Thomson Scattering Research Articles

Development of Cost-Effective Polychromator System with Two Angled Filters for Thomson Scattering Measurement System

We constructed the cost-effective polychromator system for multi-channel Thomson scattering measurement systems, in which scattered light is reflected between two angled interference filters. The number of interference filters was reduced to less than half of the number of wavelength channels, by using the reflections between two filters whose transmitted wavelength decreases with its angle of incidence. The developed polychromator successfully separated five different wavelength bands (1055.5, 1044.9, 1050.0, 1035.0, and 1024.3 nm), reducing its cost by saving the number of interference filters.

Validation of EDGDE2D-EIRENE predicted 2D distributions of electron temperature and density against divertor Thomson scattering measurements in the low-field side divertor leg in DIII-D

Comparisons of profiles of the electron temperature (Te), density (ne) and pressure (pe) measured with Divertor Thomson Scattering in DIII-D low-confinement mode discharges to predictions from the edge fluid code EDGE2D-EIRENE [1] show that the models implemented in EDGE2D-EIRENE predict the measurements within their collective uncertainties if the Te at the separatrix (Te,sep) is 10 eV, or higher. The simulations do not predict, however, the peaked Te and ne profiles measured adjacent to the target plate when Te,sep, is below 10 eV, i.e., for the plasma downstream from the region of ionization of deuterium atoms. Inclusion of cross-field drifts and a fivefold reduction of radial transport cannot reconcile the discrepancy between the measurements and predictions.

Development of Thomson Scattering Measurement System for Long Duration Discharges on the QUEST Spherical Tokamak

The Thomson scattering control system has been modified to measure the time evolution of the electron density and temperature profiles during long duration discharges in the QUEST spherical tokamak. The system consists of a signal generator and a control circuit. The former accepts a QUEST main trigger and provides multiple triggers, each of which starts a short-term (e.g. 15 s) measurement. The latter provides triggers to synchronize the oscilloscope and laser oscillation during a short-term measurement. The system was used in 1000 s long duration discharges in QUEST, and the temporal evolutions of density and temperature profiles were obtained successfully. It was found the profiles are stationary after about 300 s.

Structural analysis of the ex-port plug collective thomson scattering transmission lines for ITER

The main function of the Collective Thomson Scattering (CTS) diagnostic system for ITER is to diagnose the alpha particles resulting from Deuterium-Tritium fusion reactions. It consists of a microwave scattering diagnostic with a probing frequency of 60 GHz and emitted power of 1.2 MW from the gyrotron, with one launcher and nine receiver transmission lines.The CTS will be installed in the equatorial port EP#12, which is one of the ports that have to be operational for the ITER First Plasma. The transmission lines outside the Port Plug (Ex-PP) are routed through the Interspace, Port Cell, Gallery, Assembly Building and Diagnostic Building, reaching more than 100 m in length. The preliminary design of the ex-PP components is currently being undertaken in the framework of an Implementing Agreement between ITER Organization, the Instituto Superior Técnico (IST) and CIEMAT. Within this collaboration, CIEMAT is responsible for the structural analyses and calculations required to ensure the structural integrity and performance of the preliminary design of the Ex-PP transmission line components, which will be summarized in this paper.In this work, the required analysis and calculations will be presented together with the redesign performed for the transmission lines in order to guarantee that their components will withstand the loads defined in the Ex-PP CTS Load Specifications. The evaluation of the structural integrity of the CTS Ex-PP components will be carried out in accordance with the 2007 RCC-MR Code for mechanical components in nuclear installations.

A model of non-Maxwellian electron distribution function for the analysis of ECE data in JET discharges

Recent experiments performed in JET at high level of plasma heating, in preparation of, and during the DT campaign have shown significant discrepancies between electron temperature measurements by Thomson Scattering (TS) and Electron Cyclotron Emission (ECE). In order to perform a systematic analysis of this phenomenon, a simple model of bipolar distortion of the electron distribution function has been developed, allowing analytic calculation of the EC emission and absorption coefficients. Extensive comparisons of the modelled ECE spectra (at both the 2nd and the 3rd harmonic extraordinary mode) with experimental measurements display good agreement when bulk electron distribution distortions around 1-2 times the electron thermal velocity are used and prove useful for a first level of analysis of this effect.

Gamma-ray Vortex Burst in Nonlinear Thomson Scattering with Refocusing Spiral Plasma Mirror

The gamma-ray vortex burst in the nonlinear Thomson scattering when the laser wakefield accelerated electron bunch collides with an ultra-intense Laguerre–Gaussian laser that was reflected from the refocusing spiral plasma mirror. The orbit angular momentum of the scattering laser would be transferred to the gamma radiation through the scattering process. The 3-dimensional particle-in-cell simulations gave the electron dynamics in the scattering, which determines the characteristics of the vortical radiation. The radiation calculation results illustrated the burst of gamma-ray vortex and surprisingly revealed the radiation pattern distortion phenomenon due to the nonlinear effect. This scheme can not only simplify the experimental setup for the generation of twisted radiation but also boost the yield of vortical gamma photons. The peak brightness of the gamma-ray vortex was estimated to be 1 × 10 22 photons/s/mm 2 /mrad 2 /0.1% BW at 1 MeV, which might pave the way for the researches on angular momentum-related nuclear physics.

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

Portable diagnostic package for Thomson scattering and optical emission spectroscopy on Princeton field-reversed configuration 2 (PFRC 2).

An Advanced Research Projects Agency-Energy funded diagnostic system has been deployed to the Princeton field-reversed configuration 2 (PFRC-2) device, located at Princeton Plasma Physics Laboratory. The Portable Diagnostic Package (PDP), designed at Oak Ridge National Laboratory, allows for the measurement of Thomson Scattering (TS) for electron density and temperature and Optical Emission Spectroscopy (OES) for ion temperature, impurity density, and ion velocity. A tunable spectrometer on the PDP with three gratings provides the flexibility to measure low (1eV) and high (1000eV) electron temperature ranges from TS. Additionally, using a second spectrometer, the OES diagnostic can survey light emission from various ion excitation levels for wide wavelength ranges. The electron density (<2 × 1019m-3) of plasmas generated in PFRC-2 has been below the PDP TS discrimination threshold, which has made TS signal detection challenging against a high-background of laser stray light. The laser stray light was iteratively reduced by making modifications to the entrance and exit geometry on PFRC-2. Rayleigh scattering experiments on PFRC have yielded the TS discrimination sensitivity to be >1 × 1020m-3 for the PDP. A recently implemented narrow-band notch spectral filter that masks the second harmonic 532nm Nd:YAG laser wavelength has increased the system's TS light discrimination sensitivity 65 times compared to the instance when the notch filter was not implemented. The hardware implementation including design changes to the flight tubes and Brewster windows will be discussed, along with results from Rayleigh and rotational Raman scattering sensitivity analyses, which were used to establish a quantitative figure of merit on the system performance. The Raman scattering calibration with the notch filter has improved the PDP electron density threshold to 1 ± 0.5 × 1018m-3.

Implementation of a portable diagnostic system for Thomson scattering measurements on an electrothermal arc source.

To fulfill the increasing needs of diagnostic support for researchers in plasma technology, a portable diagnostic package (PDP) equipped for both laser Thomson scattering (TS) and optical emission spectroscopy has been designed and constructed at Oak Ridge National Laboratory (ORNL), aiming to measure the temperature and number density of electrons and temperatures of ions in plasma devices. The PDP has been initially implemented on a high density and low temperature electrothermal arc source (ET-arc) at ORNL to test its TS capability. TS from the plasmas in the ET-arc has been obtained using the PDP. The electron temperature and number density were determined from TS spectra. These results were then compared to measurements from previous studies on the ET-arc. The TS diagnostic measured 0.8 ± 0.1, 1.3 ± 0.2, and 0.7 ± 0.1eV and (4.4 ± 0.5) × 1021, (5.9 ± 0.7) × 1021, and (4.3 ± 0.5) x 1021m-3, respectively, from three lines of sight that transect the plasma column.

Advances in Magnum-PSI probe diagnosis in support of plasma–surface interaction studies

Magnum-PSI is a linear plasma generator equipped with a superconducting magnet, assuring fusion devices relevant conditions at plasma–surface interface. The plasma column was diagnosed using 64 probes embedded in the target. The cross-sectional distributions of plasma parameters (floating potential, ion saturation current and electron temperature) were measured for hydrogen and deuterium plasmas under various discharge conditions. The radial profile of the floating potential across the plasma column can be described by a reversed Mexican hat-like wavelet, having the most negative potential at the center of the plasma column. The negativity of the floating potential diminishes when the discharge current increases or the magnetic field decreases. The axial gradient of the floating potential is reduced by increasing the magnetic field. The ion saturation current is maximum at the center of the plasma column, increasing with both the discharge current and magnetic field. The ion flux to the target, estimated from Thomson scattering (TS) data, was confirmed by probe measurements. The electron temperature estimated from the ion branch of the probe current–voltage characteristic is few times larger than that obtained from TS. By increasing the gas pressure in the target chamber, the time-dependent ion saturation current measured by probes changes from a constant average current (when the plasma column is attached to the target) to a fluctuating average current with scattered peaks (in a partially detached regime) which vanishes completely in the fully detached regime. With respect to hydrogen, the plasma column is wider in deuterium and is characterized by less negative floating potential distributions.

Radiatively driven evaporation from magnetar’s surface

ABSTRACT The luminosity of the Soft Gamma Repeater flares significantly exceeds the Eddington luminosity. This is because they emit mainly in the E mode, for which the radiative cross-sections are strongly suppressed. The energy is released in the magnetosphere forming a magnetically trapped pair fireball, and the surface of the star is illuminated by the powerful radiation from the fireball. We study the ablation of the matter from the surface by this radiation. The E-mode photons are scattered within the surface layer, partly being converted into O-photons, whose scattering cross-section is of the order of the Thomson cross-section. The high radiation pressure of the O-mode radiation expels the plasma upwards. The uplifted matter forms a thick baryon sheath around the fireball. If an illuminated fraction of the star’s surface includes the polar cap, a heavy, mildly relativistic baryonic wind is formed.

Studying fusion-born alpha particles in the ITER experiment

Details of ITER’s Collective Thomson Scattering diagnostic, which will monitor the dynamics of energetic alpha particles and other fast ions

Fast-Ion Diagnostics with Collective Thomson Scattering of Microwave Radiation for the GDT Open Magnetic Trap

Fast-Ion Diagnostics with Collective Thomson Scattering of Microwave Radiation for the GDT Open Magnetic Trap

Fundamental Studies on Electron Dynamics in Exact Paraxial Beams with Angular Momentum

Classical electromagnetic radiation with orbital angular momentum (OAM), described by nonvanishing vector and scalar potentials (namely, Lorentz gauge) and under Lorentz condition, is considered. They are employed to describe paraxial laser beams, thereby including non-vanishing longitudinal components of electric and magnetic fields. The relevance of the latter on electron dynamics is investigated in the reported numerical experiments. The lowest corrections to the paraxial approximation appear to have a negligeable influence in the regimes treated here. Incoherent Thomson scattering (TS) from a sample of free electrons moving subject to the paraxial fields is studied and investigated as a beam diagnosis tool. Numerical computations elucidate the nature and conditions for the so called trapped solutions (electron motions bounded in the transverse plane of the laser and drifting along the propagation direction) in long quasi-steady laser beams. The influence of laser parameters, in particular, the laser beam size and the non-vanishing longitudinal field components, essential for the paraxial approximation to hold, are studied. When the initial conditions of the electrons are sufficiently close to the origin, a simplified model Hamiltonian to the full relativistic one is introduced. It yields results comparing quite well quantitatively with the observed amplitudes, phase relationships and frequencies of oscillation of trapped solutions (at least for wide laser beam sizes). Genuine pulsed paraxial fields with OAM and their features, modeling true ultra-short pulses are also studied for two cases, one of wide laser beam spot (100 μm) and other with narrow beam size of 6.4 μm. To this regard, the asymptotic distribution of the kinetic energy of the electrons as a function of their initial position over the transverse section is analyzed. The relative importance of the transverse structure effects and the role of longitudinal fields is addressed. By including the full paraxial fields, the asymptotic distribution of kinetic energy of an electron population distributed across the laser beam section, has a nontrivial and unexpected rotational symmetry along the optical propagation axis.

Feasibility Study of Line Integrated Backward Thomson Scattering Measurement in Nuclear Fusion Reactors

In order to control or suppress edge localized modes in nuclear fusion reactors, an accurate pedestal pressure profile measurement is necessary. A line integrated backward Thomson scattering measurement is an attractive method because of its long scattering length. Assuming that the first mirror is located far from the plasma to avoid degradation of the mirror due to erosion and impurity deposition, the measurement accuracies of density and temperature and pressure are estimated. For the target plasma, we adopt the pedestal profile with the shoulder density of 1019 - 1020 m-3 and the dimensions of the JA DEMO reactor. The calculation results show that, the Poisson noise due to finite detected scattered photon number is much larger than that due to bremsstrahlung emission. In addition, noise is enhanced by reconstruction process. The resultant total noise levels of reconstructed density, temperature and pressure profiles are at most 1.5%, 3%, 3%, respectively in the steep gradient region, and this method is feasible in the reactor.

Upgrade of the helically symmetric experiment Thomson scattering diagnostic suite.

The Helically Symmetric eXperiment (HSX) Thomson Scattering (TS) diagnostic is being upgraded to decrease uncertainty in electron temperature and density measurements. Upgrades to the HSX TS diagnostic will consist of a novel redesign of polychromator electronics and digitization of the TS output signal. Here, we also present a study of the benefits of an additional spectral channel that will sample the red-shifted band of the scattered spectrum. To maximize system bandwidth (BW) and gain, while minimizing noise, the existing low-BW polychromator electronics on HSX will be replaced by high-BW, high gain circuitry designed in-house.

Bayesian inference applied to electron temperature data: computational performances and diagnostics integration

Bayesian inference proves to be a robust tool for the fitting of parametric models on experimental datasets. In the case of electron kinetics, it can help the identification of non-thermal components in electron population and their relation with plasma parameters and dynamics. We present here a tool for electron distribution reconstruction based on MCMC (Monte Carlo Markov Chain) based Bayesian inference on Thomson Scattering data, discussing the computational performances of different algorithms and information metrics. Along, a possible integration between Soft X-ray spectroscopy and Thomson Scattering is presented, focusing on the parametric optimization of diagnostics spectral channels in different plasma regimes.

Observations of Thomson Scattering from a Loop-prominence System

We describe observations of the white-light structures in the low corona following the X8.2 flare SOL 2017-09-10, as observed in full Stokes parameters by the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory. These data show both bright loops and a diffuse emission region above them. We interpret the loops as the white-light counterpart of a classical loop-prominence system, intermediate between the hot X-ray loops and coronal rain. The diffuse emission external to the loops is linearly polarized and has a natural interpretation in terms of Thomson scattering from the hot plasma seen prior to its cooling and recombination. The polarimetric data from HMI enable us to distinguish this contribution of scattering from the HMI pseudocontinuum measurement, and to make a direct estimation of the coronal mass in the polarized source. For a snapshot at 16:19 UT, we estimate a mass 8 × 1014 g. We further conclude that the volumetric filling factor of this source is near unity.

Combined Thomson Scattering and Laser-Induced Fluorescence for Studying Divertor and X-point Plasmas in Tokamak with Reactor Technologies

Combined Thomson Scattering and Laser-Induced Fluorescence for Studying Divertor and X-point Plasmas in Tokamak with Reactor Technologies

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