Collective Thomson Scattering Research Articles

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.

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.

Core ion measurements with collective Thomson scattering for DEMO burn control

DEMO burn control will require measurements of a range of plasma parameters, but the suite of feasible diagnostics for this purpose is limited. Here we assess the accuracy with which a collective Thomson scattering (CTS) diagnostic can provide key measurements for burn control in the planned European DEMO (EU-DEMO). This is based on estimated signal-to-noise ratios for a conceptual diagnostic design and trial fits to synthetic DEMO CTS spectra. We show that a diagnostic with a single probe- and receiver beam setup will be able to provide simultaneous measurements of core fusion alpha density and ion temperature to mean accuracies better than 5% and 10%, respectively, along with detecting intrinsic toroidal rotation velocities down to within ∼5 km s−1. Adding a second CTS receiver view furthermore enables inference of the core fuel-ion ratio, allowing discrimination between, e.g. a 50%/50% and 55%/45% D/T mixture, while also providing useful information on the thermalized He content. A DEMO CTS diagnostic would thus be able to monitor fusion alpha densities as well as anomalous transport of fast alphas and heat from the plasma core, quantify plasma rotation for confinement enhancement, and track the core isotope mix for optimum fusion performance. This versatility makes such a diagnostic a potentially valuable tool for real-time burn control on DEMO.

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.

Development of a Collective Thomson Scattering diagnostic system on SNU X-pinch device

The Collective Thomson Scattering (CTS) diagnostic system has been developed for the X-pinch device at Seoul National University. The system is designed to measure various parameters of plasma jets, including plasma temperature and plasma flow velocity. For the flow velocity measurement, the second harmonic Nd:YAG laser and the collection optics are oriented in order to ensure the scattering vector is aligned with the flow direction. The collection optics have been optimized to maximize photon efficiency. Due to the requirement of high spectral dispersion and resolution for the diagnosis of CTS spectra, the spectrometer is designed with a dispersion of 0.004 nm/pixel. The spectral dispersion and resolution of the system has been measured. The CTS diagnostic system will contribute to a deeper understanding of X-pinch plasma dynamics and the development of advanced High Energy Density Plasma (HEDP)-based technologies.

The latest developments of microwave diagnostics for high temperature plasma in ELVA-1 company

For nearly 30 years, we have been designing and supplying instruments for microwave diagnostics of high temperature plasma. This report provides a description of the mm-wave components we utilize to make diagnostics within the frequency range of 26–330 GHz. While most of these components are standard and readily available on the market, we have also developed a few specific devices that simplify the architecture of our instruments. The article includes descriptions of these devices: Backward Wave Oscillators (BWO), Impact Ionization Avalanche Transit-Time diode (IMPATT) sources, IMPATT Active Frequency Multipliers (AFM), Noise Sources, and Electronically Controlled Attenuators. Furthermore, we offer an overview of the microwave plasma diagnostics we have supplied, including ECE radiometers operating at 50–220 GHz, as well as heterodyne interferometers operating at fixed frequency 94 GHz, 140 GHz, or 300 GHz. We also discuss methods employed to ensure measurement stability and present the achieved results. The advent of the new era of modern Monolithic Microwave Integrated Circuit (MMIC) based devices has brought forth exciting possibilities. As an example, we discuss the upgrade of the low noise receiver for the Collective Thomson Scattering (CTS) diagnostic at Wendelstein 7-X, which enables ion temperature measurements in the plasma core [1]. Lastly, we provide a list of MMIC-based devices that are currently available and have garnered the attention of the plasma diagnostics community.

Preliminary results of the 105GHz collective Thomson scattering system on HL-2A.

A 105GHz collective Thomson scattering (CTS) diagnostic has been successfully developed for fast-ion measurements on the HL-2A tokamak, and it has been deployed during an experimental campaign. Enhanced signals exhibiting synchronous modulation characteristics have been observed across all CTS channels upon the launch of a modulated probe wave. Results show that the intensity of the CTS signal increases with Neutral Beam Injection (NBI) power and is proportional to neutron count, indicating that the scattering signal contains a contribution from fast ions. Compared with the signal without NBI, the enhanced scattering spectrum due to NBI is slightly wider than the predicted fast ion range. Such broadening might be attributed to the heating effects of the gyrotron.

Thomson scattering measurements of electron temperature and electron density in laser-driven Gd plasmas

In this study, we demonstrate the laser intensity scaling of electron temperature in Gd laser-produced plasmas (LPPs) through experiment and simulation. The spatial and temporal profiles of electron density ne and temperature Te in Gd LPPs were directly measured during a drive laser pulse duration of 7 ns at a laser wavelength of 1064 nm using collective Thomson scattering. We found that the measured maximum Te value in Gd LPPs increases with increasing laser intensity IL , with the dependence , in the IL range of 1010–. Radiation-hydrodynamic simulation code of the STAR-2D was performed under identical conditions to those used in the experiment, and extended further to higher laser intensities of up to ; the simulated Te was found to be in good agreement with the experimental data over the used IL range. The simulation indicates that higher overall maximum Te typically exists 50–70 above the target and modifies the dependence as . Experiments reveal that a laser intensity of is required to achieve the optimum condition ( 100 eV and ion charge states , at –) for efficient beyond extreme ultraviolet (EUV) light source. In addition, two spot sizes (150 and 250 in diameter) were used to study the effect of the spot size on the Te profile. Our experimental findings, supported by the simulations, show that larger spots can create uniform Te profiles, higher maximum Te , and larger high-Te regions in LPPs. The results and scaling laws presented in this study provide important information for developing more powerful and energy-efficient EUV light sources.

Short-pulse frequency stabilization of a MW-class ECRH gyrotron at W7-X for CTS diagnostic

At the Wendelstein 7-X stellarator, a 174 GHz Collective Thomson Scattering (CTS) diagnostic will be implemented. One of the 140 GHz Electron Cyclotron Resonance Heating (ECRH) gyrotrons will be operated at around 174 GHz in a higher cavity mode, using it as source for the CTS mm-wave probing beam. To prevent any damage to the CTS receiver, a notch filter cuts out the high-power gyrotron signal at the entrance of the receiver. The bandwidth of the gyrotron signal determines the notch filter bandwidth. First proof-of-principle experiments on frequency stabilization were conducted on W7-X ECRH gyrotrons employing Phase-Locked Loop techniques. The gyrotron output frequency was controlled with the accelerating voltage, which is applied between the anode and cathode of the gyrotron diode-type Magnetron Injection Gun. Frequency stabilization experiments with 10 ms pulses were conducted at the gyrotron nominal frequency of 140 GHz as well as at 174 GHz. It is concluded that the gyrotron frequency could be stabilized for at least 3 ms at 140 GHz and 8 ms at 174 GHz. In the frequency spectrum, a clear main peak of the gyrotron frequency at 140 GHz with a full -15 dB linewidth of below 500 Hz was achieved.

Investigation of gyrotron-based collective Thomson scattering for fast ion diagnostics in a compact high-field tokamak

As a promising method for fast ion diagnostics, collective Thomson scattering (CTS) can measure the one-dimensional velocity distribution of fast ions with high spatial and temporal resolution. The feasibility of diagnosing fast ions in a compact high-field tokamak by CTS was studied in this work, and the results showed that a wide range of probing frequencies could be applied. A high-frequency case and a low-frequency case were mainly considered for fast ion diagnostics in a compact high-field tokamak. The use of a high probing frequency could effectively avoid the refraction effect of the beams, while the application of a low probing frequency allows greater flexibility in the selection of scattering angle which may help to improve the spatial resolution. Based on typical plasma conditions (B 0 = 12.2 T, n e0 = 4.3 × 1020 m−3, T e0 = 22.2 keV, T i0 = 19.8 keV) for a compact high-field tokamak, a 220 GHz CTS diagnostic that utilizes a small scattering angle of θ = 30° and a 160 GHz CTS diagnostic that utilizes an orthogonal geometry were proposed. Further study showed that the high-frequency case could operate in a wider range of plasma conditions and provide more information on fast ions while the low-frequency case could achieve higher spatial resolution of the poloidal direction.

On the influence of plasma turbulence on collective Thomson scattering measurements

Plasma turbulence can result in significant distortion of probing and receiving microwave beams, and this effect can modify the registered spectrum in a collective Thomson scattering (CTS) experiment. An analytical description of the CTS experiment is provided in this paper for the probing beam distortion due to the plasma edge turbulence. The effect of the registered frequency spectrum distortion by the turbulence is evaluated for different turbulence levels for plasma parameters similar to those excepted in ITER.

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.

Ion-acoustic feature of collective Thomson scattering in non-equilibrium two-stream plasmas

We theoretically and numerically investigate the ion-acoustic features of collective Thomson scattering (CTS) in two-stream plasmas. When the electron distribution functions of two (stationary and moving) components overlap with each other at the phase velocities corresponding to the two resonant peaks of the ion-acoustic feature, the theoretical spectrum shows asymmetry because the rate of electron Landau damping is different for the two peaks. The results of numerical simulations agree well with the theoretical spectra. We also demonstrate the effect of a two-stream-type instability in the ion-acoustic feature. The simulated spectrum in the presence of the instability shows an asymmetry with the opposite trend to the overlapped case, which results from the temporal change of the electron distribution function caused by the instability. Our results show that two-stream plasmas have significant effects on CTS spectra and that the waves resulting from instabilities can be observed in the ion-acoustic feature.

Laboratory tests of CO2 laser collective Thomson scattering for measurements of ion temperature in the divertor.

Collective Thomson scattering (CTS) is a diagnostic method that measures the ion velocity distribution of a plasma. CO2 laser CTS measurements are challenging because of the inherently small Doppler broadening and scattering signals that are difficult to detect. We implemented a heterodyne detection scheme to measure spectrum changes of less than a GHz. To maximize the collected light at small scattering angles, we designed a unique light collection approach consisting of a customized conical-shaped (axicon) lens with a hole in the center. The axicon lens is used to collect the scattered light emitted within an annular cross-section from the scattering volume while the probe beam is passed through the hole at the center of the lens. The performance of the heterodyne detection scheme and annular collection approach was demonstrated using a Transverse Excited Atmospheric pressure CO2 laser with a pulse energy of 160 mJ at λ = 10.59 µm.

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

ITER collective Thomson scattering-Preparing to diagnose fusion-born alpha particles (invited).

The ITER Collective Thomson scattering (CTS) diagnostic will measure the dynamics of fusion-born alpha particles in the burning ITER plasma by scattering a 1MW 60GHz gyrotron beam off fast-ion induced fluctuations in the plasma. The diagnostic will have seven measurement volumes across the ITER cross section and will resolve the alpha particle energies in the range from 300keV to 3.5MeV; importantly, the CTS diagnostic is the only diagnostic capable of measuring confined alpha particles for energies below ∼1.7MeV and will also be sensitive to the other fast-ion populations. The temporal resolution is 100ms, allowing the capture of dynamics on that timescale, and the typical spatial resolution is 10-50cm. The development and design of the in-vessel and primary parts of the CTS diagnostic has been completed. This marks the beginning of a new phase of preparation to maximize the scientific benefit of the diagnostic, e.g., by investigating the capability to contribute to the determination of the fuel-ion ratio and the bulk ion temperature as well as integrating data analysis with other fast-ion and bulk-ion diagnostics.

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

Collective Thomson scattering diagnostic with in situ calibration system for velocity space analysis in large helical device.

A collective Thomson scattering (CTS) diagnostic with a ±3 GHz band around a 77 GHz gyrotron probe beam was developed to measure the velocity distribution of bulk and fast ions in high-temperature plasmas. We propose a new in situ calibration method for a CTS diagnostic system combined with a raytracing code. The method is applied in two situations for electron cyclotron emission in plasmas and in a CTS diagnostic with a modulated probe beam. Experimental results highlight the importance of refraction correction in probe and receive beams. The CTS spectrum is measured with the in situ calibrated CTS receiver and responds to fast ions originating from a tangential neutral beam with an energy of 170 keV and from a perpendicular beam with an energy of 60 keV, both in the large helical device. From a velocity space analysis model, the results elucidate the measured anisotropic CTS spectrum caused by fast ions. The calibration methods and analyses demonstrated here are essential for CTS, millimeter-wave diagnostics, and electron cyclotron heating required under fusion reactor conditions.

Analysis of small scale fluctuations in Hall effect thrusters using virtual Thomson scattering on PIC simulations

Hall effect thrusters are yet not fully understood due to multiple open questions, among which the anomalous electron transport is the most challenging. Particle-In-Cell (PIC) simulations suggested that electron transport is strongly affected by small-scale instabilities which can be investigated experimentally using Collective Thomson Scattering (CTS). In this paper, we perform a virtual CTS diagnostic on PIC data in order to investigate these small scales and to relate simulation and experiments. The virtual diagnostic is performed on the electron density maps from a simplified 2D axial-azimuthal PIC simulation. Analysis along the channel axis showed two dominant modes at 8 and 3 rad mm−1. These modes exhibit ion-acoustic wave features and appear to be selectively affected by the acceleration of the ions when transitioning from the ionization zone to the acceleration zone. A numerical study of the electron density fluctuation rate from the virtual CTS is also performed and the obtained profiles are compared to PIC. This reveals that the virtual CTS integrates both axial and azimuthal fluctuations of the electron density due to the spatial extension of the scattering volume. Moreover, it also highlights the importance of a good estimation of the electron density in the scattering volume for an accurate estimation of the fluctuation rate.

Development of a 105 GHz fast ion collective Thomson scattering diagnostic on HL-2A tokamak

Collective Thomson Scattering (CTS) diagnostic technique has great potential in measuring velocity distribution of fast ions in magnetically confined fusion devices. Here we present design and development of a 105 GHz fast ion CTS system on HL-2A tokamak. The gyrotron with high power transmission/antenna is used to generate a probe beam. To better focus the scattering beam and effectively avoid the stray contamination, a W-band Cassegrain antenna is utilized to receive the scattering beam from the central chord. The scattering signal is estimated at 10–30 eV and the frequency broadening is less than 2 GHz for typical HL-2A plasmas. To pick out the weak signals, a multi-channel receiver system with working frequency of 103–107 GHz is developed. The steerable direction of probe beam enables that the scattering volume can move from core to edge, with which the spatial resolution range varies from 70 mm at low field side to 260 mm at high field side.