Questions about fusion (from a high-schooler)

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Astronuc

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At this point I get curious about the nature of antimatter. Even if one could imagine as much as microgram of antimatter, it could not be simply carried about in a jar - could it? Surely there would be enormous energy-gobbling infrastructure just to keep a little of it existing for fractions of a second, even if it were aquired for free, yes?
As far as we know, antimatter behaves the same as matter in terms of it's physical properties with repect to gravity and EM fields, and so on.

In an imaginary matter-antimatter fusion, is there the same need to overcome all sorts of forces to push the stuff together, as with present fusions that make helium?
The reaction between matter and antimatter is annihilation. Positrons and electrons annihilate with the product being at least two photons. Positrons behave in normal matter as electrons do, however they are repelled from the nucleus and attracted to electrons.

Protons and anti-protons annihilate with the product being pions, or possibly gammas.

Anti-matter has to be stored carefully around matter so that it does not contact matter. Here is a paper on some storage concepts. Unfortunately it has to be purchased to get the details. http://link.aip.org/link/?APCPCS/504/1230/1 [Broken]

PPT of Howe-Smith Concept - http://www.niac.usra.edu/files/library/meetings/annual/mar99/24Howe.pdf

Here is a student term paper which describes an application of anti-matter to fusion (and fission) - http://fti.neep.wisc.edu/neep602/SPRING00/TERMPAPERS/mcmahon.pdf

Here is another paper describing a storage concept
http://www.engr.psu.edu/antimatter/Papers/web_LiH_final.pdf [Broken]

Penning-Malmberg storage systems seem to be the approach for anti-matter storage.

Some experience - CERN's Antihydrogen TRAP Collaboration - ATRAP
http://ad-startup.web.cern.ch/AD-Startup/Atrap/atrap-en.html
 
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Thanks for the links Astronuc. :)

Especially the McMahon student paper which is full of understated sobering numbers.
re: Fermi National Accelerator Laboratory at Batavia Illinois.
FNAL is currently (year2000) capable of producing, at full capacity operation, approximately 14ng of antiprotons per year. This method of producing antiprotons is an extremely inefficient and expensive process .. .. the current efficiency in producing antiprotons has been estimated by Schmidt, et al to be 4E-8. At this efficiency and 10 cents/kW-hr energy supply, the cost to produce antiprotons is currently around 62.5 trillion/gram.
That, along with good stuff about Penning Traps and how to store tiny amounts of the stuff for a few seconds gives good perspective to newbies. Unless as a temporary product involved in a fusion reaction, its clear that antimatter fuel remains a Star Trek nutter's fantasy.
 

Astronuc

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Most anti-matter on earth is kept in storage rings, IIRC.

I'm not sure how much is collected in traps. I'm not sure what CERN has done recently.

The problem is accumulating antimatter and storing it out of contact with matter.


I think Howe had an experiment at Fermilab in which he used anti-protons for analyzing assays of fissile materials.
 

vanesch

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Just as a side-remark: most people think that the way to have "full conversion" of matter into energy is the matter-anti-matter annihilation - but the culprit is the absence of anti-matter, and its production is energetically just as expensive as what you eventually could get out of it.

However, there is another principle which allows almost full "matter into energy" conversion. For sure it is not practical, but at least it doesn't hit any fundamental physical problem: you can convert almost all of the energy (E = mc^2) in any material "garbage" into useful work - at least in principle, and if you're not affraid of REALLY BIG constructions.

It's illustrated here http://www.bigear.org/CSMO/HTML/CS06/cs06p32.htm but you can also read upon it in more authoritative sources like MTW.
 
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Well, the fusion pellet is very small compared to the volume of the chamber in which the fusion pellet ignited. One concept would put a layer of liquid lithium, like a water fall, cascading down the inner surface of the ignition chamber. The hot liquid would be collected and pumped to a heater exchanger where the heat (thermal energy) would be transferred to another working fluid which would in turn be used to drive a turbine/generator set.
This seems (at least from my POV) to be a really low tech and inefficient way to turn the heat into actual work. The turbine method was invented in the 19th century, surely there must be a more advanced method for getting work out of it. The Tokamak operates on plasmas, maybe that could be utilized somehow.
 

Astronuc

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This seems (at least from my POV) to be a really low tech and inefficient way to turn the heat into actual work. The turbine method was invented in the 19th century, surely there must be a more advanced method for getting work out of it. The Tokamak operates on plasmas, maybe that could be utilized somehow.
Well, nuclear systems generate thermal energy, so they are a fancy way to generate heat, which is usually transferred to a working fluid. The working fluid(s) transfer energy and momentum to turbomachinery, which is used to drive a generator to produce electricity.

In the case of a plasma, two possibilities are extracting energy directly from the plasma as it expands against the magnetic field, or use charge separation. The strategy depends on the system geometry, i.e. plasma confinement and magnetic field configuration.
 
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In the case of a plasma, two possibilities are extracting energy directly from the plasma as it expands against the magnetic field, or use charge separation. The strategy depends on the system geometry, i.e. plasma confinement and magnetic field configuration.
How much energy can we theoretically get out of a system like this? How much more (or less) efficient is it?

Well, nuclear systems generate thermal energy, so they are a fancy way to generate heat, which is usually transferred to a working fluid. The working fluid(s) transfer energy and momentum to turbomachinery, which is used to drive a generator to produce electricity.
True, and so for fission there isn't anyother way. But fusion doesn't just make steam, it makes plasma and so maybe we can use that directly instead of having to go through working fluids.
 

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