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The local measurements of electron density and temperature by Thomson scattering (TS) diagnostics are essential for research of energy confinement, plasma heating, and control at nuclear fusion devices. This paper presents a digital filter polychromator designed for TS spectrum registration. A distinguishing feature of such a digital polychromator is the use of an analog-to-digital converter (ADC) having analog memory with discretization frequency of 5 GHz and 12-bit sampling. The low heat dissipation and compact design of the ADC allow us to integrate the recording and data handling systems in the spectral unit to obtain a standalone device that is totally isolated from other systems and equipment in the voltaic sense. The scattered laser radiation received from the plasma comes to the entrance of the polychromator through a fiber-optic cable, and the processed scattering signals and calculated electron density and temperature are available on a digital interface. The polychromator was tested within the Thomson scattering system at the Globus-M tokamak using two probing lasers: Nd:YAG 1064 nm and Nd:Glass 1055 nm operating with pulse energy up to 2J and FWHM of 4 and 40 ns, respectively. The employed ADCs allowed us to perform superfast signal digitizing in the oscilloscope mode and to demonstrate the possibility of stray signal time separation despite the modest size (~1 m) of the vacuum chamber. The results of measurements performed during the plasma experiment at the Globus-M tokamak are presented, and their comparative analysis with the data obtained at the operating TS system is made.

Thomson scattering (TS) is the most accurate and useful method of measuring plasma electron temperature and density in fusion-oriented experiments. The small power (∼10−8W) and short duration (∼10 ns and less) of scattering signal are the main technical problems of the method. That is why highest requirements are made to photodetection and recording systems. Developed by Budker Institute of Nuclear Physics (Novosibirsk, Russia) fast DAQ system allows recording profiles of short duration (3-5 ns) scattered pulses in 0-200MHz bandwidth with 2GSPS rate and 12-bit resolution. The system consists of photo detector modules (with 200MHz bandwidth), fast (2GSPS) and slow (10MSPS) ADC modules and synchronization subsystem. The 48-channel version of this system was developed as a prototype for ITER (Cadarache, France) divertor Thomson scattering diagnostic. The system was tested and put into operation on GLOBUS-M tokamak (St. Petersburg, Russia).