Speaker
Dmitrii Prisiazhniuk
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1008.pdf
Application of the microwave beam steering from poloidal correlation
reflectometry for investigation of the L- and I-mode turbulence
D.Prisiazhniuk1 , G.D.Conway1 , T.Happel1 , S.Freethy1 ,
P.Manz1 , A.Krämer-Flecken3 , U.Stroth1,2 and the ASDEX Upgrade Team
1 Max Planck Institute for Plasma Physics, 85748 Garching, Germany
2 Physik-Department E28, Technische Universität München, 85748 Garching, Germany
3 Institut für Energieforschung - Plasmaphysik, Forschungszentrum Jülich, 52425, Germany
Poloidal correlation reflectometry (PCR) is a powerful tool to study correlation properties of
turbulent density fluctuations [1, 2]. In the typical application of PCR several poloidally and
toroidally separated receiving antennas simultaneously measure the reflected beam from the
cut-off layer in the plasma. The correlation of the receiving antenna signals allows to determine
the velocity, the correlation length and life time of turbulent density fluctuations [3]. In this
contribution an alternative application of the PCR diagnostic is proposed. All receiving antenna
signals are combined in post-processing software with different phases to create a total receiving
beam in a specific direction using the phased antenna array concept. The principle of this method
is similar to the synthetic aperture microwave imaging (SAMI) system [4, 5], but with only 4
receiving horn antennas. The method is robust and can be applied to every discharge. Using the
PCR antenna cluster at ASDEX Upgrade the total receiving beam can be steered in the poloidal
direction (θ ' ±10◦ ) and in the toroidal direction (φ ' ±4◦ ) with characteristic 3 dB half-width
beams of order ∆θ ≈1.5◦ and ∆φ ≈2.7◦ - thus operating as a steerable Doppler reflectometer
with corresponding backscaterring wavenumbers k⊥ ' ±3 cm−1 and ∆k⊥ ' 0.6 cm−1
The application of the method to L- and I-mode plasmas is presented. The measured velocity
from the Doppler shift is compared with classical PCR time delay analyses [2] and with other
diagnostics. Influence of the magnetic field line pitch angle is also shown. Quasi coherent modes
with k⊥ ≈ 1 cm−1 can be decoupled from background turbulence and enhanced. Observations
of the intermittent events reported in [6] are discussed.
References
[1] A.Krämer-Flecken et al., Nucl. Fusion 57, 066023 (2017)
[2] D.Prisiazhniuk et al., Plasma Phys. Control. Fusion 59, 025013 (2017)
[3] D.Prisiazhniuk et al., "Density fluctuation correlation measurements in ASDEX Upgrade
using poloidal correlation reflectometry", sumbitted to PPCF (2018)
[4] D.A. Thomas et al., Nucl. Fusion 56, 066023 (2016)
[5] S.J. Freethy et al., Nucl. Fusion 55, 124010 (2013)
[6] T.Happel et al., Nucl. Fusion 56, 064004 (2016)
