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ITER is like electric cars. There’s no point in spending millions to design a new EV until the battery technology exists. That’s the key limiter, not the “rest

ITER is like electric cars. There’s no point in spending millions to design a new EV until the battery technology exists. That’s the key limiter, not the “rest of the car”. For fusion, this key technology limiter is the superconducting magnetic tape. Even small improvements in field strength have a dramatic non-linear improvement in fusion power gain. ITER started their design work decades ago and will continue construction for decades more. Meanwhile, SC magnetic tape technology has moved on, making the entire enterprise a dead-end waste of time and money. They got bogged down in the paperwork and bureaucracy of the “rest of the facility” with no hope of making actual working reactor. There are many instances of this issue in industry, and in my experience large government bureaucracies are pathologically incapable of planning ahead for where the puck will be instead of where the puck was. I like to imagine what would happen if a rich industrialist like Bezos or Musk approached the problem: First, spend a few billion on superconductor tape research and then start building many small reactors that are minimal test beds while in parallel improving the magnets. Only “go big” once the reactor can produce net power. See also: NASA spending billions per launch on the SLS with a couple of test launches per decade while SpaceX spends millions per Starship and plans half a dozen test launches this year!

XorNot 3y ago
So how's the Lockheed Martin skunkworks project going? That was the last poster child for "REBCO tape will quickly solve all the problems". Oh right - incepted in 2010, cancelled in 2021. 11 years - over a decade - and no reactor in sight.
- willis936 3y ago
  They never mentioned REBCO or HTS. It was obvious bullshit from the beginning. It was more likely a cover for a black project, like the SR-72.
  - pfdietz 3y ago
    I wonder if some of these whacky military things are actually honeypots for espionage. That's been my assumption for the Navy work on Polywell.
  - XorNot 3y ago
    Right but that's the point: the parent post is talking about those things as though they've obviously and clearly obsoleted the ITER design. Except that can't be true, because no reactor based on those technologies exists now, or is likely to complete construction in the near future. So ITER is the correct bet: take boring technologies and build a functional fusion device with them that gets Q > 1. Because there's a fairly obvious corollary, which is that if you can somehow build better magnets, then the next reactor - DEMO, and actual power plants - can obviously be redesigned to take advantage of those magnets - they will not fundamentally change the internal dynamics of a tokamak, since it's the magnetic field shapes which matter, not the physical generators. Everyone working with REBCO has always talked about "rapid breakthroughs" in about 5 years, and then 5 years later the story is always the same: it's considerably harder to build with these things then you'd think, they're still working through the engineering etc. It's not that it can't work, but it's not magically faster in the way people keep claiming and nor does it get you any closer to the actual goal, which is to get a Q > 1 fusion device functioning - which will, at all times, fundamentally require a very large vacuum chamber to do so unless magnetic field intensities are being vastly increased (and they're not: low-temperature superconductors can achieve far higher field intensities then high-temperature ones which is why the LHC and other particle accelerators use them[1] - some YBCO tapes might be able to do it, but manufacturing suitable quantities, of suitable quality, in long enough reels, and then winding magnets with them is an unsolved problem). [1] https://www.researchgate.net/figure/Engineering-critical-current-density-versus-magnetic-field-for-low-temperature_fig1_51930024 https://www.researchgate.net/figure/Engineering-critical-cur...
    - willis936 3y ago
      >Everyone working with REBCO has always talked about "rapid breakthroughs" in about 5 years, and then 5 years later the story is always the same: it's considerably harder to build with these things then you'd think, they're still working through the engineering etc. Please cite the earliest REBCO-based fusion reactor promise date that has lapsed. I don't think reality agrees with your perception. Importantly you can draw a straight line from REBCO-based fund raising and the amount of REBCO needed to be purchased for them. If "the engineering wasn't there" then that amount of money could not have purchased that amount of tape. Also, how could ITER be the right bet when it costs so much and takes so long to build that it could never scale to anything more than a multi-generational science experiment (e.g. not a power source)?
pfdietz 3y ago
No, actually the key technology (for DT fusion) is the blanket and first wall (and possibly limiter/diverter). The problem is maximizing power/area, since if this is too low the reactor is too large and cannot be economical. The most plausible IMO DT fusion scheme is Zap's, since it allows thick liquid lithium to cover much of the exposed inner surfaces. Zap's scheme doesn't even use magnets, never mind high temperature superconducting ones.

XorNot 3y ago

So how's the Lockheed Martin skunkworks project going? That was the last poster child for "REBCO tape will quickly solve all the problems". Oh right - incepted in 2010, cancelled in 2021. 11 years - over a decade - and no reactor in sight.

willis936 3y ago
They never mentioned REBCO or HTS. It was obvious bullshit from the beginning. It was more likely a cover for a black project, like the SR-72.
- pfdietz 3y ago
  I wonder if some of these whacky military things are actually honeypots for espionage. That's been my assumption for the Navy work on Polywell.
- XorNot 3y ago
  Right but that's the point: the parent post is talking about those things as though they've obviously and clearly obsoleted the ITER design. Except that can't be true, because no reactor based on those technologies exists now, or is likely to complete construction in the near future. So ITER is the correct bet: take boring technologies and build a functional fusion device with them that gets Q > 1. Because there's a fairly obvious corollary, which is that if you can somehow build better magnets, then the next reactor - DEMO, and actual power plants - can obviously be redesigned to take advantage of those magnets - they will not fundamentally change the internal dynamics of a tokamak, since it's the magnetic field shapes which matter, not the physical generators. Everyone working with REBCO has always talked about "rapid breakthroughs" in about 5 years, and then 5 years later the story is always the same: it's considerably harder to build with these things then you'd think, they're still working through the engineering etc. It's not that it can't work, but it's not magically faster in the way people keep claiming and nor does it get you any closer to the actual goal, which is to get a Q > 1 fusion device functioning - which will, at all times, fundamentally require a very large vacuum chamber to do so unless magnetic field intensities are being vastly increased (and they're not: low-temperature superconductors can achieve far higher field intensities then high-temperature ones which is why the LHC and other particle accelerators use them[1] - some YBCO tapes might be able to do it, but manufacturing suitable quantities, of suitable quality, in long enough reels, and then winding magnets with them is an unsolved problem). [1] https://www.researchgate.net/figure/Engineering-critical-current-density-versus-magnetic-field-for-low-temperature_fig1_51930024 https://www.researchgate.net/figure/Engineering-critical-cur...
  - willis936 3y ago
    >Everyone working with REBCO has always talked about "rapid breakthroughs" in about 5 years, and then 5 years later the story is always the same: it's considerably harder to build with these things then you'd think, they're still working through the engineering etc. Please cite the earliest REBCO-based fusion reactor promise date that has lapsed. I don't think reality agrees with your perception. Importantly you can draw a straight line from REBCO-based fund raising and the amount of REBCO needed to be purchased for them. If "the engineering wasn't there" then that amount of money could not have purchased that amount of tape. Also, how could ITER be the right bet when it costs so much and takes so long to build that it could never scale to anything more than a multi-generational science experiment (e.g. not a power source)?

pfdietz 3y ago

No, actually the key technology (for DT fusion) is the blanket and first wall (and possibly limiter/diverter). The problem is maximizing power/area, since if this is too low the reactor is too large and cannot be economical. The most plausible IMO DT fusion scheme is Zap's, since it allows thick liquid lithium to cover much of the exposed inner surfaces. Zap's scheme doesn't even use magnets, never mind high temperature superconducting ones.