Thomson Scattering Diagnostics Research Articles

Deep Learning Models to Reduce Stray Light in TJ-II Thomson Scattering Diagnostic

Nuclear fusion is a potential source of energy that could supply the growing needs of the world population for millions of years. Several experimental thermonuclear fusion devices try to understand and control the nuclear fusion process. A very interesting diagnostic called Thomson scattering (TS) is performed in the Spanish fusion device TJ-II. This diagnostic takes images to measure the temperature and density profiles of the plasma, which is heated to very high temperatures to produce fusion plasma. Each image captures spectra of laser light scattered by the plasma under different conditions. Unfortunately, some images are corrupted by noise called stray light that affects the measurement of the profiles. In this work, we propose the use of deep learning models to reduce the stray light that appears in the diagnostic. The proposed approach utilizes a Pix2Pix neural network, which is an image-to-image translation based on a generative adversarial network (GAN). This network learns to translateimages affected by stray light to images without stray light. This allows for the effective removal of the noise that affects the measurements of the TS diagnostic, avoiding the need for manual image processing adjustments. The proposed method shows a better performance, reducing the noise up to 98% inimages, which surpassesprevious works that obtained 85% for the validation dataset.

Commissioning and first results of the 174 GHz collective Thomson scattering diagnostic at Wendelstein 7-X

Collective Thomson Scattering (CTS) diagnostics measure the scattering spectrum of monochromatic incident radiation off collective fluctuations in the plasma. In this contribution, we present the first results from the upgraded CTS diagnostic at Wendelstein 7-X (W7-X) operating in the frequency range between 172 and 176 GHz. This frequency range allows for minimization of noise originating from the electron cyclotron emission in the plasma. Consequently, the good signal-to-noise ratio allows measurements of fast ions or bulk plasma parameters with higher temporal resolution compared with the previously used 140 GHz system.

Detection of Internal Transport Barrier in the T-10 Tokamak Using Thomson Scattering Diagnostics

At the T-10 tokamak, the Thomson scattering diagnostics was upgraded in 2016. The new system is based on the Nd:YAG laser with the pulse repetition frequency of 100 Hz; the measurements can be performed every 10 ms during the entire plasma discharge at the spatial resolution of up to 5 mm. Using the upgraded diagnostics, the electron temperature measurements were performed during experimental campaigns of the T-10 tokamak in 2016−2018. In the regimes with the electron cyclotron resonance heating, it was demonstrated that the regions with increased temperature gradients form in the plasma, which was interpreted as the formation of internal transport barrier. The ASTRA-code-based simulations of the current profile time evolution made it possible to correlate the positions of the barrier and the rational surface q = 1.

Using Thomson Scattering Diagnostics to Control Plasma Density at Globus-M2 Tokamak

Using Thomson Scattering Diagnostics to Control Plasma Density at Globus-M2 Tokamak

Divertor Thomson Scattering on Globus-M2

We present the first Thomson scattering (TS) measurements of electron temperature and densityin the lower divertor of the Globus-M2 tokamak. The divertor TS diagnostics is designed for local measurementsof the Te(z, t) in the range of 1–100 eV and ne(z, t) in the range of m–3. Parameters of theprobing Nd:YAG laser are as follows 1064 nm/2 J/100 Hz/3 ns. The probing chord is launched vertically atR = 24 cm and covers areas of the inner leg, vicinity of separatrix and private flux region. Along probing chordof 110 mm, 9 spatial points were realized. Advanced filter polychromators were used to analyze Thomsonscattering spectra.

Evaluation of ITER Real-Time Framework in plasma diagnostics applications

The ITER Real-Time Framework (RTF) is a software suite designed and developed to facilitate the implementation of various real-time applications for ITER plant systems. The main driver to implement RTF was the Plasma Control System (PCS). RTF was designed as a base and development environment for PCS. However, due to its universal architecture, it can also be applied in other systems requiring real-time control or data processing.This paper presents the demonstration system to evaluate RTF in Thomson Scattering (TS) diagnostics. The system was developed to validate the integration of data acquisition hardware with RTF and check it in real-time data processing applications. The presented system covers the whole path of data acquisition, processing and archiving required for a typical Instrumentation and Control (I&C) system for ITER diagnostics.The main components of the RTF-based application developed for the system are device support for the pulsed giga-sample analog-to-digital converter, functional blocks implementing algorithms for analysing pulses from polychromator and calculating plasma electron temperature as well as interfaces for archiving raw data and publishing the measurement results.The overriding goal of the presented work was a detailed functional and performance evaluation of the implemented RTF-based system. The system was tested in laboratory using simulated data and in tokamak conditions at Korea Superconducting Tokamak Advanced Research (KSTAR). During the test campaign at KSTAR, the developed RTF-based application was integrated into the Thomson Scattering system and tested during regular operation of the tokamak with signals from a real polychromator. The results of measurements and performance evaluation are presented and discussed in the paper.

Upgrade of Thomson Scattering Diagnostic on HL-2A

The Thomson scattering diagnostic of the HL-2A tokamak device was upgraded to improve its multi-point diagnostic capability, including new collection optics, fibers bundles, and data analysis code. The small old collection lens was replaced by a six-piece lens with a Cooke optical design. The aperture of its first standard sphere face is 310.125 mm, which successfully increases the amount of collected scattering light by about three times. The new collection optic module allows for up to twenty-six spatial points. A kind of Y-type fiber bundle has also been used to ensure that the fiber end-face matches the image of the laser beam exactly. Additionally, the new data analysis code can provide preview results in seconds. Finally, the multi-point Te diagnostic ability has been significantly improved.

Application of Machine Learning to Determine Electron Temperature in Globus-M2 Tokamak Using the Soft X-Ray Emission Data and the Thomson Scattering Diagnostics Data

Application of Machine Learning to Determine Electron Temperature in Globus-M2 Tokamak Using the Soft X-Ray Emission Data and the Thomson Scattering Diagnostics Data

Thomson Scattering Diagnostics of Plasma Electron Component for the Tokamak with Reactor Technologies

Thomson Scattering Diagnostics of Plasma Electron Component for the Tokamak with Reactor Technologies

Fast Signal Modeling for Thomson Scattering Diagnostics and Effects on Electron Temperature Evaluation

Fast Signal Modeling for Thomson Scattering Diagnostics and Effects on Electron Temperature Evaluation

First Results from the Thomson Scattering Diagnostic on the Large Plasma Device

We present the first Thomson scattering measurements of electron density and temperature in the Large Plasma Device (LAPD), a 22 m long magnetized linear plasma device at the University of California Los Angeles (UCLA). The diagnostic spectrally resolves the Doppler shift imparted on light from a frequency-doubled Nd:YAG laser when scattered by plasma electrons. A fiber array coupled to a triple-grating spectrometer is used to obtain high stray light rejection and discriminate the faint scattering signal from a much larger background. In the center of the plasma column, the measured electron density and temperature are about ne≈1.5×1013 cm−3 and Te≈ 3 eV, respectively, depending on the discharge parameters and in good agreement with Langmuir probe data. Optical design considerations to maximize photon count while minimizing alignment sensitivity are discussed in detail and compared to numerical calculations. Raman scattering off of a quartz crystal probe is used for an absolute irradiance calibration of the system.

Broadband Signal Amplification Paths for Semiconductor Radiation and Particle Detectors (Review)

This study is devoted to the development of amplifying paths for plasma diagnostics, a significant part of which use semiconductor detectors as sensors that form low-intensity current signals. One feature of these diagnostics is the oscillographic form of registering sensor signals. In tandem with detectors, broadband transimpedance amplifiers that are based on operational amplifiers are used to amplify and normalize sensor signals. The principles of constructing such amplifying paths are considered taking the factors affecting their final noise and frequency characteristics into account. Practical examples of the construction of amplifying paths of corpuscular and neutron plasma diagnostics, as well as the Thomson-scattering diagnostics, that are used at the plasma installations of the Institute of Nuclear Physics (Siberian Branch, Russian Academy of Sciences) are presented.

Optical Properties of Thomson Scattering Diagnostics Lower Window Glass under Laser Irradiation.

Tokamak diagnostic window glass is an indispensable optical medium in fusion research. The transmittance of the device affects the optical performance and accuracy of the diagnostic system. Especially, the window glass serves as the entrance of the light source while performing the sealing function for the active diagnosis method represented by Thomson scattering diagnostics. In this work, we studied the influence of the laser irradiation and tokamak discharge on the EAST (Experimental Advanced Superconducting Tokamak) Thomson scattering diagnostic borosilicate glass window. Using X-ray photoelectron spectroscopy (XPS) and Raman scattering, we found that carbon-based impurities in the device aggravated the film damage due to laser irradiation, reducing the performance of the coating of the glass. Besides, the laser and the various rays of tokamak discharge generated many point defects in the glass, increasing the light absorption of the glass. These two factors caused the glass transmittance to drop significantly (from 99.99% to 77.62%). In addition, the long-term laser irradiation primarily reduced the transmittance, while environmental rays had a minor impact on the same. This work provides valuable insights into the selection and effective use of glass in optics-based diagnostics.

Измерение температуры электронов плазмы токамака Глобус-М2 методом мультилазерного томсоновского рассеяния

Diagnostics of the plasma electron component by the method of Thomson scattering (TS) of laser radiation makes it possible to reliably measure the spatial distributions of the electron temperature and density. One of the obstacles to the implementation of TS diagnostics in thermonuclear reactors is the distortion of the spectral characteristics of the optical system due to radiation-induced absorption and contamination of optical elements with erosion products of the first wall. As a consequence, the reliability of measurements by the TS method will decrease over time. The paper describes the method of multi-laser Thomson scattering, which will solve this problem. The results of the first experiments on the Globus-M2 tokamak are also presented.

Digital filter polychromator for Thomson scattering applications

The paper describes the digital filter polychromator developed for Thomson scattering (TS) diagnostics. The device having ultra-low noise, high-speed detection system and up to 7 spectral channels is equipped with digitizer and single board computer for system control and data processing. The data acquisition system is capable to detect very short laser pulses of few ns width with low magnitude. This feature opens up new possibilities for the TS diagnostics design in modern fusion devices, which includes: operation with high background illumination, measurement of very low electron temperature and density at the plasma edge and scrape-off layer (SOL), separation of the TS signal and the stray light coming with a delay of several ns. The analysis of the TS signal waveform also gives a possibility to distinguish the TS and Mie scattering from the dust particles that is important for measurements in SOL. Owing to compactness and ultra-low energy consumption both optical and data processing units interfaced with optical Gigabit Ethernet were combined in a stand-alone device. Such all-in-one design with optical fiber input and optical digital output provides enhanced resistance to electromagnetic disturbances and simplify operation. A set of such polychromators can be mounted in a standard 19” rack and can be integrated with outer CODAC (Control, Data Access and Communication) system. Testing of the polychromators at the Globus-M2 tokamak has shown excellent performance of the developed serial devices.

Oscillation Characteristics of a High Power 300 GHz Band Pulsed Gyrotron for Use in Collective Thomson Scattering Diagnostics

Oscillation Characteristics of a High Power 300 GHz Band Pulsed Gyrotron for Use in Collective Thomson Scattering Diagnostics

Data Acquisition System for Thomson Scattering Diagnostics on GDT

This paper describes a data acquisition system for Thomson scattering diagnostics on a gas-dynamic trap (GDT) (the Budker Institute of Nuclear Physics, Novosibirsk, Russia). It allows recording scattered laser radiation pulses of ~10-ns duration with 5-GSPS sampling rate and 14-bit amplitude resolution. The data acquisition system includes eight-channel high-speed recorders and photodetector modules. The photodetector modules are based on avalanche photodiodes and low-noise transimpedance amplifiers. The recording module design uses switched-capacitor array technology.

The Measuring System for the Thomson Scattering Diagnostics of the GOL-3 and GDT Facilities

The measuring system for Thomson scattering diagnostics of the GOL-3 and GDT facilities at the Budker Institute of Nuclear Physics is described. The system has a modular architecture and is based on eight-channel measuring subsystems, including photodetectors, two-channel recorders (ADC12500), synchronization modules, and the Ethernet/UART communication channel adapter. The photodetectors are based on avalanche photodiodes and are operable in the frequency range of 0–50 MHz. The ADC12500 recorders are used to measure scattering signals with a duration of ~20–30 ns at a sampling rate of to 500 MHz and an amplitude resolution of 12 bits and accumulate data in a buffer memory with a capacity as large as 2 MB.

Digital filter polychromator for Thomson scattering applications

Incoherent Thomson scattering diagnostics (TS) is a proven technique capable of reliable and robust instantaneous measurement of electron temperature (Te) and density (ne) local values in wide area of plasma physics experiments: from hall-effect thrusters to tokamaks and stellarators. The TS cross section is very low (∼ 6.7 × 10−30 m2), and the corresponding TS signals, measured in fusion experiments, are usually of ∼10−15 of incident power. This paper represents 6 (7) channel filter polychromator equipped with avalanche photodiodes and low-noise preamplifiers. The incorporated ADC system (5 GS/s, 12 bit) provides digital optical output preventing acquisition system from electromagnetic interferences. The calibration techniques and Te, ne with corresponding errors measured in Globus-M plasma are given for the digital polychromator test-bench.

Multiple Laser System for High-Resolution Thomson Scattering Diagnostics on the EAST Tokamak

A multiple laser system for high-resolution Thomson scattering diagnostics has been developed in ASIPP. The system includes laser controller, high-energy lasers, transfer optics, focusing lens, and beam alignment system. Each Nd:YAG laser can be fired for measuring the electron temperature and density profiles periodically at 10 Hz, and consequently, four lasers can be fired alternately for an average measurement frequency of 40 Hz. In order to measure transient events, they will be fired in rapid succession, and produce a burst of pulses. After about one month trial running on the superconducting EAST tokamak, the system was proven to be capable of working well with improved time resolution. The system setup and analysis are described in detail, as well as the measurement capability, spatial and temporal resolutions ~7 mm and tens kilohertz, respectively. So as to monitor and adjust the laser beam, two beam position sensitive detectors are installed in the 40-m beam path. Finally, the experimental results are presented.