It has been suggested that runaway electrons (REs) generated in DIII-D quiescent runaway electron (QRE) discharges can excite kinetic whistler waves. Recent simulations further showed that quasilinear wave-particle scattering of the RE beam significantly weakens the avalanche growth mechanism. However, kinetic instabilities will not occur in normal post-disruption discharges (PDD) because of rapid collisional damping. In an investigation of the possibility of using a fixed frequency antenna to launch a fast wave into a RE beam to mitigate REs in order to answer the question of how much the wave power attenuates when it reaches the central region of the plasma due to collisional damping, an analytic expression for the local imaginary part of the perpendicular propagation vector k was derived, finding the scaling k ~ Z(n_e/B)^3. For cross-field wave propagation to a distance equal to the minor radius a, the wave power attenuated is simply exp(-2ak). For typical PDD parameters the wave power launched by the DIII-D helicon antenna will be completely damped in a temperature range of 2 - 30 eV. However, it was recently discovered that massive injection of D2 into a mature avalanched RE beam on DIII-D can greatly decrease the electron density n_e by some less unknown mechanism (possibly recombination cooling). Antenna actuated RE mitigation may then be possible in a window of plasma densities ~ (10^12 – 10^13), above which fast wave collisional damping is severe and below that the fast wave is evanescent and cannot propagate.

The APS-DPP invited paper “Transport barriers in bootstrap-driven tokamaks” by Gary Staebler and co-authors was the “editor's pick” featured article for the May issue of Physics of Plasmas (https://aip.scitation.org/journal/php/). An article in the SciLight on-line magazine about this work was published May 25, 2018 at (https://aip.scitation.org/journal/sci).

This week (May 14-18) General Atomics hosted an OMFIT/AToM code camp for rapid development and improvement of OMFIT, IPS, and related integrated modeling frameworks and components. 25 people (from GA-theory, DIII-D, and offsite) were actively involved in the camp. A number of code improvements were made during the week as a result of efforts by many participants. OMFIT was coupled to IPS to be able to run many parallel workflows, taking advantage of High Performance Computing (HPC) capabilities. The IPS-FASTRAN self-consistent predictive workflow has also been made available as an OMFIT module. Progress was made on determining and propagating the coordinate orientations (COCOS) of various codes. An effort to make the GACODE FORTRAN routines callable from Python has been started. Profiles fit within the OMFITprofiles module can now be written to MDS+. Development of a new module for consolidating the calculation of the core transport source terms has also started. A wrapper for running the GINGRED code for generating 2d meshes for SOL codes was obtained. Progress was also made on incorporating impurity transport interpretations using the STRAHL code. Finally, the library dependencies used for OMFIT have been consolidated to use a single package manager.

Several theory staff gave invited presentations at the Transport Task Force (TTF) meeting in San Diego this week. Emily Belli showed recent work on the “Critical role of sonic rotation on ion and impurity transport.” Eric Bass presented the latest results in his work on “Prediction of alpha and neutral beam ion profiles in ITER scenarios,” and Federico Halpern discussed the “Physics of the narrow heat flux feature.” Also, on behalf of the OMFIT development team (see http://gafusion.github.io/OMFIT-source/contributors.html#team), O. Meneghini, B. Grierson, K. Thomek, and P. Vaezi, gave a live demonstration of the suite of analysis and predictive transport capabilities publicly available via OMFIT. The demonstration began by showcasing on-the-fly generation and exploration of datasets built from experimental data, leveraging the SCOPE module in OMFIT. This was followed by a detailed time-dependent analysis of kinetic profiles within the OMFITprofiles module. The GYRO module in OMFIT was then used to set up and execute a series of GYRO simulations aimed at modeling the linear growth rate spectrum. Finally, the TGLFscan module in OMFIT was used to rigorously perform a validation study of the TGLF reduced transport model. Although the tutorial demonstrated DIII-D cases, all of the OMFIT modules that were presented can also be applied to other tokamaks.

The US Transport Task Force Workshop will be hosted by General Atomics at the Bahia Hotel in San Diego next week May 8-11. Over 120 participants will attend with 17 plenary talks and 22 working group talks. See the meeting website for details: https://fusion.gat.com/conference/event/65/.