6 ms·

For SPARC the big innovation sounds like it is being able to use some special superconducting electromagnets to generate the massive magnetic field in the tokam

by xt00 4y ago

For SPARC the big innovation sounds like it is being able to use some special superconducting electromagnets to generate the massive magnetic field in the tokamak -- since that part is such a critical part, it would seem like in the next say 5-10 years that it takes to get SPARC up and running there should be a parallel group just trying to improve that magnet design by say 2X, which would likely have a massive impact.. seems like a smart thing for National science foundation or darpa or whatever to be funding that.. (maybe already happening) but it would be a bummer to be talking about this in 2030 and them saying, ok now we just need to design a more powerful magnet..

TaylorAlexander 4y ago
Well SPARC and the planned successor ARC can successfully generate power without needing more powerful magnets. Assuming all goes to plan (lol) ARC will be commercially viable with existing magnet tech. They have said that as you go towards higher field strengths, the physical forces pushing and pulling between magnets gets so extreme that it is difficult to build a machine that doesn't tear itself apart. So stronger magnets are only useful in conjunction with an entire machine design that can handle them. It looks to me like a good path is to get commercially viable machines with existing magnets, and then iterate on the entire machine once they have learned the basics of operating commercial fusion. But I am just a robotics engineer who has watched a lot of the SPARC lectures, so I have no domain expertise here.
- jacquesm 4y ago
  This goes for permanent magnets as well. I've had a ceramic magnet and a neo explode on me and to say that I was surprised at the incredible forces unleashed would be an understatement. I'm a sucker for working with proper safety gear and if not for wearing very good safety glasses I'd have been in serious trouble, multiple magnet fragments sat embedded in the glasses and a couple in my skin where it wasn't covered by the glasses (easily removed with another magnet :) ).
  - dTal 4y ago
    How large of a magnet are we talking, and what were you doing with it? So I know what to be terrified of, for future reference.
    - jacquesm 4y ago
      The ceramic one was a 2x2" square 1/4" thick one that had one stuck corner, trying to remove it shattered it, the other was a neo that accidentally jumped up when I put down a heavy piece of steel and that in turn allowed the magnet to start flying towards it, it shattered on impact. That one was a lot larger (2"x2"x1"), and neos are a lot more powerful for the same size as ceramics. In both cases it was to test sets of magnets under controlled circumstances to see which ones I would order in bulk for the rotor of a windmill. Lessons learned: make no assumptions on whether or not a magnet really is free to be released, do not place magnets loose on a workbench even if they are far away from your work area because when the friction unexpectedly disappears you are going to be in for a surprise. Don't mess around with very large neos unless you know what you are doing, they can really hurt you. (And when you do know what you are doing: observe safety precautions religiously and always wear safety glasses until your whole rig is assembled and the magnets are safely enclosed). Something like this just scares me: https://www.apexmagnets.com/magnets/6-x-2-disc-neodymium-magnet https://www.apexmagnets.com/magnets/6-x-2-disc-neodymium-mag...
      - willis936 4y ago
        I saw a PPPL group propose the use of permanent magnets to assist in stellarator geometry. My first and continued thought has been "this is completely insane". Permanent magnets are fragile, violent, and cannot be turned off. All engineering challenges aside, they propose making an industrially sized death machine that cannot be turned off.
        jacquesm 4y ago
        You actually can turn them off. You can use mu-metal to short circuit the magnetic field. https://en.wikipedia.org/wiki/Mu-metal https://en.wikipedia.org/wiki/Mu-metal
ajnin 4y ago
That's basically what's going on with ITER, it needs to be so massive because the technology available at the time of conception was not capable of generating more intense magnetic field. There is a very strong relationship between the strength of the field and the required size of the tokamak (hence time and cost of construction). By the time you're done better technology will be available, but that's how progress goes.
- sigmoid10 4y ago
  Unfortunately, it's not so simple. SPARC is just the latest attempt to benefit from stronger magnet technology and thus smaller designs, but another big problem remains unsolved: turbulence. Since smaller designs and stronger magnets directly imply higher field strength gradients, the plasma becomes harder to control for the necessary burn time to achieve Q>1. Lockheed also thought they could simply use stronger magnets to build smaller reactors faster, but in the end they discovered that smaller is not automatically better. I wouldn't be surprised if we also see the eventual SPARC redesign that's 100 times more massive. Unless we get a major theoretical breakthrough in the near future, ITER will probably remain the most likely design candidate for near term net energy production.
  - DennisP 4y ago
    Can you provide a source for that? Because here's the head of MIT's fusion program, claiming the exact opposite: https://www.youtube.com/watch?v=KkpqA8yG9T4&t=2221s https://www.youtube.com/watch?v=KkpqA8yG9T4&t=2221s
    - sigmoid10 4y ago
      See here for example: https://www-pub.iaea.org/mtcd/publications/pdf/csp_019c/pdf/th1_1.pdf https://www-pub.iaea.org/mtcd/publications/pdf/csp_019c/pdf/... - but note that this stuff is not trivial. The intricacies of turbulence in MHD are incredibly complex and hard to study (near-impossible analytically and very hard numerically). Nevertheless, these scaling behaviours (see the figures in section 2) have been known for more than 20 years by now. Also, beware that the head of MIT's fusion program (your source) is the head of SPARC. Since he siphoned a huge amount of money from gullible venture capitalists outside his field by now, you definitely shouldn't rely on him for an obective analysis of SPARC's fundamental design.

by xt00 4y ago

TaylorAlexander 4y ago

Well SPARC and the planned successor ARC can successfully generate power without needing more powerful magnets. Assuming all goes to plan (lol) ARC will be commercially viable with existing magnet tech. They have said that as you go towards higher field strengths, the physical forces pushing and pulling between magnets gets so extreme that it is difficult to build a machine that doesn't tear itself apart. So stronger magnets are only useful in conjunction with an entire machine design that can handle them. It looks to me like a good path is to get commercially viable machines with existing magnets, and then iterate on the entire machine once they have learned the basics of operating commercial fusion. But I am just a robotics engineer who has watched a lot of the SPARC lectures, so I have no domain expertise here.

jacquesm 4y ago
This goes for permanent magnets as well. I've had a ceramic magnet and a neo explode on me and to say that I was surprised at the incredible forces unleashed would be an understatement. I'm a sucker for working with proper safety gear and if not for wearing very good safety glasses I'd have been in serious trouble, multiple magnet fragments sat embedded in the glasses and a couple in my skin where it wasn't covered by the glasses (easily removed with another magnet :) ).
- dTal 4y ago
  How large of a magnet are we talking, and what were you doing with it? So I know what to be terrified of, for future reference.
  - jacquesm 4y ago
    The ceramic one was a 2x2" square 1/4" thick one that had one stuck corner, trying to remove it shattered it, the other was a neo that accidentally jumped up when I put down a heavy piece of steel and that in turn allowed the magnet to start flying towards it, it shattered on impact. That one was a lot larger (2"x2"x1"), and neos are a lot more powerful for the same size as ceramics. In both cases it was to test sets of magnets under controlled circumstances to see which ones I would order in bulk for the rotor of a windmill. Lessons learned: make no assumptions on whether or not a magnet really is free to be released, do not place magnets loose on a workbench even if they are far away from your work area because when the friction unexpectedly disappears you are going to be in for a surprise. Don't mess around with very large neos unless you know what you are doing, they can really hurt you. (And when you do know what you are doing: observe safety precautions religiously and always wear safety glasses until your whole rig is assembled and the magnets are safely enclosed). Something like this just scares me: https://www.apexmagnets.com/magnets/6-x-2-disc-neodymium-magnet https://www.apexmagnets.com/magnets/6-x-2-disc-neodymium-mag...
    - willis936 4y ago
      I saw a PPPL group propose the use of permanent magnets to assist in stellarator geometry. My first and continued thought has been "this is completely insane". Permanent magnets are fragile, violent, and cannot be turned off. All engineering challenges aside, they propose making an industrially sized death machine that cannot be turned off.
      - jacquesm 4y ago
        You actually can turn them off. You can use mu-metal to short circuit the magnetic field. https://en.wikipedia.org/wiki/Mu-metal https://en.wikipedia.org/wiki/Mu-metal

ajnin 4y ago

That's basically what's going on with ITER, it needs to be so massive because the technology available at the time of conception was not capable of generating more intense magnetic field. There is a very strong relationship between the strength of the field and the required size of the tokamak (hence time and cost of construction). By the time you're done better technology will be available, but that's how progress goes.

sigmoid10 4y ago
Unfortunately, it's not so simple. SPARC is just the latest attempt to benefit from stronger magnet technology and thus smaller designs, but another big problem remains unsolved: turbulence. Since smaller designs and stronger magnets directly imply higher field strength gradients, the plasma becomes harder to control for the necessary burn time to achieve Q>1. Lockheed also thought they could simply use stronger magnets to build smaller reactors faster, but in the end they discovered that smaller is not automatically better. I wouldn't be surprised if we also see the eventual SPARC redesign that's 100 times more massive. Unless we get a major theoretical breakthrough in the near future, ITER will probably remain the most likely design candidate for near term net energy production.
- DennisP 4y ago
  Can you provide a source for that? Because here's the head of MIT's fusion program, claiming the exact opposite: https://www.youtube.com/watch?v=KkpqA8yG9T4&t=2221s https://www.youtube.com/watch?v=KkpqA8yG9T4&t=2221s
  - sigmoid10 4y ago
    See here for example: https://www-pub.iaea.org/mtcd/publications/pdf/csp_019c/pdf/th1_1.pdf https://www-pub.iaea.org/mtcd/publications/pdf/csp_019c/pdf/... - but note that this stuff is not trivial. The intricacies of turbulence in MHD are incredibly complex and hard to study (near-impossible analytically and very hard numerically). Nevertheless, these scaling behaviours (see the figures in section 2) have been known for more than 20 years by now. Also, beware that the head of MIT's fusion program (your source) is the head of SPARC. Since he siphoned a huge amount of money from gullible venture capitalists outside his field by now, you definitely shouldn't rely on him for an obective analysis of SPARC's fundamental design.