html

http://www.lle.rochester.edu/pub/conferences/APS02/MeyerhoferAPS02.pdf

http://library.thinkquest.org/17940/texts/inertial_confinement/inertial_confinement.html

http://www-ferp.ucsd.edu/FPA/ARC00/fpn00-16.shtml

Dr. Gregory Greenman
Physicist

 

[malawi_glenn]

Dropout:

As they have pointed out here, we have big difficulties with making enoguh nucleis fusion in order to gain energy.

It is a HUGE difference between fusing 2 protons in a collider, and having 10^30 confined in a quite small region and trying to both make them fusion, continue to fusion and also to extract the energy from there.

I hope you understand this.

 

[mheslep]

mheslep,

The designs for the NIF - the National Ignition Facility are intended to "do ignition".

Yes, certainly. I meant IEC does not require ignition for net power, though it has many other problems.

 

[JeffKoch]

The designs for the NIF - the National Ignition Facility are intended to "do ignition"

Yes, but it's hard to imagine making a practical fusion reactor with ICF, in large part because of the required repetition rate. Ignition may be achieved at NIF (that alone will be extremely challenging), but those target shots will be at best once every couple weeks - that's a very long way from firing it at 5-10 Hz, which is what you want for a practical reactor. If you scale up the energy you can get away with less-frequent bursts of energy, but that's going in the direction of a nuclear bomb, not a reactor.

Maybe these problems will eventually be solved, but probably not in our lifetimes. Doesn't mean we shouldn't work on them, but anyone looking for a quick solution to fusion energy production will be disappointed.

 

[Morbius]

Yes, but it's hard to imagine making a practical fusion reactor with ICF, in large part because of the required repetition rate.
Maybe these problems will eventually be solved, but probably not in our lifetimes.

Jeff,

We're ALREADY working on the reactor designs!

There are MANY designs ALREADY on the drawing boards.

Nuclear designers can do an awful lot of work while they are waiting for the laser to be built.

You don't have to do the designs in the order you envision. You can do A LOT of the design
work even before you have the proof of principle. We know what the output product of a successful
fusion reaction is - so you can take the design from there. You don't have to wait for the proof
of principle shot.

Dr. Gregory Greenman
Physicist

 

[JeffKoch]

Yes, I know people are thinking about reactors - there are some interesting concepts, and some interesting work going on for example at General Atomics. But it's not just the laser (firing multimegajoule shots at 10 Hz from hundreds of separate beams, each with very fine tolerances on timing, pulse shaping, pointing, etc.), it's the stream of targets - all currently conceived (even with fast ignition) as having more-or-less beautifully smooth DT ice layers that take a day to craft, and are extremely difficult to adequately characterize. They have to be fired somehow into the reactor at 10 Hz, aimed with micron precision over meter distances, in a manner that doesn't ruin the ice.

And at this point we don't really even understand the requirements on an ignitable target, all we have are simulation predictions that (based on long history) will almost certainly turn out to be wrong in significant ways, and we'll have to sort out how to do it properly by performing many experiments. We may learn, for example, that we really need 5-10 times more laser energy, reducing the rep-rate requirements but making much bigger individual bangs that will have a significant impact on reactor designs.

I'm not pessimistic in the long term, clever people can figure these things out given enough time and money, but it certainly won't happen soon.

 

[Morbius]

Yes, I know people are thinking about reactors - there are some interesting concepts, They have to be fired somehow into the reactor at 10 Hz, aimed with micron precision over meter distances, in a manner that doesn't ruin the ice.

Jeff,

ALL of your concerns HAVE been addressed. Those involved have been designing and testing such devices. After all, you don't have to
wait for a shot to reach ignition before you design, test, and certify equipment that can position tartgets with the required precision at 10 Hz.
[ I believe current designs may go to 20 Hz ].

And at this point we don't really even understand the requirements on an ignitable target, all we have are simulation predictions that (based on long history) will almost certainly turn out to be wrong in significant ways.

You are wrong again here. We DO understand - not just in simulations - but from experiment what
the requirements of an ignitable target are. We used the one driver that we KNOW works:

http://www.princeton.edu/~globsec/publications/pdf/1_3-4Fenstermacher.pdf

Courtesy of Princeton University; read the following on page 198:

"However, in its FY 1987 report, the House Science and Technology Committee disclosed that
explosions at the Nevada Test Site have provided data for the laser fusion program. In a program
called Centurion-Halite, the intense radiation from undergound nuclear explosions have apparently
been used in attempts to ignite ICF targets, ultimately to help design pellets that could be ignited
with currently available drivers, thus circumventing the need for the next-generation short-pulse
laser at a price of almost one billion dollars"

As the above indicates; there was no need to build another experimental laser bigger than Nova in
order to find out what conditions were necessary for ignition. This allowed the program to skip
building another experimental laser that could not reach ignition - and jump directly to the scale of
the NIF - National Ignition Facility.

That's why NIF is called the National Ignition Facility; because it was designed knowing
what conditions it needed to produce.

Dr. Gregory Greenman
Physicist

 

[JeffKoch]

ALL of your concerns HAVE been addressed.

I assure you that they have not been. Particularly the target problem, which I am intimately involved with. We struggle to make one suitable target, and there is no one working in the field, knowledgeable about the process, who is seriously thinking about making them at 10 Hz - there are only wild, utterly untested concepts from outsiders. Fast ignition might relax some of the target constraints, but that's a concept in it's infancy - we don't even know yet how we'll deliver the spark energy to the implosion.

You are wrong again here. We DO understand - not just in simulations - but from experiment what the requirements of an ignitable target are.

You sound like a designer. This is very naive, because Halite/Centurion experiments used a multi-terrajoule driver (a bomb), not a megajoule laser - you can afford to be sloppy when you have so much energy available. There were other very key target differences, perhaps (?) you are aware of them. Those experiments demonstrated the basic concept, but cannot tell us whether or not NIF will succeed at it's mission - or how our concept of an ignitable target will evolve as we learn more. We know how to ignite a target with terrajoules, but not with megajoules except through simulations - and long experience shows that every time we make a leap forward, we discover how much important physics is missing from the simulations.

One key uncertainty that was never addressed with Halite/Centurion is laser-plasma interactions, which scatter laser light out of the target, drive plasma waves that create preheating electrons, steer beams away from their aim points, and cross-couple energy, degrading symmetry. We are very unsure what will happen in a NIF ignition target, and this uncertainty drives a large part of the uncertainty in what an ignitable target looks like for NIF - if it's worse than we think, we'll have to use more laser energy to drive a larger target with less power, but that tradeoff only goes so far (unless you're driving things with a nuclear bomb). At some point you run out of available laser energy. You can win some of it back by going to longer laser wavelengths (second harmonic vs. third, you can run with more energy because final optics damage is less severe), but that will make the laser-plasma problem worse (things tend to scale as intensity*wavelength^2).

Another uncertainty is 3D plasma hydrodynamics. 3D simulations are very slow and expensive even on the fastest modern computers, so essentially all target design requirements are based on 2D simulations. These miss inherently 3D effects, and are themselves based on physics that is known to be incomplete, for example in the treatment of radiation transport and high-mode instability growth.

A good review of the program from two years ago, discussing these issues and many more, is here: http://www.fas.org/irp/agency/dod/jason/nif.pdf

I wouldn't be working in the field if I didn't think it was worthwhile, but people need to appreciate that it's difficult and uncertain, and commit to it over the long haul.

 

[Morbius]

You sound like a designer. This is very naive, because Halite/Centurion experiments used a multi-terrajoule driver (a bomb), not a megajoule laser - you can afford to be sloppy when you have so much energy available.

Jeff,

For Heaven's sake - use your BRAIN!

When you have more than enough energy - but you are interested in what can be done with lesser
amounts - you can throw a bunch of the excess energy away!

FYI - I'm NOT a designer - I'm a code developer.

Dr. Gregory Greenman
Physicist

 

[mheslep]

If you are citing the Federation of American Scientists website - then you are NOT on the
"cutting edge" of the technology like those of us who are actually developing the software
and designs. [ Besides that JASON report is nearly 3 years out of date. ]

From the referenced Jason's report:

...5. What is the prospect for achieving ignition in 2010?
First attempts to achieve ignition on NIF are likely to take place in 2010 — this is an
important and valuable goal that has strongly focused the efforts of the NIF Program. The
scientific and technical challenges in such a complex activity suggest that success in the
early attempts at ignition in 2010, while possible, is unlikely. ...

Care to comment? Did NIF implement any of the Jason report's recommendations?

 

[JeffKoch]

For Heaven's sake - use your BRAIN!

Between this and your mildly amusing private messages, I think I am done discussing this with you. I will point out, however, that having worked in ICF/NIF target experiments at LLNL for the last 15 years, and having attended the Jason review as well as having made some of the material that was presented, I've never heard of you. Perhaps if we run into each other sometime, we can discuss further over coffee.

 

[JeffKoch]

Did NIF implement any of the Jason report's recommendations?

Yes, many of them.

 

[JeffKoch]

If you are citing the Federation of American Scientists website - then you are NOT on the "cutting edge" of the technology like those of us who are actually developing the software and designs.

I missed this, it must have been edited out. I don't care about the FAS site, the link was to the Jason report. You appear to not know who I am, either.

 

[GTrax]

Does confinement of the 'Polywell' type for fusion have a future?

I have seen videos of attempts (from Google Tech Talk lectures). But, there are hundreds of 'videos', and I find it hard to separate the deluded and downright fraudulent from the genuinely feasible.

The work of the late Robert Bussard comes across to me as being the real deal.

I am less sure of the scheme promoted by Eric Lerner where he proposes a small pulsed device (340Hz or so) where the resulting intense ion beam energy is collected from a transformer device.

Here in UK we have had about 30 years of fine university minds working on Tokamak -type fusion devices at Culham (like JET Joint European Torus) and now there is to be a bigger effort in France (ITER). There seems no great impetus for any other scheme.

I would welcome some informed discussion on which schemes have substantial credibility in this community.

 

[Dropout]

Is the released electromagnetic radiation totally random? Like white noise. Or do Hydrogen atoms only emit certain photons, or wavelengths.

What happens when you combine an electromagnetic pulse of one half a wavelength of another electromagnetic pulse, would that create a photon?

 

[Astronuc]

Photons are electromagnetic radiation.

In a fusion reactor, recombination of electrons with protons would produce photons. In addition the interaction of electrons with the magnetic fields produces 'cyclotron' (radio-frequency, IIRC)) radiation (photons). The interaction of electrons with nuclei produces brehmsstrahlung radiation.

In the atom, photons are produced at specific (discrete) frequencies. Bremsstrahlung and cyclotron radiation are more continuous.

 

[GleefulNihilism]

All I'm going to say is that when the worse case scenario is the cleansing of all life on Earth in a massive firey wave of death when the atmosphere ignites I'll cut some slack and let them take their time.

 

[GTrax]

Er..no, not at all
First, accept that I am not in the league of some of the contributors here ..but ..
as I understand it, unlike fission, FUSION conditions are difficult to create and maintain. You don't get a meltdown, and you don't get an atmospheric ignition (which was a concern of Oppenheimer, Fermi and others when the first bang was being attempted)

If the slightest little thing breaks, it quits!

I suppose the land is full of secret experimenters (in addition to the frauds) who are hoping to make a plasma confined enough to increase the probability of actually colliding enough material into fusion. The stuff is largely empty space. Making enormous pulsed magnetic fields in structures designed to persuade these helical streams into a small place is what is spoken of.

It is not enough to persuade a few neutrons off , as proof of a reaction. There has to be whole galloping loads of them. The notion that one could make a line of 400Hz pulsing ion streams deliver up significant power directly via transformer structures sounds .. kind of difficult. Hence my original question. Is there any mileage in these schemes?

In this company, I would hate to found impressed by charletans!

 

[GleefulNihilism]

All I said was worse case scenario, I said nothing about how likely this scenario was- now did I?

Point still stands. If it has the potential to kill us all I'll allow them to take their sweet time.

 

[theCandyman]

But that's not the worst case scenario, I doubt it even close. It's taken thousands of man hours worth of work to try and get ignition, so it's more than obvious it won't happen spontaneously.

 

[GleefulNihilism]

I'm an astrophysicist. When someone talks to me about fusion the poet in me always pictures a tiny star in a lab somewhere, . . .

 

[Coin]

http://www.theoildrum.com/node/2164 It is kind of long but it is worth the effort. Basically there are several very serious engineering hurdles to making a fusion reactor that can be used to actually produce power. Even once you can sustain a plasma, some of the parts involved in actually getting energy out of that plasma present multi-decade engineering challenges all by themselves! There is also the problem that operating a fusion reactor consumes some unusual substances like tritium, so you have to engineer your reactor to for example create more tritium as it goes... there's a timetable they expect to resolve all these issues on, but it is not trivial. Worth a look...

 

[Astronuc]

http://www.theoildrum.com/node/2164 It is kind of long but it is worth the effort. Basically there are several very serious engineering hurdles to making a fusion reactor that can be used to actually produce power. Even once you can sustain a plasma, some of the parts involved in actually getting energy out of that plasma present multi-decade engineering challenges all by themselves! There is also the problem that operating a fusion reactor consumes some unusual substances like tritium, so you have to engineer your reactor to for example create more tritium as it goes... there's a timetable they expect to resolve all these issues on, but it is not trivial. Worth a look...

Thanks, Coin, that's a good article. Nice little summary of power input into ITER.

Power will be feed into the ITER plasma in three main ways: by transformer action causing up to 15 million amps to flow in the plasma; by neutral high energy beams of deuterium and tritium fired into the plasma; and by radio frequency energy fed in from antenna patches in the walls to excite resonances in the plasma, Transformer action is very efficient but necessarily pulsed. The other two forms of heating are less efficient but can be continuous. ITER is expected to generate 500MW of fusion energy output, with less than a tenth of that input power (Q>10) and hold that power for 400 seconds. Also it should generate 500MW output for an hour at an input of one fifth the input energy (Q>5). Although it is not stated as an aim, there is the hope that it might achieve what is called ignition where enough of the fusion energy remains in the plasma to keep the reaction going without the need of external input energy (Q = infinity). This will require higher plasma densities than needed with external energy input.

It would be desirable to have a continually operating plant. The power generation cycle is critical for a viable system, at least in todays environment.

Interestingly, it seems primarily based on DT reaction. The blankets and tritium generation/processing will add to the difficulties.

 

[gdp]

Confinement time ala Larsen would apply to confinement approaches, inertial or magnetic. Confinement time does not seem to apply to any of the several beam - beam approaches (e.g. http://en.wikipedia.org/wiki/Inertial_electrostatic_confinement" ). That is, there's no intention to do ignition; they are purely 'driven' schemes. - Not that IEC has shown any possibility of power production

Todd H. Rider investigated such systems from a very generic (e.g., Kinetic Theory and 2nd Law) viewpoint in his Ph. D. Thesis in Nuclear Engineering, http://dspace.mit.edu/handle/1721.1/11412"

His basic (and quite depressing) conclusions are as follows:

1.) "Nonthermal" or "nonequilibrium" plasmas (e.g. IEC, or "colliding beam" reactors such as "Migma") relax to "thermal" plasmas at a much faster rate than they undergo fusion reactions --- and the denser the plasma or beam is, the faster it relaxes. (This fact has been obscured in most IEC experiments because so far, the particles have been lost to the grids even faster than the thermalization timescale.)

2.) The 2nd Law of Thermodynamics implies that any attempt to maintain the beam or plasma in a "nonequilibrium" state will cost power --- and the further from equilibrium the system is maintained, the more power it will cost. Rider shows that under very general considerations, the additional power-gain from using a nonthermal plasma is always less than the power required to maintain the nonequilibrium state.

3.) Furthermore, from an economic standpoint, any generating system that has to "recycle" a large fraction of its generated power just to keep itself running is a money-loser. (This is already a problem for "conventional" fusion reactors unless "ignition" can be achieved --- in which case the power will be "recycled" internally to the reactor, rather than externally (i.e., by running it back from the power conversion systems to the beam-drive or plasma heating systems, with inevitable losses and inefficiencies along the way).

4.) Finally, the increased bremmstrahlung losses faced by "advanced" fuels make "breakeven" highly unlikely for nearly all of them. The only reactions that are likely to "break even" appear to be D+T, D+D, and D+He3; for all other known reactions, http://en.wikipedia.org/wiki/Nuclea..._losses_in_quasineutral.2C_isotropic_plasmas"

Furthermore, even D+He3 looks rather marginal, and pure D+D looks even worse. Despite D+D having a lower bremmstrahlung loss rate than D+He3 (bremmstrahlung loss rates scale as the mean of the squares of the nuclear charges), pure D+D has an even lower "gain" than D+He3, so that the ratio of bremmstrahlung loss rate to fusion power for D+D is much worse than D+He3, which in turn is much, much worse than for D+T. Under even the most optimist possible assumptions --- that power can be "recycled" at 100% efficiency (impossible!), and that the only loss mechanism is bremmstrahlung --- a "non-ignited" D+He3 reactor would have to "recycle" nearly 20% of its total generated power to make up for bremmstrahlung losses, and a pure D+D reactor over 1/3 of its total power, whereas a D+T reactor would only need to "recycle" a mere 0.75% of its total power. Factor in reasonable estimates of power-conversion, transfer, and beam-drive or heating efficiencies, and one finds that, even ignoring all other losses except bremmstrahlung and "power handling," absent "ignition," only D+T is likely to "break even." The loss rates for D+D and D+He3 are simply far too high to be practical --- let alone economically viable.

 

[Count Iblis]

http://news.bbc.co.uk/2/hi/science/nature/3336701.stm"

ITER was delayed because the participants couldn't agree on where to build it. When most were in favor of building it in France, the Iraq war started and the US didn't like that idea anymore:

The US has been against the French option because of France's opposition to the US-led invasion of Iraq.

What a way to make decisions on science and technology

 

[ZapperZ]

http://news.bbc.co.uk/2/hi/science/nature/3336701.stm"

ITER was delayed because the participants couldn't agree on where to build it. When most were in favor of building it in France, the Iraq war started and the US didn't like that idea anymore:



What a way to make decisions on science and technology

But this isn't a decision on "science and technology". They are not designating some scientific/technological result to be valid or not. Politics has always played a role in choosing a site from a selected list of candidates. No one isn't aware of such a thing.

Zz.

 

[Astronuc]

http://news.bbc.co.uk/2/hi/science/nature/3336701.stm"

ITER was delayed because the participants couldn't agree on where to build it. When most were in favor of building it in France, the Iraq war started and the US didn't like that idea anymore:


What a way to make decisions on science and technology

Come up with 10 billion euros, and one can put a fusion reactor anywhere one likes.

ITER construction costs are estimated at 4.57B€ (at 2000 prices), to be spread over about ten years. Estimated total operating costs over the expected operational lifetime of about twenty years are of a similar order.

http://europa.eu/rapid/pressReleasesAction.do?reference=MEMO/05/226

Science 13 June 2008:
http://www.sciencemag.org/cgi/content/summary/320/5882/1405

This month, funders of the €10 billion ITER fusion project, which seeks to demonstrate that a burning plasma can be controlled to produce useful energy, face the daunting task of keeping the project's budget under control, as scientists present a wish list of design changes.

Look what happened to the Superconducting Supercollider in Waxahachie, TX. They dug a $2 billion hole.

During the design and the first construction stage, a heated debate ensued about the high cost of the project. In 1987, Congress was told the project could be completed for $4.4 billion, but by 1993 the cost projection exceeded $12 billion.

http://en.wikipedia.org/wiki/Superconducting_Super_Collider#Cancellation

Detailed design and early construction work was proceeding on all major machine components. "The conventional construction for the first stage of the injection complex, consisting of the ion source and a linear accelerator stationed in a 250-meter tunnel, was complete." The first circular accelerator in the chain, the Low Energy Booster (LEB), consisting of a 600-meter circumference ring filled with resistive magnets, was designed and 90% of the tunnel complete. The next element in the sequence, the Medium Energy Booster (MEB), consisting of a ring of 4.0 kilometers in circumference, again using resistive magnet technology, was designed and excavation of the tunnel had started. The third and final accelerator before entering the large collider rings, the High Energy Booster (HEB), consisting of 10.8 kilometer circumference tunnel filled with superconducting magnets, was under design. Finally, for the 87.1 kilometer circumference collider ring, the excavation of seventeen shafts was complete, and the tunnel boring, begun in January 1993, had proceeded rapidly, with 77,065 feet (roughly 23 kilometers) completed by fall 1993.

http://www.hep.net/ssc/new/history/appendixa.html

 

[mheslep]

Todd H. Rider investigated such systems from a very generic (e.g., Kinetic Theory and 2nd Law) viewpoint in his Ph. D. Thesis in Nuclear Engineering, http://dspace.mit.edu/handle/1721.1/11412"

His basic (and quite depressing) conclusions are as follows:

...

I find Rider helpful. He shows why some of the IEC and other ideas, as envisioned at the time must fail, and, like any good work, shows you where not to waste your time and the obstacles that must be overcome. He does not shut the door on everything fusion; towards the back of that thesis there are some work-around suggestions and a good quote from Mark Twain about the perils of 'knowing absolutely' that a problem can never be solved.

 

[beeresearch]

I find Rider helpful. He shows why some of the IEC and other ideas, as envisioned at the time must fail,...

The Rider paper was written some time ago, and makes assumtions that may not apply to all fusion devices now.

Combinations of confinement metods may solve the problem, the Bussard polywell device uses magnetic and electrostatic, and my own S.T.A.R. reactor uses physical and electrostatic.

There are also a number of other inventions in the pipeline, which have not been published yet.

If we had blind faith in the Rider paper, we would have closed up shop long time ago.

Steven Sesselmann

 

[mheslep]

...If we had blind faith in the Rider paper, we would have closed up shop long time ago...

No, per the point I made above, even if one had 'blind faith' in Rider, there's no need to close up shop. Rider doesn't claim to close all doors, he even makes suggestions for alternatives.

 

[mheslep]

Monday the WSJ ran a front page interest piece on the the group of amateurs that construct basement/garage made fusion reactors based the Hirsch/Farnsworth inertial electrostatic confinement concept.
http://online.wsj.com/article/SB121901740078248225-email.html

 

[beeresearch]

Monday the WSJ ran a front page interest piece on the the group of amateurs that construct basement/garage made fusion reactors based the Hirsch/Farnsworth inertial electrostatic confinement concept.
http://online.wsj.com/article/SB121901740078248225-email.html

Yes, it was a good article, and has generated quite a bit of interest in amateur fusion. I belong to this group and I know all these guys well, they are really dedicated and know everything there is to know about fusion.

Here is a link to a short video of my latest fusion reactor http://www.youtube.com/watch?v=XdEE0ry7Mxc"

Steven

 

[chayced]

Thanks Steven, I've now found my new garage project. Just need to find a use for all those neutrons so I can convince my wife.

 

[gdp]

Monday the WSJ ran a front page interest piece on the the group of amateurs that construct basement/garage made fusion reactors based the Hirsch/Farnsworth inertial electrostatic confinement concept.
http://online.wsj.com/article/SB121901740078248225-email.html

No one has ever claimed that the "Farnsworth Fusor" was hard to make.

The problem with the FF is that it consumes several BILLIONS of times more power than it produces --- and there are very strong arguments based on fundamental physical laws, and in particular the 2nd Law of Thermodynamics, that the FF will NEVER be able to "break even." It is a cheap, portable neutron source --- but it will NEVER be a net producer of energy.

You might as well try to heat your house by burning sand.

 

[mheslep]

No one has ever claimed that the "Farnsworth Fusor" was hard to make.

The problem with the FF is that it consumes several BILLIONS of times more power than it produces --- and there are very strong arguments based on fundamental physical laws, and in particular the 2nd Law of Thermodynamics, that the FF will NEVER be able to "break even." It is a cheap, portable neutron source --- but it will NEVER be a net producer of energy.

You might as well try to heat your house by burning sand.

I don't believe its a 2nd law limitation. Grid impacts are the main loss IIRC.

 

[gdp]

I don't believe its a 2nd law limitation. Grid impacts are the main loss IIRC.

No, grid losses are merely the current dominant loss mechanism. But even if grid-losses could be impossibly reduced to zero, the 2nd Law still kills you two ways:

1.) The coulomb collision rate is many times larger than the fusion reaction rate. Therefore, the plasma will thermalize before it reaches breakeven density. By the 2nd Law, to maintain a nonequilibrium particle distribution costs power --- and from the 2nd Law, Rider has shown that under very general conditions, attempting to maintain the plasma out of equilibrium costs more power than one gains from the nonequilibrium distribution.

2.) Even if all other loss mechanisms were reduced to zero, the plasma will still emit Bremsstrahlung Radiation (X-rays from collisions between the ions and the electrons). Rider has show that for every fuel combination except D+T and possible D+D, bremsstrahlung losses will greatly exceed the fusion power. Therefore, unless one can find a magic way to convert X-rays into energy and recycle that energy with near-100% efficiency (which is forbidden by the 2nd Law!), the reactor cannot produce more power than it consumes.

 

[mheslep]

No, grid losses are merely the current dominant loss mechanism. But even if grid-losses could be impossibly reduced to zero, the 2nd Law still kills you two ways:

Ok, but that would be _one_ way, not two. X-rays from the collisions are not dependent on the system entropy.

1.) The coulomb collision rate is many times larger than the fusion reaction rate. Therefore, the plasma will thermalize before it reaches breakeven density. By the 2nd Law, to maintain a nonequilibrium particle distribution costs power --- and from the 2nd Law, Rider has shown that under very general conditions, attempting to maintain the plasma out of equilibrium costs more power than one gains from the nonequilibrium distribution.

2.) Even if all other loss mechanisms were reduced to zero, the plasma will still emit Bremsstrahlung Radiation (X-rays from collisions between the ions and the electrons). Rider has show that for every fuel combination except D+T and possible D+D, bremsstrahlung losses will greatly exceed the fusion power. Therefore, unless one can find a magic way to convert X-rays into energy and recycle that energy with near-100% efficiency (which is forbidden by the 2nd Law!), the reactor cannot produce more power than it consumes.

Nebel, formerly of Los Alamos, recently on an IEC machine w/ no grid:

...1. The theory says that you can beat Bremstrahlung, but it's a challenge. The key is to keep the Boron concentration low compared the proton concentration so Z isn’t too bad. You pay for it in power density, but there is an optimum which works. You also gain because the electron energies are low in the high density regions.
...
4. The machine does not use a bi-modal velocity distribution. We have looked at two-stream in detail, and it is not an issue for this machine. The most definitive treatise on the ions is : L. Chacon, G. H. Miley, D. C. Barnes, D. A. Knoll, Phys. Plasmas 7, 4547 (2000) which concluded partially relaxed ion distributions work just fine. Furthermore, the Polywell doesn’t even require ion convergence to work (unlike most other electrostatic devices). It helps, but it isn’t a requirement.

The title of that paper: Energy gain calculations in Penning fusion systems using a bounce-averaged Fokker-Planck model. That is, after Rider, Chacon et al went through the very difficult Fokker-Planck path and found one doesn't necessarily need a mono energetic distribution to get net gain. Nebel is referring to B-P fusion here.
Here's the recent, complete conversation. Most of it is about the feasibility of magnetic confinement of the electrons which form the electrostatic well in their particular design, but there's some discussion of Bremm. and equlibrium issues as well.
http://www.newmars.com/forums/viewtopic.php?f=29&t=5395&st=0&sk=t&sd=a&start=20

 

[beeresearch]

Your extracts are correct, the simple problem facing most IEC systems is that the electrostatic field can not penetrate a thermal plasma, and that is of course because it becomes conductive. So once that happens you can no longer confine the plasma and wahlah fusion stops.

This might not be a problem in my S.T.A.R. device, for a couple of reasons. the novel design features a hollow cathode centered inside and insulated from a spherical anode.

Apart from being physically confined by the cathode, the cathode has an amazing ability to syphon off electrons. This happens when the plasma becomes thermal.

When a cold surface is in contact witrh a thermal plasma, the cold surface is bombarded by charged particles, and because electrons in a thermal plasma move much faster than the ions, that surface is hit many more times by negative chaarges than by positive charges.

It is natural for a conducting surface to attemt to reach thermal equilibrium with the plasma, but in a hollow sphere, this is not possible, because the negative charges are constantly absorbed by the inside surface and moved to to the outside surface (as in a Van DeGraaf generator).

So once again, as long as I can retain an ion beam in the accellerator tubes, I don't care if the plasma inside the cathode becomes thermal.

http://www.beejewel.com.au/research/images/Reactor.gif"

Steven

 

[gdp]

Ok, but that would be _one_ way, not two. X-rays from the collisions are not dependent on the system entropy.

No, two ways:

1.) The IEC concept, and in particular the "gridless" IEC concept, depends crucially on maintaining a disequilibrium state between the electrons and ions, in order to create the electron space-charge potential well that the ions fall into. Due to coulomb scattering of the electrons off the ions, the electron and ion distributions will necessarily relax toward mutual thermodynamic equilibrium, which relaxation creates entropy. Maintaining a disequilibrium state between the electrons and ions necessarily costs power, to make up for the energy lost to the entropy being produced as the distributions continuously try to relax back toward equilibrium. Rider has proved using a 2nd Law argument that the power consumed to maintain the electron/ion disequilibrium exceeds the gain in fusion power obtained from operating the IEC reactor in an electron/ion disequilibrium state; this portion of Rider's argument does not depend on nor involve any specific loss mechanism --- it depends only on kinetic theory, and the 2nd Law of Thermodynamics.

2.) Since according to the 2nd Law, maintaining a disequilibrium state costs power, a portion of the reactor's output must therefore necessarily be "recycled" to maintain the disequilibrium state, over and above the power required to make up losses. By the 2nd Law, this power-recycling process cannot be 100% efficient. Furthermore, since an IEC reactor does not operate in an "ignited" mode, power must necessarily also be recycled to make up for losses in the reactor itself (of which the single largest loss is bremsstrahlung). Rider shows that for any fuel combinations except D+T and D+D, both the amount of recycled power and the losses incurred during power recycling will be prohibitively high (i.e., a large fraction of the reactor's total power output) --- and therefore, an IEC reactor cannot reach economic breakeven, even if somehow it does manage to achieve scientific and engineering breakevens.

Nebel, formerly of Los Alamos, recently on an IEC machine w/ no grid:

..1. The theory says that you can beat Bremsstrahlung, but it's a challenge. The key is to keep the Boron concentration low compared the proton concentration so Z isn’t too bad. You pay for it in power density, but there is an optimum which works. You also gain because the electron energies are low in the high density regions.

I am extremely skeptical of this claim by Nebel. Bremsstrahlung scales as the square of the ion charge, so bremsstrahlung off Boron is 25 times worse than bremsstrahlung off D or T, and six times worse than bremsstrahlung off He3. Since the fusion power scales as the product of the proton and boron ion densities, trying to beat bremsstrahlung by running a "lean mix" (lowering the boron ion concentration relative to the proton concentration) necessarily also decreases the output power, so it is a self-defeating strategy. To achieve the same power, a "lean mix" reactor will require a proportionally higher core volume. Since bremsstrahlung power scales with ion number, at a rough estimate, I would expect that for the same bremsstrahlung loss rate, a p+B reactor would require on the order of 25 times lower boron concentration than proton concentration, requiring a core volume roughly 25 times larger for the same output fusion power, i.e., at least roughly three times larger reactor radius. Raising the reactor radius makes everything more difficult, since contrary to Bussard's claims, it is not possible to make the magnetic field also scale with radius: For superconducting coils, the maximum B is set by the critical field strength of that superconductor, not by the dimensions of the coil, while for normal coils, electrical resistive losses in the coils will become prohibitive as they get larger, plus the coils will become more and more difficult to cool.

4. The machine does not use a bi-modal velocity distribution. We have looked at two-stream in detail, and it is not an issue for this machine. The most definitive treatise on the ions is : L. Chacon, G. H. Miley, D. C. Barnes, D. A. Knoll, Phys. Plasmas 7, 4547 (2000) which concluded partially relaxed ion distributions work just fine. Furthermore, the Polywell doesn’t even require ion convergence to work (unlike most other electrostatic devices). It helps, but it isn’t a requirement.

Red Herring. The 2nd Law limit on IEC comes from the necessary disequilibrium between the electron and ion distributions --- not from the secondary disequilibrium between ion species. Two-stream instability is a collective effect that increases the thermalization rate of the plasma --- but even if two-stream and other instabilities were somehow completely eliminated, the unavoidable coulomb collisions between the electrons and ions will still cause their energy distributions to relax toward equilibrium with each other, generating entropy during the process. To maintain the electron/ion disequilibrium will cost power. Rider shows that maintaining this disequilibrium will cost more power than will be gained from operating at an electron/ion disequilibrium.

 

[gdp]

So once again, as long as I can retain an ion beam in the accellerator tubes, I don't care if the plasma inside the cathode becomes thermal.

http://www.beejewel.com.au/research/images/Reactor.gif"

Steven

Since the probability that two ions will scatter when they collide with each other is many orders of magnitude larger than the probability that they will undergo a fusion reaction, you cannot in fact maintain the beam inside the accelerator tubes: After no more than a few collisions, the scattered ions will leave the acceptance apertures of the accelerator tubes and be lost.

Google on "beam-beam scattering" for details; it's the second largest loss mechanism in a colliding-beam machine after beam/residual-gas scattering, and the primary loss mechanism in a high-luminosity collider --- which is one of the several reasons why the designers of high-energy physics machines are moving toward single-pass linear colliders with beam energy recovery, rather than circular colliders. (BTW, I used to design particle accelerators for a living...)

 

[beeresearch]

Since the probability that two ions will scatter when they collide with each other is many orders of magnitude larger than the probability that they will undergo a fusion reaction, you cannot in fact maintain the beam inside the accelerator tubes: After no more than a few collisions, the scattered ions will leave the acceptance apertures of the accelerator tubes and be lost.

Yes, I am aware of the scattering problem and I am hopeful that some of the scattered ions will reflect off the inside walls of the cathode and get another go at fusing. This may or may not work.

My latest reactor will be operational in about two weeks, and I hope to be able to run a series of experiments between 20 KV and 100 KV to get a measurement of the fusion rate.

Most of my early experiments were dogged by various problems and the reaction rate never exceeded 500,000 fusions/sec, a Q of the order 1e-10, but I hope to improve on this in the next round.

I will do some reading on the subject you suggested.

Steven

 

[gdp]

Yes, I am aware of the scattering problem and I am hopeful that some of the scattered ions will reflect off the inside walls of the cathode and get another go at fusing. This may or may not work.

It will not. Moreover, the Universe does not respond to "hope."

My latest reactor will be operational in about two weeks, and I hope to be able to run a series of experiments between 20 KV and 100 KV to get a measurement of the fusion rate.

It will be many, many orders of magnitude less than the loss rate.

Most of my early experiments were dogged by various problems and the reaction rate never exceeded 500,000 fusions/sec, a Q of the order 1e-10, but I hope to improve on this in the next round.

First, I suspect you are grossly overestimating your Q.

Second, even if your Q is correct, a low Q is to be expected because the coulomb scattering cross-section is many, many orders of magnitude larger than the fusion reaction cross-section, and no more than one or two collisions is sufficient to remove the ion from the beam.

The peak of the D+T fusion cross-section is about http://en.wikipedia.org/wiki/Tritium#Controlled_nuclear_fusion" for the D+T or D+D reaction is technically divergent, but can be regularized by inserting a maximum impact parameter on the order of your tube radius, and a maximum scattering angle on the order of the angle subtended by the tube aperture as viewed from the collision region. You will discover that the coulomb cross-section is much, much larger than 5 barns.

 

[beeresearch]

I suspect you are grossly overestimating your Q.

I have set up a java page for anyone with a BTI bubble detector to calculate their Q here.

http://www.beejewel.com.au/research/fusion_calculator.htm"

At the bottom of this page is a link that takes you to a list of various fusion results.

Steven

 

[mheslep]

No, two ways:

Yes I see now, two.

...I am extremely skeptical of this claim by Nebel. Bremsstrahlung scales as the square of the ion charge, so bremsstrahlung off Boron is 25 times worse than bremsstrahlung off D or T, and six times worse than bremsstrahlung off He3.

.
Well in a perfectly neutral system. Bremmsstrahlung is proportional to electron density, electron temperature, and the ratio of electrons to ion Z. These virtual cathode systems are by definition not perfectly neutral, as the electron/ion ratio > 1 sets up the electrostatic well.

Since the fusion power scales as the product of the proton and boron ion densities, trying to beat bremsstrahlung by running a "lean mix" (lowering the boron ion concentration relative to the proton concentration) necessarily also decreases the output power, so it is a self-defeating strategy.

Only to a point, as Nebel suggested with the 'optimum' qualifier, as the power gain function is not linear in all its parameters.

Red Herring. The 2nd Law limit on IEC comes from the necessary disequilibrium between the electron and ion distributions --- not from the secondary disequilibrium between ion species. Two-stream instability is a collective effect that increases the thermalization rate of the plasma --- but even if two-stream and other instabilities were somehow completely eliminated, the unavoidable coulomb collisions between the electrons and ions will still cause their energy distributions to relax toward equilibrium with each other, generating entropy during the process. To maintain the electron/ion disequilibrium will cost power. Rider shows that maintaining this disequilibrium will cost more power than will be gained from operating at an electron/ion disequilibrium.

As I understand it, though Rider/Nevins correctly point out the 2nd law issues in play, there are two areas where they fall short: 1) the electron confinement times for a virtual cathode device are shorter than the thermalization/collision time with ions so that the electron temperature never has the opportunity to rise enough to cause unsustainable Bremmstrahlung, 2)their mathematical treatment of collisionality is inadequate. That is, the FP model performed by Chacon et al 2000 improves power gain (Q) by 5 to 10x over that predicted by Nevins. Take this last part up with Chacon et al.