This annual meeting was held at the headquarters of the Helmholtz Society in Berlin March 12–14, 2019. Roughly forty on-site and ten remote participants provided reports on collaborations, grouped into seven topics that reviewed progress during the past year, and planned for the future. The coordinated working group actions (CWGA) serve as a basis to follow up joint actions and were agreed to be followed up in the forthcoming meetings.
Worldwide stellarator research has gained substantial momentum: On Wendelstein 7-X (W7-X, Greifswald, Germany), first campaigns with an uncooled divertor have demonstrated the highest-ever fusion performance normalized to the plasma volume and at the same time, the longest pulse lengths. Deuterium experiments in the Large Helical Device (LHD, Toki, Japan) showed confinement at higher performance than gyro-Bohm scaling—differences in terms of engineering parameters are less clear. Smaller devices are enabling experimental insights for physical understanding, such as turbulence studies in TJ-II (Madrid, Spain), fueling studies in Heliotron-J (Kyoto, Japan), and the examination of flows in HSX (Wisconsin, USA). Progress in the refurbishment of Uragan 2-M (Kharkiv, Ukraine) and new concept devices (CFQS, Chengdu, China) complement the larger experiments, creating new opportunities to assess aspects relevant to reactor-like operation and stellarator optimization.
Equally important, stellarators benefit from the latest cutting-edge developments in diagnostics, heating, and plasma fueling. Coordinated programs in the EU, the US, and Japan link innovative developments [e.g., integrated systems for overload detection (EU consortium), x-ray detectors (Princeton Plasma Physics Laboratory), super-fast surveillance cameras (EU around WIGNER Research Centre for Physics, Hungary) and phase-contrast imaging (MIT)] to the stellarator programs with obvious mutual synergies: the pace of experiments is accelerated by employing these unprecedented measuring capabilities.
More and more benefits for tokamaks are materializing: experience gained in long-pulse stellarator experiments contributes to large-scale devices such as JT-60SA and ITER. A select example is the steady-state fueling pellet injector from Oak Ridge National Laboratory (ORNL) that is being brought to W7-X with additional support from EUROfusion and NIFS, Japan, and which implements technology planned for use on ITER.
The scientific community is excited by early theoretical ideas to explain the latest results from stellarator experiments. Worldwide groups, concentrated in research centers as well as in universities, are increasingly applying their expertise in the understanding of ground-breaking physics questions, such as turbulence in three-dimensional (3D) fields, impurity transport, fast-ion confinement, and plasma flows and currents.
The above-mentioned aspects were the essence of a three-day meeting held at the headquarters of the Helmholtz Society, the funding agency of the German fusion programme (see Fig. 1). The meeting was organized and sponsored by the Max Planck Institute for Plasma Physics. Roughly forty on-site and ten remote participants provided reports on collaborations, grouped into seven topics. In an informal workshop format, the participants discussed proposals for joint action and experiments, taking advantage of comparative studies in different devices. The CWGM is not a scientific conference, but rather a interactive workshop wherein agreements on joint publications under the auspices of the IEA Technology Collaboration Program on Stellarators/Heliotrons are promoted to become the measurable outcome of the CWGM. A session on the program plans of the main contributors served to enable the exchange of information, and the community was invited to provide feedback to programmatic considerations. China’s quickly developing stellarator program, with a sound balance of sustainable build-up of know-how and scientifically interesting new concepts, namely the outline of a quasiaxially symmetric device, attracted great interest.
The sessions were led by colleagues serving as coordinators. The remainder of this report gives brief summaries of each session.
James A. Rome