Speaker
Álvaro Cappa
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1040.pdf
Impact of ECCD on Alfvén Eigenmodes in the TJ-II stellarator.
Á. Cappa1 , E. Ascasíbar1 , F. Castejón1 , J.M. García Regaña 1 , M. García Muñoz 2
A. González-Jerez3 , D. López-Bruna1 , M. Liniers1 , N. Marushchenko4 , M. Ochando1
J.L. Velasco1 , S. Yamamoto5
1 Laboratorio Nacional de Fusión, Madrid, Spain
2 Universidad de Sevilla, Sevilla, Spain, 3 Universidad Complutense de Madrid, Madrid, Spain
4 Max Planck Institut fur Plasmaphysik, Greifswald, Germany
5 Institute of Advanced Energy, Kyoto University, Japan
The impact of Electron Cyclotron Current Drive (ECCD) on NBI-driven modes has been
investigated in the TJ–II low shear stellarator. Experimental results show that a small amount of
EC driven current may modify dramatically the spectrum of observed modes (Fig. 1). Applying
240 kW of on-axis ECRH power in counter-ECCD configuration (N|| = +0.2) provokes ∼ 0.5
kA reduction in plasma current. This mild reduction of current is accompanied by a strong
change in the behaviour of alfvénic magnetic fluctuations [1]. Changes in rotational transform
profile (ι), having a strong influence on the Shear Alfvén Spectrum (SAS) of the device, are the
main candidate to explain the observations.
The high sensitivity of the SAS structure on
ι(ρ) suggests that the interpretation of the re-
sults should be made considering all the rele-
vant contributions to the plasma current (NBCD,
ECCD and to a lesser extent, the boostrap current
Iboot ). For modelling purposes, the STELLGAP
and AE3D codes are used to calculate the spec-
trum and spatial structure of possible gap modes
in several shots with different values of the total
current. No experimental information on the cur-
rent profile is available and therefore, the input
Figure 1: Spectrogram of magnetic fluctuations
VMEC magnetic equilibrium, which should be
with (bottom) and without ECCD (top).
consistent with the plasma current profile, will
be obtained using a rough approximation to the unknown NBCD profile and a rigorous theoret-
ical calculation of the ECCD profile (TRAVIS) and the bootstrap current profile.
References
[1] S. Yamamoto et al., 21th International Stellarator-Heliotron Workshop, Kyoto, Japan (2017).
