Temporal evolutions of electron density profiles in H-mode plasmas of CHS

Recently, H-mode discharges have been found not only in tokamaks but also in heliotron/torsatron stellarator. An H-mode is now going to be more important and general phenomena to improve confinement and to understand transport mechanism in toroidal plasmas. In neutral beam heated plasmas of Compact Helical System (CHS), the H-mode transition was obtained by modification of the rotational transform profile with a small ohmic heating current. In order to investigate the particle transport in the H-mode plasmas, measurements of temporal evolutions of electron density profiles before and after the transition are required. For this purpose, a two channel HCN laser interferometer has been installed in CHS. In this paper, we present temporal evolutions of electron density profiles and their characteristics related to the improvement of the particle confinement. (author) 3 refs., 5 figs