Recent progress with the MAST synthetic aperture imaging radiometer

The MAST Synthetic Aperture Microwave Imaging (SAMI) radiometer is an antenna array designed to image thermal microwave emission from MAST fusion plasmaaSAMl is now installed on MAST and preliminary data has been taken. This data clearly show the presence of electrostatic to electromagnetic mode conversion and the circumstances under which this mode conversion take place are strongly related to the pedestal density gradient and magnetic field. These quantities are valuable in understanding tokamak pedestal behaviour and are especially important to models of the Edge Localised Mode (ELM). This paper describes SAMIs design and construction, as well as fist signals showing the presence of mode conversion

Electron kinetics inferred from observations of microwave bursts during edge localised modes in the Mega-Amp Spherical Tokamak

Recent measurements of microwave and X-ray emission during edge localised mode (ELM) activity in tokamak plasmas provide a fresh perspective on ELM physics. It is evident that electron kinetics, which are not incorporated in standard (fluid) models for the instability that drives ELMs, play a key role in the new observations. These effects should be included in future models for ELMs and the ELM cycle. The observed radiative effects paradoxically imply acceleration of electrons parallel to the magnetic field combined with rapid acquisition of perpendicular momentum. It is shown that this paradox can be resolved by the action of the anomalous Doppler instability which enables fast collective radiative relaxation, in the perpendicular direction, of electrons accelerated in the parallel direction by inductive electric fields generated by the initial ELM instability.Comment: 4 pages, 6 figure

A high-k mm-wave scattering diagnostic for measuring binormal electron scale turbulence on MAST-U

Plasma turbulence plays a key role in determining the spatial-temporal evolution of plasmas in astrophysical, geophysical and laboratory contexts. In particular, turbulence on disparate spatial and temporal scales limits the level of confinement achievable in magnetic confinement fusion experiments and therefore limits the viability of sustainable fusion power. MAST-U is a well-equipped experimental facility having instruments to measure ion-scale turbulence and electron scale turbulence at the plasma edge. However, measurement of turbulence at electron scales in the core is problematic, especially in H mode. This gap in measurement capability has provided the motivation to develop a high-k microwave scattering diagnostic for MAST-U*. The turbulence is expected to be most significant in the binormal direction with scale ranges expected of order (k ρe ~ 0.1 -> 0.5) in the confinement region of the core plasma (0.5 < r/a < 1). We therefore propose a binormal high-k scattering diagnostic operating with near-perpendicular incidence to the magnetic field through the scattering region. In this paper, the results of Gaussian wave optics and beam-tracing calculations [1] are presented that demonstrate the predicted spatial and wavenumber resolution of the diagnostic along with the sensitivity of the measurement, assuming a probe beam crossing close to the diameter of the MAST-U vessel in the equatorial mid-plane. The analysis considers the variation of magnetic pitch angle ( = tan-1 (B / B)) as a function of plasma radius and its effect on the instrument selectivity function F(r) as a function of scattering location and kρe. An illustration of the proposed scattering geometry with respect to the MAST-U crosssectional schematic is given in figure 1