### Theory Weekly Highlights for December 2014

##### December 19, 2014

Lang Lao attended and chaired the Sixth ITER Integrated Modeling Expert Group (IMEG) Annual Meeting at ITER Headquarters, Cadarache, France December 15-17, 2014. The IMEG consists of two representatives from each of the seven ITER partners. The two main goals of the meeting are to discuss progress in the ITER partners domestic integrated modeling programs and to review progress and advice ITER on its Integrated Modeling Program to develop an Integrated Modeling Analysis Suite (IMAS) and an infrastructure with a workflow management system and a data model to support ITER plasma operation and plasma research.

Dr. Chengkang Pan of ASIPP-Hefei is visiting GA Theory for 8 weeks to collaborate on applications of the OMFIT integrated modeling framework to perform transport modeling of the joint DIII-D -EAST non-inductive high poloidal-beta experiments.

##### December 12, 2014

A new module for the OMFIT framework has been developed by long-term theory group collaborator O. Izacard (UCSD) that allows the user to set up, remotely execute, and analyze, simulations using the BOUT++ code. Remote execution can be on a variety of systems including the TSCC cluster at UCSD, the DROP cluster at GA and the Hopper machine at NERSC. The initial focus of this OMFIT module has been on use of BOUT++ to simulate interactions of tearing modes and microturbulence in reduced models, as part of a UCSD theory effort. It will be extended for use with various Braginskii and gyrofluid models in BOUT++ in the near future, in support of both the AToM integrated modeling SciDAC project, and separate UCSD and GA research initiatives. Initial results obtained using this module were presented at the 2014 APS-DPP meeting, as well as the “BOUT++ and OMFIT” mini-workshop held in October at LLNL.

##### December 05, 2014

A systematic scheme was formulated to calculate the gyro-averaged synchrotron radiation power from runaway electrons in a tokamak using two approaches, namely the relativistic guiding center (GC) approximation, and the exact particle equations of motion. The exact equations make use of the canonical momentum invariants in an axisymmetric system with a purely toroidal field; this is valid for the weak poloidal fields considered. The Schwinger form for the synchrotron power is expressed in terms of the square of the curvature of the particle orbit. Evaluating this with the GC model finds that the radiation power is the sum of independent contributions from the toroidal motion of the GC and the helical motion, in agreement with approximations made by previous authors. However, when the exact particle equations are used, a new interference term appears involving a coupling between the toroidal and helical curvatures. This stems from the fact that the exact particle curvature is proportional to the product of the magnetic field strength with the pitch angle, and both have rapid first order gyro angle variations that are suppressed in the GC approximation. Hence, interchanging gyro-averaging operations makes a difference, and gives rise to approximate factors of two increases in the radiation power over previously published formulas.

**Disclaimer**

These highlights are reports of research work in progress and are accordingly subject to change or modification

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