Upcoming Events

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*** New Chair in Fusion Science & Technology ***

CfAI has a vacancy at full professorial level for a talented individual to lead the group's instrumentation

activities in nuclear fusion. Further details can be found on the CfAI Vacancies page. Deadline 30 Jan 2021.

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CfAI Seminar Programme 2021

Wednesday 20th January: 1pm

Dr Ollie Farley: Characterisation of Tomographic Adaptive Optics Performance in Realistic Atmospheric Conditions

Abstract: In ground based astronomy at optical and near infrared wavelengths, the Earth's turbulent atmosphere results in aberration of light before it reaches the telescope. Adaptive optics (AO) allows astronomers to partially correct this aberration, resulting in improved resolution and sensitivity. Tomographic AO techniques have been developed that enable correction over large fractions of the sky, or over a wide field of view. These techniques are employed on current world-leading telescopes and are a key part of the instrumentation for future Extremely Large Telescopes (ELTs). An important piece of information for any tomographic AO system is the vertical distribution (profile) of optical turbulence in the atmosphere. The profile is specific to an observing site and varies temporally on timescales from minutes to seasons.

This work is concerned with quantifying the effect of changing profile on tomographic AO by using a large dataset of turbulence profiles from ESO Paranal, Chile. Using a novel clustering method, we extract 18 reference profiles from this dataset. These reference profiles can be used in slow Monte Carlo simulation to give a realistic description of the variability of the profile at Paranal.

We validate these profiles alongside other common reference profiles using a fast Fourier tomographic AO simulation. We find that reference profiles composed of the average of many profiles give worse than expected performance in simulation. Using the same simulation and dataset we also assess the impact of sub-optimal tomographic reconstruction, where the profile is sampled with a small number of layers and is temporally evolving.

Finally we present simulation and on-sky measurements from a SCIDAR turbulence profiler operating on a relatively small 0.5~m aperture. These preliminary results show that a small telescope SCIDAR may be viable for site characterisation and monitoring in the context of ELT-scale tomographic AO.

Dr Xiande Feng: Development of an 11-channel Multi Wavelength Imaging diagnostic for divertor plasmas in MAST Upgrade

Abstract: Divertor detachment and alternative divertor magnetic geometries are predicted to be promising approaches to handle the power exhaust of future fusion devices. In order to understand the detachment process caused by volumetric losses in alternative divertor magnetic geometries, a Multi-Wavelength Imaging (MWI) diagnostic has recently been designed and built for the Mega Amp Spherical Tokamak Upgrade (MAST-U). The MWI diagnostic will simultaneously capture 11 spectrally filtered images of the visible light emitted from divertor plasmas and provide crucial knowledge for the interpretation of observations and modeling efforts. This manuscript presents the optical design, mechanical design, hardware and test results of an 11-channel MWI system with a field of view of 40^o. The optical design shows less than 5mm FWHM spatial resolution at the plasma on all 11 channels across the whole field of view. The spread of angle of incidence on the surface of each filter is also analyzed to inform the bandwidth specification of the interference filters. The results of the initial laboratory tests demonstrate that a spatial resolution of less than 5mm FWHM is achieved for all 11 channels, meeting the specifications required for accurate tomography.

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CfAI is one of the major research groups in the Physics Department at Durham with approximately 70 staff and research students. It is distributed across two physical locations, one of which is in the new Ogden Centre for Fundamental Physics on the University science site in Durham, and the other is at the North East Technology Park (NETPark), an internationally recognised location for science and technology companies, based about ten miles away in Sedgefield, Co. Durham.

CfAI develops state-of-the-art instruments for application across a wide range of disciplines including astronomical instrumentation, biophysics, remote sensing and fusion diagnostics. Research outputs can be found by following the links to individual research areas listed in the menu on the left or by a search of Durham Research Online. We also have close links with the Centre for Extragalactic Astronomy and the Institute for Computational Cosmology.