Athina Kappatou

Athina Kappatou
Max Planck Institute for Plasma Physics | IPP

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30
Publications
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554
Citations

Publications

Publications (30)
Article
Capacitive plasma pickup is a well-known and difficult problem for plasma-facing edge diagnostics. This problem must be addressed to ensure an accurate and robust interpretation of the real signal measurements vs noise. The Faraday cup fast ion loss detector array of the Joint European Torus (JET) is particularly prone to this issue and can be used...
Poster
Full-text available
In future fusion devices helium will be generated in the core of a burning plasma as a product of the D-T reaction. In order to avoid fuel dilution and not degrade the confinement properties, the core helium concentration must be kept within tolerable values [1]. It will be therefore mandatory to efficiently remove helium ash from the plasma, which...
Poster
Full-text available
The removal of helium, which is the product of the D-T reaction, in magnetic fusion devices must be as efficient as possible in order to avoid fuel dilution and not degrade the confinement properties. Optimizing the strategies for a good helium pumping is possible by monitoring the behavior of the exhaust gas in helium-seeded plasma discharges in c...
Article
Full-text available
This paper summarizes the physical principles behind the novel three-ion scenarios using radio frequency waves in the ion cyclotron range of frequencies (ICRF). We discuss how to transform mode conversion electron heating into a new flexible ICRF technique for ion cyclotron heating and fast-ion generation in multi-ion species plasmas. The theoretic...
Article
The Charge Exchange Recombination Spectroscopy (CXRS) diagnostic has become a routine diagnostic on almost all major high temperature fusion experimental devices. For the optimized stellarator Wendelstein 7-X (W7-X), a highly flexible and extensive CXRS diagnostic has been built to provide high-resolution local measurements of several important pla...
Article
Full-text available
A new ion cyclotron resonance frequency (ICRF) modulation technique has been developed and exploited at ASDEX Upgrade for obtaining time perturbed boron density signals. Square wave modulation of the ICRF heating power results in a periodic modulation of the boron density in the edge, which propagates inward. From this time perturbed boron density...
Article
Full-text available
The analysis of the charge exchange measurements of helium is hindered by an additional emission contributing to the spectra, the helium 'plume' emission (Fonck et al 1984 Phys. Rev. A 29 3288), which complicates the interpretation of the measurements. The plume emission is indistinguishable from the active charge exchange signal when standard anal...
Article
The edge ion heat transport is analyzed in ASDEX Upgrade (AUG) by combining a comprehensive set of pedestal measurements with both interpretive and predictive modelling. The experimentally determined ion heat diffusivities, Xi, are compared with neoclassical theory and the impact of edge localized modes (ELMs) on the edge ion heat transport level i...
Article
A newly installed core charge exchange recombination spectroscopy (CXRS) diagnostic at ASDEX Upgrade (AUG) enables the evaluation of the core poloidal rotation (upol) through the inboard-outboard asymmetry of the toroidal rotation with an accuracy of 0.5 to 1 km s-1. Using this technique, the total plasma flow has been measured in Ohmic L-mode plas...
Article
Full-text available
The 2014–2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to...
Article
The ASDEX Upgrade (AUG) programme is directed towards physics input to critical elements of the ITER design and the preparation of ITER operation, as well as addressing physics issues for a future DEMO design. Since 2015, AUG is equipped with a new pair of 3-strap ICRF antennas, which were designed for a reduction of tungsten release during ICRF op...
Article
Full-text available
Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat and particle loads on the wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade (AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide parameter ran...
Article
Full-text available
The ASDEX Upgrade (AUG) programme is directed towards physics input to critical elements of the ITER design and the preparation of ITER operation, as well as addressing physics issues for a future DEMO design. Since 2015, AUG is equipped with a new pair of 3-strap ICRF antennas, which were designed for a reduction of tungsten release during ICRF op...
Article
Recent improvements to the heating and diagnostic systems on the ASDEX Upgrade tokamak allow renewed investigations into non-inductive operation scenarios with improved confinement in a full-metal device. Motivated by this, a scenario with βN ≈ 2.7, q95 ≈ 5.3 and a high non-inductive current fraction fNI ≳ 90% has been developed. The scenario offer...
Article
A new core charge exchange recombination spectroscopy diagnostic has been installed in the ASDEX Upgrade tokamak that is capable of measuring the impurity ion temperature, toroidal rotation, and density on both the low field side (LFS) and high field side (HFS) of the plasma. The new system features 48 lines-of-sight (LOS) with a radial resolution...
Article
In tokamak plasmas with different main ion species, a change in confinement occurs, known as the isotope effect. Experiments comparing hydrogen (H), deuterium (D), and helium (⁴He) plasmas have been performed to identify processes that define the pedestal structure and evolution in between the crashes of edge localized modes(ELMs). The pedestal top...
Article
In magnetically confined fusion plasmas controlled gas injection is crucial for plasma fuelling as well as for various diagnostic applications such as active spectroscopy. We present a new, versatile system for the injection of collimated thermal gas beams into a vacuum chamber. This system consists of a gas pressure chamber, sealed by a custom mad...
Article
ELM mitigation by magnetic perturbations is studied at low pedestal collisionalities down to ITER-like values (V∗ e PED = 0.1) in ASDEX Upgrade. A comprehensive database of ELM energy losses for varying plasma density, heating power, edge safety factor and magnetic perturbation structure has been assembled to investigate parameter dependencies of E...
Article
The impact of lithium (Li) on plasma performance was investigated at the ASDEX Upgrade tokamak, which features a full tungsten wall. Li pellets containing 1.6 × 10²⁰ Li atoms were launched with a speed of 600 m s⁻¹ to achieve deep penetration into the plasma and minimize the impact on the first wall. Homogeneous transient Li concentrations in the p...
Article
Heating with ICRF waves is a well-established method on present-day tokamaks and one of the heating systems foreseen for ITER. However, further work is still needed to test and optimize its performance in fusion devices with metallic high-Z plasma facing components (PFCs) in preparation of ITER and DEMO operation. This is of particular importance f...
Article
Full-text available
The medium size divertor tokamak ASDEX Upgrade (major and minor radii 1.65 m and 0.5 m, respectively, magnetic-field strength 2.5 T) possesses flexible shaping and versatile heating and current drive systems. Recently the technical capabilities were extended by increasing the electron cyclotron resonance heating (ECRH) power, by installing 2 × 8 in...
Article
A feasibility study for the use of core charge exchange recombination spectroscopy on ITER has shown that accurate measurements on the helium ash require a spectrometer with a high etendue of 1mm(2)sr to comply with the measurement requirements [S. Tugarinov et al., Rev. Sci. Instrum. 74, 2075 (2003)]. To this purpose such an instrument has been de...
Article
Investigation of impurity transport properties in tokamak plasmas is essential and a diagnostic that can provide information on the impurity content is required. Combining charge exchange recombination spectroscopy (CXRS) and beam emission spectroscopy (BES), absolute radial profiles of impurity densities can be obtained from the CXRS and BES inten...
Article
Full-text available
The use of active charge exchange recombination spectroscopy (CXRS) as a diagnostic for fusion-produced alpha particles on ITER is constrained by the signal-to-noise ratio, which is determined by the intensity of the line of interest, the optical throughput of the diagnostic, the neutral beam penetration, and the intensity of bremsstrahlung radiati...
Article
The 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....
Article
Full-text available
Abstract Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy...

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