Speaker
Bogdan Hnat
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1085.pdf
Experimental constraint on the radial mode number of the Geodesic
Acoustic Mode in MAST Ohmic plasma
B. Hnat1, S. Gadgil1, A. Kirk1, F. Militello2, N. Walkden2, and the MAST team2
1 CFSA, Department of Physics, University of Warwick, Coventry, UK
2 EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon, OX14 3DB,
UK
Reciprocating Mach probe data is used to estimate the radial wave number of oscillatory
zonal flows in Ohmic MAST plasma. An intermittent ~10 kHz mode, previously identified
as a Geodesic Acoustic Mode (GAM), is detected in the wavelet decomposition and
windowed spectra of plasma potential fluctuations of the MAST tokamak edge plasma.
Two-points phase differencing technique is then applied to probe pins with radial and
poloidal separations giving an estimate of the radial wave number at the desired range of
frequencies. The phase velocity of propagation and an estimate of the shearing rate of the
GAM is obtained. We measure the radial mode number range kr ~ 0.3-1.0 1/cm and a radial
propagation speed of up to ~1 km/s. The GAM shearing rate is an order of magnitude
smaller than the growth rate of drift-like turbulence. These results are consistent with the
estimates obtained previously from multi-fluid numerical simulations of GAM in MAST.
