Spectroscopic investigations of detachment on TCV: Investigating the role of atomic physics on the ion current roll-over and the dynamics of detachment in TCV

The process of divertor detachment, whereby heat and particle fluxes to divertor surfaces are strongly reduced, is required to reduce heat loading and erosion in a magnetic fusion reactor. In this thesis the physics leading to the decrease of the divertor ion current It, or ‘roll-over’, is experimentally explored on the TCV tokamak through characterization of the location, magnitude and role of the various divertor ion sinks and sources including a complete measure of particle and power balance. These first measurements of the profiles of divertor ionisation and hydrogenic radiation along the divertor leg are enabled through the development of a TCV divertor spectrometer, together with careful Stark broadening analysis and novel Balmer line spectroscopic techniques. Over a range in core plasma conditions (plasma current, impurity-seeding, density) the It roll-over is caused by a drop in the divertor ion source; recombination remains either small or negligible until later in the detachment process. In agreement with simple analytical predictions, this ion source is limited by a reduction in the power available for ionisation, Precl, sometimes characterised as ‘power starvation’. Concurrent increases in the energy required per ionisation, Eion, further reduce the number of ionizations. The detachment threshold is found experimentally (in agreement with analytic model predictions) to be Precl / Eion It < 2, corresponding to the target electron temperature, Tt ~ Eion/gamma where gamma is the sheath transmission coefficient. Target pressure loss, required for target ion current loss, is observed to be delivered by both volumetric momentum loss, as typically assumed, and by a drop of the upstream pressure. The evolution of measured divertor profiles through detachment of the various ion sources/sinks as well as power losses and charge exchange are quantitatively reproduced through full 2D SOLPS modelling of a ramp of core plasma density through the detachment process

Development and simulation of multi-diagnostic Bayesian analysis for 2D inference of divertor plasma characteristics

We present results of the design, implementation and testing of a Bayesian multi-diagnostic inference system which combines various divertor diagnostics to infer the 2D fields of electron temperature T e, density n e and deuterium neutral density n 0 in the divertor. The system was tested using synthetic diagnostic measurements derived from SOLPS-ITER fluid code predictions of the MAST-U Super-X divertor which include appropriate added noise. Two SOLPS-ITER simulations in different states of detachment, taken from a scan of the nitrogen seeding rate, were used as test-cases. Taken across both test-cases, the median absolute fractional errors in the inferred electron temperature and density estimates were 10.3% and 10.1% respectively. Differences between the inferred fields and the test-cases were well explained by solution uncertainty estimates derived from posterior sampling. This work represents a step toward a larger goal of obtaining a quantitative, 2D description of the divertor plasma state directly from experimental data, which could be used to gain better understanding of divertor physics phenomena

Investigating the impact of the molecular charge-exchange rate on detached SOLPS-ITER simulations

Plasma-molecular interactions generate molecular ions which react with the plasma and contribute to detachment through molecular activated recombination (MAR), reducing the ion target flux, and molecular activated dissociation (MAD), both of which create excited atoms. Hydrogenic emission from these atoms have been detected experimentally in detached TCV, JET and MAST-U deuterium plasmas. The TCV findings, however, were in disagreement with SOLPS-ITER simulations for deuterium indicating a molecular ion density ($D_2^+$) that was insufficient to lead to significant hydrogenic emission, which was attributed to underestimates of the molecular charge exchange rate ($D_2 + D^+ \rightarrow D_2^+ + D$) for deuterium (obtained by rescaling the hydrogen rates by their isotope mass). In this work, we have performed new SOLPS-ITER simulations with the default rate setup and a modified rate setup where ion isotope mass rescaling was disabled. This increased the $D_2^+$ content by $> \times 100$. By disabling ion isotope mass rescaling: 1) the total ion sinks are more than doubled due to the inclusion of MAR; 2) the additional MAR causes the ion target flux to roll-over during detachment; 3) the total $D\alpha$ emission in the divertor increases during deep detachment by roughly a factor four; 4) the neutral atom density in the divertor is doubled due to MAD, leading to a 50\% increase in neutral pressure; 5) total hydrogenic power loss is increased by up to 60\% due to MAD. These differences result in an improved agreement between the experiment and the simulations in terms of spectroscopic measurements, ion source/sink inferences and the occurrence of an ion target flux roll-over

Successful emergent repair of a subacute left ventricular free wall rupture after acute inferoposterolateral myocardial infarction

BACKGROUND: Myocardial rupture is an important and catastrophic complication of acute myocardial infarction. A dramatic form of this complication is a left ventricular free wall rupture (LVFWR). CASE PRESENTATION: A 70-year-old man with acute inferoposterolateral myocardial infarction and single-vessel coronary artery disease underwent emergency percutaneous coronary intervention (PCI). The circumflex coronary artery was successfully stented with a drug-eluting stent. Fifty days after PCI the patient experienced progressive fatigue and chest pain with haemodynamic instability. Transthoracic echocardiography showed a covered LVFWR of the lateral wall. The patient underwent successful emergent surgical repair of the LVFWR. CONCLUSIONS: In the current era of swift PCI, mechanical complications of acute myocardial infarction, such as LVFWR, are rare. The consequences, however, are haemodynamic deterioration and imminent death. This rare diagnosis should always be considered when new cardiovascular symptoms or haemodynamic instability develop after myocardial infarction, even beyond one month after the initial event. Timely diagnosis and emergency surgery are required for successful treatment of this devastating complication

Identification of the primary processes that lead to the drop in divertor target ion current at detachment in TCV

Using SOLPS-ITER we model a TCV conventional divertor discharge density ramp to understand the role of various processes in the loss of target ion current. We find that recombination is not a strong contributor to the rollover of the target ion current at detachment. In contrast, the divertor ion source appears to play a central role in magnitude (the source of most of the ion target current) and time, apparently dropping during the density ramps due to a drop in power available for ionization

Panel 6 : Vaccines

Objective. To review the literature on progress regarding (1) effectiveness of vaccines for prevention of otitis media (OM) and (2) development of vaccine antigens for OM bacterial and viral pathogens. Data Sources. PubMed database of the National Library of Science. Review Methods. We performed literature searches in PubMed for OM pathogens and candidate vaccine antigens, and we restricted the searches to articles in English that were published between July 2011 and June 2015. Panel members reviewed literature in their area of expertise. Conclusions. Pneumococcal conjugate vaccines (PCVs) are somewhat effective for the prevention of pneumococcal OM, recurrent OM, OM visits, and tympanostomy tube insertions. Widespread use of PCVs has been associated with shifts in pneumococcal serotypes and bacterial pathogens associated with OM, diminishing PCV effectiveness against AOM. The 10-valent pneumococcal vaccine containing Haemophilus influenzae protein D (PHiD-CV) is effective for pneumococcal OM, but results from studies describing the potential impact on OM due to H influenzae have been inconsistent. Progress in vaccine development for H influenzae, Moraxella catarrhalis, and OM-associated respiratory viruses has been limited. Additional research is needed to extend vaccine protection to additional pneumococcal serotypes and other otopathogens. There are likely to be licensure challenges for protein-based vaccines, and data on correlates of protection for OM vaccine antigens are urgently needed. Implications for Practice. OM continues to be a significant health care burden globally. Prevention is preferable to treatment, and vaccine development remains an important goal. As a polymicrobial disease, OM poses significant but not insurmountable challenges for vaccine development.Peer reviewe

Two-dimensional inference of divertor plasma characteristics: advancements to a multi-instrument Bayesian analysis system

An integrated data analysis system based on Bayesian inference has been developed for application to data from multiple diagnostics over the two-dimensional cross-section of tokamak divertors. Tests of the divertor multi-instrument Bayesian analysis system (D-MIBAS) on a synthetic data set (including realistic experimental uncertainties) generated from SOLPS-ITER predictions of the MAST-U divertor have been performed. The resulting inference was within 6\%, 5\% and 30\% median absolute percentage error of the SOLPS-predicted electron temperature, electron density and neutral atomic hydrogen density, respectively, across a two-dimensional poloidal cross-section of the MAST-U Super-X outer divertor. To accommodate molecular contributions to Balmer emission, an advanced emission model has been developed which is shown to be crucial for inference accuracy. Our D-MIBAS system utilises a mesh aligned to poloidal magnetic flux-surfaces, throughout the divertor, with plasma parameters assigned to each mesh vertex and collectively considered in the inference. This allowed comprehensive forward models to multiple diagnostics and the inclusion of expected physics. This is shown to be important for inference precision when including molecular contributions to Balmer emission. These developments pave the way for accurate two-dimensional electron temperature, electron density and neutral atomic hydrogen density inferences for MAST-U divertor experimental data for the first time.Comment: 22 pages, 8 figure

Comparison between MAST-U conventional and Super-X configurations through SOLPS-ITER modelling

MAST-U has recently started operating with a Super-X divertor, designed to increase total flux expansion and neutral trapping, both predicted through simple analytic models and SOLPS calculations to reduce the plasma and impurity density detachment thresholds. In this study, utilising the SOLPS-ITER code, we are quantifying the possible gain allowed by the MAST-U Super-X and neutral baffling geometry, in terms of access to detachment. We show that a significant reduction of the upstream density detachment threshold (up to a factor 1.6) could be achieved in MAST-U, for the Super-X, as opposed to conventional divertor geometry, mainly through an increased total flux expansion, neutral trapping being found very similar between the different configurations. We also show that variations of the strike-point angle are complex to interpret in such a tightly baffled geometry, and that a case in which the target normal points more towards the separatrix does not necessarily imply a lower detachment threshold. As in previous calculations for TCV, we quantify the role of neutral effects through developing and applying a quantitative definition of neutral trapping