First of all, congratulations to your results and to the media coverage you got!
•(1) What were the plasma temperature and density during that record shot ?
•(2) What was the background magnetic field strength and the related plasma beta value ?
•(3) What made that shot a record shot, i.e. was it particularly high heating power or better <something> than usual ?
•(4) For how long could you sustain that record pressure ?
•(5) Did you do it on purpose at the very end of the experiment's life because you were afraid of unusual high power fluxes (due to the high pressure) to the plasma-facing components ?
•(6) Did the plasma-facing components (or anything else) got any damage during that record discharge ?
•(7) What will happen now with the Alcator C-mod device and the people working on it ?
•(8) If I understand it correctly, your approach is somewhat different (although very similar) to ITER in that sense that you have a rather small device achieving nevertheless high density and temperature due to the higher magnetic field (correct me if I am wrong). There was once a device called “IGNITOR” which was planned to achieve some fusion power output, do you know the status of that device ?
•(9) Does the comparable high magnetic field strength in your approach prevent you from using superconductors at a reactor size level (or IGNITOR-size) ?
•(10) Will the scientific details about that shot be presented somewhere (or are they already somewhere?) ?
•(11) Does this record shot have a scientific significance or was it more something like “let's see what we can squeeze out of that device” ?
•(12) Thank you very much for reading all those questions and maybe even trying to answer them
I wish you all the best for your future.
[–]MIT_PSFCPlasma Science and Fusion Center[S] 21 points 4 days ago
Great, technical questions. I'll try my best to put this into laymen terms.
Check out the FAQ about the record shot for more info: https://www.psfc.mit.edu/news/2016/pressure-record-faq
(1) The plasma temperature and density during the record shot was about 30Million C in the center, the density was 5*1020 ions per cubic meter. To put this into perspective, the 2 atmosphere shot was like gas at 100,000 times hotter and 100,000 times less dense. The density was very high for a tokamak, while the temperature was not as high as been acheived on other tokamaks.
(2) The background magnet field was 5.7T or about 140,000x the Earth's magnetic field. The Beta was about 1% which is low for C-Mod.
Check out some other traces here: https://www.psfc.mit.edu/news/2016/pres ... -faq#q_3_5
(3) The record shot was not particularly unusual, just more highly tuned. We developed a better way to fuel the plasma to higher density for the record. But actually, we got very near record performance on shots that were very different in three different ways.
(4) The highest pressure shot had nearly that high of performance for the full anticipated length of 0.5s of heating power, it was not transient. Things had to be stopped because C-Mod's magnets were heating up from being on and the internal components were heating up from the power to and from the plasma. This is normal.
(5) There were many reasons to push this to the end of the experiments life time. One was we were learning as we go. We did not particularly stress the machine, only perhaps marginally more than usual. The scheduling for collaborators coming in also played an important part since many team members were traveling to C-Mod for the last day and we wanted everybody to participate. More can be found here https://www.psfc.mit.edu/news/2016/pres ... -faq#q_3_7
(6) We do no think we damaged anything. We did not see any deleterious effects in the plasma nor on cameras or signals and plasmas ran well afterwards. We'll go inside the machine to inspect next week. See how we do this: https://www.youtube.com/watch?v=q3pQgozt3cM
(7) The device is now undergoing various calibrations so we can interprete the reams of data. Once we're done with that we'll put it in "cold storage" which is one step up from mothballing it. It is unclear what it's future is. We'd like to see it used for something scientifically interesting (Like converting it for this experiment: http://www.psfc.mit.edu/research/topics ... experiment
) but it will be up to the DOE. The science team will continue to analyze data from C-Mod and will also continue collaborating as a team on the other facilities around the world. We are at the same time developing new technologies that will enable another generation of even more powerful tokamak reactor.
(8) Our device is similar to all tokamaks which includes ITER and IGNITOR. These devices are distingished by two important parameters, their size and magnetic field. If you make the field higher the size can be smaller and it is very non-linear. But there are limits from technology for the magnets. IGNITOR is still a Russian-Italy project but has not seen much progress recently due to funding, likely due to econimic down-turns.
(9) Previously the high field approach with tokamaks required using copper magnets (like C-Mod and IGNITOR) because superconductors don't work at the required magnetic field. However, we're really excited about building tokamaks at around or above 10T using new high-temperature superconductors: http://news.mit.edu/2015/small-modular- ... plant-0810
. This new magnet technology enables IGNITOR sized experiments that could simply not be done with superconductors before. But for a toroidal reactor (like a tokamak or stellerator) the minimium size is set by the neutrons penetrating the wall and getting to the magnet.
(10) The scientific details were presented at the IAEA fusion conference this week at Kyoto http://www-pub.iaea.org/iaeameetings/48 ... Conference
This is the premier world-wide conference. The results will be published in a journal article that will come out soon (it is a slow process) The results will also be presented in two weeks at the American Physics Society's Plasma Physics meeting in San Jose which is the annual large conference on plasma physics.
(11) The record shot does have scientific significance because it was significantly higher and longer than had been done before and we used a new way to fuel that was somewhat unexpected to work. Additionally, the near-record shots were in some ways even more scientifically interesting since they saw new phenomenon in the edge of the plasma and expanded the range we could get favorable operation in many ways. All the of the shots expand the international database for how tokamaks work in new directions. ...Personally though, nothing beats passing through an integer in an important parameter. P=1.95atm just doesn't seem as good as p=2.05atm....
(12) You're welcome. Glad you asked some good questions.