5 ms·

Uhh... are you aware that the 7-X design was computed in the late 80s? It was just an enormous challenge to build this thing. Things like building and validati

Uhh... are you aware that the 7-X design was computed in the late 80s? It was just an enormous challenge to build this thing. Things like building and validating the field coils required a lot of effort and some novel approaches that they had to come up with along the way.

mpweiher 8y ago
> 7-X design was computed in the late 80s? Source for that? Looking at the German Wikipedia entry, the HELIAS method was invented in the late 80s. I don't see anything about the 7-X design actually having been computed back then. In fact, even the 2002 experiment Wendelstein 7-AS wasn't fully optimised. Also, Tokamaks were invented in the 1950s. JET started operating in 1983. ITER was proposed in 1987. Given even just a little bit of path-dependency, there really wasn't any realistic overlap.
- i_am_proteus 8y ago
  Another factor in W7-X being possible today and not a few decades ago, from my understanding, is the proliferation of and improvements in precision of CNC tools. All the design computations in the world go to waste if it can't be built to spec. Which it can be, today, at a reasonable cost.
  - jacquesm 8y ago
    1980's CNC tools did the job just fine. Most improvements since then have been in materials science. Five axis milling machines have been around since the 80's.
- sballin 8y ago
  Here's a source, unfortunately paywalled, from 1989: https://www.tandfonline.com/doi/abs/10.13182/FST90-A29178 https://www.tandfonline.com/doi/abs/10.13182/FST90-A29178 I do research at W7-X, so I can confirm that to the best of my knowledge, the design was computed a long time ago. Building the actual device took a while.
  - xxgreg 8y ago
    Do you have any links to a high level description of how this would be hooked up to a powerplant? Would this be used to heat water as per a typical fission plant?
    - xenophonf 8y ago
      The W7-X isn't a fusion power plant, so such a description doesn't exist. It's the chemistry equivalent of a test tube, not an internal combustion engine.
    - mpweiher 8y ago
      "The Helias (Helical Advanced Stellarator) reactor is based on the Wendelstein stellarator line and takes into account the design criteria of a power reactor." http://epsppd.epfl.ch/Sofia/pdf/P4_192.pdf http://epsppd.epfl.ch/Sofia/pdf/P4_192.pdf Alas, it "just" seems to talk about extending the coil design for a reactor, not the rest. I am guessing most of that would be similar as for other fusion reactors, see for example MIT's Pathway to Fusion Energy: https://www.youtube.com/watch?v=L0KuAx1COEk https://www.youtube.com/watch?v=L0KuAx1COEk
      - xxgreg 8y ago
        Thanks for the links. Had a bit of a google for Helias. Looks like the Wendelstein team are exploring using something called a "Helium Cooled Pebble Bed Blanket", which was designed for ITER. To me it looks like a closed loop heat exchanger using helium. This would then be fed into a typical steam system. Though I don't really understand the significance of the "pebbles" in this system.
        gmueckl 8y ago
        The pebbles will most likely be made of Lithium because it is a solid/liquid at the operating temperatures of the cooling system and therefore has a high density. It is also an element with a very low atomic mass, which makes the crosssections for interactions with fast neutrons comparably high. So the Lithium will have collisions with the fast neutrons from the D-T-fusion that leave the plasma confinement with most of the energy from the reaction. These will heat up the pebbles due to the energy transfer and from time to time a Lithium-6 atom will catch a neutron. This will make the Lithium core fission into a Helium code amd Tritium core. Tritium is one of the two fuels required for fusion and has a very low natural abundance due to its rather short half life. So breeding it seems to be the best option to obtain it in sufficient quantities.
- gmueckl 8y ago
  https://aip.scitation.org/doi/10.1063/1.860481 https://aip.scitation.org/doi/10.1063/1.860481 This paper published in 92 mentions that the 7-X was being designex at that time. I remember having seen images of the proposed field coil configuration in 91 or 92. So I might have bern off by a few years. But the plans must have bern complete for the project start in 1994.
alimw 8y ago
The GP's comment > the stellerator design, in a deep and fundamental way, simply isn't possible without massive computational power, whereas we've been building tokamaks since before massive cheap computational power. does not square with Wikipedia: > Stellarator ... The first Model A started operation in 1953 ...

mpweiher 8y ago

> 7-X design was computed in the late 80s? Source for that? Looking at the German Wikipedia entry, the HELIAS method was invented in the late 80s. I don't see anything about the 7-X design actually having been computed back then. In fact, even the 2002 experiment Wendelstein 7-AS wasn't fully optimised. Also, Tokamaks were invented in the 1950s. JET started operating in 1983. ITER was proposed in 1987. Given even just a little bit of path-dependency, there really wasn't any realistic overlap.

i_am_proteus 8y ago
Another factor in W7-X being possible today and not a few decades ago, from my understanding, is the proliferation of and improvements in precision of CNC tools. All the design computations in the world go to waste if it can't be built to spec. Which it can be, today, at a reasonable cost.
- jacquesm 8y ago
  1980's CNC tools did the job just fine. Most improvements since then have been in materials science. Five axis milling machines have been around since the 80's.
sballin 8y ago
Here's a source, unfortunately paywalled, from 1989: https://www.tandfonline.com/doi/abs/10.13182/FST90-A29178 https://www.tandfonline.com/doi/abs/10.13182/FST90-A29178 I do research at W7-X, so I can confirm that to the best of my knowledge, the design was computed a long time ago. Building the actual device took a while.
- xxgreg 8y ago
  Do you have any links to a high level description of how this would be hooked up to a powerplant? Would this be used to heat water as per a typical fission plant?
  - xenophonf 8y ago
    The W7-X isn't a fusion power plant, so such a description doesn't exist. It's the chemistry equivalent of a test tube, not an internal combustion engine.
  - mpweiher 8y ago
    "The Helias (Helical Advanced Stellarator) reactor is based on the Wendelstein stellarator line and takes into account the design criteria of a power reactor." http://epsppd.epfl.ch/Sofia/pdf/P4_192.pdf http://epsppd.epfl.ch/Sofia/pdf/P4_192.pdf Alas, it "just" seems to talk about extending the coil design for a reactor, not the rest. I am guessing most of that would be similar as for other fusion reactors, see for example MIT's Pathway to Fusion Energy: https://www.youtube.com/watch?v=L0KuAx1COEk https://www.youtube.com/watch?v=L0KuAx1COEk
    - xxgreg 8y ago
      Thanks for the links. Had a bit of a google for Helias. Looks like the Wendelstein team are exploring using something called a "Helium Cooled Pebble Bed Blanket", which was designed for ITER. To me it looks like a closed loop heat exchanger using helium. This would then be fed into a typical steam system. Though I don't really understand the significance of the "pebbles" in this system.
      - gmueckl 8y ago
        The pebbles will most likely be made of Lithium because it is a solid/liquid at the operating temperatures of the cooling system and therefore has a high density. It is also an element with a very low atomic mass, which makes the crosssections for interactions with fast neutrons comparably high. So the Lithium will have collisions with the fast neutrons from the D-T-fusion that leave the plasma confinement with most of the energy from the reaction. These will heat up the pebbles due to the energy transfer and from time to time a Lithium-6 atom will catch a neutron. This will make the Lithium core fission into a Helium code amd Tritium core. Tritium is one of the two fuels required for fusion and has a very low natural abundance due to its rather short half life. So breeding it seems to be the best option to obtain it in sufficient quantities.
gmueckl 8y ago
https://aip.scitation.org/doi/10.1063/1.860481 https://aip.scitation.org/doi/10.1063/1.860481 This paper published in 92 mentions that the 7-X was being designex at that time. I remember having seen images of the proposed field coil configuration in 91 or 92. So I might have bern off by a few years. But the plans must have bern complete for the project start in 1994.

alimw 8y ago

The GP's comment > the stellerator design, in a deep and fundamental way, simply isn't possible without massive computational power, whereas we've been building tokamaks since before massive cheap computational power. does not square with Wikipedia: > Stellarator ... The first Model A started operation in 1953 ...