Determination of structure tilting in magnetized plasmas - Time delay estimation in two dimensions

Time delay estimation (TDE) is a well-known technique to investigate poloidal flows in fusion plasmas. The present work is an extension of the earlier works of A. Bencze and S. Zoletnik 2005 and B. T\'al et al. 2011. From the prospective of the comparison of theory and experiment it seem to be important to estimate the statistical properties of the TDE based on solid mathematical groundings. This paper provides analytic derivation of the variance of the TDE using a two-dimensional model for coherent turbulent structures in the plasma edge and also gives an explicit method for determination of the tilt angle of structures. As a demonstration this method is then applied to the results of a quasi-2D Beam Emission Spectroscopy (BES) measurement performed at the TEXTOR tokamak.Comment: 8 pages, 10 figure

Wide-angle Visible Video Diagnostics for JT-60SA utilizing EDICAM

A multi-purpose, wide-angle, visible overview video diagnostic, based on the EDICAM camera, was designed for JT-60SA superconducting tokamak, in order to fulfill both machine protection and scientific observation purposes. The detector is located inside the ‘port plug’ (a ca. 3 m long re-entrant tube), relatively close to the plasma boundary; the EDICAM can tolerate the magnetic field at this location as well as the radiation levels in the early phases of the experiment. A rail-and-carriage system is used to move the detector between the opening of the port plug and the measurement location. A 4-point docking system ensures the precise and robust positioning of the optics, firmly holding the detector also in the event of disruptions or earthquakes. The camera is running under atmospheric condition, separated by a sapphire window from the plasma vacuum. The vacuum window is protected by a water-cooled pin-hole from mechanical impacts and plasma heat; the pin-hole is also the first element of the detector’s optical system. The optics consists of two lens groups and a prism; the housing is made of stainless steel, in order to reduce eddy currents and thus avoid large forces acting on the system in a disruption

Comparison of BES measurements of ion-scale turbulence with direct gyro-kinetic simulations of MAST L-mode plasmas

Observations of ion-scale (kyρi ≤ 1) density turbulence of relative amplitude & 0.2% are available on the Mega Amp Spherical Tokamak (MAST) using a 2D (8 radial × 4 poloidal channel) imaging Beam Emission Spectroscopy (BES) diagnostic. Spatial and temporal characteristics of this turbulence, i.e., amplitudes, correlation times, radial and perpendicular correlation lengths and apparent phase velocities of the density contours, are determined by means of correlation analysis. For a low-density, L-mode discharge with strong equilibrium flow shear exhibiting an internal transport barrier (ITB) in the ion channel, the observed turbulence characteristics are compared with synthetic density turbulence data generated from global, non-linear, gyro-kinetic simulations using the particle-in-cell (PIC) code NEMORB. This validation exercise highlights the need to include increasingly sophisticated physics, e.g., kinetic treatment of trapped electrons, equilibrium flow shear and collisions, to reproduce most of the characteristics of the observed turbulence. Even so, significant discrepancies remain: an underprediction by the simulations of the turbulence amplituide and heat flux at plasma periphery and the finding that the correlation times of the numerically simulated turbulence are typically two orders of magnitude longer than those measured in MAST. Comparison of these correlation times with various linear timescales suggests that, while the measured turbulence is strong and may be ‘critically balanced’, the simulated turbulence is weak