XGC-0 code | Integrated Modeling of Tokamak Plasmas

XGC-N01: First simulation for the Alcator C-Mod discharge 1060510007.00844

Gunyoung has altered the original equilibrium that Jerry and Jim sent about two weeks ago to fit the XGC-0 requirements. The first XGC-0 simulation for this Alcator C-Mod equilibrium includes simplified model for the anomalous transport. The FMCFM interface is disabled.

XGC-A07: fm_web flows shear stabilization factor is decreased

The fm_web flows shear stabilization factor is decreased from $10^{-4}$ to $10^{-5}$ . as result, the effect of flow shear stabilization is significantly reduced for the whole plasma profile.

Theory modivation coefficient for the flow shear stabilization factor

New XGC-0 namelist parameter is implemented in order to control parameter that is responsible for flow shear stabilization factor. According to Glenn’s notes, the fm_wexb coefficient should depend on $B_T$ :

${rm fm_{wexb}} ={ rm fm_{cexb}}displaystyle{ frac{2.1 10^{-4} A_i}{B_T^2}}$ .

This computation is enabled only if ${rm fm_{cexb}}>0$ .

New high resolution kinetic equilibrium for the DIII-D discharge 132014.03000

Rich has sent an updated EFIT equilibrium for the DIII-D discharge 132014.03000. It has resolution of 129×129, kinetic equilibrium option enable and low EFIT error parameter. The TEQ code shows significantly lower residual in the near separatrix region as well.

Note that the plasma pressure profiles looks significantly different comparing to the lower resolution case at 3.023 sec (left figure below shows the derivate of the plasma pressure at 3.000 sec and right figure shows the derivative of the plasma pressure at 3.023 sec):

EFIT code has been run with higher resolution for the DIII-D equilibrium 132014.03023

EFIT grid has been set to 129×129, number of iterations has been increased to 50, the namelist value for error has been decreased from 1.e-3 to 1.e-4. The resulting layout looks very similar. However, the normalized beta is reduced by about 3%. Analysis with TEQ still indicates relatively high residual error near the separatrix. This error might be related to different input options that might be associated with different account for the bootstrap current. There are differences in FF’ and q profiles that might be more difficult to understand. Some of equilibrium profiles are shown below. Left column shows profiles obtained with the new EFIT (129×129) run, while the left column shows profiles obtained with the old EFIT (65×65) run.

XGC-A05: Options for anomalous transport inSOL region are modified

The tbl_diffusion_mode option is set to 3 to enable transition from FMCFM in the plasma core and old model in the SOL region. In addition, spacial variation is allowed in the SOL region by setting tbl_d_profile_on to 1. As result, the problem of accumulation of particles in the SOL region is resolved:

XGC-A04: Increased particle transport in the SOL region

The particle diffusivity in the outside separatrix region has been increased from 0.05 to 0.5 $m^2/sec$ :

tbl_D_coeff2=0.5D0     ! m^2/sec, D_turb for outside of separatrix (SOL+private flux region)

The resulting plasma density profile is identical to the profile obtained in the case XGC-A03.

This problem is likely related to a mistake in the particle diffusivity implementation in the SOL region.

XGC-A03: Gradients for initial temperature profiles in the plasma core are increased

There are two changes comparing to the case XGC-A02:

Gradients for initial temperature profiles in the plasma core are increased in order to see profile change at earlier times;
The parameter neu_grid_min_psi is used in the namelist and is set to 0.75 in order to extend the region where the neutral distribution is computed.

XGC-A02: Case identical to XGC-A01 but 5 times longer simulation

Problems identified in the case XGC-A02 remains at longer times (30 ion transit times in the case XGC-A02 vs 6 ion transit times in the case XGC-A01). The diffusivity remain rather high in the plasma core. Particles accumulate in the SOL region. It looks that the later problem has been introduced during recent code update and relates to the interpolation of tbl_* diffusivities used in the outer region of plasma and FMCFM diffivities in the plasma core.