Search

A prototype real-time (RT) Thomson scattering system was tested in a KSTAR Thomson scattering diagnostic system [1]. For this RT-Thomson system, 155 channels of 5 GS/s digitizer were operated (31 polychromators, each has 5 signal channels used in the KSTAR Thomson scattering system). The 5 Giga Sampling / second (GS/s) digitizer restored the pulsed Thomson scattering signals, and these acquired digital signals were fitted using a pulse function and Fast Fourier Transformation (FFT) method to remove noise with high speed on the TS signals [2]. The pulse fitting parameters (pulse height, rising time, falling time and peak position) were applied to calculate plasma parameters like the electron temperature (T e). To reduce the T e calculation time, a neural-network (NN) method was introduced using graphic processor unit (GPU) calculations. These plasma parameters were transmitted to the KSTAR plasma control system (PCS)using a reflective memory (RFM) card. The delay time of this RT-Thomson before transfer to the RFM card measured less than 7 ms for a T e calculation of 31 positions, and the transfer time from the RFM card to the PCS was 6.8 ms. Therefore, at 80.31% of KSTAR long pulse plasma shot # 32,763 (84.15 s), the end-to-end treatment time was less than 50 ms. The uniqueness of this paper is that it uses 5GS/s digitizer, Fast Fourier Transformation FFT fitting method, and neural- network (NN) analysis system, and finally succeeds in transferring Te profile data to the KSTAR PCS system in real- time (80.31% within 50 ms delay) using RFM cards for KSTAR long pulse plasma (84.15 s) for the first time. [ABSTRACT FROM AUTHOR]

A Thomson scattering diagnostic system is designed for Versatile Experiment Spherical Torus (VEST) to measure the spatial profiles of the electron temperature. The system is carefully designed to collect a sufficient number of photoelectrons and to reduce the noise sources, since relatively low electron densities and temperatures are expected in VEST due to the limited power capacity at present. The target electron temperature and the density are 10–200 eV and 5 × 10 18 m −3 , respectively which are extrapolated from the data of triple Langmuir probes measuring the edge plasma parameters at R = 0.75 m by assuming a parabolic density profile. The collecting optics is designed to have a wide-view angle and low cost by using a commercial photographic lens of low f-number and high transmittance optical fiber bundle. The bandwidths of the interference filters in the polychromator are designed for reliable measurements within the target electron temperature range. As a photo detector which is coupled with the filters, an avalanche photodiode (APD) with a low dark current and an adequate quantum efficiency near the laser wavelength is selected for the high signal-to-noise ratio. The number of photons transferred to the polychromator and the number of photoelectrons in the APD are calculated. At the commissioning phase, an oscilloscope with a high sampling rate will be adopted to check the necessity of the noise reduction by multi-shot signal accumulation. [ABSTRACT FROM AUTHOR]