Tokamak goes down
Flagship facility, too
Feelings hurt out West
Magnetic fusion has grabbed quite a few headlines in the past week as news about the failure of the NSTX-U tokamak spreads through the media. One thing that caught my eye is that multiple stories, all written by different authors, all describe the NSTX-U as the “flagship” machine in the United States. You can see this in the articles written for Physics Today (David Kramer), Nature (Jeff Tollefson), and Science (Adrian Cho). Since these authors wrote (reasonably) different accounts of the issue after getting some press release material from NSTX-U personnel, they probably got the flagship description from the same source. While fully admitting that this stood out to me because, having worked only on the other two major U.S. fusion facilities (DIII-D and Alcator C-Mod), it was surprising to realize I’ve never worked on the flagship facility, but then I started wondering whether the U.S. really has a flagship facility?
The definition of flagship is,
the best, largest, or most important one of a group of things (such as products, stores, etc.)
and this suggests that there is no flagship magnetic fusion reactor within the DOE Fusion Energy Sciences portfolio. Furthermore, there is no reason to desire a flagship facility. Consider that all these articles are about the ways in which the NSTX-U was either designed or built poorly. The basic message is, therefore, that this is the best facility we have and it is a failure.
The Largest Facility
I’m beginning with a consideration of the “largest” facility because that is the most quantitative measure. The physical size of the facility does not matter for scientific productivity, but some measure of the number of researchers working with the facility seems to provide a fair comparison. This also happens to be an analysis that I have previously performed. The image below shows a mapping of collaborators who published results in the three U.S. facilities between 2010 and 2012. These are self-reported according the facilities themselves. I created this map for an issue of the U.S. Burning Plasma Organization‘s (USBPO) monthly newsletter and details concerning this analysis are treated on that article from October 31, 2014. The numbers show that the DIII-D facility has a considerably larger number of publishing collaborators than either NSTX (now replaced by NSTX-U) or C-Mod.
Maybe this consideration should be normalized to the budget allotted to each facility? For example, if one lab receives more support for collaborator participation (e.g., advanced data sharing capability and remote participation), then that lab would be expected to have more off-site collaborators. That would be an analysis I would happily read… but not perform.
The Best Facility
It’s difficult to describe a research facility as the “best.” I would be tempted to compare the plasma characteristics of each machine to see which is best, but the machines are purposely different in order to access different kinds of fusion physics. Fortunately, I do have another graphic ready to compare at least one output of these machines: their record plasma pressure.
The graphic below is another fun output from my time contributing to the USBPO newsletter, specifically, from the February 28, 2016 issue. The plot compares the peak plasma pressures produced in C-Mod and DIII-D with the expected value in ITER and the peak pressure allowed for a regulation NFL football (the Tom Brady football deflation controversy inspired this). C-Mod is far ahead of DIII-D in this analysis, producing nearly four times the plasma pressure. Values for NSTX were not included in this graphic because the value would have been tiny. This graphic is already out of date because C-Mod broke their own record on September 30, 2016 (a piece of excitement that will hopefully get public attention soon).
A caveat of this treatment is that the machines do not necessarily try to produce new record plasma pressures. More importantly, if there was going to be a competition for some performance parameter, then it should be the Lawson Criterion because that directly correlates with actually producing net fusion energy.
The Most Important Facility
This is a touchy-feely question, so here is an appropriately touchy-feely assessment. Scientists and engineers travel between the three facilities and conduct joint experiments frequently, and we tackle the physics challenges of fusion energy through group effort. I would rather think of the set of facilities as part of the same team with a singular goal. The whole reason there are multiple facilities is that different plasma characteristics need to be produced in order to solve problems in parallel. For example, the machines use different materials for their internal walls and that produces a range of plasma-material interactions that would be difficult to study in a single device. We need all three, and language like “flagship” suggests that one is more important than the others. If you want to develop magnetically confined fusion energy, then I don’t think any of the existing facilities can be considered the most important.