Plasma spectroscopy

A brief introduction into the spectroscopy of fusion plasmas is presented. Basic principles of the emission of ionic, atomic and molecular radiation is explained and a survey of the effects, which lead to the population of the respective excited levels, is given. Line radiation, continuum radiation, opacity and line broadening mechanisms are addressed. The instrumentation used on present day devices is shortly reviewed, with special attention to the active spectroscopic techniques of laser induced fluorescence and Thomson scattering

Investigation of neutral beam arc chamber failure during helium operations at DIII-D

The Neutral Beam system on the DIII-D tokamak consists of eight ion sources using the Common Long Pulse Source (CLPS) design. During helium operation, desired for research regarding the ITER pre-nuclear phase, it has been observed that the ion source arc chamber performance steadily deteriorates, eventually failing due to electrical breakdown across the insulation. This poster presents the details and preliminary results of an experimental effort to replicate the problem in a bench top ion source with similar plasma parameters. The initial aim of the experiment is to test the hypothesis that during helium operation there is increased tungsten evaporation and sputtering due to ion bombardment of the hot cathodes, leading to the deposition of filament material on the insulation and subsequent short circuits. Ultimately the aim of the experiment is to find methods to ameliorate the problems associated with helium operation at DIII-D

Feasibility of charge exchange spectroscopy fast helium measurements on ITER

\u3cp\u3eThe feasibility to measure fast alpha particles using Active Charge Exchange Recombination Spectroscopy (CXRS) on ITER is investigated. Through modelling of the charge exchange spectral line for fast ions together with the expected background emission, the signal-to-noise ratio has been calculated as a function of the diagnostic design parameters. Combining the CXRS data from both the heating and the diagnostic neutral beams on ITER, information on the fast ion energy spectrum up to 1 MeV can be obtained for the parameters of the ITER core CXRS diagnostic design, provided that the signal is binned in 100 keV bins and a time resolution of Isec is used.\u3c/p\u3

Initial operation of a newly developed multichord motional Stark effect diagnostic in KSTAR

A photo-elastic modulator based 25-chord motional Stark effect (MSE) diagnostic has been successfully developed and commissioned in Korea Superconducting Tokamak Advanced Research. The diagnostic measures the radial magnetic pitch angle profile of the Stark splitting of a D-alpha line at 656.1 nm by the electric field associated with the neutral deuterium heating beam. A tangential view of the neutral beam provides a good spatial resolution of 1-3 cm for covering the major radius from 1.74 m to 2.28 m, and the time resolution is achieved at 10 ms. An in-vessel calibration before the vacuum closing as well as an in situ calibration during the tokamak operation was performed by means of specially designed polarized lighting sources. In this work, we present the final design of the installed MSE diagnostic and the first results of the commissioning. Published by AIP Publishing

A model-based approach for filtering magnetic pitch angles obtained by the Motional Stark Effect diagnostic

Not available

Evolution of the central safety factor during stabilized sawtooth instabilities at KSTAR

\u3cp\u3eA motional Stark effect (MSE) diagnostic has recently been installed in the KSTAR tokamak. A difficulty faced at KSTAR and common to other MSE diagnostics is calibration of the system for absolute measurements. In this report we present our novel calibration routine and discuss first results, evaluating the evolution of the the central safety factor during sawtooth instabilities. The calibration scheme ensures that the bandpass filters typically used in MSE systems are aligned correctly and identifies and removes systematic offsets present in the measurement. This is verified by comparing the reconstructed safety factor profile against various discharges where the locations of rational q surfaces have been obtained from MHD markers. The calibration is applied to analyse the evolution of q \u3csub\u3e0\u3c/sub\u3e in a shot where the sawteeth are stabilized by neutral beam injection. Within the analysed sawtooth periods q \u3csub\u3e0\u3c/sub\u3e drops below unity during the quiescent phase and relaxes close to or slightly above unity at the sawtooth crash. This finding is in line with the classical Kadomtsev model of full magnetic reconnection and earlier findings at JET.\u3c/p\u3

Observation of the bulk ion density peaking in a discharge with an impurity hole in the LHD

\u3cp\u3eRadial profiles of bulk ion and impurity ions density are simultaneously measured and quantified using charge exchange spectroscopy and peaking parameter, C\u3csub\u3ev\u3c/sub\u3e. The peaking parameter is positive for inward and negative for outward convection in a plasma with an impurity hole in the Large Helical Device. Following the formation of an impurity hole associated with the transition from L-mode to ion ITB plasma, the bulk ion becomes peaked by the inward convection (C\u3csub\u3ev\u3c/sub\u3e>0), while impurities (helium and carbon) become hollow due to the outward convection (C\u3csub\u3ev\u3c/sub\u3e<0). In contrast to the ion ITB plasma, in the L-mode plasma the impurity profiles are peaked (C\u3csub\u3ev\u3c/sub\u3e>0), where the bulk ion density profile remains flat (C\u3csub\u3ev\u3c/sub\u3e∼0). Understanding of the impurity behavior in the ion ITB plasma could lead to a self cleaning plasma reactor concept, with an efficient impurity exhaust.\u3c/p\u3

Implementation of neoclassical effects in momentum transport analysis at LHD

Plasma rotation plays an important role in the suppression of turbulence, leading to an increase in energy and particle confinement. Significant rotation also leads to a stabilisation of the resistive wall mode. The external momentum input from Neutral Beam Injection (NBI) in current generation fusion plasmas may not be available for future self-heated fusion reactors. Therefore it is important to analyse the phenomenon of spontaneous rotation. At NIFS plasma rotation and momentum transport of the Large Helical Device (LHD) plasma is analysed using a code suite called TASK3D-a. In this work neoclassical effects, which can be especially significant in non-axisymmetric plasmas, were implemented in TASK3D-a. Initial analysis of neoclassical radial momentum flux profiles shows that in NBI-driven momentum input neoclassical effects, especially neoclassical damping, become dominant in the non-center plasma region. It was also found that during and after pellet-injection the neoclassical damping force becomes strong. With the implementation of neoclassical effects new features can be examined in the momentum flux-gradient relations; in the damping-dominated situation following pellet injection a large excursion in momentum flux is found. This work can aid in the search for neoclassical transport-optimised configurations for enhanced (spontaneous) plasma rotation

New linear plasma devices in the trilateral euregio cluster for an integrated approach to plasma surface interactions in fusion reactors

New linear plasma devices are currently being constructed or planned in the Trilateral Euregio Cluster (TEC) to meet the challenges with respect to plasma surface interactions in DEMO and ITER: i) MAGNUMPSI (FOM), a high particle and power flux device with super-conducting magnetic field coils which will reach ITER-like divertor conditions at high magnetic field, ii) the newly proposed linear plasma device JULE-PSI (FZJ), which will allow to expose toxic and neutron activated target samples to ITER-like fluences and ion energies including in vacuo analysis of neutron activated samples, and iii) the plasmatron VISION I, a compact plasma device which will be operated inside the tritium lab at SCK-CEN Mol, capable to investigate tritium plasmas and moderately activated wall materials. This contribution shows the capabilities of the new devices and their forerunner experiments (Pilot-PSI at FOM and PSI-2 Ju¨lich at FZJ) in view of the main objectives of the new TEC program on plasma surface interactions