6 ms·

The only fusion project which has a chance of producing excess heat at Q>2 within a decade is the MIT SPARC, using proven plasma physics and scaling the size/co

The only fusion project which has a chance of producing excess heat at Q>2 within a decade is the MIT SPARC, using proven plasma physics and scaling the size/cost down dramatically with high-field HTS magnets (think ITER but sooner and >10x cheaper). Why is this definite solution to climate apocalypse being developed within the framework of MIT startup accelerator instead of Manhattan Project while most of the publicity goes to unproven designs which are orders of magnitude from being anywhere close to Q>1 is beyond me MIT SPARC overview presentation/recent progress: https://www.youtube.com/watch?v=h8uYNhevRtk https://www.youtube.com/watch?v=h8uYNhevRtk Journal of Plasma Physics issue with several papers about it: https://www.cambridge.org/core/journals/journal-of-plasma-physics/issue/8E169A054A534DBA94F6BBF4C3DB88A4 https://www.cambridge.org/core/journals/journal-of-plasma-ph...

pfdietz 5y ago
Definite solution? It's a definite non-solution, even if the plasma physics is more nailed down. The ARC reactor (fully scaled up SPARC with tritium breeding blanket) would have a power density 40x worse than a PWR primary reactor vessel, and supplying the world's primary energy demand with them would require 100x more beryllium than the USGS estimated resource (not reserve) of that element.
- bluepanda928752 5y ago
  Not sure why lower power density might be a show-stopper here. Beryllium angle is interesting, haven't thought about that
  - pfdietz 5y ago
    The cost of the reactor will be proportional to its size, so the cost/power will be inversely proportional to the power density. Lawrence Lidsky (who was also at MIT) (and also a similar argument from Pfirsch and Schmitter in Germany) famously pointed out back in the 1980s that DT fusion reactors will inherently have terrible power density compared to fission reactors, and this will render them noncompetitive. Despite putative rebuttals at the time, nothing we've seen since contradicts their devastating argument. http://orcutt.net/weblog/wp-content/uploads/2015/08/The-Trouble-With-Fusion_MIT_Tech_Review_1983.pdf http://orcutt.net/weblog/wp-content/uploads/2015/08/The-Trou... https://ui.adsabs.harvard.edu/abs/1987oepn.book.....P/abstract https://ui.adsabs.harvard.edu/abs/1987oepn.book.....P/abstra... Note that Helion wants to go with D-3He, and use direct conversion for at least some of the energy recovery. This might be the only hope for making fusion compete. But of course you need 3He; making it with DD fusion requires even more aggressive plasma physics. ARC at least isn't quite as absurd as a tokamak the size of ITER, which has a gross fusion power density another order of magnitude lower.
    - bluepanda928752 5y ago
      I think high-field HTS tokamaks projected costs are in a reasonable range despite the raw power density being lower. There could be additional savings related to radioactive waste processing since fusion should generate less and also containment/security for similar reasons Helion and other new fusion projects are, surely, interesting, however tokamaks are so much more ready and, with high-field magnets, likely economical
      - pfdietz 5y ago
        I don't believe cost projections for fusion. If you look at them, they're filled with assumptions that aren't supported by much of anything(*), but magically make the technology just competitive. As the competition has improved, the assumptions have gotten more desperate. They're less "this is what the technology will cost" and more "this is the least ridiculous set of assumptions we could find that would let our technology not be dead." If you apply the same level of assumptions to, say, light water fission reactors, I'm sure you'd get cost estimates vastly lower than what they actually cost in practice. (*) For example, one paper assuming the efficiency of converting thermal energy to power in the fusion reactor is 60%, a level that combined cycle power plants achieve by expanding combustion gas that starts at a temperature that would soften or even melt the turbine blades.
        ZeroGravitas 5y ago
        I've seen some claims that even a magically costless heat producing device connected to a steam turbine won't be competitive with solar PV so I'd guess Fusion would also fail that test if it is basically being used to generate heat (note, they're claiming they have some new tech that avoids this problem, but we don't know if actually does or not)
        DennisP 5y ago
        The real question is whether it'd be competitive with solar PV on cloudy winter days with enough battery to get through windless nights. If so, there's probably a place on the grid for it. (In any case, Helion is planning direct energy conversion, without a heat cycle.)
- DennisP 5y ago
  Could they replace the beryllium with lead? It multiplies neutrons the same way; last I saw, that's what General Fusion was planning to use.
  - pfdietz 5y ago
    Molten metal flowing past metal structures in their high magnetic field would be a non-starter, I think, due to induced currents and JxB forces.
    - DennisP 5y ago
      Does the metal have to flow? Let it sit there and run cooling pipes through it. Every now and then turn off the fusion when you need to fire up the pumps and swap in new lead/lithium. (Also, I'm dumb but beryllium is also a metal, how does it differ from lead in this respect?)
      - pfdietz 5y ago
        The ARC design immerses the vacuum vessel in a bath of molten salt (which is where the Be is, in lithium beryllium fluoride (FLiBe) salt). That salt is where the neutrons deposit their heat. Replacing the Be with lead means the heat is getting deposited in that lead (or, more likely, molten lead-lithium alloy). Even though ARC uses salt, it would also have to worry about voltages induced by flow across magnetic field lines -- not because of currents, but because if the voltage becomes high enough it can induce electrochemical reactions, like production of elemental fluorine (or corrosion of metal where the fluorine would have been evolved.) I think they keep the velocity x coolant channel diameter low enough to avoid that, but it's still a consideration they have to address.
willis936 5y ago
SPARC is great, but I'm under the impression that a gen 1 DT MCF reactor will almost certainly need to be a stellarator to work around the engineering challenges and pulsed nature of tokamaks. Optimization, HTS magnets, and clever coil winding enable them. Tokamaks are easier so SPARC should certainly be made to make its splash. The real problem is that DoE's Office of Science is relatively reducing funding of Fusion Energy Science. It's barely enough to meet the US' ITER contribution. The very few existing projects are running on fumes. No one in the US is making a machine and hasn't been for over a decade. https://www.energy.gov/sites/default/files/2021-05/doe-fy2022-budget-volume-4.pdf https://www.energy.gov/sites/default/files/2021-05/doe-fy202...
- DennisP 5y ago
  People are making machines, it's just with private funding. This includes SPARC, which MIT spun off into Commonwealth Energy. As of a year ago they'd raised over $200M. https://techcrunch.com/2020/05/26/with-84-million-in-new-cash-commonwealth-fusion-is-on-track-for-a-demonstration-fusion-reactor-by-2025/ https://techcrunch.com/2020/05/26/with-84-million-in-new-cas...
  - willis936 5y ago
    The context is US publicly funded projects. The reason I used this context is because fusion is not profitable, won't be for at least 30 years in the optimistic estimates, and may very well never be profitable. It is exactly the kind of thing that should be public works.
    - DennisP 5y ago
      Maybe it should, but since the government is not doing it, we're lucky that investors disagree with your assessment. CE, Tokamak Energy, Tri Alpha, General Fusion, and Helion have all gotten substantial private funding. Tri Alpha was over $700M last I checked. One of Helion's investors is YCombinator.
      - 5y ago
mensetmanusman 5y ago
If there was a definite solution it would be funded unless all the scientists involved lack communication skills to raise capital. VCs spend millions on apps that say ‘yo’…

pfdietz 5y ago

Definite solution? It's a definite non-solution, even if the plasma physics is more nailed down. The ARC reactor (fully scaled up SPARC with tritium breeding blanket) would have a power density 40x worse than a PWR primary reactor vessel, and supplying the world's primary energy demand with them would require 100x more beryllium than the USGS estimated resource (not reserve) of that element.

bluepanda928752 5y ago
Not sure why lower power density might be a show-stopper here. Beryllium angle is interesting, haven't thought about that
- pfdietz 5y ago
  The cost of the reactor will be proportional to its size, so the cost/power will be inversely proportional to the power density. Lawrence Lidsky (who was also at MIT) (and also a similar argument from Pfirsch and Schmitter in Germany) famously pointed out back in the 1980s that DT fusion reactors will inherently have terrible power density compared to fission reactors, and this will render them noncompetitive. Despite putative rebuttals at the time, nothing we've seen since contradicts their devastating argument. http://orcutt.net/weblog/wp-content/uploads/2015/08/The-Trouble-With-Fusion_MIT_Tech_Review_1983.pdf http://orcutt.net/weblog/wp-content/uploads/2015/08/The-Trou... https://ui.adsabs.harvard.edu/abs/1987oepn.book.....P/abstract https://ui.adsabs.harvard.edu/abs/1987oepn.book.....P/abstra... Note that Helion wants to go with D-3He, and use direct conversion for at least some of the energy recovery. This might be the only hope for making fusion compete. But of course you need 3He; making it with DD fusion requires even more aggressive plasma physics. ARC at least isn't quite as absurd as a tokamak the size of ITER, which has a gross fusion power density another order of magnitude lower.
  - bluepanda928752 5y ago
    I think high-field HTS tokamaks projected costs are in a reasonable range despite the raw power density being lower. There could be additional savings related to radioactive waste processing since fusion should generate less and also containment/security for similar reasons Helion and other new fusion projects are, surely, interesting, however tokamaks are so much more ready and, with high-field magnets, likely economical
    - pfdietz 5y ago
      I don't believe cost projections for fusion. If you look at them, they're filled with assumptions that aren't supported by much of anything(*), but magically make the technology just competitive. As the competition has improved, the assumptions have gotten more desperate. They're less "this is what the technology will cost" and more "this is the least ridiculous set of assumptions we could find that would let our technology not be dead." If you apply the same level of assumptions to, say, light water fission reactors, I'm sure you'd get cost estimates vastly lower than what they actually cost in practice. (*) For example, one paper assuming the efficiency of converting thermal energy to power in the fusion reactor is 60%, a level that combined cycle power plants achieve by expanding combustion gas that starts at a temperature that would soften or even melt the turbine blades.
      - ZeroGravitas 5y ago
        I've seen some claims that even a magically costless heat producing device connected to a steam turbine won't be competitive with solar PV so I'd guess Fusion would also fail that test if it is basically being used to generate heat (note, they're claiming they have some new tech that avoids this problem, but we don't know if actually does or not)
        DennisP 5y ago
        The real question is whether it'd be competitive with solar PV on cloudy winter days with enough battery to get through windless nights. If so, there's probably a place on the grid for it. (In any case, Helion is planning direct energy conversion, without a heat cycle.)
DennisP 5y ago
Could they replace the beryllium with lead? It multiplies neutrons the same way; last I saw, that's what General Fusion was planning to use.
- pfdietz 5y ago
  Molten metal flowing past metal structures in their high magnetic field would be a non-starter, I think, due to induced currents and JxB forces.
  - DennisP 5y ago
    Does the metal have to flow? Let it sit there and run cooling pipes through it. Every now and then turn off the fusion when you need to fire up the pumps and swap in new lead/lithium. (Also, I'm dumb but beryllium is also a metal, how does it differ from lead in this respect?)
    - pfdietz 5y ago
      The ARC design immerses the vacuum vessel in a bath of molten salt (which is where the Be is, in lithium beryllium fluoride (FLiBe) salt). That salt is where the neutrons deposit their heat. Replacing the Be with lead means the heat is getting deposited in that lead (or, more likely, molten lead-lithium alloy). Even though ARC uses salt, it would also have to worry about voltages induced by flow across magnetic field lines -- not because of currents, but because if the voltage becomes high enough it can induce electrochemical reactions, like production of elemental fluorine (or corrosion of metal where the fluorine would have been evolved.) I think they keep the velocity x coolant channel diameter low enough to avoid that, but it's still a consideration they have to address.

willis936 5y ago

SPARC is great, but I'm under the impression that a gen 1 DT MCF reactor will almost certainly need to be a stellarator to work around the engineering challenges and pulsed nature of tokamaks. Optimization, HTS magnets, and clever coil winding enable them. Tokamaks are easier so SPARC should certainly be made to make its splash. The real problem is that DoE's Office of Science is relatively reducing funding of Fusion Energy Science. It's barely enough to meet the US' ITER contribution. The very few existing projects are running on fumes. No one in the US is making a machine and hasn't been for over a decade. https://www.energy.gov/sites/default/files/2021-05/doe-fy2022-budget-volume-4.pdf https://www.energy.gov/sites/default/files/2021-05/doe-fy202...

DennisP 5y ago
People are making machines, it's just with private funding. This includes SPARC, which MIT spun off into Commonwealth Energy. As of a year ago they'd raised over $200M. https://techcrunch.com/2020/05/26/with-84-million-in-new-cash-commonwealth-fusion-is-on-track-for-a-demonstration-fusion-reactor-by-2025/ https://techcrunch.com/2020/05/26/with-84-million-in-new-cas...
- willis936 5y ago
  The context is US publicly funded projects. The reason I used this context is because fusion is not profitable, won't be for at least 30 years in the optimistic estimates, and may very well never be profitable. It is exactly the kind of thing that should be public works.
  - DennisP 5y ago
    Maybe it should, but since the government is not doing it, we're lucky that investors disagree with your assessment. CE, Tokamak Energy, Tri Alpha, General Fusion, and Helion have all gotten substantial private funding. Tri Alpha was over $700M last I checked. One of Helion's investors is YCombinator.
    - 5y ago

mensetmanusman 5y ago

If there was a definite solution it would be funded unless all the scientists involved lack communication skills to raise capital. VCs spend millions on apps that say ‘yo’…