Speaker
Branka Vanovac
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1085.pdf
Parameter space of low frequency inter-ELM modes
B. Vanovac1 , E. Wolfrum2 , M. Willensdorfer2 , M. Cavedon2 , M. Griener2 ,
A.F. Mink2 , S.S. Denk2 , S.J. Freethy2 , M. Hoelzl2 ,
N.C. Luhmann Jr. 3 , the ASDEX Upgrade Team
1 DIFFER - Dutch Institute for Fundamental Energy Research, Eindhoven, the Netherlands
2 Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany
3 Department of Applied Science, University of California at Davis, Davis, CA 95616, USA
The ELM cycle of type-I ELMs consists of different phases characterized by the evolution
of kinetic profiles on different time scales [1] and distinct MHD and turbulence activity. In
the latest phase of the ELM cycle, the pressure gradients are clamped. During this phase low,
medium and high frequency MHD modes develop simultaneously in the steep gradient region
[2]. The high frequency modes are located at the minimum of the Er well, and are measured as
fluctuations in the radial magnetic field on both, low and high field side [3].
In this work, the low frequency modes are studied. They are measured only at the low field
side located further inwards, towards the pedestal top. They appear as fluctuations in the electron
density, the electron temperature and as magnetic fluctuations [4]. These modes rotate poloidally
in the electron diamagnetic direction with the velocity of the background flow at that position.
The frequency of low frequency modes is inversely proportional to the input power.
In order to fully characterize the low frequency modes and correlate them with the pedestal
evolution pattern during an ELM cycle, this work focuses on exploration of the range of pa-
rameters where these modes appear. This involves the extension of the dependence on input
power and scan in the edge safety factor. Different collisionality regimes are also assessed. To
identify the nature of the fluctuations, we use the newly installed He-line ratio diagnostics at
ASDEX Upgrade that measures simultaneously electron density and electron temperature in the
plasma edge. The phase relation between the two is compared with n-T phase measurements
from reflectometer and correlation electron cyclotron emission diagnostics [5].
References
[1] A Burckhart et al 2010 Plasma Phys. Control. Fusion 52 105010
[2] F Mink et al 2016 Plasma Phys. Control. Fusion 58 125013
[3] F M Laggner et al 2016 Plasma Phys. Control. Fusion 58 065005
[4] B Vanovac et al 2018 Plasma Phys. Control. Fusion 60 045002
[5] S.J. Freethy et al 2018 Phys. Plasmas, accepted
