Development Of Optical Thomson Scattering Diagnostic Technique

Optical Thomson scattering diagnostics(OTS)is a key diagnostic method in both magnetic confinement fusion and inertial confinement fusion,with which by fitting the spectra of scattered light,basic plasma parameters can be inferred.In this thesis,we construct a non-collective OTS system for the Keda Torus eXperiment(KTX)device of USTC,and a collective OTS system for the Magnetized Laser Plasma Device(MPLD)to validate the ideal of multiple-angle scattering scheme.(1)A non-collective TS diagnostic system is built for the Keda Torus eXperiment(KTX)device of USTC to measure the plasma density and temperature.The diagnostic system utilizes a pulsed probe beam with a wavelength of 1064 nm and repeat frequency of 200 Hz.The scattered light is collected at 90°,and transferred with a customized optical fiber bundle.A spectrum dispersion and record scheme utilizing volume phase grating,spectrum optical fiber bundle and avalanche photon diodes(APDs)is proposed and built,and a high-speed oscilloscope is used to record the scattered signal.(2)Multiple stray light suppression methods of the non-collective OTS system are proposed are evaluated,which include:a spatial filter is used to block the diffracted high-order sidebands of the probe light;black coatings are added in the light-transmission pipes and mirror chambers;two key diaphragms at the entrance and exit of the KTX torus chamber are installed to directly limit the solid angle of stray light into the vacuum chamber;a polished silicon is employed as a beam dump to absorb the excessive probe light;black coatings are employed to the inner surface of KTX vacuum chamber,the inner surfaces of flanges of entrance and exit port of probe beam,and the flange inner surface of collection optics.We qualitatively evaluate the reduction of stray light with above methods by using the commercial ray-tracing software TracePro.The simulation shows that with the above methods,the amount of stray light can be reduced by about 5 orders of magnitude,when compared with scenario in which no stray light suppression methods are adopted.(3)Several automatic beam alignment systems are designed and installed on this TS diagnostic system.In order to solve the problem that the recording cameras may have a shift while the KTX discharges,an automatic beam alignment system based on relative position is proposed.Two key diaphragms mentioned above are utilized as the references for beam alignment.A control software based on LabVIEW is developed to process the images and control the movements of mirrors.The test results show that the improved system has the ability to correct the spatial pointing of a shifted beam and to suppress the long-term pointing drift of the beam.More importantly,the improved system can overcome the camera shift,with a deviation of only about 4.6 μrad when the recording camera has a translation of about 1.8 mm.(4)In order to extract electron density information from ion-acoustic-wave(IAW)feature of collective TS,a three-angle collective TS diagnostic system is built on the MLPD at USTC.This system collects scattered light from 45°,90°,and 135° with four achromatic lenses,with which a near-diffraction-limit imaging quality in the wavelength range of 480～580 nm and in the field of view of 1 mm can be achieved.Three step-index optical fibers are used to transfer the scattered light,making it easier for us to adjust the light path of three collection branches.A set of relay lenses are designed and established for blocking the un-shifted stray light.An intensified charge coupled device is used to record spectra,with the gate opening about 3.5 ns.Time-integrated IAW spectra of aluminum and carbon-hydrogen plasma with good signal-to-noise ratio are obtained.IAW spectra of aluminum plasma at 90° and 135° are fitted simultaneously.Electron density inferred from Thomson scattering are in reasonable agreement with those inferred from digital holograph diagnosis,demonstrating that IAW features of multi-angle TS can provide reliable electron density infromaton.(5)We further develop a time-resolved TS system to detect IAW and electron-plasma-wave(EPW)feature spectra simultaneously.Signal from three scattering angles is transferred with three fiber couplers,and fiber are horizontally placed at the entrance of the spectrometer so that the spectra can be recorded with only one streak camera;Electron densities inferrrd from the two-angle IAW spectra and the single-angle EPW spectrum consist with each other,which again proves the validity of extracting the electron density by the dual-angle IAW spectrum in a suitable parameter range.