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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chrismb
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Postby chrismb » Fri Feb 25, 2011 7:45 pm

Enginerd wrote: All that waste heat is going to have to be dumped to the environment..
...which then radiates out into space at night, according to the thermal equilibrium that the conditions of the insulating layer of atmosphere set for the earth.


Makes no difference, the amount of heat several dozen billion cold apes need to keep themselves warm. What matters is how the thermal equilibrium works, not how much heat energy is released into the environment.

jsbiff has it right - providing a fusion power plant has a half-decent Q, it makes no odds. If you've got space and money to build two Q=10 1GW fusion plants or one 100MW Q=200 fusion plant, it's a no-brainer because the fuel cost is trivial. Whereas if you had the option of building the same with fossil fuels, then you might well pick the more efficient one because that'd make more profit for the investment.

Some seek Q=infinity (self-burning) for fusion. Personally, I think that is a Very Bad Idea. Any energy system with 'low Q' is intrinsically more stable than one with a 'High Q'. A Q=infinity has no way of turning it off except for a direct quench. A Q=10 device will shut down near instantly once the input power is turned off. So what would you want? A plant that 'blows up', or 'half-blows up' when it goes wrong, or just have a crappy Q and shuts down near instantly when something goes wrong?

jsbiff
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Postby jsbiff » Fri Feb 25, 2011 7:51 pm

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


Imaging 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.


Well, if you are going to use a *ridiculously* low conversion efficiency, that might be true. A modern heat engine design should be able to be somewhere between 30-50% efficient, depending on operating temperature (I've heard people say that nuclear plants using high temperature inert gas (nitrogen, helium, etc) turbines, instead of steam, should be pretty close to 50% efficient. 50% isn't terribly inefficient (compared to say, 5% in your example). Even 30-45% seems like it would be acceptable, seeing as most power plants *today* operate within that range.

D Tibbets
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Postby D Tibbets » Fri Feb 25, 2011 9:17 pm

Conversion efficiency causing global warming? Minimal, if any. Compare Solar heating of up to a couple of KW per square meter during the day. Divide that by ~ 5 to account for albedo effects. That would result in ~ 400 W/ m^2 or 400 MW/ km^2. Multiply this by a rough estimate of ~ 100,000,000 km^2 exposed to the Sun at any given time, results in a thermal load of ~ 800 Terra Watts. Add to that to the the geothermal output and tidal friction. The current electrical output is perhaps 0.5% of this. The waste heat perhaps doubles that to ~ 1%.

Increasing conversion efficiency would help this, and possibly fully compensate for increased usage.
Local thermal waste management is another issue entirely.

What is important for direct conversion is of course economic. and location concerns. Thermal steam conversion is expensive , If a direct conversion scheme can be installed and maintained at less cost, it is advantageous. Also, if direct conversion decreases water needs, more locations are available, and transmission costs may improve (another large cost in delivering electricity to the end user.). Also, if plant capital cost scales with size, direct conversion, if it is more efficient than steam, allows for smaller and thus cheaper plants per unit of electricity delivered.

Finally, high efficiency direct conversion is essential if you are operating at low Q's. This may be particularly important for DPF or FRC plants. If they work, they are expected to only achieve low Q's of perhaps 2-5.
It is not only an issue of extracting more power than you put in, but also the proportional amount of excess energy.
EG: a FRC produces 5 MW of fusion power with an input of 1 MW. That is a net of +4 MW. The next step of conversion might yield 1.5 MW thermally, or 3 MW direct conversion.
The final net output would be 1.5 MW of useful (and sellable) power for a thermal conversion plant, and 3 MW of useful energy with direct conversion. Even if the direct conversion costs as much, the profit margin would still be 2 times higher.

Why has direct conversion not been developed? Technical concerns aside, there simply has not been any practical application for it.

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

chrismb
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Postby chrismb » Fri Feb 25, 2011 9:29 pm

D Tibbets wrote:Why has direct conversion not been developed? Technical concerns aside, there simply has not been any practical application for it.
Yup. There has been no use for a 100W high voltage nuclear battery that lasts for 40 years that runs on easily shielded betas from something like 50 grammes of strontium-90 that forms no radioactive daughter products and could probably be packaged up in a 6V-sized [PJ996] battery form factor. I can't see a single reason why anyone would want something like that.

KitemanSA
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Postby KitemanSA » Fri Feb 25, 2011 9:59 pm

chrismb wrote:
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?
You might try copying the first line of that reference from my post and put it into Google. The pdf of the report was the first thing that came up when I tried it.

Since I can never predict your appreciation of information provided, why not read it and decide for yourself?

KitemanSA
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Postby KitemanSA » Fri Feb 25, 2011 10:10 pm

chrismb wrote: As JMC has observantly directed our attention - if these worked out, why aren't there Po-210 alpha-capturing batteries on space craft?
I suspect that not many space craft designer's want to haul a megavolt system into space.

KitemanSA
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Postby KitemanSA » Fri Feb 25, 2011 10:21 pm

jsbiff wrote:
Enginerd wrote:
jsbiff wrote:Efficiency only matters if your fuel is expensive, limited in supply, or both, no?
Imaging 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.
Well, if you are going to use a *ridiculously* low conversion efficiency, that might be true. A modern heat engine design should be able to be somewhere between 30-50% efficient, ....
Actually, most folks have something akin to that rediculously low efficiency 100kW unit already. It is called a car. :wink:

chrismb
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Postby chrismb » Sat Feb 26, 2011 12:06 am

KitemanSA wrote:See the two documents listed in my last post. The NASA one is not a bag of hot air.
I did as you said and I do get a link, to; http://ntrs.nasa.gov/archive/nasa/casi. ... 016806.pdf , but when I click on that it comes up 'page load error'.

I did find what appears to be another reference to 'direct energy conversion' and it doesn't appear to be a deceleration grid at all. The link I found says;

Another attractive solid state power generator device investigated at JPL is based on the direct conversion of the kinetic energy of alpha particles into electricity (Patel, 1999). This device is expected to exhibit a high conversion efficiency (over 14%) and to function continuously over a long period of time in the temperature range of 20 to 800K without any recharging needs or the presence of any sunlight thanks to a unique long life design. The use of alpha particle kinetic energy for conversion into electricity using an existing SiC photodiode was reported earlier (Rybicki et al., 1996). This particular device was found to have degraded in a rapid manner because it was not specifically designed to avoid the crystal damage from implanted alpha particles. Results on similar devices using beta and gamma rays were also published (Olsen, 1974), but these power sources exhibited extremely low conversion efficiency (0.1 to 4%) and required substantial shielding to reduce the dose from its radiation to adjacent electronics. Such devices also had a relatively short lifetime (2-6 years) and delivered very low power levels (a few milliwatts)


Image



So....could you please provide a direct link to a live website document? I'm not doubting that there is a valid theoretical notion that one might be able to slow down charged nuclear emission particles and get energy from them, but it seems such a crazy way to do it when it is so easy and robust just to put in a shield and pick up the heat from those particles ramming it, albeit with thermal conversion losses. To fit in grids (which, incidentally, don't need to be the whole potential in one stage, it could be broken down into multiple stages, and each converted to a lower voltage) seems open to all manner of utterly over-complex problems that my original post herein remains unchallenged - that it has not been done and any effort on it has just be jaw-aching wind-generating power-point engineering.

KitemanSA
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Postby KitemanSA » Sat Feb 26, 2011 2:18 am

Wow, that was weird. Try the second or third listing. It is the NASA Technical Reports site and if you put the report number in that search engine it will provide it. I did it. I looked at it, it is the same as the one I have on my computer.

Good luck!

chrismb
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Postby chrismb » Sat Feb 26, 2011 12:09 pm

Kite,

I have now managed to download this document. Odd. It is the same link as I posted, but doesn't work unless accessed through the NASA portal.

Anyhow, I need to disabuse you of the notion that the report NASA CR-54256 is a decelerator type generator, as being described here.

It is, simply, a single electrode device, thus;

Image

It works by, firstly, allowing alphas to bombard what they [wrongly]** call the 'anode'. The 'anode' is linked to a circuit in which there is a very high impedance load that causes the 'anode' to charge up.

*[An 'anode' is an electrode to which electrons flow, and a cathode is an electrode from which electrons flow. Therefore, in batteries and in this device, the +ve'ly charged electrode is the cathode and the emitting electrode is the anode.]

So in the first few moments of operation, all that happens is that alphas freely bombard the 'anode', causing that side of the circuit to charge up.

Once it is charged up to a given potential, the electric field caused by that charged-up electrode then causes the alphas heading towards it to experience a retardation. If you then consider where the particles' energy is going during that retardation, you can see that all that is happening is that the charge on the electrode is being pushed around the circuit a bit, before the alpha hits it.

Therefore, it relies on alpha bombardment of the outer electrode, so as to maintain the population of charge there, as the charge flows (and is pushed) around the circuit. This isn't my understanding of the way the 'deceleration grids' we are talking about work.

There is a second diagram that might have confused you;

Image

This shows a suppression grid and this is relevant to consideration of Polywell. An alpha emitter throwing out 5MeV alphas doesn't just have alphas leaving it. The charge also pulls off electrons off of the alpha emitter - because of ambipolar diffusion. It is to be entirely expected that the same problems would occur with any such configuration of trying to capture the direct emissions of alphas - because there are always electrons knocking around. This grid reduces efficiency and reduces the capacity of the 'anode' to reach a given potential. In the case of the paper, it describes that it hasn't got over 50kV potential on the anode due to 'micro-discharges'.

Welcome to reality!!!...... you think this is easy to fix!?!

So a few point to note;

1) NASA report CR-54256 does NOT describe a multi-grid 'venetian-blind' style deceleration system.
2) I can't find any comment in the NASA report CR-54256 that demonstrates achieved efficiency, there is only wind-bagging about what is theoretically possible [for this alternative design of electrode-collisional direct energy system]
3) I can't find any comment in the NASA report CR-54256 that demonstrates achieved power, there is only wind-bagging about what is theoretically possible [for this alternative design of electrode-collisional direct energy system]
4) Points 2 and 3 looks like it is because they have made no experimental attempt to apply a real load between 'cathode' and 'anode'. In other words, all that the experimentation has done is put an alpha emitter into a chamber and measured how much charge (voltage) has accumulated on the electrode they wrongly refer to as 'the anode', and they only achieved 50kV. Compared that with where they actually need to reach, which is 5MV. So 1% on their way to demonstrating they can even capture charge, and 0% of their way to demonstrating any electrical power at all.

So.... still no experimental evidence of any such 'venetian-blind' non-collisional energy recovery device being made...

I therefore believe I am right in saying that my comments in the second post of this thread remain, entirely, uncontested.

KitemanSA
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Postby KitemanSA » Sat Feb 26, 2011 1:37 pm

chrismb wrote:Kite,
It works by, firstly, allowing alphas to bombard what they [wrongly]call the 'anode'. The 'anode' is linked to a circuit in which there is a very high impedance load that causes the 'anode' to charge up.

So in the first few moments of operation, all that happens is that alphas freely bombard the 'anode', causing that side of the circuit to charge up.

Once it is charged up to a given potential, the electric field caused by that charged-up electrode then causes the alphas heading towards it to experience a retardation. If you then consider where the particles' energy is going during that retardation, you can see that all that is happening is that the charge on the electrode is being pushed around the circuit a bit, before the alpha hits it.

Therefore, it relies on alpha bombardment of the outer electrode, so as to maintain the population of charge there, as the charge flows (and is pushed) around the circuit. This isn't my understanding of the way the 'deceleration grids' we are talking about work.
That is how the "venetian blind" process works too, so I don't understand your problem. Once the unit is charged up (however it gets charged) the alphas climb the potential gradient, DECELERATING, giving up their energy until they slowly impact the "anode". Their charge is neutralized by electrons going thru the circuit load. That is the EXACT process by which Polywell is anticipated to achieve ~85% efficiency. The sole distinction is that there are TWO "anodes" on the Polywell at two different voltages.

But the Polywell doesn't NEED to use a venetian blind approach if the designers would settle for lower efficiency (but still higher and MUCH cheaper than thermal cycle). And they could still use a thermal cycle to convert some of the direct conversion losses, achieving a fairly high TOTAL efficiency.

But I guess I see your point. Because no-one has ever built a multi-megawatt VHVDC alpha converter for no reason, it can't be done. And planes can't fly either. Oops, no, the naysayers were proven wrong there. But of course we'll never fly to the moon. That is fairy-tale land. No, wait a second...

If your burden of proof is a fully functional full scale item, then you can never be wrong, but your argument is trivial. And destructive of progress.

chrismb
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Postby chrismb » Sat Feb 26, 2011 3:02 pm

KitemanSA wrote:If your burden of proof is a fully functional full scale item, then you can never be wrong, but your argument is trivial. And destructive of progress.
The point in question is my answer to the original post of this thread. It is NOT whether or not it might be made to work.

There was a question. What is the status. I said it hadn't been done.

The PROOF of that statement is me pointing out that it hasn't been done!!!!

Has it been done, or do you have PROOF to the contrary?

Anyhow, I traverse your claim that this is the device described by 'venetian blinds'. There is no mention that the outer walls are going to be, knowingly, bombarded by alphas to charge them up!! When has that little 'nugget' every been revealed, then!?!?

So now we have THE FACT that helium product ARE DEFINITELY going to bombard the walls of the reaction vessel to get 'direct power' out of it. I have just never ever heard this admission before on this.

This thread is absolutely crazy. I have fed in an hour or so of my time trying to explain why the claims that direct energy conversion devices have already been built are false, and all you do is go try counter that by saying 'ah, but you've not proved it can't work!'

It's not for me to prove anything can't work. You can't prove a negative. It is for those proponents of the idea to build it and make it work ...

...AND NO-ONE EVER HAS. THAT'S THE CORRECT ANSWER TO THE QUESTION POSED BY THE PRINCIPAL THREAD AUTHOR.


STAY ON TOPIC!!!

D Tibbets
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Postby D Tibbets » Sat Feb 26, 2011 4:50 pm

The anode and cathode in the illustration two posts up are just that. On first glance it looked fishy to me too, but consideration revealed the situation. The cathode provides electrons that can flow through a circuit. It is externally powered. The alpha emitting layer is not actually the cathode. It does emit alphas in all directions. Those that hit the cathode are neutralized by the excess electrons aviable from the cathode. Those that are emitted towards the anode, experience a deceleration as they approach thereby giving up energy to the anode. As they touch the anode they increase the positive charge on the anode., which is then neutralized by electrons flowing from the cathode, through a useful circuit and to the anode. It is not clear in the illustration, but I believe that to work, fewer alphas must reach the cathode*. I suspect there is a grounded shield between the alpha source and the cathode. The difference from a 'venition blind' approach is that an opposing potential is used to decelerate the ions and thus harvest their kinetic energy, as opposed to a retarding potential on an electrode that the ion is passing. This second approach is necessary in a spherical geometry like the Polywell because of Gauss law effects.

*An alternative may be that since the alpha source is in contact with the cathode, the emitted alphas immediately ground on the cathode without being decelerated. That would convert the kinetic energy of the alphas to heat rather than potential(voltage). This might even help to provide electrons to the circuit by stimulating thermionic emission of electrons.


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

D Tibbets
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Postby D Tibbets » Sat Feb 26, 2011 5:00 pm

I had not seen this before, but Askmar has a page that lists several papers on direct conversion. The last might even have application in a Tokamak.

http://www.askmar.com/Direct_Energy.html

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

KitemanSA
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Postby KitemanSA » Sat Feb 26, 2011 5:01 pm

chrismb wrote:The point in question is my answer to the original post of this thread. It is NOT whether or not it might be made to work.

There was a question. What is the status. I said it hadn't been done.
chrismb wrote: Power-extracting decelerator grids remain a power-point fantasy for the ever-hopeful to jaw-ache about.
Ok. I guess in your world those to statements are equal. I did not read "power-point fantacy" as "hasn't been done" to full power... To me, the fact that a battery HAD been made and had worked to a degree consistent with it's design makes it no longer "fantasy". It may be difficult engineering to get a MW-MV system going, but not "fantasy". Guess you speak "Brit" and I speak "Merkin".


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