New Techniques for Coherence Imaging Fusion Plasmas

Imaging diagnostic techniques are desirable for fusion plasma experiments for their wide coverage and high spatial resolution, which allows for a more complete comparison with the predictions made by plasma physics models than traditional techniques. Benchmarking models against measurements made on current experiments improves our understanding of the physics and reduces the uncertainties involved with designing future experiments and reactors. This thesis presents new techniques for coherence imaging (CI), an interferometric narrowband spectral imaging technique used to measure the brightness, shift and width of spectral lines emitted by the plasma in the visible range. From these measurements, 2-D maps of emitting species flow velocity, and temperature can be inferred via Doppler shifts and broadening respectively. For passive hydrogen Balmer series emission in the tokamak divertor, Stark broadening is strong enough to provide a 2-D map of electron density $n_e$. First, we introduce novel CI instrument designs based on pixelated phase-mask (PPM) interferometry, which improve spatial resolution and robustness over typical linear carrier designs. Secondly, we introduce a new method for absolute calibration of CI flow velocity measurements using emission lines from standard gas-discharge lamps instead of a tuneable laser. This method significantly reduces hardware costs while maintaining high measurement accuracy — ±1 km/s compared to typical ion flows in the tokamak plasma edge of < 30 km/s. Lastly, we present improved methods for CI measurement of ne, using modern lineshape models to improve accuracy and using a multi-delay PPM-CI instrument design to minimise errors caused by Doppler broadening, extending the valid measurement range to lower $n_e$. This is demonstrated with experimental measurements of H$_\gamma$ and H$_\delta$ emission on the Magnum-PSI linear plasma experiment with a direct comparison to Thomson scattering measurements

Convalescent plasma in patients admitted to hospital with COVID-19 (RECOVERY): a randomised controlled, open-label, platform trial

SummaryBackground Azithromycin has been proposed as a treatment for COVID-19 on the basis of its immunomodulatoryactions. We aimed to evaluate the safety and efficacy of azithromycin in patients admitted to hospital with COVID-19.Methods In this randomised, controlled, open-label, adaptive platform trial (Randomised Evaluation of COVID-19Therapy [RECOVERY]), several possible treatments were compared with usual care in patients admitted to hospitalwith COVID-19 in the UK. The trial is underway at 176 hospitals in the UK. Eligible and consenting patients wererandomly allocated to either usual standard of care alone or usual standard of care plus azithromycin 500 mg once perday by mouth or intravenously for 10 days or until discharge (or allocation to one of the other RECOVERY treatmentgroups). Patients were assigned via web-based simple (unstratified) randomisation with allocation concealment andwere twice as likely to be randomly assigned to usual care than to any of the active treatment groups. Participants andlocal study staff were not masked to the allocated treatment, but all others involved in the trial were masked to theoutcome data during the trial. The primary outcome was 28-day all-cause mortality, assessed in the intention-to-treatpopulation. The trial is registered with ISRCTN, 50189673, and ClinicalTrials.gov, NCT04381936.Findings Between April 7 and Nov 27, 2020, of 16 442 patients enrolled in the RECOVERY trial, 9433 (57%) wereeligible and 7763 were included in the assessment of azithromycin. The mean age of these study participants was65·3 years (SD 15·7) and approximately a third were women (2944 [38%] of 7763). 2582 patients were randomlyallocated to receive azithromycin and 5181 patients were randomly allocated to usual care alone. Overall,561 (22%) patients allocated to azithromycin and 1162 (22%) patients allocated to usual care died within 28 days(rate ratio 0·97, 95% CI 0·87–1·07; p=0·50). No significant difference was seen in duration of hospital stay (median10 days [IQR 5 to >28] vs 11 days [5 to >28]) or the proportion of patients discharged from hospital alive within 28 days(rate ratio 1·04, 95% CI 0·98–1·10; p=0·19). Among those not on invasive mechanical ventilation at baseline, nosignificant difference was seen in the proportion meeting the composite endpoint of invasive mechanical ventilationor death (risk ratio 0·95, 95% CI 0·87–1·03; p=0·24).Interpretation In patients admitted to hospital with COVID-19, azithromycin did not improve survival or otherprespecified clinical outcomes. Azithromycin use in patients admitted to hospital with COVID-19 should be restrictedto patients in whom there is a clear antimicrobial indication