EPS Conference: first comments

The 38th EPS Conference on Plasma Physics kicked off on Monday in Strasbourg with an incredibly hot and sunny weather. We have some free time this afternoon and will use it to give some of my feelings on this first part of the conference. If you want to add some other points, please comment.

This conference was, as usual, rich and dense in information, covering a wide range of topics from space plasmas to fusion plasmas,  and it would be difficult to summarize these last three days in few lines.  However,  I’d like to highlight some points of the program.

Plasma turbulence is certainly one of the most active area of research in Magnetic Confinement Fusion (and astrophysics) and three major contributors, A. Hasegawa, K. Mima and P. Diamond were rewarded this year with the Alfven Prize. In their prize lecture, they gave a (mostly) theoretical overview of electrostatic turbulence (and the formulation of the Hasegawa-Mima equation) and on zonal flows (you can find a review by Diamond, Itoh and Hahm here) and drift wave turbulence. Although the presentations were for several items a bit fast, they made it possible to feel the physics at stake. And there are good reasons that plasma turbulence is now so popular: they managed to build a solid system of theories and developed clever tools.

The experimental overview was given on Wednesday by A. Fujisawa but with emphasis on the drift wave  turbulence and not on interchange instabilities; he presented more particularly a nice diagram showing the change of paradigm: in the 60s, turbulence was seen as the effect of a system of drift waves governed by the Hasegawa-Mima equation. Thanks to Diamond, the situation evolved with the discovery of mesoscale structures called zonal flows which acted as an energy sink for the energy carried by the drift waves (inverted cascade). Turbulence is now seen as the result of non-linear interactions between drift waves, meso and micro scale structures. This interaction can be modeled through powerful predator-prey models and experimentally analyzed with tools like bicoherence.

On the subject of turbulence bifurcation, a very good talk by E.G. Highcock, a PhD student. He gave two references, here and here, for details on his work.

But why all this interest for turbulence? Because this is one of the major phenomena which governs the transverse transport, thus the confinement, in magnetic confinement devices.

In this field, a huge effort is invested in the numerical tools to simulate and understand turbulent effects on transport. F. Jenko and A. Bottino gave an overview of the numerical methods (global gyrokinetic PIC code  with adjustable control variates method to address the cancellation problem) used at the IPP-Garching; one idea to keep in mind: the analysis of turbulence is a multiscale challenge which cannot be solved on tokamaks in a brute-force style (i.e. with gyrokinetic Vlasov codes); a better understanding of the physics is necessary to develop simpler models. The two main points to take into account: the non-local effects (the meso-scale structures evoked previously) but also transport barriers and the electromagnetic effects (turbulent reconnection of magnetic lines).

I would have liked to attend more sessions on space plasmas to have a look at their methods but they were almost always in parallel with the sessions on Magnetic Confinement Fusion. I saw at least the plenary talk by about sun-earth connections by T. Pulkkinen. I keep in mind this spectacular video from the STEREO Satellite, which shows the comet Encke’s tail torn off by a solar flare.

In the reviews, we also had a talk by Piero Martin from RFX Consortium on MHD stability and active control of plasmas. There are two possibilities to avoid MHD instabilities: we choose the right parameters (β) to have stability (but we limit ourselves) or we accept to be instable but we try to control the instabilities and their effects. Among such instabilities, the kink modes which can be stabilized with a grid of saddle coils around the vacuum vessel, a solution already applied on RFX. Another type of control is the injection of ECRH to pace the sawteeth.

Another interesting review was the talk by Butanov on Extreme Field Science, interesting but very difficult to grasp: the slides were overloaded with equations. It is a pity because it addressed the physics of facilities like NIF, ELI or Hiper, based on the Laser Wakefield acceleration.

That’s it for the reviews, there were also announcements of interesting results.

We were lucky  to have the first presentations on ASDEX Upgrade (AUG) operations with RMP coils, for ELM mitigation; W. Suttrop showed that the coils indeed suppressed type-I ELMs. K. Lang showed that central pellet injection) could even be used during this phase to increase the central density without triggering ELMs (contrary to DIII-D or JET), making possible operations above the Greenwald limit (proving once again that this limit is an pedestal effect).

A talk by I. Chapman on sawtooth control in tokamaks with the original idea of using off-axis ICRH to improve sawtooth mitigation with ECRH.

To finish the second day of the conference, we have a status review of ITER by its Director-General O. Motojima. I would not like to have its job at this moment: in addition to the drastic cost reduction from last year, he has now to deal with the consequences of the earthquake in Japan and the associated delays on the program. In spite of the simplification he brought to the management, the internal structure of ITER remains heavy and probably delicate to handle. It is perhaps only a feeling but Motojima looked and sounded like a bit tired, what I can perfectly understand, given the circumstances.

While hearing the long (more than 1 hour) talk, I felt a persistent discomfort on the project itself due to one fact: I got bored. Well, this Fusion Science! We work on state-of-the-art technologies and pioneer the borders of physics! ITER should be motivating, INSPIRING; instead, I was bored and I am pretty sure that I was not the only one (who can confirm?). It is a point that should really be improved: of course, ITER is a serious project with huge amounts of money at stake. Yet, it should also be the accomplishment of a dream, it should make people dream; I would like to have the same pleasure  on ITER as on ASDEX Upgrade.

All in all, this conference makes it possible to discover other topics: most (but not all) presentations about physics are very well prepared to introduce the subject and present the basic questions and methods at stake. There are still a bit too long and some slides heavily loaded with equations that you do not have time to read in 30s. Some speakers even start to adopt the “TED” method by trying to narrate a story and give enlightening examples instead of the traditional exhaustive academic approach which is badly suited to the allocated time slot.

For those interested, the four pages papers are already online (I am not sure if there is a public access).

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