Observation of reversed shear Alfvén eigenmodes during sawteeth in Alcator C-Mod
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Phase contrast imaging measurements of reversed shear Alfven eigenmodes during sawteeth in Alcator C-Mod
Reversed shear Alfvén eigenmodes (RSAEs) have been observed with the phase contrast imaging diagnostic and Mirnov coils during the sawtooth cycle in Alcator C-mod 1 plasmas with minority ion cyclotron resonance heating. Both down-chirping RSAEs and up-chirping RSAEs have been observed during the sawtooth cycle. Experimental measurements of the spatial structure of the RSAEs are compared to theo...
متن کاملObservation of reversed shear Alfvén eigenmodes between sawtooth crashes in the Alcator C-Mod tokamak.
Groups of frequency chirping modes observed between sawtooth crashes in the Alcator C-Mod tokamak are interpreted as reversed shear Alfvén eigenmodes near the q=1 surface. These modes indicate that a reversed shear q profile is generated during the relaxation phase of the sawtooth cycle. Two important parameters, q_{min} and its radial position, are deduced from comparisons of measured density ...
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Alfvén cascades (ACs) or equivalently, reverse shear Alfvén eigenmodes (RSAE) have been observed in Alcator C-Mod during current ramp experiments in the presence of intense ICRF driven energetic minority tails. These experiments were carried out at ITER relevant densities and magnetic field. Phase contrast imaging (PCI) and magnetic pick-up coils have been used for detecting the Alfvén eigenmod...
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Experiments designed to characterize both stable and unstable Alfvén eigenmodes are a key part of the Alcator C-Mod physics program. Stable intermediate toroidal mode number (3 ≤ n ≤ 14) Alfvén eigenmodes, which are expected to be the most unstable in ITER, are excited with a set of active MHD antennas and their damping rates are measured as a function of plasma parameters. This is part of an i...
متن کاملPSFC / JA - 99 - 15 Plasma Rotation During Ohmic H - modes in Alcator C - Mod Tokamak
Core plasma rotation is observed to change from the counter-to co-current direction during the transition from low (L) to high (H) confinement mode, in Alcator C-Mod plasmas that are heated purely ohmically. The changes of the toroidal velocities deduced from impurity Doppler measurements and magnetic perturbations associated with "sawteeth" are quantitatively similar. The magnitude of the chan...
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