Observation of Drift Wave Propagation as a Source of Tokamak Edge Turbulence

Core and edge turbulences were measured by Langmuir probe arrays in the KT-5C tokamak plasma.The radial wavenumber spectra show a quasimode like structure which results in a net radial outward propagation of the turbulent fluctuations.The measured fluctuation levels and wave action fluxes are in good agreement with model predictions by Mattor et al.,suggesting that drift wave propagation could be a source of edge turbulence.

Identification of Low-Frequency Zonal Flow in a Linear Magnetic Plasma Device

A low-frequency(f<2 kHz)potential structure(LFPS)is observed in a linear magnetic plasma device using Langmuir probe arrays.The center frequency of this structure is near zero.This structure has azimuthal and axial symmetries while with a finite radial wavenumber.The complete 3D spectra features of this structure have been identified to have the characteristics expected for zonal flows.

Self-Organized Criticality Properties of the Turbulence-Induced Particle Flux at the Plasma Edge of the HT-6M Tokamak

Power spectrum and the probability distribution function(PDF)of the turbulence-induced particle fluxΓin the velocity shear layer of the HT-6M edge region have been measured and analysed.Three regions of frequency dependence(f0,f-1,f-4)have been observed in the spectrum of the flux.The PDF of the flux displays aΓ-1 scaling over one decade inΓ.Using the rescaled-range statistical technique,we find that the degree of the self-similarity(Hurst exponent)of the particle flux in the measured region ranges from 0.64 to 0.83.All of these results may mean that the plasma transport is in a state characterized by the self-organized criticality.

Reynolds Stress and Sheared Poloidal Flow in the Edge Plasma Region of the HT-6M Tokamak

High spatial resolution measurements of the electrostatic Reynolds stress,radial electric field and poloidal phase velocity of fluctuations in the edge region of the HT-6M tokamak are carried out.The Reynolds stress shows a radial gradient in proximity to the poloidal velocity shear.A comparison of the profiles between the Reynolds stress gradient and the poloidal velocity damping reveals some similarity in their magnitude and radial structure.These facts suggest that the turbulence-induced Reynolds stress may play a significant role in generating the poloidal flow in the plasma edge region.

Collective Thomson Scattering from Laser-Produced Plasmas

Time-resolved Thomson scattering was successfully performed to diagnose the parameters(ZTe,Ue and Ui)of laser-produced gold plasma.The results show that the collisionless dynamic form factor is accurate enough to be used for reducing the plasma parameters from the experimental data.

Generation of Radial Electric Field with Electrode Biasing

Time and space resolved measurements of the radial electric field(Er)have been conducted during the electrode biasing experiments on the KT-5C tokamak.The suppression of the turbulent transport with the change of Er induced by the biased electrode is observed.It is found that the poloidal flow contributes to the main part of the Er,and the change of the poloidal flow has a lead of about 20μs to the formation of Er.These observations suggest that a radial current,responding to an induced voltage on the electrode,drives a poloidal flow which in turn drives the radial electric field.

A Signature of Self-Organized Criticality in the HT-6M Edge Plasma Turbulence

Power spectra of electron density and floating potential fluctuations in the velocity shear layer of the HT-6M edge region have been measured and analysed.All the spectra have three distinct frequency regions with the spectral decay indices typical of self-organized criticality systems(0,-1 and-4)when Doppler shift effects induced by the plasma E x B flow velocity have been taken into account.These results are consistent with the predictions of the self-organized criticality models,which may be an indication of edge plasma turbulence in the HT-6M tokamak evolving into a critical state independent of local plasma parameters.

Deposition of Diamond-Like Carbon Films with Femtosecond KrF Laser Pulses

Hydrogen-free diamond-like carbon (DLC) films with the optical band gaps of 2.0-2.7 e V and the microhardness of 40-55 GPa are deposited by femtosecond KrF laser pulses. The film microstructure of nanometer spheroid is observed. The filrn microhardness is improved with the increase of ion kinetic energy of plasma plume from 300 to 600 eV. The characteristics of DLC film deposition with fs pulses is discussed.

Observation of Low Frequency Ion Mode Turbulence in Tokamak Plasma

Features of a low frequency ion mode were observed together with the electron drift wave type fluctuations by a Langmuir probe array in the bulk plasma inside the velocity shear layer in the KT-5C tokamak.The measured ion mode wavenumber,scaling of the ion mode with chord-averaged density,and the estimatedηi value suggest that the observed ion mode may be the theoretically predictedηi mode driven by ion temperature gradient.

Investigation of Edge Localized Fluctuation in KT-5C Tokamak

It is found on KT-5C tokamak that an edge fluctuation mode can be excited by using a pair of floating Langmuir probes.This mode is propagating along the magnetic field with its amplitude decreasing drastically when it is off the magnetic field line.Preliminary feedback experiments show that the broadband edge turbulence can be reduced or enhanced depending upon the phase shift of the feedback network.

Experimental Investigation of Reflectometry as a Density Fluctuation Diagnostic

In this paper,a controlled laboratory experiment to investigate the response properties of reflec-tometry to the density fluctuations is presented.The reflectometer signal is observed to be highly spatially localized in the plasma.The quantitative measurement has demonstrated that the signal originates about one free space wavelength of the probe•wave in front of the critical layer and this position is independent of the fluctuation wavenumber.It is also found that the sensitivity of transverse response to wavenumbers is different from that of longitudinal response.

Observation of Thomson Scattering off Entropy Waves in a Laser-Produced Plasma

A new feature in the Thomson scattering spectrum is observed from a laser-produced aluminium plasma, which may be the Thomson scattering off entropy waves in the plasma. Such a feature is only observable when the energy of the heater beam is low enough.