Theory Weekly Highlights for December 2009
A reanalysis of the stability results from the equilibria reconstructed through consecutive cycles of the sawtooth ramp and crash phases for the ICRF-heated DIII-D discharge #96043 found that the underlying ideal mode has the characteristics of a quasi-interchange mode, similar to the case of the oval sawtooth (see highlight from November 6 2009 at Theory Weekly Highlights for November 2009). This discharge exhibited extended sawtooth periods and giant sawtooth crashes when ICRF heating was applied. The discharge typically had q on axis well below one (q0 ~ 0.9). The result has implications for giant sawteeth and suggests a re-interpretation of the giant sawtooth experiments in JET since SXR analysis of those discharges indicated quasi-interchange like flows even though q0 was reported to be well below one.
R. E. Waltz gave two talks: “GYRO simulations supporting TGLF” at the 19th International Toki Conference, Dec. 8-11; and “Is there a nonlinear subcritical MHD beta limit?” at the JITF Workshop Dec. 14-16. Both meetings were in Toki, Japan.
A mobile version of the DIII-D website has been released. It provides users an easier means of gaining information and monitoring DIII-D operations from hand-held devices. The new website includes simplified pages such as experiment summary, electronic logbook, daily schedule and announcements. Users who go to the DIII-D website from mobile devices are automatically redirected to the mobile version. Security remains the same with username and password required.
The effect of plasma resistivity on plasma response to perturbation magnetic field imposed by an external source has been studied using the MARS-F code for an equilibrium with realistic plasma rotation. It is found that on the non-resonant helicity side, the plasma response is not much affected by plasma resistivity. The plasma response is almost identical to that of an ideal plasma and differs not much from the vacuum response. On the resonant side, the overall plasma response is generally suppressed by the shielding effect caused by internal resonances. Even with resistivity and partial reconnection, the reconnection level is much lower than the full vacuum response. Thus, the field line stochasticity is much more reduced than that obtained with the assumption of vacuum response.
The calculation of the transport coefficients due to gyro-viscosity was added to the NEO code for use in transport calculations, such as TGYRO. The gyro-viscous fluxes are determined by the second-order gyrophase-dependent component of the distribution function. The gyro-viscous particle and energy fluxes are non-zero only with both up-down asymmetric flux-surface shape and strong rotation effects, while non-zero gyro-viscous momentum flux requires only up-down asymmetry. For typical DIII-D plasmas, we find that the gyro-viscous particle and energy fluxes are small compared to the neoclassical fluxes. However, it is important that the gyro-viscous particle flux not be neglected in transport calculations, as it is the sum of the gyro-viscous and neoclassical particle fluxes which is ambipolar, rather than the neoclassical fluxes themselves. For the momentum flux, we find that the gyro-viscous flux for the primary ion species and electrons in DIII-D is comparable in magnitude to the neoclassical flux, though both are expected to be small compared with the turbulent momentum flux.
Professor Yue Liu of China Dalian University of Technology is visiting GA for 1 year to collaborate on the IMFIT integrated modeling project and MHD stability of resistive wall modes and tearing modes.
These highlights are reports of research work in progress and are accordingly subject to change or modification