Sausage Waves in a Plasma Cylinder with a Surface Current

  • Lim, Daye (School of Space Research, Kyung Hee University) ;
  • Nakariakov, Valery M. (Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick) ;
  • Moon, Yong-Jae (School of Space Research, Kyung Hee University)
  • Published : 2019.04.10

Abstract

Linear sausage oscillations of a cylinder embedded in a plasma with an azimuthal magnetic field, created by a current on the surface of the cylinder, are studied. Such a plasma configuration could be applied to modelling demonstrate that the lowest radial harmonic of the sausage mode is in the trapped regime for all values of the parallel wave number. In the long-wavelength limit, phase and group speeds of this mode are equal to the Alfven speed in the external medium. It makes the oscillation period to be determined by the ratio of the parallel wavelength, e.g., double the length of an oscillating loop, to the external Alfven speed, allowing for its seismological estimations. The application of the results obtained to the interpretation of long-period (longer than 20-30 s) oscillations of emission intensity detected in solar coronal structure, gives reasonable estimations of the external Alfven speed. Cutoff values of the parallel wavenumber for higher radial harmonics are determined analytically. Implications of this finding to the observational signatures of fast magnetoacoustic wave trains guided by the plasma non-uniformity are discussed.

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Acknowledgement

Grant : Study on analysis and prediction technique of solar flares

Supported by : Institute for Information & communications Technology Promotion(IITP)