Implementation of a large-aperture Thomson scattering system for diagnosing driven ion acoustic waves on Shenguang-III prototype laser facility

Abstract

A large-aperture (f/3) Thomson scattering diagnostic system, for measuring the ion acoustic waves driven by stimulated Brillouin scattering, has been recently implemented at the bottom of the target chamber on Shenguang-III prototype laser facility. With a 4ω (263.3 nm) probe beam entering the target chamber in the horizontal plane, this system is capable of detecting the Thomson scattered light off ion acoustic waves driven by a 3ω (351 nm) interaction beam. The Thomson scattered light off a driven ion acoustic wave emits at a specific direction, for a given electron density. The f/3 aperture of the diagnostic system allows measurement of driven ion acoustic waves in plasmas with electron densities up to 4×1021 cm-3, which covers the typical density range of interest in experiments on Shenguang-III prototype. Since the driven Thomson scattered spectrum is usually orders of magnitude stronger than the accompanying thermal Thomson scattered spectrum, to record both signals, a half area filter is used in the system, which suppress the stronger signal to a comparable level with the weaker one. By reducing the system aperture, Thomson scattered light off driven ion acoustic waves can be blocked. Therefore, this system can be also used to detect the Thomson scattered light off thermal ion acoustic waves for measurement of plasma parameters. In recent experiments with gas-filled hohlraums, Thomson scattered spectra off both driven and thermal ion acoustic waves have been diagnosed.