Plus again, we also need batteries, which are still very expensive and don't last forever.
I have a big question for tokamak devices and similar: how heavy are they for a given power, including boiler and ancillary equipment? When discussing space related fusion this is a key parameter. I get the feeling that it's incredibly heavy for the power output.
Quote from: Robotbeat on 04/18/2017 10:27 amI have a big question for tokamak devices and similar: how heavy are they for a given power, including boiler and ancillary equipment? When discussing space related fusion this is a key parameter. I get the feeling that it's incredibly heavy for the power output.Excellent question. Ultimately, it's just a heat source, so the same considerations apply as to fission reactors in terms of turbines/generators and radiator mass.(aside: is the output temperature as high as a fission reactor? that will affect efficiency)If we're talking about propulsion, then direct drive concepts like *ahem* Direct Fusion Drive or that lithium liner concept (the name of which escapes me) will have the edge - if they ever get them to work.
run for your lives! it's getting bigger!http://www.nextbigfuture.com/2017/05/lockheed-compact-fusion-reactor-design-about-100-times-larger-than-first-plans.html#more-132913
It seems that pretty much all fusion concepts start small but when losses are understood better during the development, it turns out that the reactor needs to be much larger than initially thought.
Quote from: as58 on 05/02/2017 11:37 amIt seems that pretty much all fusion concepts start small but when losses are understood better during the development, it turns out that the reactor needs to be much larger than initially thought.Volume rises as a third power of scale, but surface area rises as a second power. Volume is where fusion happens. Surface area is where the hot plasma interacts with the cold walls and ruins your day. Seems like a no-brainer.The most common fusion reactor, accidentally, is extremely big. It's a star. :-P
Quote from: Eerie on 05/02/2017 03:36 pmQuote from: as58 on 05/02/2017 11:37 amIt seems that pretty much all fusion concepts start small but when losses are understood better during the development, it turns out that the reactor needs to be much larger than initially thought.Volume rises as a third power of scale, but surface area rises as a second power. Volume is where fusion happens. Surface area is where the hot plasma interacts with the cold walls and ruins your day. Seems like a no-brainer.The most common fusion reactor, accidentally, is extremely big. It's a star. :-PYes confinement using gravity definitely works, but unless we discover how to create gravity fields we need to conquer electro magnetic confinement
The problem with deuterium tritium fusion is the production of large amounts of high energy neutrons. Which are bad for ur health and will make the spacecraft radioactive...living quarters will need to be long distance from the reactor. Most people assume Tokamak's rely on D-T fusion, however you can do D-He3 fusion in a tokamak I think u just need higher temperatures which may well be feasible with high temperature superconductors.
Inertial confinement is more likely, IMHO.
Quote from: Robotbeat on 05/02/2017 11:29 pmInertial confinement is more likely, IMHO.Check out this extremely interesting video by the MIT Plasma Science and Fusion Center.TL;DR, the gist of it:1. The scientific consensus, after 50 years of research, is that the tokamak approach is 99% guaranteed to work if you build it large enough. Which is what going to happen with ITER.2. ITER is designed using older superconducting magnets, which limit the magnetic field strength, which limit the minimal size of it, making ITER expensive.3. With new super-conducting magnets, which are already in commercial production, you can make a working fusion reactor 10 times smaller than ITER.
None of that implies inertial confinement is inferior, just more poorly funded.
I can't see these magnetic confinement methods being lightweight enough for a space drive. Inertial fusion, however, could make Orion practical.