Author Topic: Pulsed Fusion Propulsion  (Read 11599 times)

Offline Gomtu

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Pulsed Fusion Propulsion
« on: 06/20/2013 04:14 PM »
Please consider voting for this. It only takes about five minutes to register and vote.
http://contest.techbriefs.com/2013/entries/aerospace-and-defense/3490

Fusion propulsion is crucial for the advancement of human spaceflight, and for opening up the solar system to mankind. This seems like a good way to make that a reality.

Offline Elmar Moelzer

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Re: Pulsed Fusion Propulsion
« Reply #1 on: 06/22/2013 06:17 PM »
I dont think that this is more feasible than John Sloughs FRC- imploding liner concept and that one is already pretty far along.
http://forum.nasaspaceflight.com/index.php?topic=30437.150

Offline Gomtu

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Re: Pulsed Fusion Propulsion
« Reply #2 on: 06/22/2013 09:25 PM »
I dont think that this is more feasible than John Sloughs FRC- imploding liner concept and that one is already pretty far along.
http://forum.nasaspaceflight.com/index.php?topic=30437.150


Why do you think this concept isn't as feasible?

Offline Elmar Moelzer

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Re: Pulsed Fusion Propulsion
« Reply #3 on: 06/22/2013 10:39 PM »
I did not say that it was less feasible, I said that it does not seem more feasible.
Without knowing all the technical details of their approach I would be careful to say more than that.
What pulls me off is that this is a comparably big device which means a lot of cost for the research. The resulting space craft also would be much larger while not decreasing trip times compared to Slough's approach.
The z-pinch at Sandia labs use 350 Terwatts and 2.7 megajoules and is much larger and is only trying to reach break even in 2013. So I am not sure how the 3 Terawatts machine could ever reach break even let allone go beyond that. Since Sandia already has a bigger device, I do have to wonder about the merrits of additional tests with this smaller machine.

Offline ChrisWilson68

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Re: Pulsed Fusion Propulsion
« Reply #4 on: 06/23/2013 08:38 AM »
Since Sandia already has a bigger device, I do have to wonder about the merrits of additional tests with this smaller machine.

Yeah, the description of this project on the contest page doesn't say why this particular research is any different from the much bigger and better-funded z-pinch research going on elsewhere.  The description doesn't even acknowledge any other research programs.  Either it is an inferior copy of the other programs, with nothing new to add, or it has some novelty that the contest page completely fails to address.

Also, the focus on spacecraft propulsion is misguided.  If they can really create a practical pulsed-fusion propulsion module, then they can get over-unity from a fusion reaction and that can easily be turned into the long-sought fusion electrical power generation solution that will have far, far more impact in the immediate future than a new spacecraft propulsion system.

Offline Elmar Moelzer

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Re: Pulsed Fusion Propulsion
« Reply #5 on: 06/23/2013 04:19 PM »
Yeah, the description of this project on the contest page doesn't say why this particular research is any different from the much bigger and better-funded z-pinch research going on elsewhere.  The description doesn't even acknowledge any other research programs.  Either it is an inferior copy of the other programs, with nothing new to add, or it has some novelty that the contest page completely fails to address.
Exactly

Also, the focus on spacecraft propulsion is misguided.  If they can really create a practical pulsed-fusion propulsion module, then they can get over-unity from a fusion reaction and that can easily be turned into the long-sought fusion electrical power generation solution that will have far, far more impact in the immediate future than a new spacecraft propulsion system.
That I am not so sure about. Fusion for space propulsion does not have to economically compete with coal. Terrestrial fusion does. E.g. I dont think that inertial confinement fusion like the NIF will ever be able to be economical. A gold plated fuel hohlraum that has to be replaced for every shot does not sound very economical to me. Plus, I dont see how they will be able to breed tritium in a device with such an architecture.
The z- pinch might work a little better in some respects, but it still sounds quite complex.
Even tokamaks might never result in economical reactors (but its really good science). For the same reason MSNW has two rather different concepts for space propulsion and terrestrial power generation.
Anyway, the question remains what this z- pinch project will do better than Sandias z- machine that warrants it to be funded.

Offline ChrisWilson68

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Re: Pulsed Fusion Propulsion
« Reply #6 on: 06/23/2013 05:16 PM »
Also, the focus on spacecraft propulsion is misguided.  If they can really create a practical pulsed-fusion propulsion module, then they can get over-unity from a fusion reaction and that can easily be turned into the long-sought fusion electrical power generation solution that will have far, far more impact in the immediate future than a new spacecraft propulsion system.
That I am not so sure about. Fusion for space propulsion does not have to economically compete with coal. Terrestrial fusion does. E.g. I dont think that inertial confinement fusion like the NIF will ever be able to be economical. A gold plated fuel hohlraum that has to be replaced for every shot does not sound very economical to me. Plus, I dont see how they will be able to breed tritium in a device with such an architecture.
The z- pinch might work a little better in some respects, but it still sounds quite complex.
Even tokamaks might never result in economical reactors (but its really good science). For the same reason MSNW has two rather different concepts for space propulsion and terrestrial power generation.
Anyway, the question remains what this z- pinch project will do better than Sandias z- machine that warrants it to be funded.

OK, that's a good point.  It would be possible to have a space fusion drive even if the electricity-generation version wasn't competitive with coal.  Still, it would at the very least be a lot closer to being viable as an electrical power source than any current fusion project, and a lot of money is going into those other fusion programs.

Offline Elmar Moelzer

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Re: Pulsed Fusion Propulsion
« Reply #7 on: 06/23/2013 07:25 PM »
OK, that's a good point.  It would be possible to have a space fusion drive even if the electricity-generation version wasn't competitive with coal.  Still, it would at the very least be a lot closer to being viable as an electrical power source than any current fusion project, and a lot of money is going into those other fusion programs.
I see a few that are getting closer:
MSNW has a good concept, but they need funding.
Tri Alpha has a simillar concept and they are fully funded. They are aiming higher though (PB11).
The Polywell has been making slow but steady progress.
And last but not least Lockheed claims to have their own confinement concept that should have a prototype reactor by 2017.
That is a bit off topic though. I think that even as a propulsion concept funding this project does not seem to make sense, since they are not more advanced than others right now, not even more advanced than simillar confinement schemes. So why would I want to give them my money over a competing project?
« Last Edit: 06/23/2013 07:27 PM by Elmar Moelzer »

Offline ChileVerde

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Re: Pulsed Fusion Propulsion
« Reply #8 on: 06/24/2013 04:36 PM »
The novelty in this research is that it will utilize lithium deuteride as the fuel source.

Which needs a separate neutron source to get things going, no?

http://www.atomicarchive.com/Fusion/Fusion2.shtml
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Offline ChrisWilson68

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Re: Pulsed Fusion Propulsion
« Reply #9 on: 06/24/2013 06:06 PM »
The novelty in this research is that it will utilize lithium deuteride as the fuel source.  Since this material exists as a solid at room temperatures, we expect the reactivities to be much higher than the gas fed deuterium experiments.  The only other pulsed power effort experimenting with lithium deuteride was from 1962 when they tested single exploding wires on a z-pinch machine much less powerful than the Charger-1.  Besides the much higher densities of the fuel, it is in great abundance and relatively low cost compared to other approaches which may require deuterium tritium or deuterium helium-3 reactions.  Both tritium and helum-3 would require a major infrastructure for production that does not exist in order to produce the tons needed for a single mission, and the fusion fuel cost would greatly exceed the launch cost.  Therefore, this can be seen as a more pragmatic approach to the problem.

The operating costs of running lithium deuteride experiments with the Charger-1 is expected to cost about $5000 to $10,000 per week.  The z-machine at Sandia Labs would cost up to 100 times this.  We can do many more experiments towards understanding the optimization and scaling with lithium deuteride targets, and help guide the design of similar targets for more powerful machines.  There are more problems to be solved than can be realistically solved by one group alone, and collaboration with as many groups as necessary is vital in order to design and build a fusion propulsion system.   

Now that is what should have been in the contest project description page in the first place!

Offline Elmar Moelzer

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Re: Pulsed Fusion Propulsion
« Reply #10 on: 06/24/2013 10:13 PM »
The novelty in this research is that it will utilize lithium deuteride as the fuel source.  Since this material exists as a solid at room temperatures, we expect the reactivities to be much higher than the gas fed deuterium experiments.  The only other pulsed power effort experimenting with lithium deuteride was from 1962 when they tested single exploding wires on a z-pinch machine much less powerful than the Charger-1.  Besides the much higher densities of the fuel, it is in great abundance and relatively low cost compared to other approaches which may require deuterium tritium or deuterium helium-3 reactions.  Both tritium and helum-3 would require a major infrastructure for production that does not exist in order to produce the tons needed for a single mission, and the fusion fuel cost would greatly exceed the launch cost.  Therefore, this can be seen as a more pragmatic approach to the problem.

The operating costs of running lithium deuteride experiments with the Charger-1 is expected to cost about $5000 to $10,000 per week.  The z-machine at Sandia Labs would cost up to 100 times this.  We can do many more experiments towards understanding the optimization and scaling with lithium deuteride targets, and help guide the design of similar targets for more powerful machines.  There are more problems to be solved than can be realistically solved by one group alone, and collaboration with as many groups as necessary is vital in order to design and build a fusion propulsion system.   
Thanks for the information! That is indeed interesting to know and might change my opinion on the project.
While I do somewhat understand why the lithium deuteride might be a better fuel than Deuterium gas for an inertial fusion device, I am not exactly sure why exactly it would work better than D+T for achieving fusion. In fact the crosssection of D+Li is almost as low (and I believe the power density is even lower) as P+B11 but is not as aneutronic due to the D+D (and probably also D+T and T+He4) side reactions. Can you give us some more details on that?
« Last Edit: 06/24/2013 10:16 PM by Elmar Moelzer »

Offline R7

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Re: Pulsed Fusion Propulsion
« Reply #11 on: 06/25/2013 07:08 AM »
While I do somewhat understand why the lithium deuteride might be a better fuel than Deuterium gas for an inertial fusion device, I am not exactly sure why exactly it would work better than D+T for achieving fusion. In fact the crosssection of D+Li is almost as low (and I believe the power density is even lower) as P+B11 but is not as aneutronic due to the D+D (and probably also D+T and T+He4) side reactions.

Is the Li mostly meant to breed T for D-T fusion like in hydrogen bombs?

6Li + n -> T + He + 4.784 MeV
7Li + n -> T + He + n - 2.467 MeV
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Offline ChileVerde

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Re: Pulsed Fusion Propulsion
« Reply #12 on: 06/25/2013 12:48 PM »

Is the Li mostly meant to breed T for D-T fusion like in hydrogen bombs?

6Li + n -> T + He + 4.784 MeV
7Li + n -> T + He + n - 2.467 MeV

Most likely, the final act in the play being D + T -> He + n + 14.1 MeV.  Note the n there.
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Offline ChileVerde

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Re: Pulsed Fusion Propulsion
« Reply #13 on: 06/25/2013 10:20 PM »
And because lithium deuteride exists as a solid at room temperature, we expect higher reaction rates even though the cross section is lower.

I may have missed this up-thread, but what reactions, specifically, do you refer to?
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Offline Elmar Moelzer

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Re: Pulsed Fusion Propulsion
« Reply #14 on: 06/25/2013 10:45 PM »
The novelty in this research is that it will utilize lithium deuteride as the fuel source.  Since this material exists as a solid at room temperatures, we expect the reactivities to be much higher than the gas fed deuterium experiments.  The only other pulsed power effort experimenting with lithium deuteride was from 1962 when they tested single exploding wires on a z-pinch machine much less powerful than the Charger-1.  Besides the much higher densities of the fuel, it is in great abundance and relatively low cost compared to other approaches which may require deuterium tritium or deuterium helium-3 reactions.  Both tritium and helum-3 would require a major infrastructure for production that does not exist in order to produce the tons needed for a single mission, and the fusion fuel cost would greatly exceed the launch cost.  Therefore, this can be seen as a more pragmatic approach to the problem.

The operating costs of running lithium deuteride experiments with the Charger-1 is expected to cost about $5000 to $10,000 per week.  The z-machine at Sandia Labs would cost up to 100 times this.  We can do many more experiments towards understanding the optimization and scaling with lithium deuteride targets, and help guide the design of similar targets for more powerful machines.  There are more problems to be solved than can be realistically solved by one group alone, and collaboration with as many groups as necessary is vital in order to design and build a fusion propulsion system.   
Thanks for the information! That is indeed interesting to know and might change my opinion on the project.
While I do somewhat understand why the lithium deuteride might be a better fuel than Deuterium gas for an inertial fusion device, I am not exactly sure why exactly it would work better than D+T for achieving fusion. In fact the crosssection of D+Li is almost as low (and I believe the power density is even lower) as P+B11 but is not as aneutronic due to the D+D (and probably also D+T and T+He4) side reactions. Can you give us some more details on that?


Part of the reason we're using lithium deuteride and not deuterium tritium is because tritium is rare, expensive, and radioactive. And because lithium deuteride exists as a solid at room temperature, we expect higher reaction rates even though the cross section is lower. In addition to this, we do plan on breeding tritium from neutron lithium reactions, which we can then provide to research groups that are pursuing deuterium tritium fusion. Collaboration like this is what's really vital for making fusion work.
I do kinda understand the reasoning behind that, even though you may also go for D+D instead. This is a research project after all. You could also go straight for PB11 an aneutronic fusion, which might actually be easier to achieve than D+Li. Fueling might be more difficult though (even though I am not even sure about that).

Offline 93143

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Re: Pulsed Fusion Propulsion
« Reply #15 on: 06/25/2013 11:34 PM »
Lithium deuteride is a D-T fuel.  Remember Castle Bravo?

You need a free neutron to start the sequence, but 7Li doesn't use up the neutron that splits it, so the neutron economy should still work...?
« Last Edit: 06/25/2013 11:44 PM by 93143 »

Offline Elmar Moelzer

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Re: Pulsed Fusion Propulsion
« Reply #16 on: 06/26/2013 12:31 AM »
Yes and no. D + Li itself is about as hard (harder) to burn as PB11. The D+T and D+D side reactions might be what you really want. If you can do D+Li, you should theoretically be able to do PB11 also and the latter is considered the holy grail of nuclear fusion.

Offline QuantumG

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Re: Pulsed Fusion Propulsion
« Reply #17 on: 06/26/2013 01:16 AM »
Yes and no. D + Li itself is about as hard (harder) to burn as PB11. The D+T and D+D side reactions might be what you really want. If you can do D+Li, you should theoretically be able to do PB11 also and the latter is considered the holy grail of nuclear fusion.

If your goal is electricity generation, at small scales, sure.
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Offline QuantumG

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Re: Pulsed Fusion Propulsion
« Reply #18 on: 06/26/2013 02:56 AM »
Seeing as it seems like we have someone from the project on this thread now, any chance of an update of sorts?
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Offline Elmar Moelzer

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Re: Pulsed Fusion Propulsion
« Reply #19 on: 06/26/2013 03:12 AM »
Yes and no. D + Li itself is about as hard (harder) to burn as PB11. The D+T and D+D side reactions might be what you really want. If you can do D+Li, you should theoretically be able to do PB11 also and the latter is considered the holy grail of nuclear fusion.

While p-B11 is a great reaction, we still expect to get higher reaction rates from D+Li. The reason again is because D+Li is a solid, whereas p-B11 would be a gas-puff system.
Ok, I see where you are coming from. So have you done any simulations that support your idea that the solid fuel pellets will work sufficiently better than the system used by Sandia? Do you have papers on the subject?