Experimental studies of lower hybrid wave propagation

Abstract

Experimental measurement of the dispersion and damping of externally excited lower hybrid waves are presented. A multiple-ring slow-wave antenna, having 2π/kz=23 cm, is used to excite these waves in the Princeton L3 or L4 linear devices (B=0.5–2.8 kG uniform to ±1% for 1.6 m, n≈1010 cm−3, Te≈3–5 eV, Ti≲0.1 eV, He gas, plasma diameter approximately equal to 10 cm). The waves are localized in a spatial wave packet that propagates into the plasma along a conical trajectory which makes a small angle with respect to the confining magnetic field. Measurements of the dependence of wavelength on frequency are in good agreement with the cold plasma dispersion relation. Measured values of the wave damping are in good agreement with Landau damping by the combination of the main body of the electron distribution and an approximately 30% high energy (Te≈15–30 eV) electron tail.