Thomson Scattering Research Articles

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.

Ripple and Lotus Phenomenon: Radiation Pattern Evolution of Nonlinear Thomson Scattering Under Cooperative and Competitive Effects of Applied Magnetic and Laser Field

Ripple and Lotus Phenomenon: Radiation Pattern Evolution of Nonlinear Thomson Scattering Under Cooperative and Competitive Effects of Applied Magnetic and Laser Field

Design of a Thomson scattering diagnostic for the SMall Aspect Ratio Tokamak (SMART).

We describe the design of a Thomson scattering (TS) diagnostic to be used on the SMall Aspect Ratio Tokamak (SMART). SMART is a spherical tokamak being commissioned in Spain that aims to explore positive triangularity and negative triangularity plasma scenarios at a low aspect ratio. The SMART TS diagnostic is designed to operate at high spatial resolution, 6mm scattering length in the low-field side and 9mm in the high-field side regions, and a wide dynamic range, electron temperature from 1eV to 1keV and density from 5×1018m-3 to 1×1020m-3, to resolve large gradients formed at the plasma edge and in the scrape-off layer (SOL) under different triangularities and low aspect ratios. A 2J @1064 nm laser will be used that is capable of operating in the burst mode at 1, 2, and 4kHz to investigate fast phenomena and at 30Hz to study 1s (or more) long discharges. The scattered light will be collected over an angular range of 60° - 120° from 28 spatial points in the midplane covering the entire plasma width and the outer midplane SOL. Each scattering signal will be spectrally resolved on five wavelength channels of a polychromator to obtain the electron temperature measurement. We will also present a method to monitor in situ laser alignment in the core during calibrations and plasma operations.

Zeptosecond-Yoctosecond Pulses Generated by Nonlinear Inverse Thomson Scattering: Modulation and Spatiotemporal Properties

Zeptosecond-Yoctosecond Pulses Generated by Nonlinear Inverse Thomson Scattering: Modulation and Spatiotemporal Properties

Analysis of the Effect of Pulse Length and Magnetic Field Strength on Nonlinear Thomson Scattering

Analysis of the Effect of Pulse Length and Magnetic Field Strength on Nonlinear Thomson Scattering

Collection optics of JT-60SA edge Thomson scattering diagnostic.

The mission of the JT-60SA project is to complement ITER's capabilities by addressing the fundamental physics and engineering challenges necessary to develop a practical and reliable fusion power plant. Diagnostics play a pivotal role in achieving this mission, especially the Thomson Scattering (TS) diagnostic systems developed by a collaborative Japan-EU team. The edge Thomson scattering of JT-60SA is tailored to measure the low field side outer region of the plasma, in particular, to resolve the electron temperature Te and density ne. The collection optics of the edge TS system have a critical role in meeting the required field of view and spatial resolution despite the limited space. This work presents a comprehensive optomechanical design of the optics assembly, whose main features are telecentricity and compactness, highlighting its capabilities. The tests undertaken to verify its performance: focal plane identification, thermal cycle, and magnification, are described.

The effect of electron temperature and density profiles on the line-averaged electron temperature obtained from PHA spectra

Electron temperature (Te) is one of the main plasma parameters, which is routinely measured during fusion experiments. The major systems for the Te determination used for tokamak and stellarator plasmas are Thomson scattering (TS) and Electron Cyclotron Emissions (ECE). Measurements of Te can be also performed by other diagnostics such as Pulse Height Analysis (PHA), which is mainly intended for impurity identification. Due to the fact that PHA system is able to provide an information about line-averaged electron temperature (<Te>), there is a need to specify experimental conditions under which 〈Te〉 determined from PHA spectra is comparable to the electron temperature from plasma centre (Te0). In this paper, the analysis related to the effect of electron temperature (Te) and density (ne) profiles on 〈Te〉 estimated from spectra collected by PHA diagnostic installed at Wendelstein 7-X (W7-X) is presented. The studies described in this work consists of simulation and experimental results, on the basis of which 〈Te〉 has been estimated for a wide range of experimental condition, that differ in combination of Te and ne profiles.

Implementation of low temperature spectrometers for the JET high resolution Thomson scattering diagnostic for disruption plasma measurements.

This work presents a system upgrade of the High Resolution Thomson Scattering (HRTS) diagnostic [Pasqualotto etal., Rev. Sci. Instrum. 75, 3891-3893 (2004)] on JET that allows it to measure low temperature (1-500eV) plasma pre- and post-Thermal quench (TQ), which would help us further understand the Shattered Pellet Injection (SPI) physics. The upgrade was done by connecting optic fibers from the original HRTS system to four spectrometers specialized in measuring low temperature plasmas. The upgraded system allows for the measurement of low temperature plasma at up to 12 spatial points, which can be flexibly distributed throughout the JET outer midplane profile during the dedicated SPI experiments. In other JET experiments, four previously unused groups of fibers were used to measure the central plasma to provide disruption data without changing the standard HRTS system. The low temperature Thomson scattering system was installed, commissioned, and cross-calibrated against the standard HRTS diagnostic in a calibration pulse. The system worked reliably during the JET experiments and provided electron density and temperature profiles for pre- and post-TQ low temperature plasmas in the SPI campaign.

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.

Experimental demonstration of polarization control in Thomson scattering X-ray sources

Thomson scattering sources are known for generating quasi-monochromatic, high-brightness, and polarization-tunable X-rays, which are widely applied in fields such as fluorescence imaging, magnetic circular dichroism, and nuclear physics. In this paper, we present an experimental demonstration of polarization control at the Tsinghua Thomson scattering X-ray source (TTX) by adjusting the laser polarization. A specially designed Compton polarimeter is employed to effectively analyze the Degree of Linear Polarization (DoLP) of the X-rays produced at the TTX. Our results indicate that the DoLP of X-rays within a collecting angle of 1/(3γ), where γ is the Lorentz factor of the relativistic electron, closely matches the DoLP of the laser. Furthermore, we demonstrate that the X-ray polarization can be continuously modulated from linear polarization to circular polarization by adjusting the laser polarization, which can significantly enhance the functionality and applicability of Thomson Scattering sources for scientific research.

An algorithm to enhance the capability of imaging Thomson scattering

Collective Thomson scattering (TS) is a powerful technique to accurately diagnose the parameters of laser-produced plasmas. However, when the scattering parameter α, which is inverse to the product of electron Debye length and wavenumber of plasma fluctuations, is significantly larger than 1, which of the conditions is easily satisfied in the experiment, the accuracy of electron density measurement is usually poor just with the single-wavenumber ion-acoustic wave feature of the TS spectrum. This situation can be greatly improved in the imaging TS experiment because the signal intensity is proportional to electron density. A novel algorithm is developed and validated for the data analysis of imaging TS through the combination of signal intensity and spectral profile. The results show that we can obtain the electron density with high confidence, as well as other plasma parameters like electron and ion temperatures.

Performance of JT-60SA Thomson Scattering data analysis system

We have developed signal processing routines for the Thomson Scattering measurement, which is planned for use in the next campaign of the JT-60SA large-scale tokamak experiment.This paper provides the data analysis system and its performance evaluated in terms of computation time and error.The sequential routine of determining the scattered light intensity from a simulated signal, including noise data from a 1 Gs/s high-speed sampling digitizer, and determining the electron temperature and density was tested for the first time on an actual machine.The data analysis system ensures that electron temperature and density can be calculated with reasonable relative errors and within a realistic time frame for operations on JT-60SA.

Set of Thomson Scattering Diagnostics for TRT

Set of Thomson Scattering Diagnostics for TRT

Thermo-mechanical analysis of the components in the launcher transmission line of ITER ex-port plug collective Thomson scattering

ITER Collective Thomson Scattering (CTS) diagnostic system is designed to analyze the alpha particles resulting from Deuterium-Tritium fusion reactions. It consists of one launcher and nine receiver transmission lines. The launcher line transports the high-power microwave emission of 1.2 MW from the gyrotron source to the front-end, while the receiver lines transport the collected microwave emission from the front-end and distribute it to the instrumentation in the Diagnostic Building.Due to the high power transported in the launcher line, it has to be water-cooled to minimize the thermal expansion resulting from the heating caused by the power losses. Therefore, this work primarily focuses on establishing the cooling system parameters for the launcher TL to ensure efficient dissipation of the ohmic losses, while meeting the ITER cooling requirements. Once the parameters of the water cooling system are defined, a thermo-mechanical analysis of the most critical components is performed to assess their temperature distribution and deformations.

Distinctive Features of Measuring Te and ne Spatial Distributions in the Globus-M2 Spherical Tokamak Using Method of Thomson Scattering of Laser Radiation

Distinctive Features of Measuring Te and ne Spatial Distributions in the Globus-M2 Spherical Tokamak Using Method of Thomson Scattering of Laser Radiation

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.

Feasibility of a collective Thomson scattering diagnostic for burning plasma control on DEMO

Diagnostic systems are essential for burning plasma control and operation of DEMO, but are at the same time challenging in terms of design and integration. The harsh environment around the DEMO plasma, and the space restrictions and need to maximize the first-wall area used for tritium breeding, set limitations on the number and type of diagnostics to be installed. This will focus the efforts on diagnostics needed for control of the DEMO plasma. The robustness and versatility of a microwave-based Collective Thomson Scattering (CTS) diagnostic make it worthwhile to investigate the potential of a DEMO CTS diagnostic. We present the initial exploratory effort on this.The study builds on the experience of existing CTS experiments on e.g. ASDEX Upgrade, and on the recent development of the ITER CTS system, which focuses on measurements of fast ion dynamics in the burning ITER plasma. The initial target of the DEMO CTS diagnostic was to use an Electron Cyclotron Resonance Heating (ECRH) gyrotron beam as the probing source, with the receiving quasi-optical system being a dedicated CTS setup. Based on raytracing calculations including signal-to-noise estimates, it is found that such a setup is not viable. Here, we present studies of alternative solutions, including assessments of which DEMO plasma parameters the CTS diagnostic may contribute to determine.

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.

Study of the spatial growth of stimulated Brillouin scattering in a gas-filled hohlraum via detecting the driven ion acoustic wave

In an experiment performed on the Shenguang-III prototype laser facility, collective Thomson scattering (TS) is used to study the spatial growth of stimulated Brillouin scattering (SBS) in a gas-filled hohlraum by detecting the SBS-driven ion acoustic wave. High-quality time-resolved SBS and TS spectra are obtained simultaneously in the experiment, and these are analyzed by a steady-state code based on the ray-tracing model. The analysis indicates that ion–ion collisions may play an important role in suppressing SBS growth in the Au plasma; as a result, the SBS excited in the filled gas region is dominant. In the early phase of the laser pulse, SBS originates primarily from the high-density plasma at the edges of the interaction beam channel, which is piled up by the heating of the interaction beam. Throughout the duration of the laser pulse, the presence of the TS probe beam might mitigate SBS by perturbing the density distribution around the region overlapping with the interaction beam.

Validation of MARS-F modeling of plasma response to RMPs using internal measurements on DIII-D

The linear resistive plasma response model is validated against the plasma internal measurement data from DIII-D edge-localized mode (ELM) control experiments with applied resonant magnetic perturbation (RMP). Considered are DIII-D discharges where the n = 1, 2, and 3 (n is the toroidal mode number) RMP field was applied. Experimental data for the plasma boundary displacement, as well as the three-dimensional (3D) pressure perturbation in the edge pedestal region, are deduced from the vertical Thomson scattering (TS) system and the horizontal charge exchange recombination (CER) system on DIII-D. The linear response model produces results that are in reasonable quantitative agreement with the DIII-D internal measurements. The plasma boundary displacement of up to 15 mm is modeled, with the pedestal pressure perturbation reaching 3 kPa. As an important insight, the larger plasma displacement measured by the vertical TS system, as compared to that measured by the horizontal CER system, is due to the contribution from the tangential component of the plasma displacement to the former. This mixing of displacement components is also found to influence the sensitivity of the CER measurement comparisons. The results of this study provide further confidence in the linear resistive plasma response model for analyzing ELM control experiments.