Congratulations to Andrew Malcolm-Neale, a York Fusion CDT student who successfully defended his thesis at viva in 2021. Andrew’s thesis is entitled “Experimental Search for Signatures of Zonal Flow Physics in a Large Spherical Tokamak using Beam Emission Spectroscopy” and his supervisors were Dr Istvan Cziegler, (University of York), Dr Anthony Field (UKAEA) and Professor Roddy Vann (University of York).
Andrew gave us this update on what he is doing next:
“I took time during the Covid-19 pandemic (’21) to work in a biomedical laboratory on LAMP testing for NHS staff while I finished writing and correcting. After a short break I have now taken a job working in the research support function of the University of York physics department. As a research technician I am continuing to build my skills in instrumentation across research groups, with a focus on plasma physics, looking after labs, kit and researchers!”
An abstract from Andrew’s thesis is below.
“Cross-field turbulent transport in magnetically confined plasmas is a highly effective loss mechanism of the heat and mass of fusion fuels and principally responsible for degrading the quality of confinement. Recently, an inter-dependence of turbulence and flows has been demonstrated in conventional tokamaks, including zonal flows that take energy directly out of turbulence. Data, in particular an experiment in a big spherical tokamak, is scarce. This project uses a Beam Emission Spectroscopy (BES) diagnostic on the MAST spherical tokamak to measure local fluctuation of plasma density. We develop correlation and spectral analysis techniques to facilitate investigation of flow structure across the plasma profile. I first developed a velocimetry routine using cross-correlation time delay estimation (CCTDE) optimising the length of correlation functions of fluctuating MAST BES data to achieve high time resolution for zonal flow detection. The new code’s performance was benchmarked using three realistic examples of spherical tokamak physics that previously had made velocimetry unusable, each with an imposed mode mimicking zonal flow and shown to be observable and measurable in the velocity spectrum. Results from this spectroscopy identify four classes of spectra observed in real BES data. Spectra with the clearest coherent peaks are shown to exist concurrently with a long-lasting magnetic mode. A systematic test of expected zonal flow physics at shot times that produce velocity spectra with coherent peaks was developed. Automating and weighting those tests created a standardised framework for GAM detection. In this project it enabled the first search of a substantial MAST data set of 63 shots in which BES observed the plasma edge. No examples matched all expected physics. The observed spectrum patterns match GAM theory that accounts for safety factor and plasma rotation, but not elongation; the modal average extent of matches covers four columns (about 8 cm plasma radius) of the detector. A scan of 209 shots at automatically found L-H transition times found 5 cases with good matches to expected zonal flow physics but relatively weak velocity modes.”
Well done Andrew!