Sensors for plasma's E & M...

Nik · Post by **Nik** » Mon May 30, 2011 1:54 pm

http://www.physorg.com/news/2011-05-sen ... stars.html

Slightly OT, but nice to know such sensors are available...

"The sensors developed for this research must guarantee a high level of accuracy to allow the theories to be validated and the plasma to be monitored. In the ITER reactor, where the plasma is confined in a space in the shape of a rubber ring of 6 meters in diameter, the measurements must detect variations in the position of the plasma to within a millimeter. In the case of the magnetic field, its orientation must be known with an angle to an accuracy of half a degree, hence the second measuring instrument that was tested."

Skipjack · Post by **Skipjack** » Mon May 30, 2011 2:35 pm

This is really cool!
The thing is that ITER will never make it to a viable commercializable reactor and I believe that it was wrong to market it as such, but it has sprouted a lot of useful technology and the research done in the course of the programme has widened our understanding of plasmas quite a bit already. I am not sure that this is worth the billions spent of the project though...

D Tibbets · Post by **D Tibbets** » Mon May 30, 2011 4:48 pm

6 Meters plasma diameter? That sounds way too low. Perhaps it refers to the inner border of the plasma. The outer border would be perhaps several meters wider. Or perhaps he misspoke and meant radius. In any case the precision of the measurements seem large. From the little I know about plasma modeling, particle in cell codes, etc. The sampling dimensions is very amall and the time slices are very short. If this is the best that actual measurements can manage then it might partially explain why the simulations are not very useful and they have to build successively larger machines to understand the physics.

Dan Tibbets

D Tibbets · Post by **D Tibbets** » Mon May 30, 2011 5:02 pm

And, just to point out other simplifications if not outright misleading information they say:

"Using stars as a model, they want to produce energy by fusing hydrogen to form helium."

Other than the operating temperature a Tokamak has little in common with a star. And they hope to fuse deuterium- tritium, not hydrogen. This is picky, but multiple people have compared fusion power density in a Tokamak or other device to the fusion power density of the Sun and pointed out the feeble performance of the Sun. What they neglect is the fuel. The Sun burns hydrogen. If a Tokamak (or Polywell for that matter) tried to fuse hydrogen the output would be billions upon billions of times less.
Also, stars are near spherical gravitaionally confined devices. Completely different. Polywells are at least nearly spherical with a centrally confining force. Still the comparisons are lose by any standard.

Dan Tibbets

TallDave · Post by **TallDave** » Sun Jun 05, 2011 3:34 am

I think they mean the ITER plasma minor diameter, which is about 4m in this estimate, though it may have gotten larger since then.

https://fusion.gat.com/iter/iter-ga/ima ... atures.pdf

Or he meant major and said diameter where he meant radius. Journalists never get this stuff right.