Digital Polychromator
Spectrum analyzing system for Thomson scattering (TS) signals registration and processing (hereinafter referred to as “system ”) is intended for laboratory plasma investigation by the Thomson scattering method in order to register local values of electrons temperature and density in plasma with detailed temporal and spatial resolution, as well as for recording, storing and processing the obtained data. Application fields: scientific research.​

Detailed description​ ​

For more detailed overview of the diagnostic system please refer the whitepaper.

Technical specifications

Spectral range λΔ, nm1064-920 (may vary on demand)
Basic wavelength of the probe laser λ (YAG), nm1064
Repetition rate of measured signals, Hz100 – 3000
Number of pulses recorded during discharge, pulses/discharge, not more than1000 (may vary on demand)
Weight of the system (without optical fiber bundles and electrical cables), kg, not more than550
Weight of the equipped cubicle, kg, not more than 500 Power consumption, V∙А, not more than3800
Power supply
Voltage, V220±22
Frequency, Hz50±1
Mean-Time-To-Failure, h, not less than10000
Average service life, y, not less than5
Average recovery time, h, not less than4
Filter polychromator
PhotodetectorAvalanche photodiode (APD)
Number of spectral channels6
Spectral ranges of the channels, nm1060-1055, 1055-1045, 1045-1025, 1025-985, 985-920, 1063-1065, (may vary on demand)
Scattering signal digital recorder
Sample rate, GSPS5
Resolution, bit12
Background radiation digital recorder
Sample rate, KSPS10
Resolution, bit12
Dimensions (LхWхH), mm, not more than88х482х842
Weight, kg, not more than23
Number of polychromators in the rack, pcs10 (may vary on demand)
Power consumption, V∙А, not more than100
Synchronization unit
Electrical signal input / output
Pulse duration, ns50
Laser pulse shape detector
Bandwidth, MHz300
Sample rate, GSPS5
Resolution, bit12
Dimensions (LхWхH), mm, not more than88х482х385
Weight, kg, not more than7
Power consumption, V∙А, not more than35
Data processing and storage unit (industrial PC)
RAM size, Gb16
Hard drive space, Tb3
Number of hard drives4
Cache/boot solid state drive space, Gb120
Number of processor cores4
Cache size, Mb8
CPU, GHz2,9
Number of 10-Gigabit network connectors2
Dimensions (LхWхH), mm, not more than175х482х570
Weight, kg, not more than20
Power consumption, V∙А, not more than700
Equipment cubicle
Dimensions (LхWхH), mm, not more than2145х800х1000
Type19-inch rack
UPS power consumption, V∙А, not more than2000
Weight (without equipment), kg, not more than250
Optical trigger unit
Laser attenuationCombination of light filters and / or attenuator
Parameters of attenuated laser radiation
Energy, mJ, not less than0,5
Divergence, rad2 * 10 -4
Dimensions (LхWхH), mm, not more than52х52х167
Weight, kg, not more than1
#Operating conditions
Ambient air temperature, °C15…28
Ambient pressure, kPa19…23
Relative humidity at 21°C, not more than, %84,0…106,7
Relative dispersion, nm/mm60
Vibrations and shocksno

General Principles of Operation

The system operation is based on analysis of electron component of laboratory plasma by the method of Thomson scattering of laser radiation. Scattered laser radiation is collected by the collection lens, the focal surface of which comprises input ends of optical fiber bundles, distributing radiation across the filter polychromators (hereinafter - “polychromator”). Each polychromator measures electron temperature and density at one spatial point. Electron temperature is determined on the basis of scattered radiation spectrum analysis. Density value is determined by intensity of the recorded scattering signals. Scattering signals registration is carried out by a small number of spectral channels (up to 6). Each spectral channel is equipped with transimpedance amplifier with avalanche photodiodes (APD). The used amplifier comprises two outputs: high-frequency (for measuring scattering signals) and low-frequency (for calibration), capable to measure quasi-permanent signals. The signals are digitized by the ADC embedded in the polychromator.

Prior to measurements, the system should be calibrated. Spectral and absolute calibrations should be carried out for the Thomson scattering diagnostics. Spectral calibration, the essence of which is to estimate relative sensitivity of spectral channels, is necessary for electron temperature determination. A set of calibration equipment supplied with the system is used for spectral calibration. Absolute calibration is necessary toSpectrum analyzing system for Thomson scattering signals registration and processing determine electrons density; its purpose is to determine the coefficient of correspondence between the number of scattered photons and magnitude of the detected signal for each spectrometer. Absolute calibration is performed using the Raman scattering method.

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