Reconstruction of Zeff Profiles at the TEXTOR Tokamak Through Bayesian Source Separation

Abstract

Abstract. We describe a work in progress on the reconstruction of radial profiles for the ion effective charge Z eff on the TEXTOR tokamak, using statistical data analysis techniques. We introduce our diagnostic for the measurement of bremsstrahlung emissivity signals. Z eff profiles can be determined by Abelinversion of line-integrated measurements of the bremsstrahlung emissivity (ǫ ff ) from the plasma and the plasma electron density (ne) and temperature (Te). However, at the plasma edge only estimated values are routinely used for ne and Te, which are moreover determined at different toroidal locations. These various uncertainties hinder the interpretation of a Z eff profile outside the central plasma. In order to circumvent this problem, we propose several scenarios meant to allow the extraction by (Bayesian) Blind Source Separation techniques of either (lineintegrated) Z eff waveshapes or absolutely calibrated signals from (line-integrated) emissivity signals, using also density and temperature signals, as required. The role of impurities and Z eff in a tokamak plasmaThe behavior of plasma impurities in a tokamak plasma is a critical issue [1]. On the one hand, these impurities increase the fuel dilution and, at reactor parameters, they can be responsible for a considerable power loss from the plasma core by bremsstrahlung. On the other hand, line radiation by low-Z impurities at the plasma edge can be advantageous for the reduction of the plasma-wall interaction. To study the behavior of impurities in the plasma, one needs a local measure for impurity concentration. A parameter of great interest is the so-called ion effective charge of the plasma, Z eff , which is averaged over all species. Once the plasma electron density (n e ) and temperature (T e ) are known, it is proportional to the bremsstrahlung emissivity (ǫ ff ) from the plasma [2], which originates mainly from the acceleration of electrons in the field of ions:and where n i and Z i are the density and charge of ion species i. A diagnostic for the determination of Z eff on TEXTORAt the tokamak TEXTOR (FZJ Jülich, Germany), we run a diagnostic for the determination of Z eff from measurements of bremsstrahlung emissivity in the visible (see also [2]). 21 fiber optic cables are directed along different lines of sight in a

Extracting Individual Contributions From Their Mixture: A Blind Source Separation Approach

“…Different algorithms have been developed, such as JADE [20] and FastICA [21]. Although many applications have been reported (see for example [2] for a list of them), there have been only very few applications to plasmas so far [22,23].…”

Notions of the ergodic hierarchy for curved statistical manifolds

“…The utility of information geometry is not only limited to thermodynamics and statistical mechanics. For instance, it has been applied in quantum mechanics leading a quantum generalization of the Fisher metric [12], and recently also in nuclear plasmas [13]. In particular, an application of information geometry to chaos can be performed by considering complexity on curved manifolds [14,15,16,17].…”