Small-scale structures with high poloidal mode numbers (m=10-20) have been observed in the TEXTOR tokamak plasma with pulsed radar reflectometry and an electron cyclotron emission diagnostic, in conjunction with large 2/1 and 1/1 islands. The small islands have a peaked density profile, similar to that of the simultaneously observed large-scale 2/1 islands. This together with the observation that high-frequency density and temperature fluctuations are very pronounced near the X points of the large islands hints to a strongly perturbed magnetic topology around the X points.
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http://dx.doi.org/10.1103/PhysRevLett.94.085001 | DOI Listing |
Rev Sci Instrum
January 2025
Plasma Prediction and Simulation Department, Tokamak Energy Ltd., 173 Brook Drive, Milton Park, Abingdon OX14 4SD, United Kingdom.
Diagnostic tools for understanding the edge plasma behavior in fusion devices are essential. The main focus of the present work is to present the infra-red (IR) diagnostics installed on Tokamak Energy's spherical tokamak (ST40) and the IR thermographic inversion tool, Functional Analysis of Heat Flux (FAHF). FAHF is designed for multi-2D thermographic inversions within the divertor tiles using the finite difference method and an explicit time stepping scheme.
View Article and Find Full Text PDFChaos
December 2024
Department of Atomic Physics, Eötvös Loránd University, 1117 Pázmány Péter sétány 1A, Budapest, Hungary.
We investigate how the magnetic structures of the plasma change in a large aspect ratio tokamak perturbed by an ergodic magnetic limiter, when a system parameter is non-adiabatically varied in time. We model such a scenario by considering the Ullmann-Caldas nontwist map, where we introduce an explicit time-dependence to the ratio of the limiter and plasma currents. We apply the tools developed recently in the field of chaotic Hamiltonian systems subjected to parameter drift.
View Article and Find Full Text PDFRev Sci Instrum
December 2024
Institute for Plasma Research, Bhat, Gandhinagar 382 428, India.
Poloidal asymmetries in neutral and impurity ion temperatures and particle and impurity transports have been observed in many tokamaks. To investigate these asymmetries, space-resolved visible spectroscopic diagnostic of the ADTIYA-U tokamak has been upgraded to measure the spatial profile of Hα and impurities spectral line profile, ion temperature, and plasma rotation from both low and high field sides of the plasma, simultaneously with a better spatial resolution. This has been done by developing a linear array of 15 optical fibers as compared to the present linear array of nine fibers having a core diameter of 400 μm and coupling it to the entrance slit of a 1 m long high-resolution spectrometer of the existing diagnostic.
View Article and Find Full Text PDFRev Sci Instrum
December 2024
Ecole Polytechnique Federale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland.
Massive material injections in the JET tokamak have been observed to substantially affect resistive bolometer measurements, resulting in a spurious radiated power signal proportional to the quantity injected and reaching up to 8 MW. These bolometers are calibrated and designed to operate in near vacuum but certain scenarios requiring large gas injections can push the neutral pressure past nominal values. This study demonstrates that the bolometry measurement can be affected at neutral pressures above 0.
View Article and Find Full Text PDFRev Sci Instrum
December 2024
UKAEA, Culham Centre for Fusion Energy, Culham OX14 3EB, United Kingdom.
Understanding the confinement of fast ions is crucial for plasma heating and non-inductive current drive, i.e., for the operation of a fusion reactor.
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