88 research outputs found
Non-ideal Ballooning Mode Instability with Real Electron Inertia
Impacts of electron inertia with an electron skin depth (ESD) longer than the realistic value used in early numerical studies on non-ideal ballooning modes (NIBMs) are numerically investigated by a linearized 3-field reduced MHD model. In this paper, 4 different ESDs,are used for an resistivity dependence study of the growth rate of NIBMs, where de s the real ESD and d*e = 10 corresponds to an order of ESD used in a numerical study on collisionless ballooning mode (CBM) reported in [Kleva and Guzdar Phys. Plasmas 6, 116 (1999)]. In the case with the real ESD d*e = de, a transition from resistive ballooning mode (RBM) to CBM occurs in the edge relevant resistivity regime, while the electron inertia effect is overestimated and the growth rate is almost independent of resistivity in the cases with d∗e =√10de and 10de. These results indicate that the real ESD is one of key factors for the edge stability and turbulence analysis
Priority concerns for people with intellectual and developmental disabilities during the COVID-19 pandemic
BACKGROUND: The approach taken to support individuals during the coronavirus disease 2019 (COVID-19) pandemic needs to take into account the requirements of people with intellectual disabilities and/or autism, who represent a major vulnerable group, with higher rates of co-occurring health conditions and a greater risk of dying prematurely. To date, little evidence on COVID-related concerns have been produced and no report has provided structured feedback from the point of view of people with intellectual disabilities and/or autism or of their family/carers. AIMS: To provide systemised evidence-based information of the priority concerns for people with intellectual disabilities and/or autism regarding the COVID-19 pandemic. METHOD: Senior representatives of major UK-based professional and service-user representative organisations with a stake in the care of people with intellectual disabilities and/or autism were contacted to provide a list of concerns across three domains: 'mental health and challenging behaviour', 'physical health and epilepsy' and 'social circumstances and support'. The feedback was developed into statements on frequently reported priorities. These statements were then rated independently by expert clinicians. A video-conference meeting to reconcile outliers and to generate a consensus statement list was held. RESULTS: Thirty-two organisations were contacted, of which 26 (81%) replied. From the respondent's data, 30 draft consensus statements were generated. Following expert clinician review, there was initially strong consensus for seven statements (23%), increasing to 27 statements (90%) following video conferencing. CONCLUSIONS: These recommendations highlight the expectations of people with intellectual disabilities and/or autism in the current pandemic. This could support policymakers and professionals' deliver and evidence person-centred care
Interplay between fluctuation driven toroidal axisymmetric flows and resistive ballooning mode turbulence
An interplay between fluctuation driven toroidal axisymmetric flows (convective cell modes) and resistive ballooning mode turbulence after the pedestal collapse is numerically studied by a four-field reduced MHD model in BOUT++ framework. The strong flow shear suppresses the radial transport of pressure filaments and the pressure profile in the pedestal region is partially recovered. As a result, a secondary instability is quasi-linearly excited, which yields a secondary collapse. The subsequent damped oscillation is also analysed by phase diagram analysis
Shaping Effects on Non-ideal Ballooning Mode
The dependence of shaping effects on the growth rate of collisionless and resistive ballooning mode (CBM/RBM) is numerically investigated. That of the drift ballooning modes (DCBM/DRBM) is also investigated by taking kinetic effects into account. Resistivity scans of linear growth rates of CBM/RBM and DCBM/DRBM in a circular geometry show that both modes have 3 branches in accordance with decreasing resistivity, fast, re- sistive and collisionless branch. The last two branches are in the edge relevant resistivity regime and are in the scope of this paper. For CBM/RBM, shaping effect on the growth rate becomes weak with increasing resistivity and the growth rate monotonically increases with decrease of the elongation and increase of the triangularity, on the other hand, the opposite tendency appears on the triangularity for DCBM, namely it weakly decreases with increase of the triangularity. This fact indicates that the inverted D-shaped equilibrium can be unstable against DCBM compared with the D-shaped equilibrium
Influence of plasma turbulence on microwave propagation
It is not fully understood how electromagnetic waves propagate through plasma
density fluctuations when the size of the fluctuations is comparable with the
wavelength of the incident radiation. In this paper, the perturbing effect of a
turbulent plasma density layer on a traversing microwave beam is simulated with
full-wave simulations. The deterioration of the microwave beam is calculated as
a function of the characteristic turbulence structure size, the turbulence
amplitude, the depth of the interaction zone and the size of the waist of the
incident beam. The maximum scattering is observed for a structure size on the
order of half the vacuum wavelength. The scattering and beam broadening was
found to increase linearly with the depth of the turbulence layer and
quadratically with the fluctuation strength. Consequences for experiments and
3D effects are considered.Comment: 16 pages, 13 figures. This is an author-created, un-copyedited
version of an article submitted for publication in Plasma Physics and
Controlled Fusion. IoP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
Aerodynamic investigations of ventilated brake discs.
The heat dissipation and performance of a ventilated brake disc strongly depends
on the aerodynamic characteristics of the flow through the rotor passages. The
aim of this investigation was to provide an improved understanding of ventilated
brake rotor flow phenomena, with a view to improving heat dissipation, as well
as providing a measurement data set for validation of computational fluid
dynamics methods. The flow fields at the exit of four different brake rotor
geometries, rotated in free air, were measured using a five-hole pressure probe
and a hot-wire anemometry system. The principal measurements were taken using
two-component hot-wire techniques and were used to determine mean and unsteady
flow characteristics at the exit of the brake rotors. Using phase-locked data
processing, it was possible to reveal the spatial and temporal flow variation
within individual rotor passages. The effects of disc geometry and rotational
speed on the mean flow, passage turbulence intensity, and mass flow were
determined. The rotor exit jet and wake flow were clearly observed as
characterized by the passage geometry as well as definite regions of high and
low turbulence. The aerodynamic flow characteristics were found to be reasonably
independent of rotational speed but highly dependent upon rotor geometry
Hermes : global plasma edge fluid turbulence simulations
The transport of heat and particles in the relatively collisional edge regions of magnetically confined plasmas is a scientifically challenging and technologically important problem. Understanding and predicting this transport requires the self-consistent evolution of plasma fluctuations, global profiles and flows, but the numerical tools capable of doing this in realistic (diverted) geometry are only now being developed. Here a 5-field reduced 2-fluid plasma model for the study of instabilities and turbulence in magnetised plasmas is presented, built on the BOUT++ framework. This cold ion model allows the evolution of global profiles, electric fields and flows on transport timescales, with flux-driven cross-field transport determined self-consistently by electromagnetic turbulence. Developments in the model formulation and numerical implementation are described, and simulations are performed in poloidally limited and diverted tokamak configurations
Ion temperature measurements of L-mode filaments in MAST by retarding field energy analyser
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