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.
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.
The strongly damped collisions of very heavy nuclei^(232)Th+^(250)Cf at the energy range of 680—1880 MeV have been studied within the improved quantum molecular dynamics model.The production probability of primary superheavy fragments with Z≥114(SHFs)for the asymmetric reaction ^(232)Th+^(250)Cf is higher than that for the symmetric reaction ^(244)pu+^(244)Pu and ^(238)u+^(238)U.The calculated results show that the mass and charge distributions of primary fragments,the excitation energy distribution of SHFs depend on the incident energies strongly.Two stages of the decay process of composite systems are distinguished by very different decay slopes,which imply different decay mechanisms of the composite system.The first stage is for the decay of giant composite systems and the second one corresponds to the decay of fragments of giant composite systems including SHFs through emitting neutron,proton or other charged particles,and also through fission or fragmentation.The slow reduction of SHFs in the second stage seems to be helpful for the survival of primary superheavy fragments.
