As part of my PhD with the Fusion CDT, I have spent two summer months working on a fusion experiment in the bustling and vibrant city of Chengdu, China. As well as boasting a population greater than that of London – both human and panda – Chengdu is home to the Southwest Institute of Physics, and the HL-2A tokamak. The purpose of my trip, besides eating as much of the local Sichuan food as possible, was to record images of the HL-2A plasma using a high-speed camera and the coherence imaging spectroscopy technique.
Doppler coherence imaging spectroscopy (CIS) is a novel diagnostic technique that records two-dimensional images of the flow and temperature of hot ions. Ostensibly, it does this by looking at the Doppler effect on light emitted by heavier elements like carbon within the hydrogen plasma. Its high-speed imaging records the transient events inside a tokamak across a wide view. The theory group at HL-2A are particularly interested in using CIS to see what ions are doing in the turbulent edge of their plasma and, to this end, have established a collaboration with Durham University’s Centre for Advanced Instrumentation and also, by extension, the fusion CDT.
The first month was beset with technical hitches – our high-speed camera became unreliable and its videos filled with static when mounted next to HL-2A’s gigantic magnetic field coils. However, following deep contemplation at the summit of the holy mountain of Emei Shan, we arrived at a solution to lengthen the diagnostic and were able to record some images of the plasma in H-mode. Fundamentally, CIS is an application of ‘Fourier transform spectrometry’ and as such, the data requires significant post-mortem analysis to extract the useful information. We expect to be able to produce demonstration images of the HL-2A plasma flow in the coming weeks. Researchers from Chengdu will be visiting the UK before the end of the year to continue this collaboration and work towards further improving the instrument.
Joe Allcock, 2nd Year Fusion CDT Student