Measurement of the Damping Rate of High-n Toroidal Alfven Eigenmodes in JET

A new set of compact in-vessel antennas has been built and installed in JET to provide for the first time the direct measurement of the damping rate (/) of stable Alfvén Eigenmodes (AEs) with toroidal mode number (n) in the range n=3-15. This paper reports the first quantitative analysis of the measurements of the damping rate for these modes as function of the edge plasma elongation (95). We find that the scaling of / vs. 95 for medium-n Toroidal AEs, with n=3-7, follows the same trend previously measured and explained theoretically for the n=1 and n=2 modes. This confirms the possibility of using the edge shape parameters as a real-time actuator for control of the stability of alpha-particles driven AEs in burning plasma experiments, such as ITER

The Dependence of the Damping Rate of Medium-n Toroidal Alfvén Eigenmodes on the Edge Plasma Elongation in JET

This paper reports the first quantitative analysis of the measurements of the damping rate (gamma/omega) for stable Alfvén Eigenmodes (AEs) with toroidal mode number (n) in the range |n|=3-15 as function of the edge plasma elongation (kappa95). We find that the damping rate gamma/omega vs. kappa95 for medium-n Toroidal AEs, with n=3 and n=7, increases for increasing elongation, i.e. its scaling vs. kappa95 follows the same trend previously measured and explained theoretically for the n=1 and n=2 TAE modes. Theoretical analysis of the measurements for the n=3 TAEs has been performed using the LEMan code. The results are in good agreement (within a factor 2) for all the magnetic configurations where there is only a very minor up/down asymmetry in the poloidal cross-section of the plasma. These experimental results further confirm the possibility of using the edge shape parameters as a real-time actuator for control of the stability of alpha-particles driven AEs in burning plasma experiments, such as ITER

AN ALGORITHM FOR THE REAL-TIME, BLIND DETECTION, DECOMPOSITION AND TRACKING OF THE INDIVIDUAL COMPONENTS IN A DEGENERATE, MULTI-HARMONICS SPECTRUM

In this work we report the successful application of an innovative method, based on the Sparse Representation of signals, to perform a real-time, unsupervised detection of the individual components in a frequency degenerate, multi-harmonic spectrum, using a small number of data un-evenly sampled in the spatial domain. This method has been developed from its original applications in astronomy, and is now routinely used in the JET thermonuclear fusion experiment to obtain the decomposition of a spectrum of high-frequency (~10-500kHz range) magnetic instabilities with a sub-ms time resolution, allowing the real-time tracking of its individual components as the plasma background evolves. This work opens a path towards developing real-time control tools for electro-magnetic instabilities in future fusion devices aimed at achieving a net energy gain. More generally, the speed and accuracy of this algorithm is recommended for instances of physics measurements and control engineering where an unsupervised, real-time decomposition of a degenerate signal is required from a small number of data

Measurement and Theoretical Modeling of the Damping Rate of Medium-N Toroidal Alfven Eigenmodes in JET

This paper reports on the results of recent experiments performed on the JET tokamak on Alfven Eigenmodes (AEs) with toroidal mode number (n) in the range |n|=3-15. The stability properties of these medium-n AEs are investigated experimentally using a set of compact in-vessel antennas, providing a direct and real-time measurement of the frequency, damping rate and amplitude for each individual toroidal mode number. First, we describe the development of a new algorithm for real-time mode detection and discrimination using the Sparse Signal Representation theory. Second, we present measurements of the dependence of the damping rate for Toroidal AEs with |n|<=8 upon various background plasma parameters. Finally, the results of theoretical modeling of the damping rate for n=3 Toroidal AEs, performed with the LEMan, CASTOR and TAEFL codes, are shown as function of the edge plasma elongation

Recent JET Experiments on Alfven Eigenmodes with Intermediate Toroidal Mode Numbers: Measurements and Modelling

This paper reports the results of recent experiments performed on the JET tokamak on Alfven Eigenmodes (AEs) with toroidal mode number (n) in the range n=3-15. The stability properties and the use of these medium-n AEs for diagnostic purposes is investigated experimentally using a new set of compact in-vessel antennas, providing a direct and real-time measurement of the frequency, damping rate and amplitude for each individual toroidal mode number. First, we report on the development of a new algorithm for mode detection and discrimination using the Sparse Signal Representation theory. The speed and accuracy of this algorithm has made it possible to use it in our plant control software, allowing real-time tracking of individual modes during the evolution of the plasma background on a 1ms time scale. Second, we report the first quantitative analysis of the measurements of the damping rate for stable n=3 and n=7 Toroidal AEs as function of the plasma elongation. The damping rate for these modes increases for increasing elongation, as previously found in JET for n=0-2 AEs. A theoretical analysis of these JET data has been performed with the LEMan, CASTOR and TAEFL codes. The LEMan and TAEFL results are in good agreement with the measurements for all magnetic configurations where there is only a minor up/down asymmetry in the plasma poloidal cross-section. The CASTOR results indicate that continuum damping is not the only mechanism affecting the stability of these medium-n AEs. The diagnostic potential of these modes has being confirmed during the recent gas change-over experiment, where independent measurements of the effective plasma isotope ratio AEFF have been provided in addition to the more routinely employed spectroscopic and gas-balance ones. These data shows a slight difference in the measurement of AEFF when using n7 modes, suggesting a radial dependence in the effective plasma isotope ratio

Sparse representation of signals: from astrophysics to real-time data analysis for fusion plasmas and system optimization analysis for ITER and TCV

Efficient, real-time and automated data analysis is one of the key elements for achieving scientific success in complex engineering and physical systems, of which two examples are the JET and ITER tokamaks. One problem which is common to these fields is the determination of pulsation modes from irregularly sampled time-series. To this end, there is a wealth of signal processing techniques that are being applied to post-pulse and real-time data analysis in such complex systems. Here we wish to present a review of the applications of a method based on the Sparse Representation of Signals, using examples of the synergies that can be exploited when combining ideas and methods from very different fields, such as astronomy and astrophysics and thermonuclear fusion plasmas. Examples of this work in astronomy and astrophysics are the analysis of pulsation modes in various classes of stars and the orbit determination software of the Pioneer spacecrafts. Two examples of this work in thermonuclear fusion plasmas are the detection of magneto-hydrodynamic instabilities, which is now performed routinely in JET in real-time on a sub-millisecond time-scale, and the studies leading to the optimization of the magnetic diagnostic system in ITER and TCV. These questions have been solved formulating them as inverse problems, despite the fact that these applicative frameworks are extremely different from the classical use of Sparse Representations, on both the theoretical and computational points of view. Requirements, prospects and ideas for the signal processing and real-time data analysis applications of this method to routine operation of ITER will also be discussed. Finally, a very recent development has been an attempt at the application of this method to the deconvolution of the measurement of electric potential performed during a ground-based survey of a proto-Villanovian necropolis in central Italy

Control of star formation by supersonic turbulence

Understanding the formation of stars in galaxies is central to much of modern astrophysics. For several decades it has been thought that stellar birth is primarily controlled by the interplay between gravity and magnetostatic support, modulated by ambipolar diffusion. Recently, however, both observational and numerical work has begun to suggest that support by supersonic turbulence rather than magnetic fields controls star formation. In this review we outline a new theory of star formation relying on the control by turbulence. We demonstrate that although supersonic turbulence can provide global support, it nevertheless produces density enhancements that allow local collapse. Inefficient, isolated star formation is a hallmark of turbulent support, while efficient, clustered star formation occurs in its absence. The consequences of this theory are then explored for both local star formation and galactic scale star formation. (ABSTRACT ABBREVIATED)Comment: Invited review for "Reviews of Modern Physics", 87 pages including 28 figures, in pres

Regulatory (pan-)genome of an obligate intracellular pathogen in the PVC superphylum.

Like other obligate intracellular bacteria, the Chlamydiae feature a compact regulatory genome that remains uncharted owing to poor genetic tractability. Exploiting the reduced number of transcription factors (TFs) encoded in the chlamydial (pan-)genome as a model for TF control supporting the intracellular lifestyle, we determined the conserved landscape of TF specificities by ChIP-Seq (chromatin immunoprecipitation-sequencing) in the chlamydial pathogen Waddlia chondrophila. Among 10 conserved TFs, Euo emerged as a master TF targeting &gt;100 promoters through conserved residues in a DNA excisionase-like winged helix-turn-helix-like (wHTH) fold. Minimal target (Euo) boxes were found in conserved developmentally-regulated genes governing vertical genome transmission (cytokinesis and DNA replication) and genome plasticity (transposases). Our ChIP-Seq analysis with intracellular bacteria not only reveals that global TF regulation is maintained in the reduced regulatory genomes of Chlamydiae, but also predicts that master TFs interpret genomic information in the obligate intracellular α-proteobacteria, including the rickettsiae, from which modern day mitochondria evolved

ECCO Guidelines on Therapeutics in Ulcerative Colitis: Surgical Treatment

This is the second of a series of two articles reporting the European Crohn's and Colitis Organisation [ECCO] evidence-based consensus on the management of adult patients with ulcerative colitis [UC]. The first article is focused on medical management, and the present article addresses medical treatment of acute severe ulcerative colitis [ASUC] and surgical management of medically refractory UC patients, including preoperative optimisation, surgical strategies, and technical issues. The article provides advice for a variety of common clinical and surgical conditions. Together, the articles represent an update of the evidence-based recommendations of the ECCO for UC

ECCO Guidelines on Therapeutics in Ulcerative Colitis: Medical Treatment

hese recommendations summarise the current evidence on the medical management of adult patients with UC. Gaps were iden-tified during the analysis of the data, which should be addressed by further research. Where evidence is lacking or is very weak and evidence-based recommendations cannot be given, ECCO provides alternative tools, such as Topical Reviews28,95,153–158 or Position Papers.159–161 It is important that clinicians use these guidelines within the framework of local regulations, and seek to understand and address the individual needs and expectations of every patient. We recognise that constraints on health care resources are an im-portant factor in determining whether recommendations can be implemented for patients in many countries. The recommendations outlined here should be used to inform treatment decisions and form part of an overall multidisciplinary treatment plan for patients with UC, which may also encompass psychological, nutritional, and other non-pharmacological interventions