Antimatter production source?

[sghill]

Did anyone else catch this announcement this week?

http://www.theverge.com/2014/5/18/5724658/photon-collider-could-turn-light-into-matter
http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_16-5-2014-15-32-44
http://www.nbcnews.com/science/science-news/scientists-lay-out-simple-plan-turn-light-matter-n109106
And a few other news sources.

Basically, the idea is to create a collider that uses laser light to turn photons into matter- electrons and positrons.

"...They would then direct the photon beam from the first stage of the experiment through the center of the can, causing the photons from the two sources to collide and form electrons and positrons. It would then be possible to detect the formation of the electrons and positrons when they exited the can [and separate them]."  "The boffins reckon they should be able to get around 100,000 of the pairs in a single shot, which could be detected as they exited the hohlraum."

I perked up an eyebrow when I saw that and immediately thought: "Hey! This could be a consistent and "pure" source of anti-matter production!"

Particle accelerators create positrons too as we all know, but they're mixed in with other matter, so they bang into stuff and turn back into energy.  Plus, they're total power hogs because you're accelerating matter.  It's just not worth it to create and try to store anti-matter with one. This looks to be far more power efficient.

No word on efficiency estimates as it's still theoretical, but it looks easy enough to engineer one with off the shelf components, so we ought to have data on production volumes of antimatter per input watt relatively soon (like within a year).

Gonna need anti-matter for that Alcubierre drive!

[aceshigh]

of course, we must know how much power is needed into the lasers to form 100 thousand pairs with each shot.

and how many times a second we can fire the lasers so we can produce a decent amount of anti-matter.


also, from Wikipedia article on antimatter
"Positrons were reported[21] in November 2008 to have been generated by Lawrence Livermore National Laboratory in larger numbers than by any previous synthetic process. A laser drove electrons through a millimeter-radius gold target's nuclei, which caused the incoming electrons to emit energy quanta that decayed into both matter and antimatter. Positrons were detected at a higher rate and in greater density than ever previously detected in a laboratory. Previous experiments made smaller quantities of positrons using lasers and paper-thin targets; however, new simulations showed that short, ultra-intense lasers and millimeter-thick gold are a far more effective source.[22]"



than you read the sources of the article:
http://www.cosmosmagazine.com/news/laser-creates-billions-particles-antimatter/
https://www.llnl.gov/news/newsreleases/2008/NR-08-11-03.html

"By shooting a laser through a gold disc no bigger than the head of a drawing pin, physicists have created more than 100 billion particles of antimatter."

"LIVERMORE, Calif. – Take a gold sample the size of the head of a push pin, shoot a laser through it, and suddenly more than 100 billion particles of anti-matter appear."

That´s 100 billion positrons with this method in comparison with 100 thousand positrons with the method of the OP article.

That´s 6 orders of magnitude difference.


"“We’ve entered a new era,” Beiersdorfer said. “Now, that we’ve looked for it, it’s almost like it hit us right on the head. We envision a center for antimatter research, using lasers as cheaper anti-matter factories"


also, both methods produce positrons, no anti-proton... even 100 billion positrons is too small a quantity of anti-matter.

I mean, since electrons are so light (and I think positrons are as light), you need 1.09e27 to get A SINGLE GRAM.


That´s what? A quadrillion laser shots each producing 100 billion positrons?


easier to produce anti-hidrogen.

"only" 6.02*10^23 anti-hidrogen atoms needed.

[MP99]

...of course, we must know how much power is needed into the lasers to form 100 thousand pairs with each shot.

and how many times a second we can fire the lasers so we can produce a decent amount of anti-matter.

I mean, since electrons are so light (and I think positrons are as light), you need 1.09e27 to get A SINGLE GRAM.

That´s what? A quadrillion laser shots each producing 100 billion positrons?

Well, the world record is 67 quadrillionths of a second for a laser shot, so we're talking just over one minute to make 1 gram of antimatter?  The 500kg we need for the Alcubierre drive will take just under a year.  I'd take that action!

http://www.wired.com/2012/09/world-record-laser-blast/

Yes, I know we're just having fun with numbers here!

Positrons would be preferable for clean matter-to-energy conversion over anti-hydrogen because fewer other particles would be created (electrons and positrons have no substructure); the conversion to energy is more complete.

Shame about all that proton "ash".

Also, can't ever be more than 0.1% efficient converting positrons to energy, due to needing all those pesky protons.

Unless you store clouds of both positrons and electrons.

cheers, Martin

[aceshigh]

...of course, we must know how much power is needed into the lasers to form 100 thousand pairs with each shot.

and how many times a second we can fire the lasers so we can produce a decent amount of anti-matter.

I mean, since electrons are so light (and I think positrons are as light), you need 1.09e27 to get A SINGLE GRAM.

That´s what? A quadrillion laser shots each producing 100 billion positrons?

Well, the world record is 67 quadrillionths of a second for a laser shot, so we're talking just over one minute to make 1 gram of antimatter?

well, we certainly don´t know how many positrons that quadrillionth of a second laser shot can produce.

[enkarha]

Antimatter (most likely) won't allow for an Alcubierre drive, for that you need negative masses.

[Stormbringer]

two things come to my mind In the article they think they can produce more massive particles (such as anti-protons) if they hold their tongues in the right position while performing their experiments. and some antimatter propulsion schemes require only a microgram or even just a nanogram to accomplish. e.g; ICAN and AIMSTAR propulsion.

[MP99]

Shame about all that proton "ash".

Also, can't ever be more than 0.1% efficient converting positrons to energy, due to needing all those pesky protons.

Unless you store clouds of both positrons and electrons.

cheers, Martin

That's exactly why you'd want this technique versus using a proton beam in an atom smasher.  Instead of blasting apart protons, you go directly from the lasers to positrons and electrons, which you then separate with magnets and store.

Electrons are easy to produce, just see any cathode ray tube (cathode rays are electrons).

Maybe the reaction mass could include some negative ions to make the vehicle as a whole electrically neutral? But, I'd think that would make for very difficult long-term storage - so LV rather than Mars lander, perhaps?

Cheers, Martin

[ChrisWilson68]

Antimatter (most likely) won't allow for an Alcubierre drive, for that you need negative masses.

Not "most likely", but "definitely".  Alcubierre's drive can't work without a large magnitude of negative mass.  Antimatter has ordinary positive mass.

Also, just having negative mass isn't enough to make Alcubierre's drive work.  You need to arrange it just right, with the right velocities for the different parts.  A paper was published pointing out that even if you start with negative mass, you can't get it into the Alcubierre configuration without already having faster-than-light travel of some sort.  Kind of a chicken and an egg problem.

Antimatter is an amazing way to store huge quantities of energy in a very small volume and mass.  Don't detract from the very real benefits of it by confusing those benefits with warp drive fantasies.

[IslandPlaya]

I seem to remember some planned experiments to determine if antimatter has +ve or -ve mass.
These experiments are difficult but the fact that people are going ahead with them shows that we just don't know the sign of the mass yet.
I think that most people expect antimatter mass to be +ve, but you never know.

[aceshigh]

Antimatter (most likely) won't allow for an Alcubierre drive, for that you need negative masses.

Not "most likely", but "definitely".  Alcubierre's drive can't work without a large magnitude of negative mass. 

actually, only 1 ton of negative mass, according to Dr Sonny White´s calculations.

the calculations for "Jupiter quantities of exotic mass" were based on a specific ring geometry

Dr Sonny White made calculations showing that a wider ring, and if you FLUCTUATE (its mass, energy? Don´t remember), it will be easier to change local spacetime geometry... like if it was "softened".

[cordwainer]

Well positrons would be easier to work with than anti-hydrogen for direct energy production as mentioned above. Theoretically they would be easier to store than anti-hydrogen for long periods of time, although not stable for as long a period of time. (Logistically anti-hydrogen is harder to contain) Anti-protons produce better yield when than positrons when used in for Anti-matter catalyzed nuclear reactions but positrons produce a higher energy yield when used in direct matter annihilation reactions. This idea seems like a boon for use in a positron-hydrogen rocket, might even have sufficient T/W for onboard manufacturing of positrons rather than storing positrons in a "positronium" exotic atomic state.

[Supergravity]

I seem to remember some planned experiments to determine if antimatter has +ve or -ve mass.
These experiments are difficult but the fact that people are going ahead with them shows that we just don't know the sign of the mass yet.
I think that most people expect antimatter mass to be +ve, but you never know.

The experiments are looking for the interaction of the gravitational mass of antimatter, not the inertial mass. We already know the inertial mass is positive, so what this really is testing is the equivalence principle of GR.

In an Alcubierre drive you only need negative mass for superluminal travel (even if you have negative mass, there are other factors preventing this from happening however such as the renormalized stress-energy tensor disrupting your bubble, and Hawking radiation that roasts the inside of it, i.e. temperatures in the area of 10^32 K). 

Actually, you still need a negative energy to create a subluminal warp bubble. The space-time geometry fundamentally requires a negative energy density and is completely independent whether or not global speed exceeds c. The problem of a subluminal warp drive only allows us to ignore the causality issues associated with the classic warp drive, but all of the other enormous technical problems still plague it.

[kkattula]

FYI, this concept estimated only 10 milligrams of positrons to do a manned Mars vehicle.

http://www.nasa.gov/centers/goddard/news/topstory/2006/antimatter_spaceship.html

[aceshigh]

^^

they mention $250 million to produce those 10mm with new techs being developed. However, the article is from 2006, and these new techs are probably not around yet.

article on Centauri Dreams about anti-matter propulsion... he says the current estimated costs for anti-matter production are based on anti-matter being produced as a BY-PRODUCT at Particle Accelerators...

and that with a "factory" dedicated to anti-matter production, costs could be lowered to $10 million per milligram, which would make it more feasible and cheaper than fission propulsion.


the problem lies more in STORING the anti-matter (CERN record is 1000 seconds) than creating it.

http://www.centauri-dreams.org/?p=22962

[Elmar Moelzer]

the problem lies more in STORING the anti-matter (CERN record is 1000 seconds) than creating it.

http://www.centauri-dreams.org/?p=22962

Why store it?  Create your electrons and positrons in flight and mix them together into the thrust chamber at once. VRoooom!

And where does the energy needed to create them come from? This process is not really net positive, you know.

[cordwainer]

The anti-matter production method mentioned in the article is from 2008, while the Centauri Dreams article is citing conventional methods from 2006. I'm curious has anybody run the numbers on what the cost would be using this new method for a Mars rocket. Also, Elmar what are you defining as net positive? Our we talking about poor T/W ratios due to massive onboard power plants that would make onboard production impractical. Or are we talking about physical impossibility in terms of the amount of onboard energy needed. Fusion drives don't have to "break even" to be practical you just have to have sufficient energy efficiency and thrust production to make for decent Isp and T/W. 

[ChrisWilson68]

the problem lies more in STORING the anti-matter (CERN record is 1000 seconds) than creating it.

http://www.centauri-dreams.org/?p=22962

Why store it?  Create your electrons and positrons in flight and mix them together into the thrust chamber at once. VRoooom!

The whole point of using anti-matter is that it allows you to pack a huge amount of energy into a small volume.  If you're creating electrons and positrons in flight, you get no benefit at all.  Whatever energy you are using to create the electrons and positrons would more usefully be used to directly drive the propulsion system.  And the systems we're talking about here to create electrons and positrons are extremely energy inefficient -- far less than 1% efficient.  So you'd need far, far more energy if you were turning it into electrons and positrons than if you were using it directly in the drive.

[aceshigh]

I have read descriptions of anti matter and is containment systems as "leaky" at best.

What i wonder is about the rate of this leaking.

Wouldn't it be possible to use this natural rate of leaking for the engine? Of course, that would mean you would have the engine always running. Maybe when turned off you would need a way to dispel excess heat or use it to generate electricity instead of thrust.

The details i could find of the containment experiences are shallow... did they try entrap a single anti particle and it leaked after 1000 seconds? Or did they trap trillions of particles and after 1000 seconds all of them had leaked?



If it's a constant but manageable leaking rate, maybe you could have two magnetic fields. One for holding the anti particles, and the ones that leak out could be caught by the second, which instead of trying too hold it, just sends it to the propulsion engine immediately, to react with matter.

[aceshigh]

Ok, reading a bit more on the subject,it seems the difficulty in storing anti matter is not related to anti matter itself, but to how it is created. Basically, the creation process is too energetic, and when the anti matter is created, is also extremely energetic (or hot). The difficulty is slow down, or cool these anti particles (making them easier to hold) before they escape the containment devices.

The cern experiment trapped 309 anti hydrogen atoms, SOME as long as 1000 seconds. It's difficult to know if they leaked steadily or some energetic atoms leaked straight away while a few took longer. But anyway, the point seems to be that storing anti matter inside a space ship for long periods of time IS NOT difficult. The problem is cooling the anti particles enough AT the production center, stop that they can be stored.

Once cooled enough at the production facility, holding them with good magnetic fields for very long periods of time seems to be not a big problem

[ChrisWilson68]

Ok, reading a bit more on the subject,it seems the difficulty in storing anti matter is not related to anti matter itself, but to how it is created. Basically, the creation process is too energetic, and when the anti matter is created, is also extremely energetic (or hot). The difficulty is slow down, or cool these anti particles (making them easier to hold) before they escape the containment devices.

The cern experiment trapped 309 anti hydrogen atoms, SOME as long as 1000 seconds. It's difficult to know if they leaked steadily or some energetic atoms leaked straight away while a few took longer. But anyway, the point seems to be that storing anti matter inside a space ship for long periods of time IS NOT difficult. The problem is cooling the anti particles enough AT the production center, stop that they can be stored.

Once cooled enough at the production facility, holding them with good magnetic fields for very long periods of time seems to be not a big problem

Where's the evidence that it's easy to hold them even after they've been cooled?  If they were able to hold some as long as 1000 seconds, isn't that because they did manage to cool them, but the fact that they didn't manage to hold them longer than 1000 seconds suggests that even after that much cooling they weren't easy to hold?

Remember, when storing these things you need to not only keep the antimatter in but you need to keep all ordinary matter out.  Every little bit.  You can't have even a few atoms sublimating off solid surfaces and getting in there.  Doing that for a handful of anti-protons is much easier than for the billions of times more of them you'd need to have meaningful amounts of energy.