Experimental studies of lower hybrid wave propagation
Experimental measurement of the dispersion and damping of externally excited lower hybrid waves are presented. A multiple-ring slow-wave antenna, having 2pi/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[approximate]1010 cm^–3, Te[approximate]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[approximate]15–30 eV) electron tail.
© 1976 American Institute of Physics. (Received 18 December 1975) We would like to thank J. Johnson and J. Taylor for their technical assistance. We would also like to thank Dr. J.P.M. Schmitt for having initiated the construction of the multiple filament plasma source. One of the authors (P.B.) would like to thank the National Research Council of Canada for having provided him with financial support during the course of this work. This work was supported by the U.S. Energy Research and Development Administration Contract E(11-1)-3073. Use was made of computer facilities supported in part by National Science Foundation Grant NSF-GP579.
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