In the process of studying the effect of Shafranov shift
stabilization in DIII-D and JET ITB discharges, an error was
found in the *n*=0 radial mode damping rate which
enters in the mixing length formula for the fluxes in the
GLF23 model. An unphysical dependence on the MHD
in through the diamagnetic drift frequency
which resulted in the quasi-linear transport being periodic in
. Once this was fixed it was discovered that the linear
growth rates did not compare well with the linear gyrokinetic growth
rates from GKS for weak or reversed magnetic shear parameters
typically found within the deep core region of ITB discharges.

Recently, the fit formula for the extended ballooning mode angle
has been retuned to give a better fit to the linear gyrokinetic
growth rates for simulations including electrons. In particular,
the magnetic shear and safety factor tuning parameters were
changed and a new parameter for the MHD was added.
See the PDF file *gam*_{v}*s*_{s}*hat*-*std*,*NCS*.*pdf* for a comparison
of the growth rates versus magnet shear at safety factor values
ranging from 1-5 for the standard test case at
and for the NCS case at and .
The NCS parameters are the same as the standard parameters
but have , , and .
For the standard parameters, the retuned model gives
roughly the same level of agreement as the original model.
However, the retuned model yields much better agreement
at weak and reversed magnetic shear for the NCS parameters.
Near agreement with the GKS growth rates begins
to be rapidly lost, so we have placed a limit on
within the code. If exceeds 4.0, then
is set to 4.0.

Once the retuning of the growth rates was completed, the
normalization of the diffusivities was performed using
nonlinear GYRO ITG simulations assuming adiabatic electrons.
See the accompanying PDF file *chii*_{v}*s*_{a}/*Lti*-*std*.*pdf*
which compares versus normalized ion temperature
gradient using the original and retuned GLF23 models
against the GYRO results. The renormalization
results in a decrease in the coefficient for the ITG/TEM
modes by a factor of 2 and in increase in the coefficient
for the ETG modes of a factor of 3 with respect to the
original GLF23 model. The norm factor for the ETG modes
was determined using a small subset of DIII-D discharges.
The radial mode damping exponent *adamp*_{g}*f* was changed from
0.5 to 0.7 to give a better fit to the saturation at higher
normalized temperature gradients. The shear
multiplier is . To use the retuned version
of the model, set **iglf=1**.

Thu Feb 20 11:20:39 EST 2003