A single-channel far-infrared(FIR)laser interferometer was developed to measurethe line averaged electron density on the EAST tokamak.The structure of the single-channelFIR laser interferometer is described in detail.The evolution of density sawtooth oscillation wasmeasured by means the FIR laser interferometer,and was identified by electron cyclotron emission(ECE)signals and soft X-ray intensity.The discharges with and without sawtooth were comparedwith each other in the Hugill diagram.
A multipulse and multipoint Nd:YAG (neodymium-yttrium aluminum garnet) laserThomson scattering diagnostic system was developed on EAST to obtain more accurate electrontemperature T_e and electron density n_e profiles. In this paper, the optical system, the VME (versamodule eurocard)-based real-time computer system for laser control, data acquisition, analysis andcalibration are discussed in detail. Furthermore, a developed data processing method is presented.
Intermittent characteristics of turbulence induced by coherent structures (blobs)was clearly observed in the ion saturation current signal, density fluctuation, particle flux andheat flux in HT-7. It is obvious that ion saturation current signal has deviated from Gaussiandistribution and the skewness (S) and flatness (K) of signal increase radially outwards in thescrape-off layer (SOL). Using conditional analysis (CA), asymmetric character of the intermittentbursts are demonstrated. Owing to the radial propagation of the coherent structures, the particledensity profile in SOL is non-exponential and flat outwards from the last close flux surface (LCFS).It is found around LCFS that the large burst fluctuations (above 2.5 rms) are responsible for about50% of the total particle transport. Burst events move radially outwards with E_θ× B velocity, andthe blob size can be calculated as δΥ～V_rΤ_c. Our experiment shows that the blob size, life time anddrift velocity experienced a pronounced decorrelation in the shear layer. The electrostatic Reynoldsstress components become very strong and show a radially steep gradient in the proximity of theshear layer. These experimental findings may imply that the coherent structures are titled by thedeveloped shear flow in the E× B shear layer.
