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Title: The next generation of electron cyclotron emission imaging diagnostics (invited)

Abstract

A 128 channel two-dimensional electron cyclotron emission imaging system collects time-resolved 16x8 images of T{sub e} profiles and fluctuations on the TEXTOR tokamak. Electron cyclotron emission imaging (ECEI) is undergoing significant changes which promise to revolutionize and extend its capabilities far beyond what has been achieved to date. These include the development of a minilens array configuration with increased sensitivity antennas, a new local oscillator pumping scheme, enhanced electron cyclotron resonance heating shielding, and a highly flexible optical design with vertical zoom capability. Horizontal zoom and spot size (rf bandwidth) capabilities are also being developed with new ECEI electronics. An interface module is under development to remotely control all key features of the new ECEI instrument, many of which can be changed during a plasma discharge for maximum flexibility.

Authors:
; ; ; ; ; ;  [1];  [2]; ; ; ;  [3]
  1. University of California at Davis, Davis, California 95616 (United States)
  2. Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784 (Korea, Republic of)
  3. FOM-Institute for Plasma Physics Rijnhuizen, Association EURATOM-FOM, 3430 BE Niewuwegein (Netherlands)
Publication Date:
OSTI Identifier:
21266595
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 79; Journal Issue: 10; Conference: HTPD08: 17. topical conference on high-temperature plasma diagnostics, Albuquerque, NM (United States), 11-15 May 2008; Other Information: DOI: 10.1063/1.2967342; (c) 2008 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ANTENNAS; CYCLOTRON RESONANCE; CYCLOTRONS; DESIGN; ECR HEATING; ELECTRIC DISCHARGES; ELECTRONS; EMISSION; FLUCTUATIONS; IMAGES; OSCILLATORS; TEXTOR TOKAMAK; TIME RESOLUTION; TWO-DIMENSIONAL CALCULATIONS

Citation Formats

Zhang, P., Domier, C. W., Liang, T., Kong, X., Tobias, B., Shen, Z., Luhmann, N. C. Jr., Park, H., Classen, I. G. J., Pol, M. J. van de, Donne, A. J. H., and Jaspers, R. The next generation of electron cyclotron emission imaging diagnostics (invited). United States: N. p., 2008. Web. doi:10.1063/1.2967342.
Zhang, P., Domier, C. W., Liang, T., Kong, X., Tobias, B., Shen, Z., Luhmann, N. C. Jr., Park, H., Classen, I. G. J., Pol, M. J. van de, Donne, A. J. H., & Jaspers, R. The next generation of electron cyclotron emission imaging diagnostics (invited). United States. doi:10.1063/1.2967342.
Zhang, P., Domier, C. W., Liang, T., Kong, X., Tobias, B., Shen, Z., Luhmann, N. C. Jr., Park, H., Classen, I. G. J., Pol, M. J. van de, Donne, A. J. H., and Jaspers, R. Wed . "The next generation of electron cyclotron emission imaging diagnostics (invited)". United States. doi:10.1063/1.2967342.
@article{osti_21266595,
title = {The next generation of electron cyclotron emission imaging diagnostics (invited)},
author = {Zhang, P. and Domier, C. W. and Liang, T. and Kong, X. and Tobias, B. and Shen, Z. and Luhmann, N. C. Jr. and Park, H. and Classen, I. G. J. and Pol, M. J. van de and Donne, A. J. H. and Jaspers, R.},
abstractNote = {A 128 channel two-dimensional electron cyclotron emission imaging system collects time-resolved 16x8 images of T{sub e} profiles and fluctuations on the TEXTOR tokamak. Electron cyclotron emission imaging (ECEI) is undergoing significant changes which promise to revolutionize and extend its capabilities far beyond what has been achieved to date. These include the development of a minilens array configuration with increased sensitivity antennas, a new local oscillator pumping scheme, enhanced electron cyclotron resonance heating shielding, and a highly flexible optical design with vertical zoom capability. Horizontal zoom and spot size (rf bandwidth) capabilities are also being developed with new ECEI electronics. An interface module is under development to remotely control all key features of the new ECEI instrument, many of which can be changed during a plasma discharge for maximum flexibility.},
doi = {10.1063/1.2967342},
journal = {Review of Scientific Instruments},
number = 10,
volume = 79,
place = {United States},
year = {Wed Oct 15 00:00:00 EDT 2008},
month = {Wed Oct 15 00:00:00 EDT 2008}
}
  • Electron cyclotron emission (ECE) has proven to be a useful diagnostic in tokamaks for measuring T/sub e/ and its radial variation. The application of ECE to mirror devices is discussed here, with emphasis on measurements of the properties of energetic electrons in tandem mirror end cells, which can be viewed both parallel and perpendicular to B. The parallel or whistler view is generally optically thick and can yield a measurement of perpendicular temperature. High harmonic perpendicular emission is optically thin and can yield important information about the hot electron buildup and the energy and spatial distribution. Experimental results from TMX-Umore » and appropriate modeling are presented.« less
  • The newly installed electron cyclotron emission imaging diagnostic on ASDEX Upgrade provides measurements of the 2D electron temperature dynamics with high spatial and temporal resolution. An overview of the technical and experimental properties of the system is presented. These properties are illustrated by the measurements of the edge localized mode and the reversed shear Alfven eigenmode, showing both the advantage of having a two-dimensional (2D) measurement, as well as some of the limitations of electron cyclotron emission measurements. Furthermore, the application of singular value decomposition as a powerful tool for analyzing and filtering 2D data is presented.
  • Measurements of the superthermal electron distribution can be made by observing the polarized electron cyclotron emission. The emission is viewed along a constant magnetic field surface. This simplifies the resonance condition and gives a direct correlation between emission frequency and kinetic energy of the emitting electron. A transformation technique is formulated which determines the anisotropy of the distribution and number density of superthermals at each energy measured. The steady-state distribution during lower hybrid current drive and examples of the superthermal dynamics as the runaway condition is varied are presented for discharges in the PLT tokamak.
  • Electron cyclotron emission (ECE) at an oblique angle to the magnetic field provides a means of probing the electron distribution function both in energy and physical space through changes in and constraints on the relativistic electron cyclotron resonance condition. Diagnostics based on this Doppler shifted resonance are able to study a variety of electron distributions through changes in the location of the resonance in physical or energy space accomplished by changes in the viewing angle and frequency, and the magnetic field. For the case of observation across a changing magnetic field, such as across the tokamak midplane, the constraint onmore » the resonance condition for real solutions to the dispersion relation can constrain the physical location of optically thin emission. A new Oblique ECE diagnostic was installed and operated on the PBX-M tokamak for the study of energetic electrons during lower hybrid current drive. It has a view 33{degree} with respect to perpendicular in the tokamak midplane, receives second harmonic X-mode emission, and is constrained to receive single pass emission by SiC viewing dumps on the tokamak walls. Spatial localization of optically thin emission from superthermal electrons (50{endash}100 keV) was obtained by observation of emission upshifted from a thermal cyclotron harmonic. The localized measurements of the electron energy distribution and the superthermal density profile made by this diagnostic demonstrate its potential to study the spatial transport of energetic electrons on fast magnetohydrodynamic time scales or anomalous diffusion time scales. Oblique ECE can also be used to study electron distributions that may have a slight deviation from a Maxwellian by localizing the emission in energy space. (Abstract Truncated)« less
  • The concepts and technical challenges related to developing a fourth generation electron cyclotron resonance (ECR) ion source with a rf frequency greater than 40 GHz and magnetic confinement fields greater than twice B{sub ECR} will be explored in this article. Based on the semiempirical frequency scaling of ECR plasma density with the square of operating frequency, there should be significant gains in performance over current third generation ECR ion sources, which operate at rf frequencies between 20 and 30 GHz. While the third generation ECR ion sources use NbTi superconducting solenoid and sextupole coils, the new sources will need tomore » use different superconducting materials, such as Nb{sub 3}Sn, to reach the required magnetic confinement, which scales linearly with rf frequency. Additional technical challenges include increased bremsstrahlung production, which may increase faster than the plasma density, bremsstrahlung heating of the cold mass, and the availability of high power continuous wave microwave sources at these frequencies. With each generation of ECR ion sources, there are new challenges to be mastered, but the potential for higher performance and reduced cost of the associated accelerator continues to make this a promising avenue for development.« less