M. Stejner
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View article: Parametric Decay Instabilities during Electron Cyclotron Resonance Heating of Fusion Plasmas, Problems and Possibilities
Parametric Decay Instabilities during Electron Cyclotron Resonance Heating of Fusion Plasmas, Problems and Possibilities Open
We review parametric decay instabilities (PDIs) expected in connection with electron cyclotron resonance heating (ECRH) of magnetically confined fusion plasmas, with a specific focus on conditions relevant for the ITER tokamak. PDIs involv…
View article: Nonlinear decay of high-power microwaves into trapped modes in inhomogeneous plasma
Nonlinear decay of high-power microwaves into trapped modes in inhomogeneous plasma Open
We present novel experimental evidence of parametric decay instability of microwave beams in the plasma edge of the Wendelstein 7-X stellarator. We propose that the instability is sustained by trapping of only one daughter wave in the non-…
View article: Momentum-space-resolved measurements using oblique electron cyclotron emission for the validation of the quasi-linear theory of electron cyclotron current drive
Momentum-space-resolved measurements using oblique electron cyclotron emission for the validation of the quasi-linear theory of electron cyclotron current drive Open
Electron cyclotron resonance heating (ECRH) can drive large current densities through electron cyclotron current drive (ECCD). ECCD is expected to be crucial for high-performance plasmas in future fusion reactors like ITER and DEMO, making…
View article: Parametric decay instabilities near the second-harmonic upper hybrid resonance in fusion plasmas
Parametric decay instabilities near the second-harmonic upper hybrid resonance in fusion plasmas Open
Parametric decay instabilities (PDIs) lead to the generation of strong frequency-shifted radiation when powerful X-mode polarized microwaves, injected for electron cyclotron resonance heating (ECRH) of fusion plasmas, cross a region of non…
View article: Inference of <i>α</i>-particle density profiles from ITER collective Thomson scattering
Inference of <i>α</i>-particle density profiles from ITER collective Thomson scattering Open
The primary purpose of the collective Thomson scattering (CTS) diagnostic at\nITER is to measure the properties of fast-ion populations, in particular those\nof fusion-born $\\alpha$-particles. Based on the present design of the\ndiagnosti…
View article: Forward modeling of collective Thomson scattering for Wendelstein 7-X plasmas: Electrostatic approximation
Forward modeling of collective Thomson scattering for Wendelstein 7-X plasmas: Electrostatic approximation Open
In this paper, we present a method for numerical computation of collective Thomson scattering (CTS). We developed a forward model, eCTS, in the electrostatic approximation and benchmarked it against a full electromagnetic model. Difference…
View article: Modeling the electron cyclotron emission below the fundamental resonance in ITER
Modeling the electron cyclotron emission below the fundamental resonance in ITER Open
The electron cyclotron emission (ECE) in fusion devices is non-trivial to model in detail at frequencies well below the fundamental resonance where the plasma is optically thin. However, doing so is important for evaluating the background …
View article: Design and development of the ITER CTS diagnostic
Design and development of the ITER CTS diagnostic Open
The Collective Thomson Scattering (CTS) diagnostic will be a primary diagnostic for measuring the dynamics of the confined fusion born alpha particles in ITER and will be the only diagnostic for alphas below 1.7 MeV [1]. The probe beam of …
View article: Observation and Modelling of the Onset of Parametric Decay Instabilities during Gyrotron Operation at ASDEX Upgrade
Observation and Modelling of the Onset of Parametric Decay Instabilities during Gyrotron Operation at ASDEX Upgrade Open
We investigate parametric decay instabilities (PDIs) occurring for gyrotron radiation near the upper hybrid resonance at the ASDEX Upgrade tokamak. The PDIs are observed through anomalous millimeter-wave scattering which is recorded using …
View article: Collective Thomson scattering diagnostic at Wendelstein 7-X
Collective Thomson scattering diagnostic at Wendelstein 7-X Open
A Collective Thomson Scattering (CTS) diagnostic is installed at Wendelstein 7-X for ion temperature measurements in the plasma core. The diagnostic utilizes 140 GHz gyrotrons usually used for electron cyclotron resonance heating (ECRH) as…
View article: Observation and Modelling of the Onset of Parametric Decay Instabilities during Gyrotron Operation at ASDEX Upgrade
Observation and Modelling of the Onset of Parametric Decay Instabilities during Gyrotron Operation at ASDEX Upgrade Open
We investigate parametric decay instabilities (PDIs) occurring for gyrotron radiation near the upper hybrid resonance at the ASDEX Upgrade tokamak. The PDIs are observed through anomalous millimeter-wave scattering which is recorded using …
View article: Electron-cyclotron-resonance heating in Wendelstein 7-X: A versatile heating and current-drive method and a tool for in-depth physics studies
Electron-cyclotron-resonance heating in Wendelstein 7-X: A versatile heating and current-drive method and a tool for in-depth physics studies Open
For stellarators, which need no or only small amounts of current drive, electron-cyclotron-resonance heating (ECRH) is a promising heating method even for the envisaged application in a fusion power plant. Wendelstein 7-X (W7-X) is equippe…
View article: Alpha-particle velocity-space diagnostic in ITER
Alpha-particle velocity-space diagnostic in ITER Open
We discuss α-particle velocity-space diagnostic in ITER based on the planned collective Thomson scattering (CTS) and γ-ray spectrometry (GRS) systems as well as ASCOT simulations of the α-particle distribution function. GRS is sensitive to…
View article: Bayesian Integrated Data Analysis of Fast-Ion Measurements by Velocity-Space Tomography
Bayesian Integrated Data Analysis of Fast-Ion Measurements by Velocity-Space Tomography Open
Bayesian integrated data analysis combines measurements from different diagnostics to jointly measure plasma parameters of interest such as temperatures, densities, and drift velocities. Integrated data analysis of fast-ion measurements ha…
View article: Main-ion temperature and plasma rotation measurements based on scattering of electron cyclotron heating waves in ASDEX Upgrade
Main-ion temperature and plasma rotation measurements based on scattering of electron cyclotron heating waves in ASDEX Upgrade Open
We demonstrate measurements of spectra of O-mode electron cyclotron resonance heating (ECRH) waves scattered collectively from microscopic plasma fluctuations in ASDEX Upgrade discharges with an ITER-like ECRH scenario. The measured spectr…
View article: Observation of short time-scale spectral emissions at millimeter wavelengths with the new CTS diagnostic on the FTU tokamak
Observation of short time-scale spectral emissions at millimeter wavelengths with the new CTS diagnostic on the FTU tokamak Open
On the FTU tokamak, the collective Thomson scattering (CTS) diagnostic was renewed for investigating the possible excitation of parametric decay instabilities (PDI) by electron cyclotron (EC) or CTS probe beams in presence of magnetic isla…
View article: Numerical and experimental study of the redistribution of energetic and impurity ions by sawteeth in ASDEX Upgrade
Numerical and experimental study of the redistribution of energetic and impurity ions by sawteeth in ASDEX Upgrade Open
In the non-linear phase of a sawtooth, the complete reconnection of field lines around the q = 1 flux surface often occurs resulting in a radial displacement of the plasma core. A complete time-dependent electromagnetic model of this type …