Observation of birefringence of waves in abounded inhomogeneous plasma confined in a magnetostatic well

Indranuj Dey,Sudeep Bhattacharjee

doi:10.1109/plasma.2010.5533983

Abstract

Summary form only given. The interaction of electromagnetic (EM) waves with magnetized plasmas is an active area of research. Most of the research so far have focused upon waves launched in the (k ∥ B o ) mode where the wave vector (k) is parallel to the static magnetic field (B o ), and B o is approximately uniform over the plasma volume with the dimension of the plasma much larger than the free space wavelength λ o , corresponding to the launched waves. There are only a few investigations in the k⊥B o mode.We study wave interaction with bounded plasmas in the k⊥B 0 mode where the waveguide cutoff wavelength λc is comparable [λc(≅14 cm) ~ λ 0 (≅12 cm)] to λ 0 . A high-density, radially inhomogeneous argon plasma is generated and confined in a cylindrically symmetric magnetostatic well (B 0 ∝ r 3 ), created by an octupole arrangement of permanent magnets surrounding the waveguide. In this work, the effect of the inhomogeneous, anisotropic magneto-plasma on the polarization of the penetrating waves is experimentally investigated. Polar measurement of the wave electric-field (E) intensity reveals that E is linearly polarized in the radial plane as expected. However, an asymmetry is observed in the lobes of the dipole-like .E-field polar intensity variation. The axis of polarization with respect to vacuum rotates with increase in plasma density and axial plasma interaction length (L 0 ). We found that for L 0 ~ 15 cm, the rotation angle Δφ ~ 10°. Such rotation hitherto unreported in laboratory bounded plasmas may be attributed to birefringence of the wave in the medium similar to optical crystals. Measurement of the wave vector k in the magnetoplasma by heterodyne technique is expected to shed further light on the nature of the birefringence.

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