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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jsbiff
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What is the state of decelerator R&D?

Postby jsbiff » Wed Feb 23, 2011 11:06 pm

So, I know that Bussard was a big fan of the idea of using p+B11 fusion to generate power using a decelerator grid. I was reading the article over at Focus Fusion about the status update on WB-8 (linked to in another thread here on the forum), and I got to wondering. . .

If they end up building WB-8.1 (which is the test of p+B11 fusion), even if it works, is the decelerator grid tech developed to a point where we could pretty quickly start generating actual electricity? I'm guessing that WB-8.1 would not be too concerned about that aspect, as its experimental mission would simply be to prove that the p+B11 fusion is *possible*, and produces enough fusion events/sec to theoretically produce net power, without actually *capturing* that net power?

If WB-8.1 is built, then succeeds at that mission, are we looking using polywells initially with D+D fusion and steam generators, while another decade or two of research on decelerators is done, or is the decelerator tech ready to go, more or less?

chrismb
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Postby chrismb » Wed Feb 23, 2011 11:28 pm

Power-extracting decelerator grids remain a power-point fantasy for the ever-hopeful to jaw-ache about.

..as is p+11B, come to that. If DD works out [in any machine], the job is done.

krenshala
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Postby krenshala » Thu Feb 24, 2011 1:49 am

chrismb wrote:Power-extracting decelerator grids remain a power-point fantasy for the ever-hopeful to jaw-ache about.

..as is p+11B, come to that. If DD works out [in any machine], the job is done.

I know alpha "capture" for conversion to DC current has been done, I don't know if anyone has tried it for alphas generated from fusion. 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.

hanelyp
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Postby hanelyp » Thu Feb 24, 2011 4:36 am

For mono-energetic particles a direct conversion decelerator is a no brainer. Pretty much a single stage electrostatic accelerator in reverse. There will be some losses for particles hitting grids and such. Given the spread of fusion alpha energy, losses with a simple configuration will be higher, but still greatly exceed thermal conversion. A fancier conversion grid able to sort particles of varying energy to different collectors is somewhat in doubt, and may not be worth the effort.

chrismb
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Postby chrismb » Thu Feb 24, 2011 7:10 am

krenshala wrote:I know alpha "capture" for conversion to DC current has been done
Can you kindly provide a reference for that? Is that to a 'useable' DC current, it is pA or kA, is it to a uV or MV potential? Please fill in some details.

scalziand
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Postby scalziand » Thu Feb 24, 2011 11:00 am

LPP are planning on using a rogowski coil instead of a decelerator grid to capture energy from the ion jet.


chrismb wrote:
krenshala wrote:I know alpha "capture" for conversion to DC current has been done
Can you kindly provide a reference for that? Is that to a 'useable' DC current, it is pA or kA, is it to a uV or MV potential? Please fill in some details.


I don't know about any prototypes for alpha capture and conversion, but it apparently has been done with beta radiation sources, with efficiencies up to 50%.
http://www.rexresearch.com/nucell/nucell.htm

jmc
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Postby jmc » Thu Feb 24, 2011 11:37 am

I've been doing quite a lot of reading up on Nuclear Batteries recently

http://en.wikipedia.org/wiki/Atomic_battery

and their general efficiency is pretty pathetic for the most part, 1-5% most nuclear batteries are thermocouple based. Some betavoltaic based designs can convert the enrgy of radioactive decay into electricity at an efficiency of 20%, but you would have thought that if grid-based decellerators were a doddle then practically all nuclear batteries would have 90% efficiency. (after all and alpha decay souce is a source of monoenergetic charged particles), what could be easier in terms of conversion.

I know there's been quite a lot of work on direct conversion of energy from neutral beams and I think they have had considerable success of this front, but a neutral beam is a monodirectional monoenergetic source, for which direct conversion would be easier to achieve than for a Polywell.

http://www.askmar.com/Fusion_files/1.6% ... ersion.pdf

chrismb
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Postby chrismb » Thu Feb 24, 2011 11:56 am

scalziand wrote:
I don't know about any prototypes for alpha capture and conversion, but it apparently has been done with beta radiation sources, with efficiencies up to 50%.
http://www.rexresearch.com/nucell/nucell.htm


Brown's first prototype power cell produced 100,000 times as much energy per gram of strontium-90 (the energy source) than the most powerful thermal nuclear battery yet in existence. The Nucell battery yielded 7500 watts per gram of strontium-90. Compare this to an advanced device recently developed by the US Dept. of Energy Byproducts Utilization Program. Their state-of-the-art thermal nuclear battery produced 0.063 watts per gram of strontium-90.

The claim here is that 1 gramme of 90Sr can be used to generate 7500W of useable power.

----

1st Analysis**:

Sr-90; has a 41 year lifetime, a specific radioactivity of 5TBq/g, and decays by a 0.5MeV beta.

5E12 decays/s/g x 0.5MeV/decay x 1.6E-13J/MeV = 0.4W/g

To achieve 7500W/g therefore requires a thermodynamic efficiency of 1875000%. Quite impossible unless you believe nonsense.

----

2nd Analysis;

To generate 7500W for 41 years (the lifetime of a g of 90Sr) would be to generate a total of ~1E13J.

The complete annihilation of 1 gramme of matter would liberate mc^2 = 9E13J. Short of anti-matter annihilation, no known process could achieve such a >10% efficiency of total matter conversion.

----

3rd Analysis;

Assume all of 1g of 90Sr decays to its end-point grand-daughter isotope, 90Zr.

Total number of atoms in 1g of 90Sr = ~7E24 atoms

Mass difference, 90Sr -90Zr = 3E-3 atomic masses = 2.8MeV

Total energy difference, 1 g of 90Sr to its decay products = 3E12J

---

Conclusion;

The claim of 7500W/g from 90Sr in your link is cobblers. Utter cobblers. Therefore, any other claims therein must be regarded as such.


The magnetic energy given off by alpha and beta particles is several orders of magnitude greater than either the kinetic energy or the direct electric energy produced by these same particles. However, the myriads of tiny magnetic fields existing at any tie cannot be individually recognized or measured. This energy is not captured locally in nature to produce heat or mechanical effects, but instead the energy escapes undetected. Brown has invented a way to "organize" these magnetic fields so the great amounts of otherwise unobservable energy could be harnessed.


Ah!! The old 'unobservable energy'. How ignorant of me!! :?



**Note;

I am forgetting the 90Yt daughter in this approximation:

90Sr decay daughter, 90Yt; has a 92 hour life, a specific radioactivity of 20,000TBq/g, and decays with a 2.2MeV beta.

2E16 decays/s/g x 2.2MeV/decay x 1.6E-13J/MeV = 7000W/g

However, if this battery is a 'Sr90' battery, the total mass of 1 g will never be '1 gramme of Yt90'. In the first few weeks of this battery's life, you can add 2.8MeV to each of the 0.5MeV 90Sr betas, as effectively all 90Sr atoms that became 90Yt will have gone on to become stable 90Zr.

So we can substitute the 0.5MeV figure with 2.8MeV per 90Sr decay making;

5E12 decays/s/g x 2.8MeV/decay x 1.6E-13J/MeV = 2.24W

2.3W is the maximum you can get out of a g of 90Sr

[looks like around 3% efficiency for the DoE thermal battery, then]

All that being said, I do like the look of 90Sr as a candidate for isotope batteries, given its slow decay to 90Yt and then a 'powerful' and rapid decay to a stable 90Zr, no left-over bits or funny decay branches, easy to shield due to all branches being betas.

chrismb
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Postby chrismb » Thu Feb 24, 2011 12:36 pm

hanelyp wrote:For mono-energetic particles a direct conversion decelerator is a no brainer.
..providing those mono-energetic particles are collimated (or 'collimate-able' at least).

chrismb
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Postby chrismb » Thu Feb 24, 2011 12:37 pm

Are there any other hair-brained claims that folks want me to debunk on this subject?

D Tibbets
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Postby D Tibbets » Thu Feb 24, 2011 8:12 pm

There is a paper from the 1970's that Bussard referenced. I once Googled it but there was no internet accessible text. Whether the paper was theoretical, or included any practical demonstration is unknown by me. Certainly, the manipulation and differentiation of ions is wide spreed in accelerators, mass spectrometers, etc. Bussard said that efficiencies with P-B11 might reach ~ 80 percent. This reflects a modest effort. With P- B11 there are two populations of Alphas. Those initially released from the initial excited C12 , and the 2 times as many alphas released by the later intermediate Be8. I don't recall the energies, but the avarage would be ~ 3 MeV.
If you add the initial velocities, and vectors of the fuel and of the intermediates, the range would vary more by several hundred KeV.
If you chose an electrostatic charge on a grid that the ions fly past that is slightly lower than the the vast majority of the these ions (you don't want many ions being decellerated to negative velosities (relative to the ground) as these could then drift around, compromizing the challenging vacuum pumping/ arcing concerns). For illistrative purposes I will make up some numbers (much easier than looking them up).
Alpha 1= 2.8 MeV
Alpha 2 and 3 = 3.0 MeV
Variation in speed due to velocity and vector of parent isotope assumed to be = +/- 300 KeV

So the overall speed range of the alphas would be ~ 2.5 MeV to 3.3 MeV. One grid charged to 2.4 million volts would capture 2.4 MeV of energy, while the rest would be carried by the alphas till they hit the wall. This would represent ~ 2.4 MeV/ 3.3 MeV or ~ 72% efficiency. This simple one grid collector is straight forward. Adding subsequent grids could theoretically capture almost all of the remaining kinetic energy. Pratical concerns and electrical engineering, size, cost, etc concerns would drive the design to some compromise. With only this one grid design there would be a large proportion of alphas hitting walls with up to ~ 800 KeV. Sputtering concerns may drive the need for more grids from a protective concern rather than a conversion efficiency concern.
From my limited understanding, this seem easily achieved if several considerations are addressed.
First, what is the collimation of the alpha beams exiting from the cusps. If narrow, the design of the grids would be simplified, magnetic shielding would be less, or perhaps not needed at all. Due to what I have read about the limits on how far away the vacuum vessel (or grounding wall) can be away from the magrid, each cusp would need it's own collector grids. No space to try to magnetically divert the cusp beams into one single beam.* With higher order polyhedra, this would become increasingly complex.

Note that direct conversion could be done with D-D fusion as well. The kinetic energy of the resultant tritium and He3 could be harvested, but the energy spread of these fusion ions is wider, so more effort would be needed for less total return (on the harvested energy due to ~ 50% of it being in the neutrons).

Like A DPF, a pulsating or oscillating Polywell could also use inductive effects for direct conversion.

* The electrons exiting the cusps need to be 'stuck' to the magnetic field lines. This apparently results in a maximum distance the grounding surface can be away from the magrid. But as the electrons are stuck on the magnetic field lines in this region, they spread out as the field lines curve. The high epeed alphas would be effected much less. So a donut type grounding electrode could be the first electrode in the direct conversion stack, followed by subsequent high voltage negative donut electrodes to capture most of the alphas kinetic energy. Alternatively, after the electron grounding electrode, subsequent electrodes/ magnetic fields could be used to divert the alpha flows into one beam that could be used for rocket thrust, or fed into a single inductor (or both for a hybrid rocket/ power generator).

This is where I could see a DPF reactor having a big advantage in thrust to weight and complexity. If it could manage to produce enough power to almost maintain itself, and with its single well collimated ion beam, it would be ideal for a high ISP, modest thrust rocket engine (like up to ~ 1000 pounds of thrust, or more with diluted fusion product schemes).

Dan Tibbets
Last edited by D Tibbets on Thu Feb 24, 2011 8:25 pm, edited 1 time in total.
To error is human... and I'm very human.

D Tibbets
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Postby D Tibbets » Thu Feb 24, 2011 8:16 pm

Another point:
If you want an example of a direct conversion scheme. Look no further than the Magrid itself. This has to be an efficient direct converter, or the whole concept of electron recirculation is worthless.

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

D Tibbets
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Postby D Tibbets » Thu Feb 24, 2011 8:58 pm

chrismb wrote:
scalziand wrote:
I don't know about any prototypes for alpha capture and conversion, but it apparently has been done with beta radiation sources, with efficiencies up to 50%.
http://www.rexresearch.com/nucell/nucell.htm


Brown's first prototype power cell produced 100,000 times as much energy per gram of strontium-90 (the energy source) than the most powerful thermal nuclear battery yet in existence. The Nucell battery yielded 7500 watts per gram of strontium-90. Compare this to an advanced device recently developed by the US Dept. of Energy Byproducts Utilization Program. Their state-of-the-art thermal nuclear battery produced 0.063 watts per gram of strontium-90.

The claim here is that 1 gramme of 90Sr can be used to generate 7500W of useable power.



chrismb wrote:.......To generate 7500W for 41 years (the lifetime of a g of 90Sr) would be to generate a total of ~1E13J. ...

Conclusion;

The claim of 7500W/g from 90Sr in your link is cobblers. Utter cobblers. Therefore, any other claims therein must be regarded as such. ...


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. Einstein rules!

Wait... crismb did consider matter- antimatter annihilation in his analysis, which is obviously what they were using for their... um... reasoning. They just left out some details. :)

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

KitemanSA
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Postby KitemanSA » Fri Feb 25, 2011 12:39 am

NASA CR-54256
THE ALPHA-CELL
DIRECT- CONVERSION GENERATOR

November 30, 1964
CONTRACT NAS 3-2797


“Venetian Blind” Direct Energy
Conversion for Fusion Reactors

Nuclear Fusion 13, January 1973
Contact information as of 2009 for Ralph Moir is
Vallecitos Molten Salt Research, <RMoir@Pacbell.net>,
607 East Vallecitos Road, Livermore, CA 94550.
This work was performed under the auspices of the US
Atomic Energy Commission.

chrismb
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Postby chrismb » Fri Feb 25, 2011 8:13 am

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?


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