A Microwave System For Time Varying Plasma Diagnostics

Author : Liubing Yu
Publisher :
ISBN 13 : 9781321024807
Total Pages : pages
Book Rating : 4.0/5 (248 download)

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Download or read book Microwave Diagnostics for Magnetic Fusion Devices written by Liubing Yu and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: To tackle the energy shortage problems that we are facing, many scientists are trying to achieve controlled fusion to provide clean and sustainable energy. Many large Tokamaks, which is the most promising device concept, have been built worldwide and three of them (DIII-D, NSTX, C-Mod) are currently in operation in the U.S. To understand the details of magnetic fusion plasma physics, a variety of microwave diagnostics are applied to measure the plasma properties from the millions of degrees plasma in a nonperturbative fashion. Our research group, the Plasma Diagnostics Group, under the Davis MM-Wave Research Center (DMRC), focuses on developing advanced microwave diagnostic tools. The Electron Cyclotron Emission Imaging (ECEI) diagnostic, a passive radiometric microwave diagnostic, is an extremely useful imaging tool invented in this group to study electron temperature and its fluctuations. The Microwave Imaging Reflectometry (MIR) technique is also another imaging tool pioneered in this group, and its purpose is to study electron density fluctuations using an imaging radar approach. Finally, the Far Infrared Tangential Interferometry/ Polarimetry (FIReTIP) system is a density and magnetic field diagnostic tool. This dissertation introduces the principles, structure, recent technology advances, and some physical studies concerning these three systems. The combined ECEI and MIR systems on the DIII-D (located at General Atomics in San Diego) provide simultaneous electron temperature and density fluctuation imaging at the same plasma volume. The ECEI system consists of two major parts: the optical and array system, which images and downconverts the millimeter wave ECE radiation, and the electronics, which detects the radiation power in each designed band. This dissertation concerns two recent upgrades made by our group: one is the use of the zero bias Schottky detectors in the IF electronics which has greatly decreased the noise level, and the other is the expanded radial coverage which doubles the radial view in the plasma. For the MIR system, the synthetic diagnostic modeling has guided the very successful optic and array design; some details concerning the transmitter, receiver, and electronics are presented. In this dissertation, several methods for the ECEI/MIR time calibration were conceived, applied, and compared; in addition, the ECEI and MIR systems are also time calibrated with respect to two other important diagnostics, the ECE radiometer and magnetic fluctuation diagnostic systems.Intense bursts of mm-wave emission with durations of 5-10 [mu]s have been observed on DIII-D by both ECE radiometer and ECEI systems during edge localized modes, Quiet H-mode (QH) modes, and the precursor before disruptions. Both the ECE radiometer system and the ECEI system employ heterodyne detection methods and have overlapping intermediate frequency (IF) bands. A new RF spectrometer, spanning this IF frequency range of approximately 2-10 GHz, has been installed on the DIII-D tokamak in order to more fully characterize the frequency, intensity, and localization of these bursts. Herein, the data for the H mode case and QH-mode case will be discussed and scrutinized in order to constrain the needed model to explain the bursts. As a trial model, the Cyclotron AutoResonance Maser (CARM) and Gyro-BWO models are proposed to explain these bursts, which require further theory, experimental, and simulation support. The multichannel FIReTIP system provides line-integrated plasma density and magnetic information from multiple viewing chords on the midplane of the NSTX device. Extremely wide bandwidth phase comparator electronics for the FIReTIP system were developed and installed on the NSTX device in 2009. This allows the system video bandwidth, previously limited to ~250 kHz, to extend out to ~500 kHz when operated as a simultaneous interferometer/polarimeter system and as high as 4 MHz when operated in an interferometry-only configuration. The new electronics provides simultaneous interferometer phase measurement data using two distinct phase comparator methods. The first is a digital fringe counter (FC) approach limited to a video bandwidth of ~500 kHz, while the second is an analog demodulator or in-phase and quadrature (IQ) approach that achieves the full 4 MHz video bandwidth. New algorithms have been developed to process the FIReTIP data for both regular (post-shot) and real-time density calculations, with reliability checks conducted using laser Thompson Scattering data where available.