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Old 09-05-2017, 07:25 PM   #61
sir_pudding
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Default Re: [Spaceships] Anti-Lithium for Drives Does this work?

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Originally Posted by Flyndaran View Post
I thought the reason why superconductors that work at liquid nitrogen temperatures were so sought after was mostly about the high cost of using liquid hydrogen.
And we are talking about major industrial and compact efficient drives, not just technically possible.
That way leads to a breakdown of TL definitions.
I don't know. It was first done in 1889, but by the 40s it was definitely a thing that people could do pretty reliably, I think.
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Old 09-05-2017, 09:59 PM   #62
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Default Re: [Spaceships] Anti-Lithium for Drives Does this work?

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Originally Posted by Johnny1A.2 View Post
ISTR a speculation from decades ago that it might be possible, at sub-cryogenic temperatures, for matter and antimatter to come into contact and not react. Was that discredited since, or it is still debated?
I have never heard of this idea. All the calculations I've done on the rates of antimatter annihilation (admittedly, this was all with electrons and positrons) have had a well defined and positive limit as temperature approaches zero.

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Old 09-05-2017, 10:09 PM   #63
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Default Re: [Spaceships] Anti-Lithium for Drives Does this work?

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Originally Posted by Flyndaran View Post
I thought super insanely strong fields required loads of power or intensities beyond that of any permanent magnets.
The classic levitating frog experiment
http://www.ru.nl/hfml/research/levitation/diamagnetic/
used 16 tesla fields to levitate a frog against Earth's gravity. In space, of course, you can get by with much less. Modern superconducting magnets using classical (i.e. low temperature) superconductors regularly reach 15 tesla and and can be engineered to reach 20 to 30 tesla.
https://en.wikipedia.org/wiki/Superconducting_magnet
High temperature superconductor magnets are being bult that are expected to reach into the 30+ tesla range.
https://nationalmaglab.org/magnet-de...s/32-tesla-scm
At TL 11 we can probably safely assume that robust, flexible, high Tc superconductive tape is a mature technology, allowing high field magnets with at most liquid nitrogen temperatures - if not replaced by something better.

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Old 09-05-2017, 10:17 PM   #64
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Default Re: [Spaceships] Anti-Lithium for Drives Does this work?

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Originally Posted by AlexanderHowl View Post
You would need a much more powerful magnet than 10 Teslas to even trap a gram of antimatter. Just using a back of the envelope calculation, you would need a 1 million Telsa magnetic field to contain a gram of antimatter for a prolonged period of time (the attraction between antimatter and matter is probably one of the most powerful forces in the Universe). Anything less is just as much handwavium as force fields and other forms of superscience.
You can levitate several gram objects with fields of around 15 tesla, such as the frog mentioned in a previous post
http://www.ru.nl/hfml/research/levitation/diamagnetic/
because the electromagnetic force does not care about whether something is matter or antimatter (C, or charge conjugation, symmetry https://en.wikipedia.org/wiki/C-symmetry), several grams of antimatter would be subject to the same force by the same field.

Bulk, charge neutral antimatter would experience no additional forces compared to bulk charge neutral matter. There is no special attraction between antimatter and matter that does not exist between matter itself (that is, the antimatter's matter counterpart would be just as attracted or repelled from another piece of matter as the antimatter itself). C-symmetry again. A lump of anti-lithium (or an anti-frog) would be levitated against Earth's gravity by the same strength field (although an anti-frog would need anti-air around it to breathe, which might have adverse consequences on your magnets).

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Old 09-05-2017, 10:18 PM   #65
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Default Re: [Spaceships] Anti-Lithium for Drives Does this work?

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Originally Posted by Flyndaran View Post
I thought the reason why superconductors that work at liquid nitrogen temperatures were so sought after was mostly about the high cost of using liquid hydrogen.
Nit-pick, but liquid helium, not hydrogen.

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Old 09-05-2017, 10:20 PM   #66
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Default Re: [Spaceships] Anti-Lithium for Drives Does this work?

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Originally Posted by lwcamp View Post
You can levitate several gram objects with fields of around 15 tesla, such as the frog mentioned in a previous post
http://www.ru.nl/hfml/research/levitation/diamagnetic/
because the electromagnetic force does not care about whether something is matter or antimatter (C, or charge conjugation, symmetry https://en.wikipedia.org/wiki/C-symmetry), several grams of antimatter would be subject to the same force by the same field.

Bulk, charge neutral antimatter would experience no additional forces compared to bulk charge neutral matter. There is no special attraction between antimatter and matter that does not exist between matter itself (that is, the antimatter's matter counterpart would be just as attracted or repelled from another piece of matter as the antimatter itself). C-symmetry again. A lump of anti-lithium (or an anti-frog) would be levitated against Earth's gravity by the same strength field (although an anti-frog would need anti-air around it to breathe, which might have adverse consequences on your magnets).

Luke
I'm a bit concerned by using levitation as a proxy for confinement. Especially in context, we're talking about confining antimatter aboard a vessel that's at least sometimes in freefall and sometimes accelerating in various ways. You can't count on a consistent gravity field as part of your system.
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Old 09-05-2017, 11:15 PM   #67
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Default Re: [Spaceships] Anti-Lithium for Drives Does this work?

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Originally Posted by lwcamp View Post
Nit-pick, but liquid helium, not hydrogen.

Luke
I conflated hydrogen with helium but I responded to what TL hydrogen was frozen at, not liquified.
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Old 09-06-2017, 09:42 PM   #68
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Default Re: [Spaceships] Anti-Lithium for Drives Does this work?

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Originally Posted by Ulzgoroth View Post
I'm a bit concerned by using levitation as a proxy for confinement. Especially in context, we're talking about confining antimatter aboard a vessel that's at least sometimes in freefall and sometimes accelerating in various ways. You can't count on a consistent gravity field as part of your system.
Meh. You've got it floating around in a potential minimum, should still be good. If it still bothers you, use active control to switch your fields around as needed.

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