TOKAMAK Instabilities

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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MSimon
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TOKAMAK Instabilities

Post by MSimon »

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http://arstechnica.com/journals/science ... or-designs

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They suggest a different design.

ITER may be money down the rat hole.
Engineering is the art of making what you want from what you can get at a profit.

rnebel
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Post by rnebel »

Simon:

I wouldn't put a lot of stock in this. The codes that Garabedian is using are inadequate, too. Among other things, they don't have plasma flow. I don't think that the ITER equilibria are a huge extrapolation from the equilibria in either JET or C-Mod. Those machines work pretty well, so I suspect ITER will as well. Although I'm not a big fan of ITER, I doubt that this is a show stopper.

hanelyp
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Post by hanelyp »

The proposed configuration looks to me like a compact stellerator.

ITER not expected to see plasma for 10 years. Depending on results and funding, the polywell might easily leapfrog the tokomak in that time.

TallDave
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Post by TallDave »

I just thought it was cute they were still saying $9.3 billion. Maybe that was in 1988 dollars.

MHD stability with concavity sure is an ugly problem.

Oh, and the joke is that fusion power is always 50 years away (as was thought when fusion was first discovered) not 20, and DEMO (the ITER follow-on) probably is about that far from providing power to a grid at anything close to a reasonable cost.
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

jmc
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Post by jmc »

I think there's something to be said with working on the most successful approach to date (i.e. the Tokamak) and seeing how far you can push it.

We should be trying as many credible solutions as we can to try to get fusion as to greater or lesser extents, they are all a stab in the dark.

I actually think the opposite, regarding adding a further degree of freedom. Sometimes I think we should put more money into research in mirror machines, simply because the topology is simpler so with luck their behaviour is easier to predict mathematically than a tokamak. That certainly seems the case with the Gas Dynamic Trap (sofar at least).

I would not shoot down other ideas as "money down a rat hole" too soon.

Before the wright brothers there were countless failed attempts at flying. The reason we succeeded in achieving heavier than air flight was because people were willing to give it a go and risk failure. Noone mathematically predicted with utter certainty the Wright Brothers plane would fly before it took off. The same goes with ITER. We shouldn't shoot it down just because we can't prove with certainty it will work.

There have been many other projects which proved to be money down a rathole.

The Vanguard rocket built by the navy exploded on its launch pad. At least even if ITER fails its objectives it will give us some useful data to study!
Last edited by jmc on Mon Sep 08, 2008 3:45 pm, edited 1 time in total.

TallDave
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Post by TallDave »

working on the most successful approach to date (i.e. the Tokamak)
Depends on the definition of "success." After billions spent, the ITER approach is still several decades from commercial fusion power.
At least even if ITER fails its objectives it will give us some useful data to study!
ITER will probably do what it was supposed to do. The problem is that what it's supposed to do may not be that useful, even after tens of billions more spent.
We should be trying as many credible solutions as we can to try to get fusion as to greater or lesser extents, they are all a stab in the dark.
True, but some stabs are more expensive than others, and funds are finite. Dollar-weighting is important.
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

rcain
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Post by rcain »

Art Carlson suggested a while ago that his money would be on Reversed Field Configurations - maybe self organized plasma is the best direction?

jmc
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Post by jmc »

Regarding this whole "cost weighted performance" I'm not sure I agree.

Plasmas are inherently unpredictable. How can you possibly assess the probability of success for any approach to even a factor of 10?

While a factor of 10 seems a realistic ball park figure for our abilitity to acertain the probability of success for a given fusion avenue of research. Programmes do not always run on budget. What's too say even if these new fusion approaches can in principle succeed, that they won't end up growing in size and cost just like a tokamak. How can you predict the cost of a new fusion concept you can't even properly predict or understand?

If the cost of the proposed new fusion approach is uncertain (as it assuredly is) then the "cost weighted risk assessment" is meaningless. And what about the time? How long will it take to smooth out all the new problems that a new fusion approach will involve? Everytime we try to achieve nuclear fusion it almost always throws new physics at us that mean that the actual device underperforms expectations.

The longer people have been studying a fusion concept, the more understanding they have of the plasmas and the less suprises the plasmas have left to throw at them. New concepts mean more suprises. Old concepts should mean less surprises left between now and the final goal.

In reality "all cost weighted risk assessment" comparing new fusion concepts and old ones will be strongly flavoured by both optimism and pessimism and no impartial concensus will be reached.

I endorse funding new fusion aswell as established fusion methods, bt it must be in conjunction with rather than instead of.

Even if a tokamak does not achieve commercial nuclear fusion, it will produce the kinds of neutron fluxes that will be able to test components and systems applicable to a wide range of other fusion reactors, so that if they do ever reach fusion plasmas, the technology and materials will be waiting there to make them economic and durable.

TallDave
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Post by TallDave »

How can you possibly assess the probability of success for any approach to even a factor of 10?
Well, obviously you can't predict commerical applicability at this point, for toks or Polywells. You can, however, easily identify past success and failure, and how much they cost.

You can also pretty accurately identify a mininum future cost/time for a given tech before which it will definitely not work.
What's too say even if these new fusion approaches can in principle succeed, that they won't end up growing in size and cost just like a tokamak.
Maybe they will. But it makes sense to spend $100M/5 years to find out before you commit to spending $100B/40 years.
Even if a tokamak does not achieve commercial nuclear fusion, it will produce the kinds of neutron fluxes that will be able to test components and systems applicable to a wide range of other fusion reactors, so that if they do ever reach fusion plasmas, the technology and materials will be waiting there to make them economic and durable.
Sure, but does it makes sense to spend $10B to do this when you might get a working fusion reactor that could do the same testing for $100M (especially since an IEC/FRC reactor may not have any neutron flux to speak of anyway)?

I'd like to see both funded too. I'm just saying that at this point, given what we know, Polywells and FRCs should be the priority, and if we can only choose one path (tok vs IEC/FRC) it's a no-brainer. If IEC/FRC doesn't pan out, we've barely lost any time/money on the ITER/DEMO cycle because it's so much longer/expensive.
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

rnebel
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Post by rnebel »

I have three questions for JMC:
1. If the mass power density of ITER is several hundred times worse than it is for a light water reactor power core (which it is), how do you expect to compete with them? Or with any other power source?
2. If all magnetic confinement D-T systems have inherently poor mass power densities (which they do), then what is the point of doing the materials development on ITER?
3. If ITER requires the combined resources of almost every industrialized nation in the world just to build a non-power-producing prototype, how are you going to entice private investors to develop fusion?
While I’m not opposed to ITER (if people want to work on it that’s fine with me), the fusion program has ignored these three questions for at least 30 years. Do they ever ask these questions at Culham? What kind of responses do you get?

Josh Cryer
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Post by Josh Cryer »

I think this might answer your last question rnebel:

ITER: Promises unkept?

Part 1: http://cdsweb.cern.ch/record/1124311?ln=en (you may skip this, just for reference)
Part 2: http://cdsweb.cern.ch/record/1124298?ln=en

From what I understand ITER was intentionally designed to be an "international programme," similarily to the ISS. This was to build industry in every partner country able to build their own DEMO in the future, since it requires pretty sophisticated tech.

The final cost for an ITER type fusion machine is comparable to current nuclear plant prices in the future. BTW, the presentation makes it clear. If ITER doesn't work then Tokamak doesn't work. Period.

rnebel
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Post by rnebel »

Josh:
I've heard those statements and I'm not convinced. I asked Najmabadi (who heads the ARES conceptual design program) how well they could do on mass power density with their most advanced designs, and the answer I gotwas a factor of 10 worse than an LWR. Put a picture of an LWR power core (to scale) next to a picture of ITER and then tell me what you believe.

Josh Cryer
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Post by Josh Cryer »

Ahh, I see what you mean. I guess an argument could be made about mining uranium vs lithium (not just environmental considerations but local abundance of both, and long term viability of reserves) but other than that I think you're right.

jmc
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Post by jmc »

rnebel wrote:I have three questions for JMC:
1. If the mass power density of ITER is several hundred times worse than it is for a light water reactor power core (which it is), how do you expect to compete with them? Or with any other power source?
2. If all magnetic confinement D-T systems have inherently poor mass power densities (which they do), then what is the point of doing the materials development on ITER?
3. If ITER requires the combined resources of almost every industrialized nation in the world just to build a non-power-producing prototype, how are you going to entice private investors to develop fusion?
While I’m not opposed to ITER (if people want to work on it that’s fine with me), the fusion program has ignored these three questions for at least 30 years. Do they ever ask these questions at Culham? What kind of responses do you get?
1. MSimon in discussions with Art Carlson said that the reactor core costs of a lightwater reactor are less than the costs of converting the steam into electricity.

There is someone in Culham called David Ward who works on the economics of Tokamak reactors. He has given a talk in the student meeting, taking into account cost reductions due to a learning curve and in his presentation, he stated that if a tokamak reactor could be made to operate reliably (which is obviously a question that is still up in the air), i.e. not get torn apart by the neutrons, eliminate ELMs, successfully mitigate the heat flow to the divertor etc., then the costs of the fusion reactor would be 1/3 of the total cost of the power station.

I don't know how true his projections were or how they were calculated. But if you like I could ask him whether he would be interested to engage in a discussion of the economics of tokamak reactors, with you. In anycase he's the expert.

Secondly, I'm not sure a tokamak does have to compete with light water reactors. Oil has peaked, gas will run out soon and at the current rate of increase of 5% per annum know coal reserves will run out in 50 years time. U235, which light water reactors use will run out in 50 years at the current rate of usage, but since they currently only supply 16% of the world's electricity, if U235 reactors were used to supply all our energy, known reserves would run out in ~5 years.

So maybe fusion really just there to compete with fast breeders and renewables. I maybe wrong, but I believe the energy density of a fusion reactor is greater that Solar power generators. In addition, in a fusion reactor it will hopefully be possible to ramp up and down power supply which will allow greater grid control than solar. And in the case of breeder reactors I believe that safety and nuclear proliferation are greater concerns then energy density, (which is higher than in a LWR). If you know of any safe 4th generation breeder I'd be interested to hear about it.

2. I don't really understand this comment. Without convergence, a Polywell is essentially a magnetically confined cusp machine. What gives the extra power density is the fact that it can run using a beta = 1 plasma. From the papers I've read on mirror machines and gas dynamic traps (also proposed magnetic confinement regimes) they hope to achieve beta=1 aswell. This would be the same as a polywell. (Although the closed field tokamak/ stellerator approach has only given beta ~(0.03-0.08 ) to date).

Your comment on DT is even more suprising since DT gives the highest mass power density of any fusion reaction at a given plasma pressure.

3. ITER does not require the combined resources of almost every industrialized nation in the world. If Britain really wanted fusion power above all else it could single handedly finance ITER. Likewise for the EU (Infact as things are they already foot 50% of the bill). The US spent 10 times as much on Apollo as we are spending on ITER. The reason that ITER is a "joint global effort" is not to spread the "burden of the cost" but rather to spread the burden of political embarassment if ITER turns out to be a failure. If there was a serious belief that there was a certainty that ITER would supply limitless cheap, clean energy to the nation that built it. First all the nations of the world would spend $10 billion building their own ITER (including Belgium and Swtzerland) and secondly the research would be top secret.

Fusion funding is limited by the expected return for those investing (many people wonder whether it can even be done at all) not by limitations in the global economy to fund it.

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Post by TallDave »

Secondly, I'm not sure a tokamak does have to compete with light water reactors. Oil has peaked, gas will run out soon and at the current rate of increase of 5% per annum know coal reserves will run out in 50 years time. U235, which light water reactors use will run out in 50 years at the current rate of usage, but since they currently only supply 16% of the world's electricity, if U235 reactors were used to supply all our energy, known reserves would run out in ~5 years.
Known reserves.

http://www.americanenergyindependence.com/uranium.html

I recall reading studies in the 1970s that earnestly stated that we only had ~20-30 years of oil and gas reserves left (based on proven reserves...In the same vein, we continually hear about how the “proven reserves” of uranium will only last ~50 years at current consumption levels. These estimates, however, have an even weaker basis than the oil/gas estimates of the 1970s, since the amount of effort and expenditure that has been put, as of today, into uranium exploration and development is far smaller than that put into gas and oil exploration, even as of the 1970s
...
Two things happened down the road which greatly reduced the demand for mined uranium, relative to the initial predictions. First of all, the use of nuclear power grew much more slowly than anticipated, due to lower-than-expected growth in electricity demand (after the 1970s), as well as other factors like the glut of cheap natural gas (in the 1990s) and the anti-nuclear movement. The second thing that happened was the nuclear arms reduction treaties, and the resulting decommissioning of nuclear warheads. The highly-enriched (weapons grade) uranium in these warheads can be blended down to make much larger quantities of low-enriched reactor fuel. It is estimated that warhead uranium will provide almost half of the nuclear power plant fuel in the US between 1990 and 2010, thus cutting the demand for mined uranium in half.

As the demand for mined uranium fell substantially (as opposed to growing as expected) the price of uranium ore plummeted. This caused all of the lower-grade ore mines to shut down. Only the few large, ultra-high grade ore sites could produce ore at a low enough price to make a profit. With only a handful of sites in operation, and a large number of known deposits (and even developed mines) not operating due to the low market price, all uranium exploration and development came to a complete halt, as there was simply no reason to look for more uranium, let alone invest significant sums of money to do so.
Also
One important fact that must be understood is that, unlike the gas and oil, the cost of the uranium ore is a negligible fraction of the cost of nuclear power (with almost all of nuclear power cost being in the form of value added by domestic labor). Specifically, at today's price of ~$40/kG of uranium, the ore costs amount to only ~0.1 cents/kW-hr (i.e., only ~2-3% of nuclear’s total power cost). The ore cost could increase by a factor of 10 (to ~$400/kg) and nuclear's power cost would only increase by ~1 cent. Thus, whereas gas and oil applications are extremely sensitive to the cost of fuel, and can be rendered uneconomical by even a small increase in fuel price, nuclear power is almost immune to ore price increases. Thus, the maximum price for uranium ore, above which nuclear power would become uneconomical, is extremely high indeed.

If an extremely high ore price is tolerable, then very low grades of uranium ore can be considered as possible reserves. As the permissible ore grade (uranium concentration) goes down, the amount of recoverable uranium (i.e., reserves) goes up exponentially. As is discussed in more detail later, limitless supplies of uranium are present in seawater and in the earth’s crust, which can be extracted at some price. The question is how much uranium is available at a cost that doesn’t truly price nuclear power out of the market.
Last edited by TallDave on Thu Sep 11, 2008 6:23 pm, edited 1 time in total.
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

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