Interesting entry in Do The Math Blog about Fusion.

[Maya]

vansig wrote: the article ignores aneutronic fusion, yet claims to cover all research. that doesnt add up.

I agree, but I think his point was that the Coulomb force barrier means that fusion generally will require significant pressure or reaction force when the reaction density, and hence the power density, reaches economic levels (even at just megawatts). So, regardless of the type of fusion considered it is very hard to do. Any of these other approaches could work but their machines will be far heavier than they lead us to believe because the pressures, again even at megawatt levels, will be extreme. So, there won’t be a “light, small or cheap” fusion reactor with any foreseeable technology. And that means you have to scale.

[vansig]

you elide heavy with extreme; it is incorrect.

as an analogy, notice that as you inflate a rubber balloon, the pressure inside it falls.

smaller is better

[Maya]

vansig wrote: you elide heavy with extreme; it is incorrect.

as an analogy, notice that as you inflate a rubber balloon, the pressure inside it falls.

smaller is better

Well, you may be right, but I don’t think so. I mean, in principle, sure it would be better. But in reality I don’t know how you could (economically) build one that is small and at the same time so massive. And I don’t think I have to rely on Ivory Towers to tell me that. If you just look at the Coulomb force, the pressures seen at ITER, etc. it is clear that as power goes up pressure gets unmanageable. Thus more and more mass is needed. If someone could convince me of another route, and there is _one_ I know of, then I’d be persuaded.

So, yea, the neutron flux would be small in a small reactor, but how do you get there? And even then, 1 megawatt of neutron flux will still cause embrittlement and other issues, so I don’t think there will be a “green” or other valuable advantage to offset this bigger cost, at least not as far as the mega-corporations are concerned that would be building these things. All they care about is margin.

[zapkitty]

Maya wrote: Yep, you did. The discussion is about fusion. Which costs more to build and run? Savannah River Site or ITER?

Pretty much irrelevant since ITER and its costs are in no way a design paradigm for a commercial fusion reactor… even a tokamak 🙂

Tokamak-style power reactors such as ITER are problematic in and of themselves and may not turn out to be workable power sources but if ITER does work out then the researchers intend to continue with DEMO, a demonstration power plant with at least 4 times the power output at 1/4 the cost.

And then they’ll try to segue the DEMO facility into PROTO, a prototype power plant… if they can.

And of course there are several current non-ITER fusion projects that operate by different rules altogether. Focus Fusion, Tri-Alpha, Polywell, Helion, General Fusion and whatever it is that Lockheed Martin calls the project that the Skunk Works is working on to name some of them.

And all of these are different projects with different designs (assuming that the lockmart design isn’t a polywell variant) and they all involve relatively small (12 to 100 MW) and inexpensive reactors that can be used to add to a distributed power grid to provide as much power as needed where it is needed.

As for your ideas about fusion economics some background on your figures would help. First you speak of single reactors providing hundreds of gigawatts at a minimum to be “viable” and then you speak of one (1) reactor that would supply all the worlds power and half again that much… how many such 21 terawatt reactors were you envisioning to be built?

Maya wrote:

The pB11 reaction is aneutronic in nature and units built along the lines envisioned by Focus Fusion, Tri-Alpha and the Polywell concept would be in the scale of a few megawatts to a gigawatt or so and their neutron flux would be pretty damn small.

It seems that you’ve set impossible-to-meet criteria and I look forward to learning what you envision as the solution to them 🙂

I don’t think so. I think the criteria are grounded in hard reality. I don’t believe that megawatt class fusion reactors will ever be economical in any foreseeable future. On this particular point the issue isn’t technical. It’s economic. Why would anyone build a megawatt class reactor that would be such a colossal construction for a single one-off?

… again, you seem to have confused ITER with actual commercial fusion power proposals.

Much of what you say is not applicable to commercial tokamak concepts and even less of it applies to non-tok designs… and none of it would seem to apply to aneutronic designs.

Maya wrote:
And the four key issues I described are part of the reason why I don’t think they’ll be economical. Even if you lower the power output you will still have phenomenal pressures to deal with. Have you looked at the structural loading on ITER

… again, you seem to have confused ITER with actual commercial fusion power plant proposals 🙂

Patient “Doctor it hurts when I do this.”
Doctor: “Then don’t do that.”

All of the non-ITER fusion startup concepts avoid the problem by handling much smaller fuel masses more efficiently than ITER. Their individual methods are different but none of them are trying to hold ITER’s 840 cubic meters of plasma at fusion temperatures.

In fact the Focus Fusion dense plasma focus design goes one step further by allowing an unstable collapsing magnetic field to do the fuel compression… no external compression required. This is one of several neat ways that the FF concept takes advantage of natural instabilities 🙂

[Maya]

zapkitty wrote:

Pretty much irrelevant since ITER and its costs are in no way a design paradigm for a commercial fusion reactor… even a tokamak 🙂

I think that mostly sums up your overall response, so I’ll just respond to that. Apparently I could have said it more clearly. The issue isn’t the particular _way_ you _do_ the fusion, its more fundamental than that. In order to get a power density sufficient to operate a power generation facility you need a minimum amount of fuel in a given volume. Whether it be a tokamak, ICF or whatever. The Coulomb barrier guarantees that in order to get _that many_ reactions in, say, one cubic meter of space, you have to compress that fuel somehow. The forces required to compress that fuel that much are either:
1.) too great to achieve with any known materials science in higher power outputs
2.) too great to make it economically viable in lower power outputs

Even in megawatt class reactors it will take every ounce of cleverness and mass from the periodic table to construct a metallic device that strong. And this first principle observation doesn’t have to depend on what anyone in an ivory tower tells us. We all (or most of us) know how to calculate Coulomb barrier forces, right?
Fm12 = κm q1 q2 * (v1 X (v2 X r12)) / r2
Now, take the reaction rates we all also know about and calculate how many reactions you need in a given, plausible volume, to get the power density you’d need, for, say, a 100 MW reactor. Now, look at F. Its millions of kg*s. The tiny devices being proposed work fine for tiny amounts of fusion and you might well get fusion reactions out of them. But they can’t scale. It’s not my opinion, bad references or whatever. It’s just math.

That’s why these schemes look good in IP proposals: it can be demonstrated as a way to generate fusion reactions but if the observer isn’t particularly mathematically literate they will miss the elephant in the living room.

[Maya]

If you prefer:

Fe12 = κe q1 q2 / r212

[zapkitty]

Maya wrote:

Pretty much irrelevant since ITER and its costs are in no way a design paradigm for a commercial fusion reactor… even a tokamak 🙂

I think that mostly sums up your overall response, so I’ll just respond to that.

Actually, what I said was that for various reasons the limits you envision do not apply to many fusion concepts and I listed some of them and briefly described one of them 🙂

Perhaps you should read through what you called “IP proposals” again… each one has their own way of dealing with what you seem to have come to believe must be an insurmountable problem.

We can discuss the details of their various solutions if you’d like.

[Maya]

zapkitty wrote:

Pretty much irrelevant since ITER and its costs are in no way a design paradigm for a commercial fusion reactor… even a tokamak 🙂

I think that mostly sums up your overall response, so I’ll just respond to that.

Actually, what I said was that for various reasons the limits you envision do not apply to many fusion concepts and I listed some of them and briefly described one of them 🙂

Perhaps you should read through what you called “IP proposals” again… each one has their own way of dealing with what you seem to have come to believe must be an insurmountable problem.

We can discuss the details of their various solutions if you’d like.

Right, but my point is that the issue is more fundamental than you seem to realize. In other words, it doesn’t matter what proposal you’re talking about if you don’t know how to calculate and contain pressure.

I don’t think I said the problems are insurmountable. In fact, I was clear to point out that I do not think they are insurmountable. My point is that too many people are ignoring the challenges and it sets the stage for, at best, costly error.

And as for each IP proposal, that is easy. If someone can show me the reaction rate and power density they expect to achieve, and hence the fuel and product density, with their proposal – lets start there – then I’d ask what is going to contain the pressure such a particle density requires. It’s just that easy. It isn’t as though I haven’t asked that question many times. I’ve never gotten an answer to that … not even one that actually addresses that question in the first place. And its a first principles, obvious question, so you can’t say “it doesn’t matter”.

And that was the gist of the author’s article, he just didn’t state it this explicitly.

[Maya]

zapkitty wrote:

Pretty much irrelevant since ITER and its costs are in no way a design paradigm for a commercial fusion reactor… even a tokamak 🙂

I think that mostly sums up your overall response, so I’ll just respond to that.

Actually, what I said was that for various reasons the limits you envision do not apply to many fusion concepts and I listed some of them and briefly described one of them 🙂

Perhaps you should read through what you called “IP proposals” again… each one has their own way of dealing with what you seem to have come to believe must be an insurmountable problem.

We can discuss the details of their various solutions if you’d like.

By example, if your material is a single-species plasma you can do a fair estimate by just calculating the electrostatic forces between the particles in a given volume. If it is a multi-species plasma you’ll probably want a coefficient to help you calculate the pressure. And the same would be true of other materials. But in every case, the pressure will be enormous. So, for _each_ proposal, as you say, it is incumbent on the proponent to provide that calculation based on their chosen material. They will get a number called Pascals. Then we can all see what it implies.

[zapkitty]

Maya wrote:
Right, but my point is that the issue is more fundamental than you seem to realize. In other words, it doesn’t matter what proposal you’re talking about if you don’t know how to calculate and contain pressure.

… actually, “it doesn’t apply” is a quite acceptable answer when a concept really doesn’t apply …

to quote:

“In fact the Focus Fusion dense plasma focus design goes one step further by allowing an unstable collapsing magnetic field to do the fuel compression… no external compression required. This is one of several neat ways that the FF concept takes advantage of natural instabilities.”

Each pulse should generate about 66 kilojoules of gross fusion energy from hydrogen-11 Boron… and yet the physical structure of the device does not support the compression of the fuel. (It did its work holding the device together when a few million amps of current was dumped into the electrodes 🙂 )

General Fusion’s rather baroque concept is another way around the “problem”… a sphere a couple of meters in diameter is hammered to create a converging spherical shockwave through molten lead that is spinning inside. When the shockwave arrives at the center the pressure is (hopefully) enough to initiate fusion in the plasmoid hanging in the vortex at the center of the spinning lead… and yet at no time is any point on the outside shell subjected to the immense pressure at the center of the vortex.

Are two examples enough to start?

Again, each of the fusion startups has their own way of handling the issue.

[Maya]

zapkitty wrote:
… actually, “it doesn’t apply” is a quite acceptable answer when a concept really doesn’t apply …

Rounnnd … and … rouunnnnd. And what we’re looking forrrrr still isn’t found. 🙂
Sorry, it was begging for a use here. Seriously, how about those pressures and reaction force equations?

zapkitty wrote:
Each pulse should generate about 66 kilojoules of gross fusion energy from hydrogen-11 Boron… and yet the physical structure of the device does not support the compression of the fuel. (It did its work holding the device together when a few million amps of current was dumped into the electrodes 🙂 )

66 kJ ? Not even a power figure here? And all for just a “few million amps”!!? You’re killing me over here.

zapkitty wrote:
General Fusion’s rather baroque concept is another way around the “problem”… a sphere a couple of meters in diameter is hammered to create a converging spherical shockwave through molten lead that is spinning inside. When the shockwave arrives at the center the pressure is (hopefully) enough to initiate fusion in the plasmoid hanging in the vortex at the center of the spinning lead… and yet at no time is any point on the outside shell subjected to the immense pressure at the center of the vortex.

And … what locates the hammer? Another way of asking it is, what is accelerating the hammer? What’s holding that?

zapkitty wrote:
Are two examples enough to start?

No, because you didn’t answer the question. In those two examples show me how much force (in the case of a conductor you can start with thermal breakdown) is required to get 100 MW out of that arc (and how much force that plasma will exert against those electrodes at 100 MW). Second, I’d like to know how much force is acting against the thing holding the “hammer”. These are basic, basic questions you should be able to rattle off easily if you’re the proponent (not that _you_ are, but you get the idea).

zapkitty wrote:
Again, each of the fusion startups has their own way of handling the issue.

Right, which works fine for demonstrating that you can produce fusion reactions, but it doesn’t demonstrate economic viability or any semblance of an ability to scale to anything useful.

Denying basic Newtonian mechanics is not a winning strategy if your goal is to figure out the riddle. But we haven’t even touched the other issues. Not to get ahead of myself or spoil an answer to the pressure question but, how about heating and energy transfer? Or what about neutron flux, whether a lot or even just enough to embrittle? Remember, what is 0.1 % of 1 GW? Not really “aneutronic”, is it? I’ll grant you that other schemes do in fact adopt the instabilities to their advantage (Lerner, et al), so I guess that one is fairly tokamak dependent.

[benf]

Maya wrote:
66 kJ ? Not even a power figure here? And all for just a “few million amps”!!? You’re killing me over here.

Maybe people don’t want the expensive, behemoth steam driven turbine AC generators anymore after the Fukushima experience and the problems with our grid. So we see the advent of the SMR, the small modular reactor. Unfortunately at this point the trend for those is going to be steam driven turbine AC fission technology.

For a large number of people even a hundred watts is a very big deal. (They aren’t living in ivory towers).

Maybe there is an issue of pressure in any size or form of fusion we could dream up. Great if you have it figured out! Bring the idea to the people in a way that’s
useful to them soon. In the meantime other approaches will have to be tested as well, that’s just reality.

You never know, 5MW could also light up a lot of folks lives.

[Maya]

benf wrote:

66 kJ ? Not even a power figure here? And all for just a “few million amps”!!? You’re killing me over here.

Maybe people don’t want the expensive, behemoth steam driven turbine AC generators anymore after the Fukushima experience and the problems with our grid. So we see the advent of the SMR, the small modular reactor. Unfortunately at this point the trend for those is going to be steam driven turbine AC fission technology.

For a large number of people even a hundred watts is a very big deal. (They aren’t living in ivory towers).

Maybe there is an issue of pressure in any size or form of fusion we could dream up. Great if you have it figured out! Bring the idea to the people in a way that’s
useful to them soon. In the meantime other approaches will have to be tested as well, that’s just reality.

You never know, 5MW could also light up a lot of folks lives.

“For a large number of people even a hundred watts is a big deal”
I think it does not follow that a large-scale production will help others any less than a small one … just because it’s “big”. The question is which approach is likely to actually solve the problem, globally, for everyone?
I hope you’re right that it can be done “small”, cheaply and easily. That would be great. It would be a liberating thing if everyone could just own their own personal fusion reactor and be energy free. That is the ideal scenario. Given enough steps, and if we’re here long enough to do it, I think it will happen.

[vansig]

Maya wrote:
The Coulomb barrier guarantees that in order to get _that many_ reactions in, say, one cubic meter of space, you have to compress that fuel somehow. The forces required to compress that fuel that much are either:
1.) too great to achieve with any known materials science in higher power outputs
2.) too great to make it economically viable in lower power outputs

point 1.) is correct. and that’s why focus fusion does not use a solid material to achieve the extremely strong magnetic field. yet the fields already obtained with the device, ie: in the gigagauss range, are much stronger than the inter-atomic forces in any known materials. and instead of one cubic meter, you have volumes on the order of the head of a pin.

[zapkitty]

A mystery appears… what could it be?

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