Quote from: aceshigh on 05/21/2014 02:56 pm...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.Thatīs 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.
...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.Thatīs what? A quadrillion laser shots each producing 100 billion positrons?
Quote from: aceshigh on 05/21/2014 02:56 pm...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.Thatīs 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?
Quote from: MP99 on 05/21/2014 04:30 pmShame 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, MartinThat'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.
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
Antimatter (most likely) won't allow for an Alcubierre drive, for that you need negative masses.
Quote from: enkarha on 05/21/2014 10:50 pmAntimatter (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.
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.
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).
Quote from: aceshigh on 05/23/2014 04:00 pmthe problem lies more in STORING the anti-matter (CERN record is 1000 seconds) than creating it.http://www.centauri-dreams.org/?p=22962Why store it? Create your electrons and positrons in flight and mix them together into the thrust chamber at once. VRoooom!
the problem lies more in STORING the anti-matter (CERN record is 1000 seconds) than creating it.http://www.centauri-dreams.org/?p=22962
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?
Big difference in creating enough energy to produce anti-hydrogen versus an anti-particle like an anti-proton or positron. They create positron beams to kill cancers these days, I'm somewhat skeptical that the energy costs would necessarily outweigh the benefits in T/W when it came to a vehicle with an onboard nuclear reactor or large enough solar panel arrays. MSNWR and Gas-Dynamic fusion rocket motors are essentially giant linear accelerators with a plasma injector. Okay, MSNWR uses a liner so it's more like a rail gun with a z-machine at the end but you get the idea. The method mentioned using photon accelerators not only produces larger positron yields but does so with less energy than CERN's atom colliders. I'm just saying somebody should crunch the numbers if you can get better Isp and T/W than even something like HiPEP it might be worthwhile.
