27 research outputs found
Synthetic conventional reflectometry probing of edge and scrape-off layer plasma turbulence
No full textInternational audienceMicrowave reflectometry techniques have been successfully applied to measure electron density fluctuations in magnetic confined fusion devices with good spatial and time resolutions. However, quantitative interpretation of turbulence measurements has driven continuous development of both analytical theory and sophisticated numerical codes in support of reflectometry. Comparisons between experimental and synthetic reflectometry have been performed previously while only recently realistic gyro-fluid simulations have been employed together with a full-wave code to simulate measured turbulence properties with reflectometry. In this work, we report on recent e orts to employ the two-dimensional full-wave code REFMUL to implement a synthetic reflectometry diagnostic to model plasma turbulence measurements on the edge and scrape-o layer (SOL) peripheral regions of fusion devices. Numerical descriptions of microscopic turbulence were obtained from both an analytical model (following a Kolgomorov-like wavenumber spectrum) and from the GEMR turbulence code based on gyro-fluid theory. Simulations of fixed frequency conventional reflectometry with ordinary mode (O-mode) wave propagation were carried out for both turbulence cases separately. Preliminary comparisons between synthetic measurements, numerical plasma characteristics, and experimental data from ASDEX Upgrade tokamak are made. As previously described in literature, regimes of linear and non-linear response occurring at low and high turbulence levels, respectively, are observed and characterized. Synthetic spectra across moderate to high turbulence levels display qualitatively good agreement with experimental data across the edge region. K : Nuclear instruments and methods for hot plasma diagnostics; Simulation methods and programs 1Corresponding author
Validation of the edge density profiles from the ICRF antenna reflectometer on ASDEX Upgrade
No full textInternational audienceA : A new multichannel X-mode reflectometer diagnostic (RIC) was recently installed in ASDEX Upgrade (AUG) to provide the electron density profiles in front of an ion cyclotron range of frequencies antenna. The diagnostic was designed to measure density profiles up to 2 ⇥ 10 19 m 3 in the typical 1.5-2.7 T magnetic fields of AUG. Profiles can be measured every 25 µs simultaneously in 3 di erent poloidal positions. The main objective of this work is to assess the measurement capabilities of the RIC diagnostic for the scrape-o layer density profiles. RIC density profiles are compared to radial profiles from lithium beam emission spectroscopy and Thomson scattering over a wide variety of plasma conditions. Although a good agreement between the di erent diagnostics is generally found at low discharge densities, RIC measurements often show steeper profiles at high discharge densities, particularly at low outer wall clearance. In addition, the location of the start of X-mode upper cuto reflection is determined as well as the plasma density at the first cuto layer. K : Nuclear instruments and methods for hot plasma diagnostics; Data processing method
Density profiles and fluctuations in front of the ICRF antenna on the ASDEX Upgrade using X-mode reflectometry
No full textCharacterization of edge turbulence in different states of divertor detachment using reflectometry in the ASDEX Upgrade tokamak
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Blob distortion by radio-frequency induced sheared flow
No full textBlob transport properties in the plasma edge in the presence and absence of radio-frequency (RF) convective cells are compared. For the first time, the interactions between RF convective cells and intermittent plasma blobs in the scrape-off layer (SOL) are observed with gas puff imaging in the ASDEX Upgrade tokamak. It is found that the RF convective cells induce a sheared flow in the far SOL, which is able to stretch, distort and even split the blobs poloidally. The observed phenomena indicate that an externally generated sheared flow in the SOL can be considered as a method to modify blob transport in a favorable way
IST Contributions to the ASDEX Upgrade Edge and Divertor Physics Using Microwave Reflectometry
No full textInternational audienceInformation of the plasma density such as provided by reflectometry is essential for the study and operation of magnetically confined fusion devices. The microwave reflectometry systems developed by IST for ASDEX Upgrade consist of: (i) a multi-band frequency modulated continuous wave O-mode reflectometer with the unique capability of providing profile and fluctuations measurements on the high-field side and low-field side (LFS) simultaneously, making it a relevant diagnostic for poloidal asymmetry studies; (ii) a fast frequency hopping O-mode reflectometer used to obtain more detailed information on density fluctuations at the LFS; and (iii) a multichannel X-mode reflectometry diagnostic recently installed to measure the edge density profile in front of the ICRF antenna. This contribution presents an overview of the scientific results obtained with the different reflectometry systems used in a complementary way in order to address some of the key issues under investigation at ASDEX Upgrade. The experimental results obtained demonstrate that the IST reflectometry systems provide a valuable contribution to a better understanding of important physics topics such as connection between midplane and divertor conditions, dynamics of the density profiles, SOL turbulence, pedestal instabilities, RF sheath effects and real-time control
