3 ms·

From my classes some years ago IIRC the main benefit of the Stellarator was the lack of a plasma current which is no longer needed for plasma heating due to adv

From my classes some years ago IIRC the main benefit of the Stellarator was the lack of a plasma current which is no longer needed for plasma heating due to advances in neutral beam injection technologies. The plasma current seems to create some instabilities so we may be able to achieve better confinement with a device that doesn't have one. I would also agree with the other comments that we can't afford to put all our eggs into one basket - we spend a pitifully small amount on fusion research.

cygx 8y ago
The promise of stellarators is continuous operation, whereas tokamaks traditionally rely on inductive pulses for the two-fold purpose of confinement and heating.
pfdietz 8y ago
The big advantage of stellarators vs. tokamaks is their lack of disruptions. Tokamak disruptions are a very serious problem that, if not well-solved, promise to put tokamaks into the technology garbage can. A disruption can, in the worst case, generate runaway relativistic electron beams that can melt holes through the first wall. The first and primary goal of ITER is to show that the disruption problem can be and has been solved. If they don't do this, ITER will never be allowed to operate with a DT plasma. And they are still scrambling to solve the problem.
- lambdadmitry 8y ago
  Are talking about ELMs? Isn't it a basically solved problem then? I was under impression that between KSTAR's active field disruption coils and pellet injection they are more or less controlled (and we'll have confirmation from MAST Upgrade quite soon). Or am I wrong?
  - pfdietz 8y ago
    No, disruptions are catastrophic events where confinement is lost very rapidly. As the plasma cools an electric field builds up from the decaying current, and this field can accelerate runaway electrons in narrow beams to relativistic energies. Worst case >70% of the stored magnetic energy from the current in the plasma gets dumped into these electrons. If they hit the wall they can explode a hole in it. https://en.m.wikipedia.org/wiki/Tokamak#Plasma_disruptions https://en.m.wikipedia.org/wiki/Tokamak#Plasma_disruptions
    - lambdadmitry 8y ago
      Ah, I see. It looks they did something about it though https://www.iter.org/newsline/-/3183 https://www.iter.org/newsline/-/3183 are you skeptical that that can work?
      - pfdietz 8y ago
        Some disruptions occur almost instantly. The system will have very little time to react. And how are they going to train or test it? A single unmitigated disruption will damage the reactor. https://wsx.lanl.gov/Disruptions/Disruption-Risk-poster-Wurden-LAUR-11-11465.pdf https://wsx.lanl.gov/Disruptions/Disruption-Risk-poster-Wurd... https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-17-24821 https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lar...

cygx 8y ago

The promise of stellarators is continuous operation, whereas tokamaks traditionally rely on inductive pulses for the two-fold purpose of confinement and heating.

pfdietz 8y ago

The big advantage of stellarators vs. tokamaks is their lack of disruptions. Tokamak disruptions are a very serious problem that, if not well-solved, promise to put tokamaks into the technology garbage can. A disruption can, in the worst case, generate runaway relativistic electron beams that can melt holes through the first wall. The first and primary goal of ITER is to show that the disruption problem can be and has been solved. If they don't do this, ITER will never be allowed to operate with a DT plasma. And they are still scrambling to solve the problem.

lambdadmitry 8y ago
Are talking about ELMs? Isn't it a basically solved problem then? I was under impression that between KSTAR's active field disruption coils and pellet injection they are more or less controlled (and we'll have confirmation from MAST Upgrade quite soon). Or am I wrong?
- pfdietz 8y ago
  No, disruptions are catastrophic events where confinement is lost very rapidly. As the plasma cools an electric field builds up from the decaying current, and this field can accelerate runaway electrons in narrow beams to relativistic energies. Worst case >70% of the stored magnetic energy from the current in the plasma gets dumped into these electrons. If they hit the wall they can explode a hole in it. https://en.m.wikipedia.org/wiki/Tokamak#Plasma_disruptions https://en.m.wikipedia.org/wiki/Tokamak#Plasma_disruptions
  - lambdadmitry 8y ago
    Ah, I see. It looks they did something about it though https://www.iter.org/newsline/-/3183 https://www.iter.org/newsline/-/3183 are you skeptical that that can work?
    - pfdietz 8y ago
      Some disruptions occur almost instantly. The system will have very little time to react. And how are they going to train or test it? A single unmitigated disruption will damage the reactor. https://wsx.lanl.gov/Disruptions/Disruption-Risk-poster-Wurden-LAUR-11-11465.pdf https://wsx.lanl.gov/Disruptions/Disruption-Risk-poster-Wurd... https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-17-24821 https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lar...