### Theory Weekly Highlights for January 2019

##### January 25, 2019

A public installation of the OMAS (Ordered Multidimensional Array Structure) library has been made officially available on the ITER computation cluster [https://gafusion.github.io/omas/iter.html] by the ITER IO. OMAS is a Python library designed to simplify the interface of third-party codes with the ITER Integrated Modeling and Analysis Suite (IMAS). ITER IMAS defines a data model, a data get/put API, and a data storage infrastructure used for manipulating ITER data. Importantly, this development provides the necessary environment for the OMFIT framework to access ITER data, including remotely. OMAS can be used to access the ITER plasma scenario database maintained by the ITER IO.

##### January 18, 2019

A new formulation of the runaway electron (RE) drift orbit model has been implemented and tested in MARS-Q. This RE model takes account of the modification of the particle momentum and pitch angle due to parallel electric field, small angle scattering by impurity ions, synchrotron radiation damping, and bremsstrahlung force. The RE trajectory equations, in both configuration and velocity spaces, are time-advanced directly in the MARS-Q flux coordinate system, ensuring the best numerical resolution of the 3-D field perturbations computed by MARS-Q. An adaptive ODE solver (LSODE) is used for the orbit tracing. The new module (REORBIT) was used to study the effect of an unstable resistive kink instability on RE confinement, for a realistic plasma from DIII-D RE discharge 177040. Preliminary results show that (i) 3-D field perturbations associated with an unstable resistive external kink can substantially expand the radial orbit width of REs; (ii) a passing RE can be lost with the perturbation amplitude of about dBp~50 Gauss (as measured at the high field side DIII-D wall position), largely due to 3-D field modification of the particle pitch angle, converting a passing particle into a trapped one; (iii) at even higher perturbation amplitude, of about 150 Gauss for this DIII-D plasma, prompt orbit loss occurs for passing REs located near the plasma edge, due to orbit expansion.

Phil Snyder visited the Swiss Plasma Center at the École Polytechnique Fédérale de Lausanne (EPFL) this week and presented a colloquium on “Physics of the Tokamak Pedestal, and Implications for Magnetic Fusion Energy.”

##### January 11, 2019

New modules for the CHEASE and MARS codes were imported into OMFIT. CHEASE is a standalone inverse equilibrium solver but also serves as a mapping of a prior equilibrium, such as from EFIT or CORSICA, to the grid used in the MARS stability code. The new modules currently support the main standard MARS workflows for ideal and resistive stability calculations using a single equilibrium from EFIT. A flexible iteration capability over smoothing of the boundary X-point, required for diverted equilibria, is included. Upgrades are underway to add the scripts used in the other major CHEASE-MARS workflow, namely for investigating the plasma response to external fields, and to include an additional CORSICA simulation step prior to the CHEASE calculation that was requested by a number of users in order to facilitate sensitivity scans over profile and shape variations.

**Disclaimer**

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

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