Theory Weekly Highlights for January 2018

January 26, 2018

The MARS-F/K extended MHD code has been used to study the linear stability of a special class of the infernal mode, namely the one localized near the plasma edge. Unlike the peeling-ballooning instabilities, which are responsible for the type-I edge localized modes, the edge localized infernal mode may be responsible for accessing quiescent H-mode regimes in certain tokamak discharges, in particular in plasmas with locally flattened safety factor profile near the plasma edge due to large bootstrap current. Finite plasma pressure near the plasma edge drives this instability. It is found that the plasma toroidal flow shear in the pedestal region, as well as the plasma resistivity, further destabilizes the edge localized infernal mode. The drift kinetic effects from thermal particles, on the other hand, partially stabilize the mode. The flow shear and the drift kinetic effects also modify the symmetry of the mode spectrum, by enlarging the unstable domain towards higher local minimum safety factor value. No substantial modification of the mode eigenstructure is observed by the plasma flow, resistivity, or the kinetic effects.

January 12, 2018

OMAS (Ordered Multidimensional Array Structure) [] 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. At the heart of OMAS is the idea of providing a convenient API that can store data in a format that is compatible with the IMAS data model, but using other storage systems in addition to the one provided by IMAS itself. OMAS itself does not address the problem of mapping of I/O from physics codes to the IMAS data model; for OMFIT this is done within the definition of the data classes of the OMFIT framework. Thanks to OMAS, the data stored in the official IMAS scenario database hosted at ITER can be easily loaded, explored, plotted, and manipulated in OMFIT. The OMAS library was presented at the 2017 IMAS technical meeting, as well as at the December 2017 ITER Integrated Modeling Expert Group (IMEG) meeting.

January 05, 2018

The paper “Effects of two-dimensional magnetic uncertainties and three-dimensional error and perturbation fields on the Small Angle Slot divertor geometry and topology” by GL Trevisan et al. was recently published in Nuclear Fusion ( The paper investigates the new SAS divertor with a twofold approach. First, a Monte Carlo analysis of equilibria, reconstructed using EFIT, helps to quantify the uncertainty of the reconstructed strike point and angle of the separatrix onto the SAS. Then, a 3D field-line tracing analysis studies the effects of both error fields and typical perturbation fields on the topology of the SAS and of the footprints on the divertor. Finally, the uncertainties on the strike point position and its expected modulation due to Resonant Magnetic Perturbations are compared and discussed.

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