Theory Weekly Highlights for November 2009

November 25, 2009

A few attempts at applying the TGLF transport model within the H-mode pedestal region have been performed. Using a high-resolution transport analysis of a DIII-D H-mode discharge, TGLF was successful in predicting the energy transport with the boundary conditions extended out to a normalized radius of 0.99. While the predicted electron temperature profile is somewhat too high near the top of the pedestal, the model was successful in predicting the formation of an H-mode pedestal. Analysis of the diffusivities shows that the ion channel is mildly turbulent and the ETG modes contribute to roughly half of the electron energy transport.

A first version of the IMFIT Integrated Modeling and Fitting tool has been released for general public testing. IMFIT provides a convenient central platform to perform equilibrium, transport, and stability analysis using tools such as EFIT, ONETWO, GATO, ELITE, DCON, and PEST3. IMFIT also provide convenient GUI's to support experimental data viewing and analysis using tools such as EFITViewer, REVIEW+, GAProfiles, and PLOT12. A GUI to perform kinetic EFIT analysis is also available, as well as support for other tokamak devices such as EAST, ITER, and SST-1. New ones can be conveniently added. More information can be found at the IMFIT web site, as well as through various Help buttons available within IMFIT.

November 20, 2009

The capability to include non-axisymmetric external currents has recently been implemented in the M3D-C1 code. M3D-C1 is a resistive two-fluid code, used to calculate non-ideal axisymmetric steady states and linear stability. The new capability will allow for the study of non-ideal, dynamical RMP response, including the response at the X-point. Also, a semi-implicit two-fluid operator has been recently developed and implemented which allows axisymmetric two-fluid calculations to be performed stably at realistic Lundquist values.

November 13, 2009

The capability to treat compressional magnetic fluctuations (fluctuations in B_parallel) has been added to the GYRO code. The new fluxes associated with nonlinear magnetic compression are also now available, although these are not expected to be significant in DIII-D. On the contrary, for NSTX plasmas, retaining the full (compressional) electromagnetic response is critical for an accurate description of the linear physics. This was also demonstrated previously by GS2 studies. The modified version of GYRO has been benchmarked with the GS2 code, and the two codes agree very closely as long as sufficiently high grid resolution is maintained. The new capability is available to users in the current GYRO CVS version simply by setting the parameter N_FIELD=3.

November 06, 2009

Stability calculations for DIII-D discharges with Bean and Oval shaped cross sections confirmed a role for the ideal quasi-interchange mode in the respective sawtooth crashes and MHD relaxation events that occur in both discharges. In both discharges, after the sawtooth crashes the axis safety factor is reset to near one and the underlying ideal mode is a quasi-interchange. The mode remains a quasi-interchange through the relaxation events. For the Bean cross section, the mode subsequently transitions to a conventional internal kink but for the Oval the quasi-interchange persists until the next sawtooth crash. The difference in underlying ideal modes at the crash time is reflected in differences in the sawtooth crashes; for the Bean, the crash is consistent with a Kadomtsev reconnection but for the Oval there is no observed reconnection event, consistent with the sawtooth model proposed by Wesson in 1985 for the quasi-interchange mode. The MHD relaxation events with underlying quasi-interchange modes also behave much like the Oval sawtooth crash. This result was highlighted in an invited talk at the APS meeting in Atlanta.

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