The Current-Diffusive Ballooning Mode (CDBM) model

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The factor F(s,α,κ,ω_E1) represents the reduction due to weak or negative magnetic shear and large Shafranov shift. It is defined as:

for s'=s-a>0
and as:

for s'=s-a<0

The magnetic shear is defined as:

The pressure gradient is defined as:

It should be noted that the presure gradient is calculated using the thermal pressure for the term α^3/2 and with the total pressure (ubcluding fast ions) in the term F(s,α,κ,ω_E1), as recommended by prof A. Fukuyama and by dr N. Hayashi.
The magnetic curvature is defined as:

and the ExB rotation shear is defined as:

Settings

There are several options in TRANSP to select which model to use, depending on the strength of the magnetic reverse shear. The models are selected with the flag MODELCDBM.

MODELCDBM=0

This is the original CDBM model, described in the paper by Fukuyama et al, Plasma Phys. Controll. Fusion .

In this case, F(s,α,κ,ω_E)=1. The coefficient C can be selected in the TRANSP namelist with CKCDBM, with default value CKCDBM=12.

MODELCDBM=1

This option adds a dependence on the elongation to the original model.

MODELCDBM=2

This option selects the original model, with the parametrization in F valid for weak EXB shear.

MODELCDBM=3

This option selects the model with elongation, with the parametrization in F valid for weak EXB shear.

MODELCDBM=4

This option selects the original model, with the parametrization in F valid for strong EXB shear.

MODELCDBM=5

This option selects the model with elongation, with the parametrization in F valid for weak EXB shear.