A recently introduced tool for the analysis of turbulence, wavelet bicoherence [van Milligen, Hidalgo, and Sanchez, Phys. Rev. Lett. 16, 395 (1995)], is investigated. It is capable of detecting phase coupling—nonlinear interactions of the lowest (quadratic) order—with time resolution. To demonstrate its potential, it is applied to numerical models of chaos and turbulence and to real measurements. It detected the coupling interaction between two coupled van der Pol oscillators. When applied to a model of drift wave turbulence relevant to plasma physics, it detected a highly localized coherent structure. Analyzing reflectometry measurements made in fusion plasmas, it detected temporal intermittency and a strong increase in nonlinear phase coupling coinciding with the L/H (low‐to‐high confinement mode) transition.

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Wavelet bicoherence: A new turbulence analysis tool

Experiments on dust-acoustic waves (DAW) in a magnetized anodic plasma are presented for the regime of low collisionality. The dust trapping and the self-excited and synchronized DAW dynamics are studied. Based on Langmuir and emissive probe measurements the dust confinement is found to be well described with respect to size, stability, and position of the dust cloud by an effective potential well formed by ion drag and Coulomb forces. Moreover, the measurements indicate the necessity for a kinetic model for the wave dispersion. By means of singular value decomposition the local wavelengths and growth rates of the waves are measured systematically. It is found that the measured mean wave number is well described by kinetic theory, while the theoretical growth rates overestimate the experiments. A novel observation for the DAW is a systematic variation of the wavelength inside the dust cloud.

Dust confinement and dust-acoustic waves in weakly magnetized anodic plasmas

This chapter reviews multichannel broadband measurement of the soft-X-ray radiation and total radiation in magnetically confined fusion plasma experiments Common detector types used (including bolometers), details of their application, and interpretation of their measurements are described An introduction is given to the application of computed tomography methods in the mathematical reconstruction of emission profiles from multiple (approximately) line-integral measurements, taking into account the specific circumstances common in magnetically confined fusion plasma experiments Although the emphasis is on two-dimensional tomography of poloidal cross sections, the applications of Abel inversion, three-dimensional tomography, vector tomography, and other specific methods are briefly discussed Several examples of the application and the plasma parameters that can be derived are given

Chapter 7: Tomography Diagnostics: Bolometry and Soft-X-Ray Detection

The solar EUV irradiance is a key input for thermospheric and ionospheric models. Difficulties in continuously measuring the calibrated spectrum has prompted the use of various surrogate quantities. Although most proxies correlate quite well with the spectral variability, their use for modelling purposes becomes increasingly unsatisfactory. A different and data-driven approach is considered here, in which the EUV spectrum is reconstructed from a linear combination of a few, calibrated and carefully selected spectral lines. This approach is based on a statistical analysis of the temporal variability of EUV spectra, as recorded by the TIMED satellite. A basic set of lines is extracted, from which the salient features of the spectral variability can be reconstructed. The best results are achieved with a selection of 5 to 8 of these lines. This study focuses on the methodology for selecting these lines, which can also be used for instrument specification and provides new insight into the comparison of solar proxies against the EUV irradiance.

/pdf/retrieving-the-solar-euv-spectrum-from-a-reduced-set-of-1hgt0sm22n.pdf

Retrieving the solar EUV spectrum from a reduced set of spectral lines

The propagation of transverse waves in a two-dimensional particle suspension in a plasma is studied in the solid and liquid phase. The different states of the suspension are realized by raising the kinetic temperature of the dust particles with a new laser method. An additional laser beam is used to excite shear waves and the wave is observed by videomicroscopy in terms of the individual velocities of the dust particles. For recovering the spatial wave patterns the method of singular value decomposition is applied and compared with the method of spatial Fourier analysis of complex wave numbers. In the solid phase, weakly damped waves are found which follow the expected dispersion relation. In the liquid phase the existence of strongly damped waves is demonstrated. The real part of the wave number is in overall agreement with the predictions of the Quasi Localized Charge Approximation model for a two-dimensional system. The damping of the waves is discussed.

http://dusty.physics.uiowa.edu/%7Egoree/papers/piel-laser-excited-shear-waves-POP-2006.pdf

Laser-excited shear waves in solid and liquid two-dimensional dusty plasmas

The biorthogonal decomposition (also referred to as the singular value decomposition) has recently emerged as a powerful tool for analysing and processing multichannel data. It is shown how this method can be used to enhance the signal-to-noise ratio of such data in a self-consistent way. Three applications to multichannel diagnostics that are routinely used on plasma devices, are presented: a soft X-ray camera, an XUV spectrometer and a microwave reflectometer. In each case, a physical interpretation of the enhancement is given. Furthermore, a robust criterion is presented, allowing data to be processed without making restrictive assumptions about their noise properties.

http://iopscience.iop.org/article/10.1088/0741-3335/37/2/005/pdf

T Dudok de Witt

Papers

Enhancement of multichannel data in plasma physics by biorthogonal decomposition