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Sputtering From Alpha Impacts
Posted: Sat Dec 29, 2007 12:49 pm
by MSimon
Alpha impacts on the grid(s) is going to be a problem. If alpha impacts knock metallic elements from the grid(s) they could poison the reactions or at the very least waste electrons and energy.
One solution - coat the grids with a sufficiently thick layer of Boron and run the machine such that the Boron in the reactor replenishes the Boron on the grid(s).
Thus - any elements knocked off the grids are a reaction species and thus do no harm to the reaction.
Posted: Sat Dec 29, 2007 1:36 pm
by drmike
The alternative is to create a material that can absorb the alphas well.
The trick is to make it vacuum compatible too. Soft materials tend to out gas too much. But they absorb nuclear impacts really well. I'd bet some kind of plastic with long chains and lots of boron in it will work pretty well.
You have to combine it with something. Natural boron is not very strong.
Posted: Sat Dec 29, 2007 5:49 pm
by MSimon
drmike wrote:The alternative is to create a material that can absorb the alphas well.
The trick is to make it vacuum compatible too. Soft materials tend to out gas too much. But they absorb nuclear impacts really well. I'd bet some kind of plastic with long chains and lots of boron in it will work pretty well.
You have to combine it with something. Natural boron is not very strong.
I was not aware of Boron's structural weakness.
However, I believe ITER (some other fusion experiment?) uses a boron coating (evaporated on the surfaces?) to solve the sputtering problem.
If you use pure Boron you have one segment of the problem solved (reaction species) the other problem is to maintain a balance between the coating and the reactants.
Once you get into hydrocarbons you have problems with non-reactant species.
The question then is do thin films have significantly different properties from bulk Boron.
This might be a place to start:
really long url
Search Boron on this page:
http://www.psfc.mit.edu/research/alcato ... needs.html
also a look here:
http://www.osti.gov/energycitations/pro ... id=5785157
and here:
http://www.iop.org/EJ/abstract/0029-5515/45/7/018
I'm pretty confident that the thermal problems can be solved. So this is the next hump IMO.
Posted: Sat Dec 29, 2007 7:52 pm
by drmike
Thanks! I think it's just time and money - there will be an effective solution to the "first wall" problem in a Bussard reactor just like there is one in tokamaks. I like the sputtered Boron idea, especially if you can create the crystaline form. You'd have a nice carrier substrate and a good surface which would be a conductor as well.
It's "just" engineering.
Posted: Sun Jan 20, 2008 9:09 pm
by Tom Ligon
If you look at the photos of the interior of the vacuum chamber used with WB6, when we received it, the interior was mirror-bright electropolished (per my specification). 'Twas a true thing of beauty. WB4 was probably the device that turned it all purple and blotchy.
Sputter coating is going to happen naturally ... might as well take advantage of it.
I'm more concerned about this problem than almost anything else discussed. Alpha impact is very likely to create the power limit for these machines.
Posted: Mon Jan 21, 2008 12:10 am
by drmike
Then we have to assume that alpha impact on the coils is one part of the power generation, and take advantage of it. It's two problems: absorbing the impact and converting that to heat, and sucking the heat away. The latter is easy, balancing the sputtering with the impact poisons will be harder.
But I still think it is doable.
Posted: Mon Jan 21, 2008 1:54 am
by MSimon
If we can keep the direct heat loss down to 20% of output I'd just throw it away. Using it in any kind of thermal engine is way too expensive.
There are silicon thermoelectric devices coming. We should wait for them. Moving parts are a killer.
I do agree that the first wall problem is difficult but solvable.
Compared to that thermal problems are relatively trivial. One thing we can do is make the reaction density smaller so that the "blue sky" covered by the coils is reduced. If we operate at the pB11 resonance region that may be inherent.
Silicon Thermoelectric Power Conversion
Posted: Mon Jan 21, 2008 2:00 am
by MSimon
*
http://spectrum.ieee.org/jan08/5879
*
Finally, they doped the silicon with boron to introduce defects at an atomic level.
It is looking more and more like Boron is a magic material.
Re: Silicon Thermoelectric Power Conversion
Posted: Mon Jan 21, 2008 2:44 am
by scareduck
MSimon wrote:It is looking more and more like Boron is a magic material.
IIRC boron has been used as a semiconductor doping material for years now.
Japanese researchers recently found
boron-doped silicon carbide superconducts at 1.4K.
Posted: Mon Jan 21, 2008 8:56 am
by tonybarry
Good to have your posts here, Tom. Please keep posting as you have time.
Is it possible that the helium nuclei (alpha particles) exit from the zone of fusion at predetermined angles from the entry paths? If so perhaps we can avoid having things in their way?
Regards,
Tony Barry
Posted: Mon Jan 21, 2008 9:31 am
by MSimon
Tony,
As far as we know at this time the paths are isotropic. i.e equal in all directions in the center of mass frame.
This is true for neutron emission from fission and also neutron reemission from any kind of neutron absorbing process that doesn't capture the neutron.
Posted: Mon Jan 21, 2008 10:03 am
by tonybarry
Thank you Simon for the quick reply. I was reading elsewhere about a spinning black hole (surely something totally unlike a polywell) and thought that if you could spin things very fast, you might get preferential emission from something like the polar jets and the equatorial edge. Of course it is most probably impractical to arrange in the polywell, and probably detracts from stability of the well. The heavy stuff (B11 etc) will all want to escape anyway ... but there you go.
Sorry for the noise
Regards,
Tony Barry
Posted: Mon Jan 21, 2008 10:14 am
by MSimon
tony,
I love answering questions. Signal. Not noise.
Re: Silicon Thermoelectric Power Conversion
Posted: Mon Jan 21, 2008 6:31 pm
by 93143
MSimon wrote:
It is looking more and more like Boron is a magic material.
Quintessential, even? The legendary Fifth Element...
Supposedly the MBDA Meteor's ramrocket uses boron-loaded solid propellant to triple the specific impulse...
...yeah, yeah. Noise, not signal...
Re: Silicon Thermoelectric Power Conversion
Posted: Tue Jan 22, 2008 4:44 am
by dch24
93143 wrote:Quintessential, even? The legendary Fifth Element...
Supposedly the MBDA Meteor's ramrocket uses boron-loaded solid propellant to triple the specific impulse...
...yeah, yeah. Noise, not signal...
And not depleted uranium? Huh.
Well, it's interesting how the periodic table has worked out. (Maybe for a quantum physicist this isn't as surprising, but for me it's a moment of epiphany...)
Code: Select all
+------+ +------+
|H | |He |
|Energy| |Cool- |
| | |ant |
+------+------+------+-------+------+------+ +------+
|Li |Be |B |C |N |O |
|Batt- |Hi-V |Energy|Organic|Cool- |H2O |
|ery |Uses? | |Life |ant | |
+------+------+------+-------+------+------+
The one I can't be sure about is the use of Beryllium. It has obvious high-temperature and high-voltage uses. (Of course, Hydrogen and Nitrogen are also essential for life, but I'm emphasizing the Polywell here.) And Lithium's use isn't obvious, so I just thought of batteries. But those 8 elements are the key to biology and limitless energy. Pretty cool