As reported by G.L. Trevisan and A. Wingen in the Friday Science Meeting (FSM) talk on Feb 10th (see https://diii-d.gat.com/diii-d/FSM2017#February_10.2C_2017), the TRIP3D and MAFOT codes have been exploited to analyze the magnetic topology of 3D fields near the small angle slot (SAS) divertor region through field-line-tracing “vacuum” simulations. TRIP3D analyses have shown that 3D fields produced by I-coils determine, as expected, the splitting of the stable and unstable manifolds of the separatrix and the comparison of lobe structures that protrude towards the scrape-off-layer (SOL) together with magnetic stochastization. Such lobes are much more energetic than SOL-only field lines, since they gather field lines that had access to the inner plasma regions. The lobes appear to be hitting inside the SAS at all toroidal angles for the simulated case of an n=1 I-coil configuration, with highest current 5 kA. Analyses carried out through MAFOT on the divertor footprint confirm such results and furthermore show that the typical modulation of the strike point along the torus is roughly a few millimiters at 5 kA, not enough to be exploited to counteract the intrinsic asymmetries of the SAS as discussed in the FSM talk on Feb 3rd (https://diii-d.gat.com/diii-d/FSM2017#February_3.2C_2017).
OMFIT (http://gafusion.github.io/OMFIT-source/) is a workflow manager that is used to couple fusion physics codes, execute them in complex workflows, and provide them with streamlined interfaces. OMFIT is a growing community effort, which is gathering the contributions of many physicists across domestic and international institutions. To advance the ongoing development of OMFIT, we are organizing a series of code-camps, where participants self-organize into small working groups to address outstanding issues and quickly bring new ideas to life. Co-location and face-to-face conversation allow users to take full advantage of the community support. The first OMFIT code camp (Nov 2016) was a successful experience, which led to important framework and physics developments (https://diii-d.gat.com/diii-d/Weekly111816). A second code-camp will be hosted at General Atomics this coming week (Feb 27th). The intent is to have a focused opportunity for users and developers in small working groups to address outstanding issues and quickly bring new ideas to life. OMFIT users and developers of all levels of experience are welcome to join.
Dr. Yueqiang Liu arrived at GA this week as a new Theory group employee. His research encompasses extended MHD theory and simulation, including the physics of kink, tearing, and resistive wall modes, as well as plasma response to non-axisymmetric fields, with a focus on understanding ELM mitigation and suppression. Dr. Liu, an APS Fellow and recent recipient of the Landau-Spitzer Award, will also develop and support the MARS suite of codes, and engage in comparisons of theory and code predictions to DIII-D results.
A first implementation of a 6-moment edge/SOL transport and stability fluid code has been developed which allows for arbitrary magnetic field line pitch without the use of flux or field-aligned coordinates. The goal is to model electromagnetic edge and SOL turbulence in DIII-D size plasmas with realistic geometry and parameters. Parallel dynamics have been implemented using non-field-aligned methods specifically designed to reduce aliasing and to eliminate discrete null-spaces. This numerical approach allows arbitrary magnetic field line pitch without the use of flux or field-aligned coordinates. Consequently, the method would be appropriate for modeling magnetic nulls (X-points). Both 2nd and 4th order accurate spatial discretization has been implemented. Test simulations have been performed using cylindrical geometry with a quadratic safety profile in an open magnetic field line with a toroidal limiter. The non-linear turbulent steady-state shows drift-ballooning turbulence aligned to the radially-varying equilibrium magnetic field line pitch angle.
A recent breakthrough in the modeling of DIII-D high-betap regime discharges has provided significant new insight on transport. We have demonstrated the existence of multiple transport states due to Shavranov shift stabilization in this regime using TGLF modeling. This result has very promising implications for improved energy confinement in high bootstrap fraction reactor operating regimes that will be explored in the near future.
These highlights are reports of research work in progress and are accordingly subject to change or modification