| In the magnetic confined plasmas,micro-turbulence and its induced anomalous transport are one of the factors that limit the confinement performance.In the past years,I have developed a 2D multi-channel Beam Emission Spectroscopy(BES)diagnostic system on HL-2A tokamak and also investigate the turbulence characteristics in the edge during high performance discharges on HL-2A and DIII-D.The BES system on HL-2A provides the 2D fluctuation information of electron density via measuring the relative intensity of the emitted Da line from the interaction between neutral beam and plasma.The design of the whole BES system,including light collection,transmission,optical-electric transform and also data acquisition subsystems,was totally based on the size and parameters of HL-2A device.The BES port located under the mid-plane,looked at the neutral beam along the magnetic field line with a tilted angle.The radiation resistive,high transmission optic lenses consisted of 018cm objective lenses and 010cm field lens,was installed inside the vacuum to image the 2D region r= 12cm?44cm radially and z=-7.5cm?7.5cm poloidally with the magnification equals 4.The 2D fiber mount was installed just outside the BES port could cover the whole image plane was designed for fiber holding and configuration.The highly customized fiber bundles were used for light transmission,the neutral aperture of the fiber is 0.37 and the transmission efficiency is more than 95%.For the optical-electric transform subsystem,2nm bandwidth interference filter was used to filter out the target line,PIN-photodiode was chosen to transfer light signal to current,four-stage amplifiers electro circuit transfers current to voltage and enlarge the signal,suitable cooler ensures to achieve low dark noise and high quantum efficiency measurement.Multi-channels data acquisition system collects and save the data with 2MHz sampling rate.The development of the system was divided into three steps:At first,the 16 channels initial system was installed and tested on HL-2A.Secondly,based on the success of the initial system,the system was extended to 32 channels with modification of both fibers and fiber mount.2D turbulence measurement was achieved Thirdly,a new 16-channel integrated detector module was developed and achieved better signal to noise performance and the whole 48 channels BES system is available now.On HL-2A tokamak,the 32-channels BES system observed the 2D structure and its evolution of the turbulence in the edge just before the L-H transition.While in Super H mode discharges on D?-D,the 2D BES system captured both the 60?200kHz ion-direction turbulence mode and the 300-450kHz electron-direction turbulence mode.The characteristics of the both modes,calculated with BES channels,coupled with the simulation results with GYRO code showed that the lower-frequency mode should be ITG(Ion temperature mode),while the other mode may be MTM(Micro tearing mode).By now,the BES system on HL-2A is already extended to 48b channels and available for 2D measurement of turbulence.The time resolution is 0.5?s,the spatial resolution in radial direction is 1cm and is 1.2cm poloidally.The turbulence measurement band is 200kHz,and for turbulence frequency from 20 to 100kHz,the signal to noise ratio is up to 100.These performance ensures it support the experimental research of L-H transition,turbulence energy transport and the interaction between turbulence and drift wave.The results of the turbulence measurement in high performance discharges with 2D BES on both HL-2A and D?-D will help to understand the relations between turbulence,pedestal dynamics and the improvement of the confinement. |
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