High resolution polarimeter-interferometer system for fast equilibrium dynamics and MHD instability studies on Joint-TEXT tokamak (invited)

Chen, J.; Zhuang, G.; Li, Q.; Liu, Y.; Gao, L.; Zhou, Y. N.; Jian, X.; Xiong, C. Y.; Wang, Z. J.; Brower, D. L.; Ding, W. X.
November 2014
Review of Scientific Instruments;2014, Vol. 85 Issue 11, p1
Academic Journal
A high-performance Faraday-effect polarimeter-interferometer system has been developed for the J-TEXT tokamak. This system has time response up to 1 µs, phase resolution < 0.1° and minimum spatial resolution > 15 mm. High resolution permits investigation of fast equilibrium dynamics as well as magnetic and density perturbations associated with intrinsic Magneto-Hydro-Dynamic (MHD) instabilities and external coil-induced Resonant Magnetic Perturbations (RMP). The 3-wave technique, in which the line-integrated Faraday angle and electron density are measured simultaneously by three laser beams with specific polarizations and frequency offsets, is used. In order to achieve optimum resolution, three frequency-stabilized HCOOH lasers (694 GHz, >35 mW per cavity) and sensitive Planar Schottky Diode mixers are used, providing stable intermediate-frequency signals (0.5-3 MHz) with S/N > 50. The collinear R- and L-wave probe beams, which propagate through the plasma poloidal cross section (a = 0.25-0.27 m) vertically, are expanded using parabolic mirrors to cover the entire plasma column. Sources of systematic errors, e.g., stemming from mechanical vibration, beam non-collinearity, and beam polarization distortion are individually examined and minimized to ensure measurement accuracy. Simultaneous density and Faraday measurements have been successfully achieved for 14 chords. Based on measurements, temporal evolution of safety factor profile, current density profile, and electron density profile are resolved. Core magnetic and density perturbations associated with MHD tearing instabilities are clearly detected. Effects of non-axisymmetric 3D RMP in ohmically heated plasmas are directly observed by polarimetry for the first time.


Related Articles

  • Short wavelength far infrared laser polarimeter with silicon photoelastic modulators. Akiyama, T.; Kawahata, K.; Tanaka, K.; Okajima, S.; Nakayama, K. // Review of Scientific Instruments;Oct2008, Vol. 79 Issue 10, p10E720 

    A short wavelength far infrared laser whose wavelength λ is about 50 μm is preferable for a polarimeter and an interferometer for high density operations in the Large Helical Device (LHD) and on future large fusion devices such as ITER. This is because the beam bending effect (∝λ2)...

  • Recent developments of the JET far-infrared interferometer-polarimeter diagnostic. Boboc, A.; Gelfusa, M.; Murari, A.; Gaudio, P.; JET-EFDA Contributors // Review of Scientific Instruments;Oct2010, Vol. 81 Issue 10, p10D538 

    The far-infrared diagnostic provides essential internal measurements of the plasma density and magnetic field topology (q-profile via Faraday rotation angle) in real-time. The diagnostic capabilities have recently been extended in a number of key areas. Fast interferometer data, with 10 μs...

  • A polarimeter for localized continuous measurement of the poloidal magnetic field in a tokamak. Huang, L. K.; Finkenthal, M.; Moos, H. W. // Review of Scientific Instruments;May91, Vol. 62 Issue 5, p1142 

    A polarimeter for the circular polarization of Zeeman-split spectral line emissions has been developed to measure the poloidal magnetic field in tokamak plasmas. The Li I 6708 Ã… line originating from a monoenergetic lithium beam provided a localized spectral source. In the polarimeter,...

  • Multiple view fan beam polarimetry on Tokamak devices Geck, W. R.; Domier, C. W.; Luhmann, Jr., N. C. // Review of Scientific Instruments;Jan1997, Vol. 68 Issue 1, p416 

    Describes a polarimeter diagnostic which utilizes several fan beams to accumulate line integrated Faraday rotation data in a Tokamak plasma. Magnetic expansion technique; Multiple view reconstruction method.

  • The Milano polarization experiment devoted to the study of the cosmic microwave background. Gervasi, M.; Battistelli, E. S.; Boella, G.; Cavaliere, F.; Passerini, A.; Sironi, G.; Zannoni, M. // AIP Conference Proceedings;2002, Vol. 609 Issue 1, p164 

    In the last years several experiments have been devoted to the search for CMB polarization, but no positive detection has been obtained so far. In fact the expected degree of polarization is very low and its detection is extremely difficult. Very special design and system stability are necessary...

  • Measurements of Faraday rotation in TFTR plasmas. Ma, C. H.; Hutchinson, D. P.; Vander Sluis, K. L.; Mansfield, D. K.; Park, H.; Johnson, L. C. // Review of Scientific Instruments;Aug1986, Vol. 57 Issue 8, p1994 

    Recent results of simultaneous measurements of line electron density and poloidal field-induced Faraday rotation on the multichannel far infrared (FIR) interferometer/polarimeter on tokamak fusion test reactor (TFTR) are presented. The procedures and results of the calibration are described in...

  • Parsec-scale structure in the warm ISM from polarized galactic radio background observations. Haverkorn, M.; Katgert, P.; de Bruyn, A. G. // AIP Conference Proceedings;2002, Vol. 609 Issue 1, p72 

    We present multi-frequency polarization observations of the diffuse radio synchrotron background modulated by Faraday rotation, in two directions of positive latitude. No extended total intensity I is observed, which implies that total intensity has no structure on scales smaller than...

  • Polarization surveys of the galaxy. Reich, Wolfgang; Fu¨rst, Ernst; Reich, Patricia; Wielebinski, Richard; Wolleben, Maik // AIP Conference Proceedings;2002, Vol. 609 Issue 1, p3 

    We report on sensitive λ21 cm and λ11 cm polarization surveys of the Galactic plane carried out with the Effelsberg 100-m telescope at arcmin angular resolution and some related work. Highly structured polarized emission is seen along the Galactic plane as well as up to very high Galactic...

  • Radio polarimetry: A historical development at Effelsberg. Wielebinski, R.; Lochner, O.; Reich, W.; Mattes, H. // AIP Conference Proceedings;2002, Vol. 609 Issue 1, p291 

    To measure radio polarization one needs to analyze the incoming wave by means of a polarimeter. This is the crucial device that allows to determine the Stokes parameters after abstraction of the incoming wave in two orthogonal planes. The development of polarimeters in Effelsberg over the past...


Read the Article


Sorry, but this item is not currently available from your library.

Try another library?
Sign out of this library

Other Topics