Speaker
Valentin Borzosekov
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1099.pdf
Evolution of energy losses and of microturbulence at modulated ECRH of
L-2M stellarator plasmas
G.M. Batanov, V.D. Borzosekov, S.E. Grebenshchikov, N.K. Kharchev, A.A. Kharchevsky,
Yu.V. Kholnov, L.V. Kolik, E.M. Konchekov, A.A. Letunov, A.E. Petrov, N.N. Skvortsova
V.D. Stepakhin, D.G. Vasilkov
A.M. Prokhorov General Physics Institute RAS, Moscow, Russia
After recent upgrade of the electron-cyclotron resonance heating (ECRH) system of
the L-2M stellarator it is possible to study plasma dynamics at 100% modulated ECRH. Such
modulation implies that heating goes in a form of a sequence of microwave pulses and
between pulses high-temperature current-free plasma is confined without auxiliary heating.
One of many interesting aspects to study in this operational regime is evolution of energy
losses namely the steep increase of energy losses that happens shortly after (~ 1 ms) start of
each heating pulse (Fig.1).
Fig.1. Diamagnetic signal – black solid line; shaded rectangle is the time interval with steep increase of
energy losses.
Experiments reported here were carried out at average electron density ne = 2·1019 m-3
and 400 kW of central X2 ECRH. Lengths of microwave pulses and time interval between
pulses (quiet interval) were varied. Main focus of this report is an attempt to find relation
between the steep increase of energy losses and evolution of microturbulence that was
investigated using microwave scattering techniques at the L-2M. Four collective scattering
diagnostics operate in the ECRH cross-section while Doppler reflectometry is installed in
another cross-section. For density fluctuations in the local region near plasma axis it was
found that intensity of density fluctuations 𝑛2~ is maximal in the time interval of the energy
losses increase. Line averaged measurements of density fluctuations yielded same results.
However, results of edge localized measurements of Doppler reflectometry demonstrate no
change of fluctuations intensity. But change of Doppler reflectometry spectra is prominent:
till the onset of the energy losses steep increase the peak near zero-frequency dominates in
the spectrum and when the increase starts the spectrum becomes broader while the side peak
arises near 750 kHz. The reported study was funded by RFBR project № 18-02-00621.
