Thomson Scattering System Research Articles

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.

Systematic Error Analysis of Thomson Scattering System on VEST With Rotational Raman Calibration

Systematic Error Analysis of Thomson Scattering System on VEST With Rotational Raman Calibration

Design of the Collective Thomson Scattering System on HL-3 tokamak

A collective Thomson scattering (CTS) diagnostic system is being developed to measure fastion velocity distribution on HL-3 tokamak. A 140 GHz gyrotron belonging to electron cyclotron resonance heating (ECRH) system would be used to generate probe beam. The scattering spectra among HL-3 parameter ranges are calculated to assess diagnostic feasibility. Scattering signals will be detected by a heterodyne system, which is proposed to optimize diagnostic performance.

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.

High Te discrepancies between ECE and Thomson diagnostics in high-performance JET discharges

The present paper is dedicated to the study of the discrepancies encountered in electron temperature (Te) measurements carried out with electron cyclotron emission (ECE) and Thomson scattering (TS) diagnostics in the core of the JET tokamak. A large database of discharges has been collected, including high-performance scenarios performed with deuterium only and deuterium–tritium mixtures. Discrepancies have been found between core Te measurements taken with an X-mode ECE interferometer (TECE) and a LIDAR TS system (TLID) for Te>5 keV. Depending on the plasma scenario, TECE has been found to be systematically higher or lower than TLID. Discrepancies have also been observed between the peaks of the ECE spectrum in the second (X2) and third (X3) harmonic domains, even in high optical thickness conditions. These discrepancies can be interpreted as evidence of the presence of non-Maxwellian features in the electron energy distribution function (EEDF). In order to investigate the relation between the shape of the EEDF and the measured discrepancies, a model for bipolar perturbations of Maxwellian EEDF has been developed. The model allows analytical calculations of ECE absorption and emission coefficients; hence, the comparison of modeled ECE spectra with experimental data. The different experimental results observed for the various JET scenarios have been found to be qualitatively reproducible by adapting the model parameters, suggesting that bipolar distortions of the bulk EEDF could play a role in giving rise to the reported discrepancies between ECE and TS measurements.

Design study of the collection optics for Polarimetric Thomson Scattering on ITER

The ITER Core Plasma Thomson Scattering (CPTS) system is the primary diagnostic for the electron temperature (Te ) and electron density (ne ) profiles. For high performance ITER operating scenarios in which core Te > 20 keV, the conventional spectral CPTS will not provide measurement accuracy sufficient for advanced machine control. Addition of polarimetric measurement capability to the CPTS diagnostic is projected to increase measurement accuracy in high temperature/low density plasmas to required levels. To determine the feasibility of Polarimetric TS implementation on ITER, the polarization characteristics of the CPTS scattered light collection system have been modeled as part of a conceptual design study. When linearly polarized light is propagated through the CPTS collections optics, polarization is rotated and ellipticized. This characteristic of the ITER collection optical system complicates separation and analysis of the depolarized component of the Thomson scattered light that is produced at high Te . To address this challenge, a custom waveplate and polarizing beamsplitter should be mounted before the final lens in the CPTS collection optical system. Additionally, polarization performance should be one of the criteria by which materials and coatings are selected for the CPTS collection optical system.

Design Study of a Line Integrated Thomson Scattering System for TST-2 Spherical Tokamak Device

Design Study of a Line Integrated Thomson Scattering System for TST-2 Spherical Tokamak Device

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.

Neural Network Data Analysis in the Large Helical Device Thomson Scattering System

Neural Network Data Analysis in the Large Helical Device Thomson Scattering System

Pedestal analysis of MAST ELMy regimes

Mega Ampere Spherical Tokamak (MAST) pedestal data has been analysed, where a pedestal database of 892 shots was obtained, using the upgraded MAST Thomson scattering (TS) diagnostic. Various edge localised mode (ELM) types are discussed, where characteristics and trends of MAST pedestals are shown. The data from the upgraded TS diagnostic confirms pedestal characteristics found in earlier analysis, using previous TS systems. Using the database, calculations of the bootstrap current are obtained using the different analytical formulae (Sauter and Redl), and comparisons are performed. The upgraded MAST TS system now spans the full plasma mid-plane, such that direct comparisons between inboard and outboard pedestals can be obtained, and asymmetries in the density pedestal width were found. To increase confidence in spherical tokamak pedestal predictions, the assumptions of Europed have been validated from the MAST pedestal data, and a value for the kinetic ballooning mode constraint () has been obtained. The first spherical tokamak pedestal predictions were performed in Europed and compared to experimental values. Using C = 0.145 the temperature pedestal height was predicted to within 10% of the experimental value. In addition type II ELMs on MAST are analysed, and stability analysis and parameter scans have been performed using ESSIVE. Similar magneto-hydrodynamic (MHD) stability properties are observed for type I and type II ELMs, originating from the mixed ELM regimes; it is therefore difficult to distinguish these ELMs using the ideal MHD codes.

Assessment of shutdown dose rates in the ITER Collective Thomson Scattering system and in equatorial port plug 12

The ITER Collective Thomson Scattering (CTS) system will be the main diagnostic responsible for measuring the velocity distribution function of fusion-born alpha particles in the plasma. As the CTS diagnostic is integrated in the equatorial port plug 12 (drawer 3), with direct apertures to the port interspace where maintenance hands-on operation will be carried out, it is essential to assess the shutdown dose rates (SDDR) in these maintenance areas. In this work, the D1S-UNED3.1.4 Monte-Carlo transport code, based on the implementation of the direct-one-step methodology in MCNP5 v1.60, was used to estimate the dose rate level 12 days (106 s) after shutdown in the port interspace. The results show that the CTS system does not contribute significantly to the SDDR in the area where hands-on maintenance is foreseen with contribution to dose rates less than 1 µSv/h. This is consistent with previous estimates, although with the most recent model of the CTS design there is a slight increase of the SDDR values. This deviation can be attributed to design changes and improved shielding modelling and/or most importantly, to statistical fluctuations of the D1S simulations. From a neutronics point of view, the increase in the SDDR falls within the range of the statistical fluctuations, and the design is still compliant with the radiation safety ALARA principle aiming at minimizing radiation doses, and there is no requirement for further design optimizations.

Study of detached plasma profile in the divertor simulation experimental module of tandem mirror GAMMA 10/PDX

A divertor simulation experimental module (D-module) in the tandem mirror GAMMA 10/PDX was used for the study of plasma detachment. In previous studies, it was difficult to measure far-upstream plasma parameters in the D-module, and only electrostatic probes on the target plate were used to perform electron temperature and density measurements. To study the detached plasma structure, a Thomson scattering (TS) system and a microwave interferometer system have been installed to measure the inside plasma parameters of the D-module, and a movable electrostatic probe has been placed at the inlet of the D-module to measure the inlet plasma density and temperature. The TS system in the central cell observed the electron temperature and density of the core plasma simultaneously. These measurements revealed the entire density and temperature structure from the core plasma to the divertor plate. The line average electron density measured by the microwave interferometer showed a rollover behavior during detachment. The results indicated that the ionization region was located around the center of the D-module, and it appears to move upstream along the axis.

Conceptual design of Thomson scattering diagnostics for the COMPASS-U tokamak.

The Thomson scattering (TS) diagnostic, one of the key diagnostics used on the tokamaks around the world, is planned for the COMPASS-U tokamak, which is recently under design and construction in the Institute of Plasma Physics in Prague, Czech Republic. This tokamak is supposed to be a world-unique, high magnetic field device with hot walls, allowing for the study of the plasma exhaust in advanced operational scenarios and testing cutting-edge technologies relevant to future fusion reactors, e.g., use of liquid metals. The core and edge TS systems are planned to be designed and operational, with a limited performance, already in the early stage of the tokamak operation. In this contribution, requirements and the most important constraints defining the TS system design are presented. The impact of both the possible collection lens location and spatial resolution on the plasma pedestal observation is simulated. Design considerations also take into account the high-resolution TS core and edge systems available from the COMPASS tokamak, which will be reused. The collection lenses will be newly built. Extension of the detection system will complete the plasma radius coverage in the future. The divertor TS is considered for later periods.

RAMI analysis of the Collective Thomson Scattering system front-end – Part2 – reliability block diagram analysis

ITER is an experimental tokamak nuclear fusion reactor with the goal of achieving afusion energy gain factor of 10. Nuclear fusion presents an extreme environment for materials during operations while requiring continuous uninterrupted operation.The Reliability Block Diagram (RBD) is a graphic methodology for system reliability modelling which is constructed from the reliability-wise relations between different subsystems/components and their respective reliability and maintenance data. In this paper, we construct andanalyse the RBD for the Collective Thomson Scattering (CTS) front-end both in terms of fulfilling its functions and its effects in the ITER tokamak operations. Our RDB analysis results were then used to propose mitigation actions which include design changes and operational procedures to deal with the identified failure modes.Our initial results indicate that the system's mean availability at the end of its lifecycle of 20 years is no greater than 82.55% which was due to low Mean Time Between Failures (MTBF) of a critical system component – theSplit Biased Waveguide (SBWG) – aswell as several thermally loaded components. After mitigation actions, which aimed at controlling the system's exposure to heat loads, the MTBFs increased and the resulting mean availability achieved values over 97%, in conformity with design specifications. Furthermore, considering the CTS failure modes with impact on ITER operations, the expected value for the mean availability is of 99.995%. Therefore, we concluded that these failure modes did not require mitigation actions.In this article, we cover the second half of the RAMI analysis of the CTS diagnostic, the RBD analysis.

Simulation of stray laser light of Thomson scattering systems in the HL-2M tokamak.

Stray laser light is a serious problem that interrupts the measurement of electron temperature and density in Thomson scattering (TS) systems. This paper presents a ray-tracing simulation of stray laser light in HL-2M TS systems. A model including (i) a simplified laser-beam injection system, (ii) the scattered-light collection systems for central-point TS (CPTS) and edge TS (ETS), and (iii) the HL-2M vessel is built using the TracePro and CATIA software packages based on measurements of the bidirectional scattering distribution function at a wavelength of 532nm. The simulation results show that no stray laser light reaches the injection surface of the collection lens of the CPTS system, and only a few stray laser rays of all the rays reaching the injection surface of the collection lens of the ETS system can be collected when the energy threshold per ray is 1 × 10-16. The stray laser rays that reach the scattered-light collection systems are mainly from the first and second parts of the slides of the beam dump, so decreasing the roughness of those parts could be effective in reducing the level of stray laser light.

Influence of Neutron Irradiation on the Large Helical Device Thomson Scattering System

Influence of Neutron Irradiation on the Large Helical Device Thomson Scattering System

Incoherent and Collective Thomson Scattering for the Determination of Electron and Ion Properties in Low-Temperature Plasma

In this lecture an overview of applications of incoherent Thomson scattering (TS) as well as collective Thomson scattering (CTS) will be given. These are the most accurate methods for measuring the electron and ion properties, because the method is direct and non-intrusive. A CTS system based on the fundamental wavelength of a seeded Nd:YAG laser, being developed for the high density, low-temperature plasma of the linear plasma generator Magnum-PSI will be described also. The small Debye length of dense low temperature plasma enables application of CTS at relatively short laser wavelength. The combination of this CTS system and existing incoherent TS system enables determination of electron density and temperature as well as ion temperature and plasma velocity of the near surface plasma. In this lecture, the theoretical background and experimental challenges of the work will be given along with some examples that demonstrate the capabilities of such systems.

Shielding analysis of the ITER Collective Thomson Scattering system

• A neutronics analysis is presented for the ITER Collective Thomson Scattering. • The n0 uxes are underestimated by a 2–3 factor by the use of a homogeneous DSM. • The equatorial port plug 12 will exceed the 100 _Sv/h limit in the port interspace. • The accurate modelling of the modular DSM is recommended in future studies. The Collective Thomson Scattering (CTS) system will be the ITER diagnostic obtaining the plasma fast alpha-particle velocity distribution and will be implemented in drawer #3 of the Equatorial Port Plug #12 of the reactor. In this work, a neutronics analysis is presented for the in-vessel front-end parts of the CTS system, including neutron and gamma-ray fluxes and nuclear heat loads for the main components of the system calculated with the Monte Carlo radiation transport code MCNP6. In previous analyses the shielding materials were modelled as a homogeneous mixture, a crude approximation which did not consider the small gaps between the different components and between the CTS system and the shielding structure. In this work, a detailed model of the modular Diagnostics Shield Module (DSM) was developed, including all the shielding trays and all the individual boron carbide bricks. The results obtained with this model are compared with the ones obtained using a homogeneous mixture, to assess the effect of this approximation on the estimation of the neutron fluxes in the port interspace. The results show that the total neutron flux reaching the closure plate is estimated to be 2–3 times higher when the shielding is accurately modelled. This shows that the often-used homogeneous mixture approach underestimates the neutron fluxes during operation – a fact that could have great importance in the global shutdown dose rate estimates. On the other hand, the shielding implementation does not affect the heat loads in the front-end components of the system. Simulations to assess the Shutdown Dose Rates are performed using the D1S-UNED code. The results suggest that the entire port plug where the current CTS design is included will exceed the dose rate limit of 100 μSv/h in the port interspace. The contribution from the CTS system alone, however, is not sufficient to exceed the threshold.

Recent diagnostic developments at ASDEX Upgrade with the FPGA implemented Serial I/O System “SIO2” and “Pipe2” DAQ periphery

Abstract ASDEX Upgrade (AUG) since many years has been using a built to purpose FPGA PCIe computer interface with fast serial interconnects – called “SIO” – connecting to peripheral crates based on a pipeline organized backplane – called “Pipe” [ 1 ] 1 – containing modular DAQ devices. The combination of custom built input channels, aggregated into multi-channel FPGA controlled backplanes and streamed by one or more SIO2 FPGA cards via DMA into computer memory enables the deterministic delivery of data for real-time applications with minimum latency. The renewal of large diagnostics for the Mirnov probes, the Soft-X-Ray cameras and others have been successfully conducted. These diagnostics have undergone the transition from Solaris to Linux CentOS with real-time kernel. These systems, receiving a stream of measured samples from the SIO2 periphery via DMA, directly provide data for plasma control via sharing the DMA memory sections with dedicated application processes (APs) running on the same node as part of the AUG distributed discharge control system [ 2 , 3 ]. The SIO2 DAQ is further applied to a Thomson-Scattering (TS) system located in the AUG Divertor (DTS). New GigaSample ADCs developed for this diagnostic expand the range of measuring periphery into the GHz range. The same ADCs are planned to be used to refurbish and real-time enable the main chamber Thomson-Scattering system. The paper describes the concepts of the “Pipe2” periphery and the “SIO2” interface card. It briefly summarizes specifics of the diagnostics mentioned above and puts further emphasis on design modifications of the FPGA firmware to address new requirements. It will also give a short description of the developed GSPS ADC/FPGA periphery cards.

The Stray Laser Light Simulation of the Beam Dump for Thomson Scattering Systems in HL-2M Tokamak

The Stray Laser Light Simulation of the Beam Dump for Thomson Scattering Systems in HL-2M Tokamak