Abstract
The coupling between the transport and magnetic topology is an important issue because the structure of magnetic islands, embedded in a toroidal equilibrium field, depends on the nature of the transport at the edge of the islands. Measurements of modulated heat pulse propagation in the DIII-D tokamak have revealed the existence of self-regulated oscillations in the radial energy transport into magnetic islands that are indicative of bifurcations in the island structure and transport near the q = 2 surface. Large amplitude heat pulses are seen in one state followed by small amplitude pulses later in the discharge resulting in a repeating cycle of island states. These two states are interpreted as a bifurcation of magnetic island with high and low heat pulse accessibility. This report describes the discovery of a bifurcation in the coupled dynamics between the transport and topology of magnetic islands in tokamak plasmas.
Highlights
Inside an island can influence the evolution of magnetic island[17]
A key technique to be featured in the experiment in this paper is modulated electron cyclotron heating (MECH), which has been applied in LHD9,18 to study the change of magnetic topology, i.e., nested flux surfaces, small isolated magnetic islands, mixed islands and stochastic layers and regions of strong stochasticity, due to intrinsic resonant magnetic fields and applied resonant magnetic perturbation (RMP) fields
The electron cyclotron heating (ECH) power is deposited near the q = 1 surface at ρ = 0 .42 with a modulation frequency of 50 Hz
Summary
Inside an island can influence the evolution of magnetic island[17]. the study of transport properties inside the magnetic islands is an urgent issue in the study of high temperature plasmas. Two states of the magnetic island (high and low heat pulse accessibility) are clearly observed both in the temperature at the magnetic island and magnetic field B(200°) − B(307°) measured with two probes located at the low field side for the C-coil toroidal phase of 185°.
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