Resonant wave-filament interactions as a loss mechanism for HHFW heating and current drive

Perkins et al. PRL 2012 [1] reported unexpected power losses during High Harmonic Fast Wave (HHFW) heating and current drive in NSTX. Recently, Tierens et al [2] proposed that these losses may be attributable to surface waves on field-aligned plasma filaments, which carry power along the filaments, to be lost at the endpoints where the filaments intersect the limiters. In this work, we show that there is indeed a resonant loss mechanism associated with the excitation of these surface waves, and derive an analytic expression for the power lost to surface wave modes at each filament.

Constraining the 410-km discontinuity and slab structure in the Kuril subduction zone with triplication waveforms

SUMMARY The detailed structure near the 410-km discontinuity provides key constraints of the dynamic interactions between the upper mantle and the lower mantle through the mantle transition zone (MTZ) via mass and heat exchange. Meanwhile, the temperature of the subducting slab, which can be derived from its fast wave speed perturbation, is critical for understanding the mantle dynamics in subduction zones where the slab enters the MTZ. Multipathing, i.e. triplicated, body waves that bottom near the MTZ carry rich information of the 410-km discontinuity structure and can be used to constrain the discontinuity depth and radial variations of wave speeds across it. In this study, we systematically analysed the trade-off between model parameters in triplication studies using synthetic examples. Specifically, we illustrated the necessity of using array-normalized amplitude. Two 1-D depth profiles of the wave speed below the Tatar Strait of Russia in the Kuril subduction zone are obtained. We have observed triplications due to both the 410-km discontinuity and the slab upper surface. And, seismic structures for these two interfaces are simultaneously inverted. Our derived 410-km discontinuity depths for the northern and southern regions are at 420$\pm $15 and 425$\pm $15 km, respectively, with no observable uplift. The slab upper surface is inverted to be located about 50–70 km below the 410-km discontinuity. This location is between the depths of the 1 and 2 per cent P-wave speed perturbation contours of a regional 3-D full-waveform inversion (FWI) model, but we found twice the wave speed perturbation amplitude. A wave speed increase of 3.9–4.6 per cent within the slab, compared to 2.0–2.4 per cent from the 3-D FWI model, is necessary to fit the waveforms with the shortest period of 2 s, indicating that high-frequency waves are required to accurately resolve the detailed structures near the MTZ.

Surface Electroencephalography (EEG) During the Acute Phase of Stroke to Assist With Diagnosis and Prediction of Prognosis: a Scoping Review.

BackgroundStroke is a common medical emergency responsible for significant mortality and disability. Early identification improves outcomes by promoting access to time-critical treatments such as thrombectomy for large vessel occlusion (LVO), whilst accurate prognosis could inform many acute management decisions. Surface electroencephalography (EEG) shows promise for stroke identification and outcome prediction, but evaluations have varied in technology, setting, population and purpose. This scoping review aimed to summarise published literature addressing the following questions:1. Can EEG during acute clinical assessment identify:a) Stroke versus non-stroke mimic conditionsb) Ischaemic versus haemorrhagic strokec) Ischaemic stroke due to LVO. 2. Can these states be identified if EEG is applied <6hrs since onset. 3. Does EEG during acute assessment predict clinical recovery following confirmed stroke.MethodsWe performed a systematic search of five bibliographic databases ending 19/10/2020. Two reviewers assessed eligibility of articles describing diagnostic and/or prognostic EEG application <72hrs since suspected or confirmed stroke. ResultsFrom 5892 abstracts, 210 full text articles were screened and 39 retained. Studies were small and heterogeneous. Amongst 21 reports of diagnostic data, consistent associations were reported between stroke, greater delta power, reduced alpha/beta power, corresponding ratios and greater brain asymmetry. When reported, the area under the curve (AUC) was at least good (0.81–1.00). Only one study combined clinical and EEG data (AUC 0.88). There was little data found describing whether EEG could identify ischaemic versus haemorrhagic stroke. Radiological changes suggestive of LVO were also associated with increased slow and decreased fast waves. The only study with angiographic proof of LVO reported AUC 0.86 for detection <24hrs since onset. Amongst 26 reports of prognostic data, increased slow and reduced fast wave EEG changes were associated with future dependency, neurological impairment, mortality and poor cognition, but there was little evidence that EEG enhanced outcome prediction relative to clinical and/or radiological variables. Only one study focussed solely on patients <6hrs since onset, for predicting neurological prognosis post-thrombolysis.ConclusionsAlthough studies report important associations with EEG biomarkers, further technological development and adequately powered real-world studies are required before recommendations can be made regarding application during acute stroke assessment.

Study of the Design and Assembly of a High Harmonic Fast Wave Antenna for an LAPD

The simulation survey of TAE Technologies has demonstrated that high harmonic fast wave (HHFW) heating is a promising method for core electron heating of FRC plasma. This study mainly describes the HHFW antenna mechanical design and assembly on the basis of the results of electromagnetic simulations performed by Oak Ridge National Laboratory (ORNL), the available port dimensions, and antenna installation position of the LAPD. Compared to the original scheme, this antenna is also optimized in the design. It is found that the E field distribution of optimized antenna becomes even, and the maximum electric field decreases by approximately 14%. The current on the antenna box and FS is reduced after optimization, whereas the maximum J density decreases from 53.3 kA to 14.5 kA. The reflection performance of the port at 30 MHz is also improved after the structural optimization; The k// spectrum distribution is sharper at the monopole phase (0, 0, 0, 0) and dipole phase (0, π, 0, π) and (0, 90, 270,180) than other phases. The optimized antenna can obtain a maximum |k//| spectrum, which peaks about |k//| = 30 m−1 at the dipole phase (0, π, 0, π). The analysis results and assembly strategy can provide useful reference and guidance for the study of HHFW antenna design and fabrication in LAPD or other magnetic confined fusion devices.