Some progress has been made to develop the multipoint Thomson scattering (TS) diagnostic for the HL-2A tokamak physics experiments. Hardware of silicon avalanche photodiode detector electronics is improved, which provides two output signal channels. In one channel, only the rapid TS signal is the output after deducting the influence of the background slow-varying plasma light. In the other, both the rapid TS signal and the plasma background signal are the output. In the latest HL-2A experiment campaign, the newly developed electronics are tested and TS signals can be obtained from each of the two channels, where the signal is digitized by 12-bit transient recorder sampled at 1 GS/s. Laser beam alignment is fulfilled by using motorized stages to control the laser beam passing through ∼10 mm-wide narrow throats of the lower and upper closed divertors with small movements and then the stray laser light is reduced. New modules of fast digitizers with more than 100 channels are installed and will be used to record TS pulse signals. On the basis of these achievements, about 15-point measurements of plasma electron temperature and density by Thomson scattering diagnostic will come into operation in the upcoming HL-2A experiment campaign.
The edge tangential Thomson scattering system (ETTSS) was developed for the first time on a HL-2A tokamak. A Nd:YAG laser with a 1064 nm wavelength, 4 J energy, and 30 Hz repetition rate is employed on the ETTSS. The laser beam injects the plasma in the tangential direction on the mid-plane of the machine, and the angles between the laser injection direction and the scattered light collection direction are in the range from 157.5° to 162.8°. The scattered light collection optics with 0.21-0.47 magnification is utilized to collect the scattered light of measurement range from R = 1900 mm to 2100 mm (the normalized radius is from r/a = 0.625 to 1.125). Spatial resolution of the preliminary design could be up to Δr/a = 0.016. The measurement requirements could be achieved: 10 eV < Te < 1.5 keV, and 0.5 × 10 m < n < 3 × 10 m with errors less than 15% and 10%, respectively.
Some new progress has been made to develop the multi-point Thomson scattering (TS) diagnostic for the HL-2A tokamak physics experiments. Hardware of silicon avalanche photodiode detector electronics, motorized stages to control the laser beam for beam alignment, 3 modules of fast digitizers with more than 100 channels to record the time evolution of the TS pulses at 2.5 GS/s with 12-bit resolution, and 15 polychromators for 15-point measurements of core plasma electron temperature. The data processing code is further adjusted to manage the digitized raw data. The TS intensity is obtained by direct summing method and by Gaussian-function fitting, respectively, and then different value of electron temperature is derived by the technique of weighted least-squares regression. As to the latter, the electrical noise and perturbations of the TS signal is significantly reduced, the resulting value of electron temperature has a better quality than that of the former. New processing code is in development.
Er 3+ upconversion (UC) fluorescent characteristics of ErNbO 4 phosphor were studied for temperature sensing purposes. This letter shows that the ErNbO 4 phosphor emits more UC fluorescence than the Er 3+ -doped LiNbO 3 singlecrystal and Er 3 NbO 7 phosphor. Both energy-transfer UC and excited state absorption play a role in the UC emission. Both the peak and integrated UC intensities decrease with the raised temperature, and the 530, 560, and 670 nm UC intensities reduce by ∼26%, 42%, and 34%, respectively, with the temperature rise of only 57°C from 21°C, implying that the phosphor is applicable to temperature sensing based upon either the 560-or 670-nm emission. The feasibility to realize the temperature sensing is discussed from the application requirements of smartness and low-cost, suggesting that not only the single 560-or 670-nm band, but the combined 530-and 560-nm bands can be also utilized.Index Terms-ErNbO 4 phosphor, upconversion, thermal effect.
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