Electron Cyclotron Emission Imaging Observations of m/n = 1/1 and Higher Harmonic Modes during Sawtooth Oscillation in ICRF Heating Plasma on EAST

Abstract

The 𝑚/𝑛 = 1/1 and its higher harmonic modes are observed in sawtooth oscillations by using the novel highresolution 2D ECE imaging system on the experimental advanced superconducting Tokamak (EAST). Higher harmonic modes are appearing for a short time during the crash phase of sawtooth oscillation in lower 𝛽p plasma, which is not the preferable position in the poloidal cross section. These modes generate sharp pressure points on the inversion radius during the crash phase of sawtooth oscillation. Furthermore, reconnection events proceed in two distinctive phases. In the first phase, a small amount of heat is expelled through the weak reconnection while in the second phase the remaining large quantity of heat and particles emerged rapidly from the hot core to the peripheral region of the inversion radius. In addition, these harmonic modes are only found before and after the ICRF pulse, while in the ICRF pulse only the (1,1) mode exists in the sawtooth oscillation.

Evidence and relevance of spatially chaotic magnetic field lines in MCF devices

“…This will be presented elsewhere. Integrating the exact electron trajectories, we could reproduce electron temperature patterns very close to that found in electron temperature measurements by ECE [35,36] using the e.m. with chaotic magnetic field lines for which the experimental nickel behavior was reproduced. The time evolution of the central temperature drop predicted by our model is close to that of the nickel penetration to the central region (see figure 4).…”

Magnetic reconnection rate during sawtooth crashes in ASDEX Upgrade

“…This allows us to investigate the reconnection from a new perspective. The ECEI measurements of the sawtooth crash has been conducted before in several tokamaks (in TEXTOR [9,10], HT-7 [11], ASDEX-Upgrade [12], DIII-D [13], HL-2A [14], EAST [15] and KSTAR [16]). However, to our knowledge, the described approach of obtaining the radial velocity and comparing it directly with the simulation is novel.…”

The co-located arrangement of ECEI and MIR microwave imaging diagnostics on EAST tokamak

“…The front-end optics systems requires larger poloidal opening size window for high spatial resolution images. On EAST, the active MIR and passive ECEI [8,9] are required to provide 10∼20 mm poloidal resolution for plasma physics study, including sawtooth, Alfven eigenmodes, ELMs, etc. The passive imaging radiometer, ECEI, receivers the high-frequency emission signal from plasma for temperature measurement.…”