FoSS: ISHW2024

The 1st meeting of the Forum of Small Stellarators (1st Uncoordinated Working Group Meeting) took place as a satellite meeting to the 24th ISHW in Hiroshima, Japan on 12 September, 2024.

Agenda

• Welcome and introduction
• ~ 1.5 hours for group introduction presentations. These should be 2-3 slide, <5 minute presentations that provide a brief project overview and any particular strategies to being relevant although small. Each will be followed by 5 minutes of questions / discussion.
  • STAR_Lite, Hampton University
  • Polaris, École Polytechnique Fédérale de Lausanne
  • CSX, Columbia University
  • ETOS, University of Wisconsin-Madison
  • TJ-K, Universität Stuttgart
  • ALPES, Technische Universität Graz
  • University of Science and Technology of China
  • EPOS, Max-Planck-Institut für Plasmaphysik, Garching
  • HU-Heliac, Hiroshima University
  • MUSE, Princeton Plasma Physics Laboratory
  • Renaissance Fusion
  • Heliotron-DR, Kyoto University
• ~ 30 minutes for a coffee break. Opportunity for continuing discussions and engineering questions that are not of general interest.
• ~ 1 hour for brainstorming small stellarator physics investigations and possible joint experiments.

Discussion

training

• training students is a very important and common motivation
• as part of coursework, project management and teamwork can also be trained
• with so many small devices, we should consider collaboration as an important aspect of training
• interest in an arduino-mentality stellarator kit (proposed by F. Volpe)
  • standardize a kit to make startup easy, but allow for flexibility
  • would be good for exporting stellarators to places with a limited budget, engineering groups without the physics support
• related motivation: outreach
  • can we develop some interesting experiments/experiences ?
  • moving coils around ? moving a permanent magnet around ?
  • something like RGDX at PPPL ?
    • web-browser-based control system, providing an experiment remotely
    • if also standardized, could have a common web interface for multiple devices (proposed by Y. Suzuki)
    • suggest a workshop or bootcamp for development of the interface
• any workshop by the Forum should probably have a strong education aspect

configuration design / physics investigations

• small devices are test bed for integrated design, single-stage optimization
• configuration exploration ? QA, QH, QP, QI, tokamak, RFP ?
  • benefits of some good configurations are not trivial to demonstrate at small size when collisionally dominated
  • can look at electrons at low pressure, demonstrate drift effects
• turbulence studies, zonal flows
  • don't need a big machine, just a big gradient. Columbia had a 10cm linear device doing ITG studies. They had the advantage of open field lines. What are stellarator options to create a large gradient ?
  • see validation work at TJ-K. also turbulence work at TORPEX.
  • small devices are often studying interchange turbulence. interactions of interchange with energetic particles could be interesting.
  • also should look at validation of fluid turbulence codes
• fast particle transport, if can inject dimensionally correct electrons ?
• validate neoclassical flow damping
• explore boundaries of MHD stability
• what is the value of long discharges in small devices ?
• the renormalization parameter in ISS04 hides the physics of deviation from the trend. a greater variety of devices in the database, even at lower performance, could provide this missing information.
• small devices are challenged by background neutral gas. can we make this an advantage ? some sort of plasma-neutral interaction study ? atomic physics ?
  • but we don't need a stellarator to study the atom

diagnostics

• variety of diagnostics already being used on small stellarators, some of which are also suitable for fusion plasmas
  • field line mapping common to all devices
  • probe access is particularly good on small devices
  • spectrometers
  • magnetic diagnostics
  • imaging
• what is the typical budget for diagnostics ?
  • wide range, but often zero. they are secondary to an operating device
• consider shared diagnostics ?
  • we are happy to get old diagnostics from other machines !
  • sharing diagnostics often comes with a lot of paperwork. its not easy to share a fast camera or oscilloscope. but sharing a probe head is easy.
  • you need a human to operate diagnostics. it is a natural area for people exchange
  • simplest way to get started is to share information. start with sharing how to make diagnostics and how to analyze.
  • Forum activity could be to create diagnostic kits. include information, part list, instructions for assembly, tools for analysis. then share people for expertise.
• what is used for data management at small devices ? MDSplus ?
  • often use custom format, manual data management
  • may be an area for collaboration. standardized data access would facilitate cross-machine comparisons

plasma generation

• can be expensive, but often determines physics capability of device
• radio frequency: can be used for microwave studies, mode conversion, current drive, generation of high-energy electrons ?
• helicon
• electric discharge ?
• MUSE puts a tesla coil outside the vessel, a fun method for outreach physics experiments with a glass vessel
• consider non-neutral plasma, easy to generate