Filaments or blobs are well known to strongly contribute to particle and energy losses both in L- and H-mode, making them an important plasma characteristic to investigate. They are plasma structures ...narrowly localized across a magnetic field and stretched along magnetic field lines. In toroidal devices, their development is observed to take place in the peripheral plasma. Filament characteristics have been studied extensively over the years using various diagnostic techniques. One such diagnostic is the Doppler backscattering (DBS) method employed at the spherical tokamak Globus-M/M2. It has been observed that the DBS signal reacts to the backscattering from filaments. However, the DBS data have proven difficult to analyze, which is why modelling was undertaken using the code IPF-FD3D to understand what kind of information can be extrapolated from the signals. A circular filament was thoroughly investigated in slab geometry with a variety of characteristics studied. Apart from that, the motion of the filaments in the poloidal and radial directions was analyzed. Additionally, other shapes of filaments were presented in this work. Modelling for the real geometry of the Globus-M/M2 tokamak was performed.
In the future COMPASS Upgrade (Vondracek et al. in Fusion Eng Des 169:112490,
https://doi.org/10.1016/j.fusengdes.2021.112490
, 2021) tokamak (
R
0
=
0.894
m
,
B
t
∼
5
T
), three distinct types of ...edge transport barrier are anticipated: ELMy H-mode, EDA H-mode and I-mode. The main auxiliary heating system used to access H-mode will be Neutral Beam Injection (NBI) power. The NBI will have a nominal injection energy of
80
keV
at a maximum injection radius
R
tan
=
0.6
m
. A significant neutron yield will occur from the interaction of the beam with the plasma background. Using our orbit-following code EBdyna (Jaulmes et al. in Nucl Fusion 61, 046012,
https://doi.org/10.1088/1741-4326/abd41b
, 2021), we calculate the trajectories of the NBI ions during the complete thermalization process, calculate the amount of NBI ions losses and evaluate the neutron rate in steady state from the beam–plasma and beam–beam interaction. Combining it with the thermal yield, we can derive detailed synthetic spectrogram of the energy distribution of the neutrons. The markers can be further used to provide synthetic neutron spectrometer diagnostics data. Due to the reduction of the simulated neutron count seen by the detectors when the peaking of the neutron source is lower, we anticipate the need for absolute-calibration in order to recover quantitative results.
La thèse porte sur l'interprétation des données de réflectométrie pour extraire les caractéristiques de la turbulence construites à partir de simulations numériques bidimensionnelles. Il a été ...démontré que la résonance due au piégeage de l'onde peut apparaître dans le plasma fluctuant et produire des sauts de phase. Cette interprétation à faible niveau de turbulence est directe. Cependant, le niveau de turbulence du bord du plasma est généralement élevé menant ainsi le réflectomètre à un comportement non linéaire. En conséquence, il y a une perte de cohérence de l'onde de sondage et un élargissement du faisceau-sonde après la traversée de la couche de turbulence. Cette étude a montré qu'une petite longueur de corrélation de la turbulence conduit à un faible élargissement et à de fortes variations de la phase du faisceau-sonde. Pour étudier comment une forte turbulence de bord affecte le signal de réflectométrie à balayage ultra rapide en fréquence (USFR) obtenu lors d'un sondage. Pour étudier cela des séries de simulations 2D ont été réalisées. Simultanément les spectres de variations de phase et de variations d'amplitude du réflectomètre ont été analysés. Il a été constaté que des pics spectraux correspondant à une diffusion accrue dans la région de turbulence de bord peuvent être observés dans les spectres de variations d'amplitude du signal. Un USFR utilisant une configuration de réflectométrie poloïdale a été proposé pour accéder à plus d'informations sur la turbulence de bord où le déplacement poloïdal des antennes réceptrices entraîne un glissement du pic de diffusion. En perspective, ces mesures peuvent fournir des informations supplémentaires sur, la déformation du faisceau-sonde, les propriétés de la turbulence et faciliter la mesure du signal cohérent porteur de l'information sur la turbulence de cœur du plasma. En plus, le code 2D "full-wave" a été appliqué en tant que diagnostic synthétique aux données de simulation gyro-cinétique du code de turbulence Gysela pour une décharge du tokamak de Tore-Supra. Les signaux de réflectométrie à fréquence fixe ont montré un bon accord entre la longueur de corrélation d'amplitude du signal avec celle de la turbulence utilisée comme donnée d'entrée. Il en a été de même pour analyser la longueur de corrélation et les spectres de nombre d'onde obtenus par un USFR pour le tokamak ASDEX-Upgarde
Plasma turbulence studies are essential for successful operation of magnetic confinement fusion devices. Ultra-Fast Swept Reflectometry (USFR), a diagnostic widely used for the measurement of turbulence radial wave-number spectra. While the interpretation of reflectometry data is quite straightforward for small levels of turbulence, it becomes much trickier for larger levels as the reflectometer answer is no longer linear with the turbulence level. It has been shown for instance that resonances due to probing field trapping can appear in turbulent plasma and produce jumps of the signal phase. In the plasma edge region the turbulence level is usually high and can lead to a non-linear regime of the reflecetometer response. The loss of probing beam coherency and beam widening when the probing beam crosses the edge turbulence layer can affect USFR core measurements. Edge turbulence with a long correlation length leads to small beam widening and strong distortion of the probing wave phase. However backscattering effects from turbulence with short correlation lengths are also able to cause reflectometer signal change. To study turbulence wave-number spectra together with reflectometer signal phase variations, signal amplitude variations can be analyzed. Unlike signal phase variation, amplitude does not suffer from resonant jumps, and can give more clear qualitative evaluation of turbulence structure. In the case when the turbulence amplitude peaked in the edge region, it can be detected as spectral peak near local Bragg resonance wave-number. USFR with a set of receiving antennas arranged poloidally was proposed to obtain more information on the edge turbulence properties. A displacement of the spectral peak appears when the receiving antenna is misaligned with the emitting one. In perspective peak displacement measurements can provide additional information on probing beam shaping and turbulence properties and help in coherent mode observation. A 2D full wave code was applied as a synthetic diagnostic to Gysela gyro-kinetic for study of Tore-Supra tokamak core turbulence. Radial correlation lengths computed from the amplitude of multi-channel fixed frequency reflectometry signals have shown good agreement with the turbulence correlation length. The synthetic diagnostic was then applied to analyze the correlation length and wave-number spectra obtained by USFR in the ASDEX-Upgrade tokamak. A comparison between 1D and 2D results have shown different behavior. However correlation lengths measured with UFSR signals are in the same order with turbulence ones
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