Faraday-effect polarimeter diagnostic for internal magnetic field fluctuation measurements in DIII-D

Abstract

Motivated by the need to measure fast equilibrium temporal dynamics, non-axisymmetric structures, and core magnetic fluctuations (coherent and broadband), a three-chord Faraday-effect polarimeter-interferometer system with fast time response and high phase resolution has recently been installed on the DIII-D tokamak. A novel detection scheme utilizing two probe beams and two detectors for each chord results in reduced phase noise and increased time response [δb ∼ 1G with up to 3 MHz bandwidth]. First measurement results were obtained during the recent DIII-D experimental campaign. Simultaneous Faraday and density measurements have been successfully demonstrated and high-frequency, up to 100 kHz, Faraday-effect perturbations have been observed. Preliminary comparisons with EFIT are used to validate diagnostic performance. Principle of the diagnostic and first experimental results is presented.

System-on-chip integrated circuit technology applications on the DIII-D tokamak for multi-field measurements

“…The coherence between multi-field fluctuation plays an important role in determining turbulence transport and ELM suppression [14]. Taking advantage of the proximity between the ECEI and RIP [13] diagnostics in the DIII-D tokamak, the localized measurement of the correlation between multi-field fluctuations (δn e , δT e , δB r ) is made possible. The diagnostic arrangement of RIP and ECEI is illustrated in figure 7; ECEI is installed at 270 • of the DIII-D torus near the low field side midplane, while RIP is installed at 285 • .…”

“…The F-band chip for ECEI instruments, which has a higher frequency extending from 110 GHz to 140 GHz, has been presented in this paper and will be applied on DIII-D for high field side temperature fluctuation measurement in late 2021. The Radial Interferometry Polarimetry (RIP) system [13], (developed by the UCLA group), can provide information concerning the line-integrated turbulent density fluctuations and radial magnetic field fluctuations. Then, correlating with the RIP, the 2D MMIC based microwave imaging diagnostics system has the potential to localize interferometric measurement of turbulent fluctuations at the pedestal.…”

A combined Phase Contrast Imaging and heterodyne interferometer for multiscale fluctuation measurements in tokamak plasmas

“…A further goal of this project is to demonstrate that a density interferometer and PCI diagnostic can share laser, optics, and tokamak windows, making PCI an attractive add-on to the required density interferometer. While combined interferometerpolarimeters have been designed and implemented [27][28][29][30], the combination with PCI described herein maximizes the contribution as a diagnostic for turbulence and transport.…”

Laser-based Faraday effect polarimetry for real-time feedback control of plasma parameters on EAST

“…The three-wave Faraday-effect polarimetry technique has been demonstrated to work successfully on several toroidal confinement devices, such as JTEXT [9], DIIID [10]. Two of the three beams are made collinear with orthogonal, counter-rotation circular polarization (R-and L-waves), there will be a phase difference due to their different phase velocities in plasma.…”