DETECTION O F P LASMA W AVES IN TUI~BULENT PLASMA ON THE B ASIS O F S ATELLITES OF FORBIDDEN H ELIUM T RANSITIONS

Interaction between intense electromagnetic radiation and collisionless plasmas is accompanied by excitation of a spectrum of plasma (longitudinal) waves. When the plasma-wave field strength is high enough, the method of satellites of forbidden helium lines can be used to detect it. It is known [1] that an external rf electric field results in the appearance of satellites of forbidden helium lines, whose intensity is related in a certain fashion to the amplitude of the external field, while the spectral distance from a forbidden line is governed by the frequency of the external field. Paper [2] gives calculated Stark profiles for some helium lines and plots of relative intensities of satellites and allowed lines as functions of the rms field strength in the plasma. Satellites were experimentally detected and used for turbulent plasma diagnostics in papers [3, 4], which investigated c~rrent turbulence (0- and Z-pinch). In this paper we will employ the method for a plasma that is turbulized by intense electromagnetic radiation as a result of the development of parametric instability. The following transitions w ere used for measurements: the 4'D- 2'P allowed transition (k = 4922 ,~) and the 4'F- 2'P forbidden transition. The experimental setup is shown in Fig. 1. A vacuum chamber 20 cm in diameter and 100 cm long was placed in a relatively weak (H 0 ~ 200 Oe) magnetic field. An electromagnetic beam in the millimeter range was generated by a system of quasioptical converters and focusedby a Teflonlens into the center of the vacuum