Publication Date:
2011
abstract:
Experiments on JET have shown that stiffness of ion energy transport above a threshold
gradient is strongly reduced in the plasma core due to flow shear. Initially transport models
had difficulties to reproduce this feature. Later TGLF2 has reproduced the trend, particularly
in the region of low normalized heat flux, i.e. near threshold3. Also Gyro4 simulations have
been made but these are still uncertain. The experimental observations also indicated in more
detail that it is the combination of high flow shear and small magnetic shear that leads to
stiffness reduction. This naturally limits the region of stiffness mitigation to the interior of
tokamaks3. Since flow shear stabilizes drift wave transport by damping out primarily long
wavelength perturbations, it is obvious that it influences the correlation length. Thus it was
natural to generalize our previous work on making the correlation length for drift waves
parameter dependent to include also the effect of flow shear. This has now been implemented
and is found to reproduce the experimental feature that stiffness is reduced for a combination
of large flow shear and small magnetic shear. The reason is that for large magnetic shear the
radial correlation length is determined primarily by magnetic shear, whilst for low magnetic
shear it is determined by flowshear. The first results of this modified correlation length model
show good quantitative agreement with experiment.
gradient is strongly reduced in the plasma core due to flow shear. Initially transport models
had difficulties to reproduce this feature. Later TGLF2 has reproduced the trend, particularly
in the region of low normalized heat flux, i.e. near threshold3. Also Gyro4 simulations have
been made but these are still uncertain. The experimental observations also indicated in more
detail that it is the combination of high flow shear and small magnetic shear that leads to
stiffness reduction. This naturally limits the region of stiffness mitigation to the interior of
tokamaks3. Since flow shear stabilizes drift wave transport by damping out primarily long
wavelength perturbations, it is obvious that it influences the correlation length. Thus it was
natural to generalize our previous work on making the correlation length for drift waves
parameter dependent to include also the effect of flow shear. This has now been implemented
and is found to reproduce the experimental feature that stiffness is reduced for a combination
of large flow shear and small magnetic shear. The reason is that for large magnetic shear the
radial correlation length is determined primarily by magnetic shear, whilst for low magnetic
shear it is determined by flowshear. The first results of this modified correlation length model
show good quantitative agreement with experiment.
Iris type:
04.01 Contributo in Atti di convegno
Keywords:
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List of contributors:
Mantica, Paola
Book title:
ECA
Published in: