Details on ITER ELM problems

MSimon · Post by **MSimon** » Fri Apr 11, 2008 11:16 pm

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http://www.iterfan.org/index.php?option ... 7&Itemid=2

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Experiments now suggest that these ELM eruptions occur around once every second and are much bigger than had been realised. Although they last only one millisecond, or thousandth of a second, each eruption has a power of 20 gigawatts - about the expected capacity of China's Three Gorges Dam. The journal Nature was told that this was like "throwing a handful of hand grenades" at the wall of the device every second.

MSimon · Post by **MSimon** » Fri Apr 11, 2008 11:20 pm

"We have to convince ourselves that the coils can be manufactured to a standard which will make them essentially 100 per cent reliable inside the Iter device, and that including them doesn't imply design changes to other systems inside the device which would make those other systems more costly or less reliable," says Dr Campbell.

That could be a real help for Polywell reactors.

rnebel · Post by **rnebel** » Sat Apr 12, 2008 8:07 pm

Elms have been known about for almost 20 years. I don't know why they have suddenly come to the forefront. There are a whole zoo of these MHD-like modes that could potentially bite ITER in the butt. The most catastrophic one is a major disruption. I suspect that one would enlarge ITER's real estate footprint significantly.

MSimon · Post by **MSimon** » Sat Apr 12, 2008 8:23 pm

rnebel wrote:Elms have been known about for almost 20 years. I don't know why they have suddenly come to the forefront. There are a whole zoo of these MHD-like modes that could potentially bite ITER in the butt. The most catastrophic one is a major disruption. I suspect that one would enlarge ITER's real estate footprint significantly.

Oh yeah. The "if only we build the next one 3X larger we can fix the problem" deal.

rnebel · Post by **rnebel** » Sat Apr 12, 2008 9:11 pm

One of the more interesting numbers for ITER is that the total stored energy in the magnetic fields is about the same as 8 tons of TNT. Although a major disruption won't release all of it, it can release enough of it to do some serious damage. I believe (but I could be wrong) that ITER is designed to handle 1 or 2 of these events during it's lifetime. These don't happen regularly on tokamaks, but they do happen. Should be an interesting experiment to watch. But at a distance......

drmike · Post by **drmike** » Sun Apr 13, 2008 2:54 am

I found a reference that says the ITER mag field is about 640 MJ. From a conversion chart this is about 0.153 Tons of TNT. Enough to do plenty of damage for sure.

TallDave · Post by **TallDave** » Sun Apr 13, 2008 6:32 pm

I assume the 8T refers to the energy confined by the fields as opposed to the energy used to generate them.

I remember reading an ITER scientist was very upset about the "hand grenade" analogy, saying that the force was much more dispersed than that.

"The ELM can neither break components inside the device nor breach the walls of the device. The ELM doesn't "damage" the reactor in the everyday sense of the word. It is grinding away at the surface of the components inside the vessel and that disturbs the operation of the plasma to the point that it could shut off."

http://www.telegraph.co.uk/earth/main.j ... ter111.xml

What worries me about their solution is that they are talking about bleeding off energy from the plasma to solve this. Given that the whole challenge in a maxwellian setup like a tokamak is to confine as much energy in as small an area as possible, the fact they are resorting to leaking some out doesn't seem to bode well.

Norbert Holtkamp, the project's construction leader, will be told to use a complex arrangement of magnets to dampen the effects of the erosive blasts, by in effect poking holes in the reactor's magnetic bottle to bleed out some energy

I also worry whether they really know if this will even work:

Dr Moyer concludes: "By adding a little bit of chaotic behaviour to the magnetic field that forms the "bottle" holding the plasma, it's possible to suppress these instabilities without degrading the overall plasma performance."

They're going to make the magnetic field more stable by adding instability? OK, that could work in theory, but I have to wonder if that won't in turn lead to new unforeseen instabilities. I don't have a lot of faith in our ability to accurately model these interactions.

And with that, they're hoping, maybe, this can be done by 2016. Argh. And they don't say how much more it will cost now.

MSimon · Post by **MSimon** » Sun Apr 13, 2008 8:03 pm

Once I started looking into it, it seemed obvious that trying to make a plasma act like a Maxwellian gas was a fools errand. The epicycles start multiplying.

Taking advantage of the reactions instead of trying to suppress them seems much more sensible.

rnebel · Post by **rnebel** » Sun Apr 13, 2008 10:37 pm

Dr Mike:

Just for fun I went back and checked my numbers. I had assumed ~ 10 Tesla fields. The spec is 5.3 T. I also used the 870 m**3 on the ITER website for the volume. That gives ~ 9.7 GJ of stored energy. The 870 number must include more than the volume of the magnetic field....

drmike · Post by **drmike** » Mon Apr 14, 2008 2:42 am

That would explain it! Even with the correction though - they'd better have a good way to dump that energy in a controlled manner or it could take a few years to repair the damage.

Tom Ligon · Post by **Tom Ligon** » Mon Apr 14, 2008 3:11 am

Dr. Nebel, you've touched on one of Dr. Bussard's favorite critiques of large tokamaks, but you left out a detail.

That detail is the 5 meter thick blanket of molten lithium snuggled just inside the magnets, distributed to that larger footprint.

We'll neglect the radioactive materials from the neutron bombardment, as that would assume they got the thing to run at a high power level for a while.

rnebel · Post by **rnebel** » Mon Apr 14, 2008 4:59 pm

Dr. Bussard and I shared a lot of similar opinions on ITER. However, he was bitterly opposed to it and my views are a little less strident.

First of all, the issue as to whether or not ITER is going to be built is moot. It's going to happen whether the US participates or not. In my view, it is unlikely that the US will participate in this program through its completion.

In 1999 and 2002 the US fusion program held week long summer retreats to decide if we (US) would participate in ITER or some other large tokamak. The purpose of these meetings was largely to build a concensus within the program so they could approach Congress and the administration with a unified voice. They were largely successfull in doing that. I made the following comments at the 2002 meeting:

"We have tried to take the burning plasma experiment step 8 times in the last 20 years (ETF, FED1, FED2, TFCX, CIT, BPX, TPX, ITER). Each time we've failed. Each time we've sacrificed part of our program and come up empty. Why is this time any different? What is fundamentally different about any of these devices which will allow them to actually be built and operate rather than be just another paper tokamak?
I don't want to repeat the past. I think our political problems are at least as formidable as our technical and structural problems. I would like to see the proponents of these devices present a credible plan for addressing these problems."

You see, this version of ITER isn't the first time that the program has tried to take the burning plasma step. It's the ninth time. The behavior of the program is a little like Lucy and Charlie Brown with the football. The program gets all excited about a new experiment, goes charging down the field only to have Congress or the administration pull the football away at the last moment. And then, instead of learning something, the process repeats.

The only amazing thing about ITER's funding being slashed was that it shocked the fusion program. Every other time when the "big experiment" got cut it was when they tried to make it a line item construction project in the budget and asked for a big plus up in the funding. That's exactly where they were with the 2008 budget. Surprise, surprise. I believe it was Albert Einstein (or so I've been told) who said that the definition of insanity is when you keep trying the same thing over and over again and expect to get a different answer.

My own view on ITER is to leave them alone. Their program will die of its own accord. It is supposed to last for 30 years. Congress and the administration both get to shoot at them every year. That's 15 Congresses and perhaps 7 administrations. And they only have to kill them once. Regardless of the merit, the US political system isn't compatible with this type of project. It's kind of silly to think that the Congress is going to give up their Constitutional powers just to accomodate a big science experiment.

drmike · Post by **drmike** » Mon Apr 14, 2008 6:18 pm

I forget who pointed this out to me, but the gist of it was that any project longer than 15 years will never finish in the US. Vietnam and the Apollo programs were examples. ITER has been a paper tokamak (I love that term!) since I was a student some 25 years ago. In the US it really is important to create projects that are small and fast. Having a long term agenda can be worked out, like going to Mars - but it has to be seen as "sometime in the future" not as part of a present project.

I'd say you hit the nail on the head. Too bad "big science" isn't about to listen.

MSimon · Post by **MSimon** » Tue Apr 15, 2008 12:23 am

drmike wrote:I forget who pointed this out to me, but the gist of it was that any project longer than 15 years will never finish in the US. Vietnam and the Apollo programs were examples. ITER has been a paper tokamak (I love that term!) since I was a student some 25 years ago. In the US it really is important to create projects that are small and fast. Having a long term agenda can be worked out, like going to Mars - but it has to be seen as "sometime in the future" not as part of a present project.

I'd say you hit the nail on the head. Too bad "big science" isn't about to listen.

Actually Dr. Mike if you listened to one of the major ITER proponents he did get it. He called the funding cuts "the will of Congress and the people".

I can't find a link right now but if one turns up I will post it.

Now I don't know if this has sunk in deep. It may just be reaction and not a change in philosophy. Only time will tell.

Thank the Maker for the US Navy.

If WB-7 green lights WB-100 (the 100 MW demo) I'd like to see Adm. Cohen as head of the project. There is a man who seems to be able to keep his eye on the prize.

I think Congress would be willing to put big bucks into this if we could give results in 5 years or less. If the program was run on a 24/7 basis I think it could be done in three years with a number of mile stones along the way. So funding could be cut or scaled back if problems developed.

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"The message of this year's appropriation is unmistakable. The American public, through its duly elected Congress, has made its priorities clear: short-term applied research wins over the full spectrum of long-term basic research."

http://www.iterfan.org/index.php?option ... 8&Itemid=2

I don't think they get it. Long term research is fine as long as there are intermediate milestones. A way to gauge if progress is being made without spending all the funds.

The Big Bang theory of science is not workable.

drmike · Post by **drmike** » Tue Apr 15, 2008 3:24 am

That's an interesting quote. There are two things missing from it. Short term basic research, and long term applied research! We need a lot more short term basic research.
The concept of long term basic research doesn't really make sense because you learn
things that cause you to change the direction of the research.

I suppose one could argue that going to mars or building large scale colliders falls under "long term basic research", but it's more like using things you know how to build to get at the things you don't, and the actual research doesn't take long to do. We really need to do a lot of basic research to fully understand plasmas and none of it requires huge machines. I won't deny they are fun toys and I'd love to play with them, but there is so much complexity in even a simple plasma that a whole lot of small devices spread out over many people will get us more useful information over the short run.

Lots of small operations does not allow large egos to expand much, and that's the crux of "big science". It would be great if Google could fund things too small for governments to deal with, but bigger than what we can do in our basements. But it still takes politiking.