Experimental constraint on the radial mode number of the Geodesic Acoustic Mode in MAST Ohmic plasma

Experimental constraint on the radial mode number of the Geodesic Acoustic Mode in MAST Ohmic plasma

Experimental constraint on the radial mode number of the Geodesic Acoustic Mode in MAST Ohmic plasma 150 150 Mathew
CCFE-PR(17)60

Experimental constraint on the radial mode number of the Geodesic Acoustic Mode in MAST Ohmic plasma

Reciprocating Mach probe data is used to estimate the radial wave number of oscillatory zonal flows in Ohmic MAST plasma. An intermittent 10kHz mode is detected in the wavelet decomposition and windowed spectra of plasma potential fluctuations of the MAST tokamak edge plasma. Previously, this mode has been identified as a Geodesic Acoustic Mode (GAM) using probe observations and numerical simulations. Two-points phase differencing technique applied to probe pins with radial and poloidal separations give 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 then obtained. We measure the radial mode number to be 0:05 kr p 0:15 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.

Collection:
Journals
Journal:
Plasma Physics and Controlled Fusion
Publisher:
IOP (Institute of Physics)
Published date:
02/07/2018