Abstract
We describe the multi-band template analysis (MBTA) search for gravitational waves signals from coalescences of compact objects in the LIGO–Virgo data, at the time of the third observing run ...(2019–2020), both for low-latency detections and for offline analysis. Details are given on the architecture and functioning of the pipeline, including transient noise mitigation strategies, parameter space for the searched signals, detection of candidates and evaluation of a false alarm rate associated to them. The performance of the low-latency search is demonstrated based on the LIGO–Virgo third observing run, during which MBTA has contributed to 42 alerts, submitting candidates with a median latency of 36 s. The performance of the offline search is illustrated on a subset of data collected during the second LIGO–Virgo observation run in 2017, and are quantified based on injections of simulated signal events on the same data.
•New simple accurate formulas for geometric quantities for tokamak plasmas are given.•The formulas are valid for both positive and negative triangularity.•They are typically useful for DEMO and ...system codes studies.•A formula for the trapped fraction is also given.
Formulas for the volume, poloidal and toroidal surfaces, poloidal length, plasma current, and hence average poloidal field, are determined using global parameters of tokamak plasmas. Previous formulas did not include systematically the effect of triangularity and in particular are inaccurate for negative triangularity cases. Since tokamaks with negative triangularity can be attractive for DEMO reactors 1,2, it is important to have updated formulas. It is also shown that the combined effect of finite triangularity and inverse aspect ratio was not correctly taken into account. Previous formulas were also using in some cases shaping parameters at the 95% poloidal flux surface. It is shown that this is misleading and the new formulas, including Ip and q95, use the effective parameters, κ, δ, Rgeom, ϵ of the relevant flux surface, in this case of the last closed flux surface. Only the value of the safety factor, q, is ill-defined at the plasma edge for divertor cases, thus q95 is still being used. A new global parameter, w07, related to the radial width of the plasma shape at 70% of the maximum height is introduced to take into account the squareness present in most plasma shapes, in particular single-null diverted ones. We also provide a simple formula for the trapped fraction which includes the effects of triangularity. The trapped fraction is required for evaluating the neoclassical conductivity and bootstrap current in particular.
The effects of plasma shaping, in particular triangularity (δ), on temperature fluctuations in the tokamak à configuration variable have been studied using the correlation electron cyclotron emission ...system. It has been found that, in ohmic discharges with comparable density profiles, the relative fluctuation level measured at the edge is significantly reduced in plasmas with negative triangularity with respect to positive triangularity ones. Additionally, the critical temperature gradients for the onset of turbulence are observed to increase in the negative triangularity plasmas. An estimation of the correlation length of the fluctuating structure shows smaller structure size in the negative triangularity cases, which are known to be associated with improved confinement. Together, these observations suggest that changing triangularity from positive to negative strongly influences the nature of the turbulent fluctuations excited in the plasma.
Magnetic-fusion plasmas are complex self-organized systems with an extremely wide range of spatial and temporal scales, from the electron-orbit scales (1011 s, 105 m) to the diusion time of ...electrical current through the plasma (102 s) and the distance along the magnetic eld between two solid surfaces in the region that determines the plasmawall interactions (100 m). The description of the individual phenomena and of the nonlinear coupling between them involves a hierarchy of models, which, when applied to realistic congurations, require the most advanced numerical techniques and algorithms and the use of state-of-the-art high-performance computers. The common thread of such models resides in the fact that the plasma components are at the same time sources of electromagnetic elds, via the charge and current densities that they generate, and subject to the action of electromagnetic elds. This leads to a wide variety of plasma modes of oscillations that resonate with the particle or fluid motion and makes the plasma dynamics much richer than that of conventional, neutral fluids.
The physics base for the ITER Physics Design Guidelines is reviewed in view of application to DEMO and areas are pointed out in which improvement is needed to arrive at a consistent set of DEMO ...Physics Design Guidelines. Amongst the proposed improvements, the area of power exhaust plays a crucial role since predictive capability of present-day models is low and this area is expected to play a major role in limiting DEMO designs due to the much larger value of Ptot/R in DEMO than in present-day devices and even ITER.
Abstract
The tokamak `a configuration variable (TCV) is a small-sized tokamak, where finite size effects (often called ‘rho-star’ or ‘global’ effects) could significantly impact the heat and particle ...fluxes, leading to discrepancies between gyrokinetic flux-tube results and global ones (McMillan
et al
2010
Phys. Rev. Lett.
105
155001). The impact of global effects on the radial profile of the plasma density has been investigated in a previous study for a particular TCV discharge with negligible particle source, satisfying the ‘zero particle flux’ (ZPF) condition. A radially local flux-tube analysis, reconstructing the dependence of the peaking of the density profile on the main physical parameters, invoking the ZPF constraint, was pursued close to mid-radius in (Mariani
et al
2018
Phys. Plasmas
25
012313). This analysis was followed by a global one (Mariani
et al
2019
Plasma Phys. Control. Fusion
61
064005), where local quasi-linear (QL) and nonlinear (NL) results were compared with global simulations, showing small global effects on the density peaking. However, these gradient-driven (GD) global runs considered Krook-type heat and particle sources to keep temperature and density profiles fixed on average, which differ from the experimental radially localized sources. To remove this possible bias on the results, a different evaluation of the density peaking for the same case is performed here, based on global NL hybrid simulations where the temperature profiles are still kept fixed with the Krook-type sources, however the density profile relaxes in a flux-driven way (with zero particle source). The new hybrid simulations show a good agreement with the old GD runs. A global QL model is also developed and applied using the output from linear global runs, to estimate ratios of fluxes, showing a good agreement with the flux-tube results of global NL GD simulations. The effect of collisions on the results is also investigated, in order to evaluate their impact on the radial variation of the density peaking.
Rapidly rotating neutron stars are promising sources of continuous gravitational wave radiation for the LIGO and Virgo interferometers. The majority of neutron stars in our galaxy have not been ...identified with electromagnetic observations. All-sky searches for isolated neutron stars offer the potential to detect gravitational waves from these unidentified sources. The parameter space of these blind all-sky searches, which also cover a large range of frequencies and frequency derivatives, presents a significant computational challenge. Different methods have been designed to perform these searches within acceptable computational limits. Here we describe the first benchmark in a project to compare the search methods currently available for the detection of unknown isolated neutron stars. The five methods compared here are individually referred to as the PowerFlux, sky Hough, frequency Hough, Einstein@Home, and time domain F-statistic methods. We employ a mock data challenge to compare the ability of each search method to recover signals simulated assuming a standard signal model. We find similar performance among the four quick-look search methods, while the more computationally intensive search method, Einstein@Home, achieves up to a factor of two higher sensitivity. We find that the absence of a second derivative frequency in the search parameter space does not degrade search sensitivity for signals with physically plausible second derivative frequencies. We also report on the parameter estimation accuracy of each search method, and the stability of the sensitivity in frequency and frequency derivative and in the presence of detector noise.
A first-principles scaling law, based on turbulent transport considerations, and a multimachine database of density limit discharges from the ASDEX Upgrade, JET, and TCV tokamaks, show that the ...increase of the boundary turbulent transport with the plasma collisionality sets the maximum density achievable in tokamaks. This scaling law shows a strong dependence on the heating power, therefore predicting for ITER a significantly larger safety margin than the Greenwald empirical scaling Greenwald et al., Nucl. Fusion, 28, 2199 (1988)NUFUAU0029-551510.1088/0029-5515/28/12/009 in case of unintentional high-to-low confinement transition.
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