248 research outputs found
Conceptual design study for heat exhaust management in the ARC fusion pilot plant
The ARC pilot plant conceptual design study has been extended beyond its
initial scope [B. N. Sorbom et al., FED 100 (2015) 378] to explore options for
managing ~525 MW of fusion power generated in a compact, high field (B_0 = 9.2
T) tokamak that is approximately the size of JET (R_0 = 3.3 m). Taking
advantage of ARC's novel design - demountable high temperature superconductor
toroidal field (TF) magnets, poloidal magnetic field coils located inside the
TF, and vacuum vessel (VV) immersed in molten salt FLiBe blanket - this
follow-on study has identified innovative and potentially robust power exhaust
management solutions.Comment: Accepted by Fusion Engineering and Desig
Implications of Vertical Stability Control on the SPARC Tokamak
To achieve its performance goals, SPARC plans to operate in equilibrium
configurations with a strong elongation of ,
destabilizing the vertical instability. However, SPARC also features a
relatively thick conducting wall that is designed to withstand disruption
forces, leading to lower vertical instability growth rates than usually
encountered. In this work, we use the TokSyS framework to survey families of
accessible shapes near the SPARC baseline configuration, finding maximum growth
rates in the range of s. The addition of steel
vertical stability plates has only a modest () effect on reducing the
vertical growth rate and almost no effect on the plasma controllability when
the full vertical stability system is taken into account, providing flexibility
in the plate conductivity in the SPARC design. Analysis of the maximum
controllable displacement on SPARC is used to inform the power supply voltage
and current limit requirements needed to control an initial vertical
displacement of of the minor radius. From the expected spectra of plasma
disturbances and diagnostic noise, requirements for filter latency and vertical
stability coil heating tolerances are also obtained. Small modifications to the
outboard limiter location are suggested to allow for an unmitigated vertical
disturbance as large as of the minor radius without allowing the plasma
to become limited. Further, investigations with the 3D COMSOL code reveal that
strategic inclusion of insulating structures within the VSC supports are needed
to maintain sufficient magnetic response. The workflows presented here help to
establish a model for the integrated predictive design for future devices by
coupling engineering decisions with physics needs
Explaining Cold-Pulse Dynamics in Tokamak Plasmas Using Local Turbulent Transport Models
A long-standing enigma in plasma transport has been resolved by modeling of cold-pulse experiments conducted on the Alcator C-Mod tokamak. Controlled edge cooling of fusion plasmas triggers core electron heating on time scales faster than an energy confinement time, which has long been interpreted as strong evidence of nonlocal transport. This Letter shows that the steady-state profiles, the cold-pulse rise time, and disappearance at higher density as measured in these experiments are successfully captured by a recent local quasilinear turbulent transport model, demonstrating that the existence of nonlocal transport phenomena is not necessary for explaining the behavior and time scales of cold-pulse experiments in tokamak plasmas.United States. Department of Energy (Award DE-FC02-99ER54512)United States. Department of Energy (Grant DESC0014264
Effect of plasma elongation on current dynamics during tokamak disruptions
Plasma terminating disruptions in tokamaks may result in relativistic runaway
electron beams with potentially serious consequences for future devices with
large plasma currents. In this paper we investigate the effect of plasma
elongation on the coupled dynamics of runaway generation and resistive
diffusion of the electric field. We find that elongated plasmas are less likely
to produce large runaway currents, partly due to the lower induced electric
fields associated with larger plasmas, and partly due to direct shaping
effects, which mainly lead to a reduction in the runaway avalanche gain.Comment: 11 pages, 3 figure
Effect of plasma elongation on current dynamics during tokamak disruptions
Plasma terminating disruptions in tokamaks may result in relativistic runaway electron beams with potentially serious consequences for future devices with large plasma currents. In this paper, we investigate the effect of plasma elongation on the coupled dynamics of runaway generation and resistive diffusion of the electric field. We find that elongated plasmas are less likely to produce large runaway currents, partly due to the lower induced electric fields associated with larger plasmas, and partly due to direct shaping effects, which mainly lead to a reduction in the runaway avalanche gain. \ua9 Cambridge University Press 2020
Increased levels of ligands of Toll-like receptors 2 and 4 in type 1 diabetes
Type 1 diabetes is a proinflammatory state characterised by increased levels of circulating biomarkers of inflammation and monocyte activity. We have shown increased Toll-like receptor 2 (TLR2) and TLR4 expression and signalling in monocytes from type 1 diabetic patients. Several endogenous ligands of TLR2 and TLR4 have been identified; however, there is a paucity of data on levels of these endogenous ligands in diabetes. Thus, the aim of this study was to examine circulating levels of exogenous/endogenous ligands of TLR2 and TLR4 in type 1 diabetic patients and to compare these with the levels in matched healthy controls.
Healthy controls (n = 37) and type 1 diabetic patients (n = 34) were recruited, and a fasting blood sample was obtained. Circulating levels of endotoxin, heat-shock protein 60 (Hsp60), high-mobility group box 1 (HMGB1) and growth arrest-specific 6 (GAS6) proteins were assessed by ELISA, and TLR2 and TLR4 expression was determined by flow cytometry.
Levels of the classical TLR4 ligand, endotoxin, were significantly elevated in type 1 diabetic patients compared with those in matched controls. Hsp60 and HMGB1 concentrations were also significantly increased in the patients (p < 0.01 and p < 0.001, respectively). No significant differences were observed in GAS6.
We report the novel observation that levels of ligands of TLR2 and TLR4 are significantly elevated in type 1 diabetes, and this, in concert with hyperglycaemia, accounts for the increase in TLR2 and TLR4 activity, underscoring the proinflammatory state of type 1 diabetes
MHD stability and disruptions in the SPARC tokamak
SPARC is being designed to operate with a normalized beta of beta(N) = 1.0, a normalized density of n(G) = 0.37 and a safety factor of q(95) approximate to 3.4, providing a comfortable margin to their respective disruption limits. Further, a low beta poloidal beta(p) = 0.19 at the safety factor q = 2 surface reduces the drive for neoclassical tearing modes, which together with a frozen-in classically stable current profile might allow access to a robustly tearing-free operating space. Although the inherent stability is expected to reduce the frequency of disruptions, the disruption loading is comparable to and in some cases higher than that of ITER. The machine is being designed to withstand the predicted unmitigated axisymmetric halo current forces up to 50 MN and similarly large loads from eddy currents forced to flow poloidally in the vacuum vessel. Runaway electron (RE) simulations using GO+CODE show high flattop-to-RE current conversions in the absence of seed losses, although NIMROD modelling predicts losses of similar to 80 %; self-consistent modelling is ongoing. A passive RE mitigation coil designed to drive stochastic RE losses is being considered and COMSOL modelling predicts peak normalized fields at the plasma of order 10(-2) that rises linearly with a change in the plasma current. Massive material injection is planned to reduce the disruption loading. A data-driven approach to predict an oncoming disruption and trigger mitigation is discussed
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