Collective Thomson scattering, using a high-power pulsed D2O laser at 385 μm and a heterodyne receiver system, has provided local ion temperature (Ti) measurements of the plasma in the tokamak chauffage Alfvén (TCA) tokamak. Recent improvements in the noise-equivalent power of the Schottky barrier diode mixers permitted us to achieve a typical precision of ±12% for a single shot measurement at densities above 1020 m−3. Even at densities of standard TCA discharges (5×1019 m−3) the uncertainty is better than ±25%. For the interpretation of the measured spectra and the evaluation of Ti the local value of the electron temperature (Te) is an important parameter. Therefore, Te was measured simultaneously by incoherent Thomson scattering at 0.694 μm during a series of shots. The density was obtained from a far-infrared interferometer. An independent measurement of Ti on TCA can be obtained from a neutral particle analyzer. Comparison of the results from the two methods showed good agreement. The precision of a Ti measurement depends strongly on the plasma density. Since an uncertainty of ±25% at standard densities may still not be regarded as satisfactory, further investigations using a numerical simulation code have been carried out to find ways of improvement.

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In order to study the spherical aberration of thermal lens when the laser crystal is pumped with the pump light distributed differently and the pump light under the end-pumping condition, in this paper we establish a single-ended pump and constant temperature thermal model to analyze the working characteristics of the Nd:YVO4 crystal. The steady state heat conduction equation and Zernike polynomials are solved, and the relationship between thermal spherical aberration and distribution of pump laser is established. The model is used in simulation, and the simulation results are further analyzed theoretically, showing that under the same pump power, the spherical aberration is greatest when the pump beam is of 2-order super-Gaussian distribution. The spherical aberration decreases with the increase of pump distribution coefficient k (except the Gaussian distribution). With the increase of pump power, the influence of pump distribution coefficient k on spherical aberration is aggravated gradually, and the difference in spherical aberration caused by different values of distribution coefficient k increases gradually. The range of strongest laser power of the 2-order super-Gaussian distribution pump is analyzed and simulated. Under same pump power, the maximum range of the strongest laser power of 2-order super-Gaussian distribution pump is 0.3-0.63 times the Gauss radius. The research methods and conclusions obtained in this paper have universal applicability and can be used for quantitatively analyzing the temperature distributions, thermal deformations, optical path difference distributions, and spherical aberration distributions of other laser crystals. At the same time, this study also provides a theoretical reference for improving spherical aberration from the perspective of changing the distribution of pump light and the laser output characteristics.

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