Speaker
Dr
Francois Ryter
(Max-Planck-Institut fuer Plasmaphysik)
Description
Turbulence-driven ion heat transport in tokamak H-modes is driven by
the ion temperature gradient (ITG) instability,
while electron heat transport is driven by the ITG, trapped electron
mode (TEM) and/or electron temperature gradient (ETG) instabilities.
These three instabilities appear above their respective threshold in
normalized temperature gradient
(R/LT) and drive transport.
We present results on the role of these contributions to heat
transport in the ASDEX Upgrade tokamak.
We performed dedicated experiments with neutral beam injection (NBI)
which heats both electrons and ions
and electron cyclotron resonant heating (ECRH) which heats the electrons.
From modulating of the electron temperature with ECRH
we deduce the electron heat pulse diffusivity (chi_HP) which
reflects the stiffness directly and is complementary to the power
balance diffusivity (chi_PB).
The predicted dependences of the ITG-driven ion heat transport on
Ti/Te and ExB rotational shear are found:
the ITG is clearly more stable for high values of Ti/Te and/or
rotational shear.
The ITG threshold itself could not be assessed experimentally with
accuracy yet and experiments are foreseen in the near future to
improve this situation.
The electron heat flux is partly driven by the ITG, but
when increasing the electron heat flux with ECRH above the flux
driven by the ITG, the TEM and/or ETG instabilities become unstable
which is particularly visible in the modulation data.
Indeed, a moderate increase of chi_PB and a stronger increase
of chi_HP above R/LTe = 5 indicates unambiguously
that an electron instability (TEM or ETG) develops above this
threshold. The stiffness is close to that found in ASDEX Upgrade for
TEM-driven electron heat transport.
Below the threshold, chi_HP and chi_PB exhibit about
the same value of 1.5 m2/s. This rather high value is
attributed to the ITG-driven electron heat transport,
in agreement with chi_HP = chi_PB which reflects
the fact that the ITG
does not depend on grad(Te). So far, we have found no indication
of an ETG contribution predicted to exhibit a stronger stiffness.
Transport modelling and comparisons of the experimental results with
gyro-kinetic calculations will be presented for both the ITG and
TEM/ETG studies.
| Country or International Organization | Germany |
|---|---|
| Paper Number | EX/P8-3 |
Primary author
Dr
Francois Ryter
(Max-Planck-Institut fuer Plasmaphysik)
Co-authors
Dr
Alexander Lebschy
(Max-Planck-Institut fuer Plasmaphysik)
Dr
Bernd Kurzan
(Max-Planck-Institut fuer Plasmaphysik)
Dr
Clemente Angioni
(Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, D-85748 Garching, Germany)
Dr
Eleonora Viezzer
(Max-Planck-Institut fuer Plasmaphysik)
Dr
Giovanni Tardini
(Max-Planck-Institut fuer Plasmaphysik)
Dr
Matthias Willensdorfer
(IPP Garching)
Dr
Mike Dunne
(Max-Planck-Institut fuer Plasmaphysik)
Dr
Rachael McDermott
(Max Planck Institut fuer Plasmaphysik)
Dr
Rainer Fischer
(Max-Planck-Institut fuer Plasmaphysik)
Dr
Wolfgang Suttrop
(Max-Planck-Institut fuer Plasmaphysik)
