What is the state of decelerator R&D?

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

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jmc
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Postby jmc » Fri Feb 25, 2011 10:00 am

The alpha particle "beams" emerging from the cusps will be spiralling around magnetic fieldline, thus while their gyro averaged velocity may be in a "beam" their actual velocity will not and their energy component perpendicular to the decellerating fields of the decellerator will be continous rather than just having two components.

I realize there has been quite some work on direct conversion of energy from fusion plasmas to electricity, but ultimately the problem of converting fusion products to electricity is the same as the problem of converting decaying alpha particles to electricity, so the question stil stands: if its easy to convert fusion products to electricity at an efficiency of 80%, then why is the efficiency of state-of-the-art nuclear batteries 20%?

chrismb
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Postby chrismb » Fri Feb 25, 2011 12:38 pm

jmc wrote:The alpha particle "beams" emerging from the cusps will be spiralling around magnetic fieldline, thus while their gyro averaged velocity may be in a "beam" their actual velocity will not and their energy component perpendicular to the decellerating fields of the decellerator will be continous rather than just having two components.
You are rather confusing 'velocity' with 'speed'. A magentic field can do no work, so a charged particle with, say, 4MeV energy passing through a magnetic field will always have 4MeV of kinetic energy [in whatever direction it happens to be going] unless it is ac-/de-celerated by an e-field, hits something, and excepting what energy it emits by synchrotron radiation.

I realize there has been quite some work on direct conversion of energy from fusion plasmas to electricity
Really? What work? A bag load of hot-air-gassing by wind-bag snake-oil sellers, maybe. There again, I'd not describe what snake-oil retailers do to sell their wares as 'work', so maybe I misunderstand you.


but ultimately the problem of converting fusion products to electricity is the same as the problem of converting decaying alpha particles to electricity, so the question stil stands: if its easy to convert fusion products to electricity at an efficiency of 80%, then why is the efficiency of state-of-the-art nuclear batteries 20%?
Ah!! Now you're talking analytically. Actually I think you will find atomic batteries have yet to get over 5%. But your point is very valid:

If you take a gramme of polonium 210, with specific radioactivity of 166500GBq/g at 5.4MeV per alpha, you'd have access to 140W of alpha energy streaming off of it.

So if these power-point fusion engineers think catching MeV-fast alphas is a breeze, then they should start making 100W Po-210 5MV battery our of a gramme of Po-210. Those'd sell like 'hot cakes' (!) in many industries. And those alphas are all mono-energtic, so there is no question of making that challenge as easy as possible!

So if these wind-bags can't make a Po-210 battery, then they sure as heck can't make a 'direct energy conversion fusion reactor'.

Nice point to make, JMC. Didn't occur to me to make the point so clearly by asking that question; where are the Po-210 batteries??

OK, so Po-210 only last a couple of months, but you could make an Americium 241 battery out of 1 kg of the stuff that'd pump out 100W of alphas for a few hundred years.

I'm sick of reading this unsubstantiated shyte about direct energy conversion. If someone has an actual bona-fide link to a working device that HAS harvestED usable electrical energy directly from decelerating alphas or betas, then I am all ears. Until then....

KitemanSA
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Postby KitemanSA » Fri Feb 25, 2011 1:12 pm

chrismb wrote:
I realize there has been quite some work on direct conversion of energy from fusion plasmas to electricity
Really? What work? A bag load of hot-air-gassing by wind-bag snake-oil sellers, maybe. There again, I'd not describe what snake-oil retailers do to sell their wares as 'work', so maybe I misunderstand you.
See the two documents listed in my last post. The NASA one is not a bag of hot air.

chrismb
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Postby chrismb » Fri Feb 25, 2011 1:51 pm

KitemanSA wrote:See the two documents listed in my last post. The NASA one is not a bag of hot air.
How do I access these documents? Are they 'theory [unfulfilled and unused theory, still, after 4 decades]' or 'real work'? Have you got a photo of an illuminated light bulb that plugged into them, or something?

My definition of 'a bag of hot air' is a 4-decade-old theory that amounted to nothing.

As JMC has observantly directed our attention - if these worked out, why aren't there Po-210 alpha-capturing batteries on space craft?

Why would I need to consider trying to dig these ancient doucments out, if I can see, self-evidently, that they did not amount to viable devices?

jsbiff
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Postby jsbiff » Fri Feb 25, 2011 2:09 pm

krenshala wrote:While DD would allow electricity via thermal conversion (however you wanted to do it) I would definitely NOT say "it is done" when that happens. Direct DC conversion to electricity has much higher efficiency than running things through a thermal cycle, so the effort of getting the decelerator grids developed would be well worth it.


Here's a question: with D+D fusion, don't we effectively have an infinite energy source? How important is efficiency, really, when there's no scarcity? So, you lose 50% of the energy with thermal conversion. Who cares? The fuel is so cheap, it would be a miniscule portion of the cost of running the reactors, wouldn't it?

Efficiency only matters if your fuel is expensive, limited in supply, or both, no?

The only counter argument I could see to this is if the decelerator grids were so cheap to build and maintain, that they significantly reduced the cost of building and maintaining a power plant (e.g. say you could expect to save $100Million over the life of the power plant by using a decelerator instead of a turbine, because of the added cost and complexity of the turbine system).

At that point, lower capital/operational costs might be worth using decelerators for fusion plants, but certainly fuel/efficiency costs are not an issue, right?

Aero
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Postby Aero » Fri Feb 25, 2011 3:26 pm

Efficiency only matters if your fuel is expensive, limited in supply, or both, no?

No. Efficiency relates directly to mass. It takes a lot of massive machinery to convert heat energy to electricity as well as to remove the excess waste heat. If you want a smaller energy producing device to produce equal energy, then you want a more efficient device. Applications abound where smaller, less massive devices are feasible but large devices are not.
Not to mention that when the technology matures, the construction cost of mature devices can be reasonably estimated as proportional to their mass.
Aero

jsbiff
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Postby jsbiff » Fri Feb 25, 2011 5:15 pm

Aero wrote:
Efficiency only matters if your fuel is expensive, limited in supply, or both, no?

No. Efficiency relates directly to mass. It takes a lot of massive machinery to convert heat energy to electricity as well as to remove the excess waste heat. If you want a smaller energy producing device to produce equal energy, then you want a more efficient device. Applications abound where smaller, less massive devices are feasible but large devices are not.
Not to mention that when the technology matures, the construction cost of mature devices can be reasonably estimated as proportional to their mass.


I think this is a case of "I don't think that word means what you think it means". Sometimes words are used differently, in a legitimate way, by different people in different contexts.

When I'm talking about power plants, to me efficiency just means how much of the total energy released by fuel is converted to electric energy.

I did mention that I realized that there is a very real potential that a delelerator grid could be much more economical than a steam or gas turbine heat engine, which seems to be the same point you are making.

You make one additional point - size, and that could definitely have a huge impact for some applications - use aboard space craft, ocean-crossing ships (like cruise ships and cargo ships). So, that's definitely a potential advantage - but to me, that is not 'efficiency'. It's important, but not 'efficiency'.

But, as far as utility-scale (100MW or larger) power plants, while cheaper is certainly better, D+D fusion would be a big jump in price/performance, even with heat engine electric generators, than any current technology, wouldn't it, as long as you get a reasonably good net power ratio in your fusion reactors?

rjaypeters
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Postby rjaypeters » Fri Feb 25, 2011 5:26 pm

jsbiff wrote:Here's a question: with D+D fusion, don't we effectively have an infinite energy source? How important is efficiency, really, when there's no scarcity? So, you lose 50% of the energy with thermal conversion. Who cares?
The people and local environment around the power plant. Sometimes a beneficial effect: manatees in Florida hang out around powerplant water exhausts in the winter (a small consolation for being killed wholesale by boat propellers).

Or, if the local cooling media capacity doesn't match the heat rejection requirements of the power plant, the powerplant generating capacity is limited.
"Aqaba! By Land!" T. E. Lawrence

R. Peters

D Tibbets
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Postby D Tibbets » Fri Feb 25, 2011 5:55 pm

chrismb wrote:
D Tibbets wrote:Why is chrismb skeptical? Small magnetic fields, etc do indeed sort of contain several orders of magnitude more energy than what can be released from feeble nuclear events. All they have to do is figure out how to harvest it.
Oh Boy!

Your grip on the laws of physics are worse than I feared. Pray tell; where does the energy in these 'magnetic fields' come from?


I was actually supporting your view point, did you read the entire post and notice the smiley face.

As far as magnetic fields or other fields containing energy, of course they do. So does matter. I was purposely vague and implied such when I used the "sort of" qualifier. I also gave a hint when I said "Einstein Rules".
The underlining assumption is of course E=MC^2. Now tell me , are you now contesting Einsteins conclusions?

PS: I don't know where the energy contained in force fields and matter comes from. The furtherest I can follow the link is the Big Bang. String theory and derivative brane theories (if they have any relevance at all) would only push the question further back. Perhaps you can enlighten me?

Dan Tibbets
To error is human... and I'm very human.

chrismb
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Postby chrismb » Fri Feb 25, 2011 6:05 pm

D Tibbets wrote:I was actually supporting your view point, did you read the entire post and notice the smiley face.
I missed the irony, if that was the meaning.

D Tibbets wrote:I don't know where the energy contained in force fields and matter comes from. The furtherest I can follow the link is the Big Bang.
I've explained my theory on 'energy' before. It is very simple, but folks here just said "well, that doesn't explain anything we don't already know" - which of course such a theory probably wouldn't. Why would it, if it were a simple explanation of what we already know?!

Aero
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Postby Aero » Fri Feb 25, 2011 6:18 pm

rjaypeters wrote:
jsbiff wrote:Here's a question: with D+D fusion, don't we effectively have an infinite energy source? How important is efficiency, really, when there's no scarcity? So, you lose 50% of the energy with thermal conversion. Who cares?
The people and local environment around the power plant. Sometimes a beneficial effect: manatees in Florida hang out around powerplant water exhausts in the winter (a small consolation for being killed wholesale by boat propellers).

Or, if the local cooling media capacity doesn't match the heat rejection requirements of the power plant, the powerplant generating capacity is limited.

I see. Yes, there is "Fuel efficiency," Mass efficiency," "Economic efficiency," "Labor efficiency," and a host of other efficiencies. Since Deuterium is abundant and cheap, its efficient use is probably not critical and in fact it probably isn't that much of a consideration relative to the other efficiencies.

Consider, for example, the waste heat produced by a modest two GW electric power plant. At 30% efficiency that power plant is generating 6.67 GW thermal. That means 4.67 GW of waste heat must be dispersed into the surrounding environment. That will warm a lot of Manatees. It means that in California, it can only be located along the coast, for lack of cooling water elsewhere. Now, consider a direct conversion power plant, at a guess, 85% efficient. This power plant is only 2.35 GW thermal meaning only 350 MW of waste heat dispersed into the environment. That is still a lot of heat but it is quite doable as it compares to the waste heat from a 150 MW coal power plant and coal power plants of that general size abound.

I won't go into the other efficiencies though capital cost is always very important. Turbo-generators are not "Off-the-Shelf" items, but must be built to specification for each power plant. That makes them surprisingly expensive. Direct conversion grids are expected to be much cheaper but of course some expensive research and development will be needed.
Aero

D Tibbets
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Postby D Tibbets » Fri Feb 25, 2011 6:56 pm

chrismb's last posts (second above) are valid points. But he is confusing physics with engineering. Nuclear batteries as used in satallites use direct conversion through thermocouples, not because they are efficient, but because the engineering, weight concerns are paramount. I have seen mention that a heat engine like a Stearling engine could be used, but the weight penalty (and probably reliability, vibratory, etc. concerns) ruled them out.
As far as 100 W long lasting nuclear batteries, the cost of the fuel is a concern, along with safety concerns.

As far as using direct electrostatic conversion of MeV alphas, or any other energetic ion, the obvous problem is the scaling, not the underlieing physics. Do you think an electrical engineer would not laugh if you asked him to build a lunch boxed size device that could control megavolts, and down convert it to a usefull end use voltage?. The problem is not physics, but engineering. And don't forget cost per unit of output power. If you are talking about a powerful reactor with plenty of realistate to handle the voltages, etc, the problem is completely different.

Again I point out that the Magrid is a perfect example of a direct conversion system. If the charged particles are not recycled (kinetic energy to potential energy stored in the magrid casing to kinetic energy again) but was instead wired to drain the potential energy from the grid casing, it would be a complete high voltage direct conversion system, outputting excess current at the ~ 10,000 volts that the escaping electrons imparted (in the case of WB6). Judging by the claimed efficiency of recirculation, this would translate into an efficacy well above 90% . There would be other losses in down voltage conversion, etc, but I think the point is made. This is direct experimental evidence of high voltage direct conversion of charged particles at high efficiencies. Of course you can contest this because you are not privy to the detailed data, but that is a convenient dodge.

Also, keep in mind, that ion engines are also direct converters of high voltage electrical energy to kinetic energy of charged particles. It is a two way street. I have not mentioned all of the related processes represented by diverters, repellers, etc that have been used in various fusion schemes like mirror machines, and accelerators.

At least in my mind, the details may prove difficult, but the concept is not only reasonable, but proven.

What is a question I have is the interaction of escaping electrons and fusion ions. The fusion ions would be decelerated, allowing for positive energy conversion. But the electrons would be accelerated, and be a negative energy converter (potential to kinetic). Some of the energy might be recovered by thermal conversion, but that would still leave the sputtering effect of the accelerated MeV electrons. My assumption is that in a working positive Q reactor the number of electrons reaching the ion direct converters must be less. To avoid charge build up, most of the electrons would need to be leaving the system through some other means, Perhaps by transport through the magnetic fields to the magrid, or a grounding (actually a few thousand positive volt plate) preceding the ion attracting plates. This would work because the electrons would only be a few thousand eV (assuming the electrons are not tightly coupled to the ions) while the fusion ions are at a few million eV. The cost would be minimal, and most (?) of the added energy of the ions could be recovered by a simple slight increased voltage on the ion collecting plates.
Also, if ion guns are used, the charge balance picture is different.

Dan Tibbets
To error is human... and I'm very human.

chrismb
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Postby chrismb » Fri Feb 25, 2011 7:02 pm

jsbiff, Aero, I think you're both getting into recognising the importance of being specific about terminology. But it's a bit much to watch you both wandering around the definitions of things!

jsbiff, your question is actually more relevant that, perhaps, you might know. The issue for an 'efficient' fusion reaction is that the energy fed into it is less than the energy out. But for that to be an energy out that can be converted to usable 'primary' energy, it has to be a sufficient multiple of the energy in to clear it of the conversion inefficiencies. For example, a 30% thermal plant would not generate ANY net energy if the energy out were less than 3 times the energy in. Similarly, a plant that can't deliver a few multiples out, net, than is put in isn't much use. So that adds up to a minimum Q of around 10, in all practical terms. If a Q=10 is achievable from a device, then, yet, what you are saying is largely correct. The actual inefficient consumption of D would become a triviality. But drop below Q=3 and it is no longer just a matter of inefficient usage, it may well be a matter of non-viability.

Aero, in terms of 'wanting the max efficiency', I think you prob know (but I'll repeat in context here) that this is not the be-all-end-all. Let's say that you could construct an 80% efficient plant, that doesn't mean, at all, that you can efficiently pump GW through it. The GW power station that puts out most power and build to a given budget on a given amount of land, may not necessarily be the most efficient.

Indeed, most plants are built to run up to around 550C, the softening point for stainless steels. This then imposes a 30%, or so , efficiency on a thermal power plant. Run higher temps, and your efficiency goes up, but that may be more costly and the equipment to manage the higher temperatures may actually be more bulky that the less efficient plant. So we want the max energy out versus total equipment required [be that by cost, land usage, bulk tonnage of equipment, whatever your criteria].

So I think what you are both looking for here is 'specific net-power output', which may or may not necessarily be related to efficiency. It is true to say that it generally is related, but who can really say, for a new technology. In any case, below Q=3 for fusion it doesn't matter because it is so close to non-viability it is a poor prospect, and above Q=10 it begins not to really matter that much.

D Tibbets
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Postby D Tibbets » Fri Feb 25, 2011 7:13 pm

chrismb wrote:
D Tibbets wrote:I was actually supporting your view point, did you read the entire post and notice the smiley face.
I missed the irony, if that was the meaning.

D Tibbets wrote:I don't know where the energy contained in force fields and matter comes from. The furtherest I can follow the link is the Big Bang.
I've explained my theory on 'energy' before. It is very simple, but folks here just said "well, that doesn't explain anything we don't already know" - which of course such a theory probably wouldn't. Why would it, if it were a simple explanation of what we already know?!


I think I read some of you posts on this subject, though I didn't follow them. But, that is not the question. The question is how did it start? Hoyle, and other steady state cosmologists dodged this question by invoking infinity. The Big Bang does not have this dodge, unless you invoke an infinite multiverse that hiccuped to form the observable universe. Irregardless, it is point of philosophy (or religion if you prefer).

Question: Where did the universe come from?
Answer: God created it.
Question: OK, but where did God come from?
Answer: Well, ....

Dan Tibbets
To error is human... and I'm very human.

Enginerd
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Postby Enginerd » Fri Feb 25, 2011 7:26 pm

jsbiff wrote:Efficiency only matters if your fuel is expensive, limited in supply, or both, no?


Image that everybody in town has a Mr Fusion in their kitchen that is 5% efficient converting thermal to electrical, and each Mr Fusion is generating 100 kW thermal to power each home... Now, scale that up to several billion Mr Fusion plants, one per household, plus an untold number of additional big plants for industrial use (processing aluminum, desalination, etc, etc). All that waste heat is going to have to be dumped to the environment. Human induced global warming may or may not be real right now, but at some point, it surely will become a serious consideration. More efficiently fusion means far less less waste heat to dispose of.
Last edited by Enginerd on Fri Feb 25, 2011 7:51 pm, edited 1 time in total.


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