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Title: Measurement of the runaway electrons in the HT-7 tokamak

Abstract

A thermographic camera and four hard x-ray detectors have been developed to measure the runaway electrons in the HT-7 tokamak. The synchrotron radiation originated from the runaway electrons was measured by an infrared (IR) camera working in the wavelength ranges of 7.5-13 {mu}m. With a tangential viewing into the plasma in the direction of the electron approach on the equatorial plane, the synchrotron radiation from the runaway electrons was measured in a full poloidal cross section. Three NaI scintillators are used to monitor the hard x-ray radiation (HXR) in the energy ranges of 0.5-7 MeV, and a CdTe detector is used to monitor the low-energy HXR in the energy ranges of 0.3-1.2 MeV. The combination of infrared camera and hard x-ray detectors provides a powerful tool to investigate the runaway electron dynamics in HT-7. Runaways in the core and edge regions are monitored simultaneously. The parameters of runaway beam in the core are deduced from the IR pictures. The interaction of runway electrons with toroidal magnetic field ripple is monitored from the HXR emission.

Authors:
; ; ; ; ; ; ;  [1]
  1. Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)
Publication Date:
OSTI Identifier:
20778556
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 77; Journal Issue: 1; Other Information: DOI: 10.1063/1.2140488; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BOUNDARY LAYERS; CAMERAS; CDTE SEMICONDUCTOR DETECTORS; HARD X RADIATION; HT-7 TOKAMAK; MAGNETIC FIELD RIPPLES; MONITORS; PLASMA; PLASMA CONFINEMENT; PLASMA DIAGNOSTICS; RUNAWAY ELECTRONS; SODIUM IODIDES; SYNCHROTRON RADIATION

Citation Formats

Chen, Z.Y., Wan, B.N., Lin, S.Y., Shi, Y.J., Hu, L.Q., Gong, X.Z., Lin, H., and Asif, M. Measurement of the runaway electrons in the HT-7 tokamak. United States: N. p., 2006. Web. doi:10.1063/1.2140488.
Chen, Z.Y., Wan, B.N., Lin, S.Y., Shi, Y.J., Hu, L.Q., Gong, X.Z., Lin, H., & Asif, M. Measurement of the runaway electrons in the HT-7 tokamak. United States. doi:10.1063/1.2140488.
Chen, Z.Y., Wan, B.N., Lin, S.Y., Shi, Y.J., Hu, L.Q., Gong, X.Z., Lin, H., and Asif, M. Sun . "Measurement of the runaway electrons in the HT-7 tokamak". United States. doi:10.1063/1.2140488.
@article{osti_20778556,
title = {Measurement of the runaway electrons in the HT-7 tokamak},
author = {Chen, Z.Y. and Wan, B.N. and Lin, S.Y. and Shi, Y.J. and Hu, L.Q. and Gong, X.Z. and Lin, H. and Asif, M.},
abstractNote = {A thermographic camera and four hard x-ray detectors have been developed to measure the runaway electrons in the HT-7 tokamak. The synchrotron radiation originated from the runaway electrons was measured by an infrared (IR) camera working in the wavelength ranges of 7.5-13 {mu}m. With a tangential viewing into the plasma in the direction of the electron approach on the equatorial plane, the synchrotron radiation from the runaway electrons was measured in a full poloidal cross section. Three NaI scintillators are used to monitor the hard x-ray radiation (HXR) in the energy ranges of 0.5-7 MeV, and a CdTe detector is used to monitor the low-energy HXR in the energy ranges of 0.3-1.2 MeV. The combination of infrared camera and hard x-ray detectors provides a powerful tool to investigate the runaway electron dynamics in HT-7. Runaways in the core and edge regions are monitored simultaneously. The parameters of runaway beam in the core are deduced from the IR pictures. The interaction of runway electrons with toroidal magnetic field ripple is monitored from the HXR emission.},
doi = {10.1063/1.2140488},
journal = {Review of Scientific Instruments},
number = 1,
volume = 77,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2006},
month = {Sun Jan 15 00:00:00 EST 2006}
}
  • The nature of runaway electrons is such that the confinement and dynamics of the electrons can be strongly affected by magnetic fluctuations in plasma. Experimental results in the HT-7 tokamak indicated significant losses of runaway electrons due to magnetic fluctuations, but the loss processes did not only rely on the fluctuation amplitude. Efficient radial runaway transport required that there were no more than small regions of the plasma volume in which there was very low transport of runaways. A radial runaway diffusion coefficient of D{sub r} Almost-Equal-To 10 m{sup 2}s{sup -1} was derived for the loss processes, and diffusion coefficientmore » near the resonant magnetic surfaces and shielding factor #Greek Upsilon With Hook Symbol#=0.8 were deduced. Test particle equations were used to analyze the effect of magnetic fluctuations on runaway dynamics. It was found that the maximum energy that runaways can gain is very sensitive to the value of {alpha}{sub s} (i.e., the fraction of plasma volume with reduced transport). {alpha}{sub s}=(0.28-0.33) was found for the loss processes in the experiment, and maximum runaway energy could be controlled in the range of E=(4 MeV-6 MeV) in this case. Additionally, to control the maximum runaway energy below 5 MeV, the normalized electric field needed to be under a critical value D{sub {alpha}}=6.8, and the amplitude normalized magnetic fluctuations b(tilde sign) needed to be at least of the order of b(tilde sign) Almost-Equal-To 3 Multiplication-Sign 10{sup -5}.« less
  • Poloidal beta {beta}{sub {theta}} and internal inductance l{sub i} measurements are very important for tokamak operation. Much more plasma parameters can be inferred from the two parameters, such as the plasma energy confinement time, the plasma toroidal current profile, and magnetohydrodynamics instability. Using diamagnetic and compensation loop, combining with poloidal magnetic probe array signals, poloidal beta {beta}{sub {theta}} and internal inductance l{sub i} are measured. In this article, the measurement system and arithmetic are introduced. Different experimental results are given in different plasma discharges on HT-7 superconducting tokamak.
  • The runaway electrons have been measured by hard x-ray detectors and soft x-ray array in the J-TEXT tokamak. The hard x-ray radiations in the energy ranges of 0.5-5 MeV are measured by two NaI detectors. The flux of lost runaway electrons can be obtained routinely. The soft x-ray array diagnostics are used to monitor the runaway beam generated in disruptions since the soft x-ray is dominated by the interaction between runaway electrons and metallic impurities inside the plasma. With the aid of soft x-ray array, runaway electron beam has been detected directly during the formation of runaway current plateau followingmore » the disruptions.« less
  • A diagnostic neutral beam will be added to the diagnostic set so that charge-exchange recombination spectroscopy (CXRS) can be used to acquire ion temperature and rotation, and to study the role of the ion thermal transport, the radial electric field, and turbulence in the high performance HT-7 plasma. In normal operation, the diagnostic neutral beam (DNB) can produce 5.5 A of extracted beam current in hydrogen at an energy of 50 keV with a pulse length of 0.1 s. D and He beams can be produced as well. The beam can be modulated at 0.5 kHz. The CXRS system willmore » have 45 spatial observation chords and employ a spectrometer, which can acquire spectra at the rate of 100 Hz. In this article, the capabilities and implementation of the DNB and CXRS systems are presented.« less
  • Time resolved neutron flux diagnostic systems based on BF{sub 3} proportional counter and ZnS(Ag) scintillator have been developed and implemented on the HT-7 superconducting tokamak. A ten-channel flexible data acquisition system designed with a PCI-8554 general digital counter and industry PC is equipped. Calibrations are made with several neutron sources. The consistencies of experimental data from two techniques have been proven; the BF{sub 3} based system is more reliable with better detection efficiency. The measured neutron yield shows good agreement with the simple numerical calculation. The observed photo-neutron production indicates that photon-nuclear reactions are dominant in several special cases suchmore » as low density and disruption conditions. Good agreement on ion temperature deduced from neutron diagnosis and neutral particle analyzer under high parameter plasma conditions implies that neutron flux diagnostics can be used as an effective higher temporal resolution ion temperature monitor.« less