Author Topic: Fusion with space related aspects thread  (Read 584772 times)

Offline gospacex

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Re: Fusion with space related aspects thread
« Reply #2780 on: 04/18/2017 11:42 AM »
Plus again, we also need batteries, which are still very expensive and don't last forever.

Some types of batteries are cheap and last some 50 years. For example, nickel–iron batteries.
Ni-Fe drawback is that they are 2 times heavier than, say, lead-acid. Bad for cars, but for stationary storage, this factor is not significant.

Offline momerathe

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Re: Fusion with space related aspects thread
« Reply #2781 on: 04/18/2017 02:04 PM »
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.

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.
thermodynamics will get you in the end

Offline Elmar Moelzer

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Re: Fusion with space related aspects thread
« Reply #2782 on: 04/18/2017 11:25 PM »
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.

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.
I think that Tokamaks are the least ideal reactor type for space applications. They are just the ones we know best. The problems with Toks is that they are pretty much only suitable for "burning" deuterium and tritium and that comes with a large can of heavy equipment.
Reactors that do advanced fuels can usually use direct conversion. This would be much more compact and light weight. Plus you don't need FLiBe for breeding tritium (though for space applications, you could probably supply that from earth).

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Offline Elmar Moelzer

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Re: Fusion with space related aspects thread
« Reply #2784 on: 05/02/2017 11:16 AM »
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
Well, a few of us already thought that their confinement concept might have some issues. I think there are others that are better. Though with high temperature superconductors it would turn out OK, I guess.

Offline as58

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Re: Fusion with space related aspects thread
« Reply #2785 on: 05/02/2017 11:37 AM »
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.

Offline corneliussulla

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Re: Fusion with space related aspects thread
« Reply #2786 on: 05/02/2017 11:52 AM »
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. Also 100 MegaWatt fusion reactor is under development at Tokamak Energy. This reactor could fit inside a couple of average size sitting rooms certainly feasible as a spaceship engine in a world where Musk could be launching 300 tonnes into orbit on BFR in a reusable format.

Online Eerie

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Re: Fusion with space related aspects thread
« Reply #2787 on: 05/02/2017 03:36 PM »
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.

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: Jim
Wrong.

Offline corneliussulla

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Re: Fusion with space related aspects thread
« Reply #2788 on: 05/02/2017 08:49 PM »
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.

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

Yes confinement using gravity definitely works, but unless we discover how to create gravity fields we need to conquer electro magnetic confinement
« Last Edit: 05/02/2017 08:50 PM by corneliussulla »

Offline Robotbeat

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Re: Fusion with space related aspects thread
« Reply #2789 on: 05/02/2017 11:29 PM »
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.

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

Yes confinement using gravity definitely works, but unless we discover how to create gravity fields we need to conquer electro magnetic confinement
Inertial confinement is more likely, IMHO.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Elmar Moelzer

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Re: Fusion with space related aspects thread
« Reply #2790 on: 05/03/2017 12:17 AM »
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.

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
Even better for magnetic confinement concepts is to increase the B- field. In a tokamak and probably in most magnetic confinement and possibly also some magneto- inertial concepts fusion power increases with B to the 4th power. This is a well established scaling factor. So if you can double the magnetic field, you get 16 times the fusion power. Tokamak Energy and MIT's ARC/SPARC concepts use new high temperature super conductors to increase the B field without increasing the volume of the reactor. This is why they think that they can do Tokamaks that are smaller than JET and still achieve a GWe output with a Q of over 10.
I had completely written off Tokamaks as an economic reactor concept until I saw Dennis Whyte's presentation on this.
That said, I still believe that other concepts like Helion's are better. But they too would benefit from the HTSC magnet technology developed by the MIT and TE.
As can be seen from the paper above, Lockheeds fusion reactor would also benefit from the HTSCs.

Offline Elmar Moelzer

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Re: Fusion with space related aspects thread
« Reply #2791 on: 05/03/2017 12:21 AM »
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.
The shielding is not that big of a problem, but I think there are other reactor concepts that are much more suitable for spacecraft propulsion. MSNW's Fusion Driven Rocket and PPPL's Direct Fusion Drive would be two examples that have been (or are currently) studied through NIAC. PPPL's DFD uses D+He3 fusion. It looks like a pretty viable concept. They also are looking into HTSCs with the help of the MIT.

Online Eerie

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Re: Fusion with space related aspects thread
« Reply #2792 on: 05/03/2017 06:34 PM »
Inertial 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.
« Last Edit: 05/03/2017 06:39 PM by Eerie »
Quote from: Jim
Wrong.

Offline Elmar Moelzer

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Re: Fusion with space related aspects thread
« Reply #2793 on: 05/03/2017 08:54 PM »
Inertial 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.
Yes, this is what we have been talking about ;)
The guy is doing a nice sales pitch but treats other concepts a bit unfairly. Most of them have not have nearly as much funding as Tokamaks and so only could make prototypes that demonstrated a specific (most critical) aspect of the design.
Also, if I am not mistaken, Helion demonstrated a Q of of 0.2 with IPA-HF.

Offline Robotbeat

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Re: Fusion with space related aspects thread
« Reply #2794 on: 05/04/2017 04:33 AM »
Inertial 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.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online Eerie

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Re: Fusion with space related aspects thread
« Reply #2795 on: 05/04/2017 02:44 PM »
None of that implies inertial confinement is inferior, just more poorly funded.

My impression from the video is not that inertial confinement as a concept is inferior, but that it still requires more basic research, before turning towards actual commercial reactor engineering. So the firms that try to make it commercial right now are, probably, going to severely disappoint us.

Quote
I can't see these magnetic confinement methods being lightweight enough for a space drive. Inertial fusion, however, could make Orion practical.

Orion, as in, The Old Boom-Boom?

No, no, no, it is not an Orion unless it involves fusion bombs exploding against that deflector plate. Forget practical, Orion should be awesome and terrifying. Its purpose is to make the enemies quiver.
« Last Edit: 05/04/2017 02:44 PM by Eerie »
Quote from: Jim
Wrong.

Offline as58

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Re: Fusion with space related aspects thread
« Reply #2796 on: 05/04/2017 02:53 PM »
None of that implies inertial confinement is inferior, just more poorly funded.

Not sure I'd call all of inertial confinement research poorly funded, with NIF and all.

Offline Elmar Moelzer

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Re: Fusion with space related aspects thread
« Reply #2797 on: 05/04/2017 07:31 PM »
I can't see these magnetic confinement methods being lightweight enough for a space drive. Inertial fusion, however, could make Orion practical.
PPPLs FRC based reactor makes a quite nice space drive, though.
My money is on magneto- inertial fusion :)

Offline momerathe

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Re: Fusion with space related aspects thread
« Reply #2798 on: 05/08/2017 01:00 PM »
Tokamak energy have been posting a bunch of new video on their youtube channel over the last couple of weeks. Maybe they're going through another funding round? ;)

Nothing desperately revelatory, but nice to see some of the nuts and bolts detail.
thermodynamics will get you in the end

Offline Nilof

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Re: Fusion with space related aspects thread
« Reply #2799 on: 05/13/2017 08:27 PM »
Tbh, I think magnetic confinement is similar to SEP: it is very sensitive to advances in applied condensed matter physics.

That fourth-power dependence on the magnetic field in the expression for the power density is huge. Find a superconductor that stays superconducting in a 100T field, and suddenly Tokamaks reach ridiculous power densities on the order of a chemical rocket engine.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

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