Charge exchange recombination spectroscopy (CXRS) is commonly used for the measurement of plasma ion temperature, rotation velocity, impurity density, and the radial electric field from the ion pressure balance equation[
Chinese Optics Letters, Volume. 13, Issue Suppl., S21202(2015)
Design of filter spectroscopy for the measurement of plasma ion temperature and rotation on the Experimental Advanced Superconducting Tokamak tokamak
A new filter spectrometer for the simultaneous measurement of plasma ion temperature and rotation velocity on the experimental advanced superconducting tokamak is proposed. The Doppler broadening and Doppler shift of the plasma spectral line is determined by the signal intensity ratio of the three-filter channels that have different peak wavelengths. A rapid calculated algorithm of the temperature and rotation velocity is presented. This filter spectrometer will allow researchers to measure spectra with a temperature and velocity range of 0.1–5 keV and
Charge exchange recombination spectroscopy (CXRS) is commonly used for the measurement of plasma ion temperature, rotation velocity, impurity density, and the radial electric field from the ion pressure balance equation[
Figure 1.Schematic for the principle of the charge exchange recombination (left). Right, CXRS spectrum; Doppler shift (
The ion temperature and the plasma velocity are determined from the Doppler broadening and Doppler shift of the measured spectral lines. To achieve a temporally and spatially resolved measurement, the standard spectrometry for the CXRS utilizes the grating spectrometers equipped with
On the EAST tokamak, the light emitted from the beam–plasma interaction zone is normally collected by the collection optics and then transferred via the fiber bundles towards the common spectrometers behind the EAST hall for spectral analysis[
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Figure 2.Top view of the filter spectrometer optical layout. Designed center wavelength for the three filters (Channel 3) is 529.55 nm, the tilt angle of the silica filter for the two short wavelength (529.05 and 528.55 nm; Channels 2 and 1, respectively) is about 3.6° and 5.1°, respectively.
The filter is one of the key parts. The spectral transmission of the filter used is usually affected by the incident angle of the light to the filter and the ambient temperature. The decrease in the central wavelength is a function of the refractive indices of the deposited films and the angle of incidence. For the collimated radiation with an incident angle
In order to control the incident angle between the light and the filter, a high-precision rotary table from JinHang Precision Bearing Co., Ltd is used to support the filter. A high-accuracy goniometer is used to measure the rotary angle of the filter and the accuracy can reach 1″. A computer-controlled stepper motor is used with encoders to ensure wavelength accuracy.
The center wavelength of the interference filter will shift linearly with changes in ambient temperature; there is about 0.016 nm/°C (Andover Corporation filter, varied from company to company) at 529 nm (it is equivalent to a velocity change of
Macrolens are positioned in the front of the PMT detectors to increase the light collection efficiency and are used to make the input light match the image size of the PMT. The metal-encapsulated PMT (Hamamatsu, PM-HV-R9880-20) is chosen as it has a constant spectral sensitivity, high photon and quantum efficiency, and low dark noise over the broad range of the measured wavelength (
A schematic view of the measurement principle for filter spectroscopy is shown in Fig.
Figure 3.Schematic representation of the measurement principle of filter spectroscopy. Three Gaussian functions with different central wavelength and width are used to represent the spectral sensitivity and a slight difference for each channel is assumed.
The signal intensity (
Then the ratio between the intensities of two side-channels and the central channel can be written as
A typical 2D data set calculated with Eq. (
Figure 4.Ion temperature and rotation velocity dependence of the line intensity ratios
In conclusion, a filter spectrometer prototype for fast measurements of the plasma ion temperature and rotation on the EAST tokamak is being designed. The Doppler broadening and Doppler shift of the plasma spectral line is determined by the signal intensity ratio of the three-filter channels that have different peak wavelengths. A rapid calculated algorithm of the temperature and rotation velocity is presented. This filter spectrometer with the suitable filter parameters will allow researchers to measure spectra with the temperature and velocity range of 0.1–5 keV and
[13] . Quality optical filters and coatings catalog(2014).
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Yingying Li, Xianghui Yin, Bangxin Wang, Yi Zhang, Jia Fu, Bo Lv, "Design of filter spectroscopy for the measurement of plasma ion temperature and rotation on the Experimental Advanced Superconducting Tokamak tokamak," Chin. Opt. Lett. 13, S21202 (2015)
Category: Instrumentation, measurement, and metrology
Received: Jan. 25, 2015
Accepted: Mar. 10, 2015
Published Online: Aug. 8, 2018
The Author Email: Yingying Li (liyy@ipp.ac.cn), Bangxin Wang (bxwang@aiofm.ac.cn)