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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.

The MAST Upgrade Super-X divertor is typically seen to detach in steady state discharges. However, divertor re-attachment is observed to occur during fast transient heat loads. In this paper the effect of edge localised modes (ELMs) on the divertor are diagnosed on fast time scales with Thomson scattering and with a new ultrafast divertor spectroscopy (UFDS) diagnostic. The Thomson scattering data show full ionisation of the detached neutral buffer during large ELM events ( >2–3 kJ) in a ∼1 ms time window after ELMs. Plasma temperature at the strikepoint varies depending on the ELM size and timing reaching up to 10 eV, which is significantly higher than inter-ELM levels but much lower than the pedestal temperatures of ∼200 eV. The UFDS diagnostic allows determination of ELM induced reattachment (burn-through) by monitoring the spatial distribution of D2 Fulcher emission across the divertor. In this initial investigation the ELM energy and divertor neutral gas pressure ( Pgas) are hypothesised to be the most influential parameters on whether an ELM causes burn-through or not without extrinsic impurities. The relationship of these parameters to burn-through as measured by UFDS is examined by a database of ELMs from MAST-U pulses. For the MAST-U Super-X divertor, the required Pgas (in Pa) to buffer an ELM of energy ΔWELM (in kJ) is estimated to follow a limit of Pgas⩾0.67ΔWELM by a simple model, which is shown to agree well with the experimental results.

The SPARC tokamak is a compact high-field device that will operate at high plasma density with the aim to demonstrate net fusion energy. The experimentally unexplored plasma conditions in SPARC will require a carefully selected set of diagnostics for plasma monitoring and control. Here we explore conceptual design options and potential measurement capabilities of a collective Thomson scattering diagnostic at SPARC. We show that a 140 GHz X-mode CTS system is the most attractive option in terms of optimizing the signal-to-noise ratio and limiting sensitivity to refraction, as well as from a technological readiness perspective. Such a setup can provide core-localized measurements of the fusion alpha distribution function, main-ion temperature and toroidal rotation, fuel-ion ratio, and 3He content with relevant spatio-temporal resolution. Our proposed diagnostic layout can in principle be integrated into SPARC and could provide a valuable addition to its diagnostic suite at limited development costs and time.

In the double-cone ignition (DCI) scheme, the unique configuration of the gold cones facilitates plasma compression. However, the gold impurity in the plasma jet have a potential impact on the energy conversion efficiency and final fusion yield. In this study, we reanalyzed the x-ray Thomson scattering spectrum from DCI-R7 experiments by combining the imaginary-time correlation function method with first-principles calculations. Our findings revise the previously diagnosed temperature of 50±10eV to 25.4±1.0eV, with a density of 8±2gcm−3 and only 0.162±0.015% of gold impurity. These results provide clear evidence of the role played by the gold cones during the compression process, and demonstrate that the gold impurity fraction is well within acceptable limits.

Reconstructing fast-ion velocity distributions from collective Thomson scattering (CTS) spectra is an ill-posed inverse problem due to the spectral nonlinearity, strong parameter coupling and measurement noise. To mitigate the ill-posed problems in single-view inversions, a hybrid spectrum–parameter conditioned encoder (HSPCE) is proposed to reconstruct two-dimensional (2D) fast-ion velocity distributions based on the electromagnetic forward model. For feasibility validation, one-dimensional (1D) inversion is firstly carried out using an electrostatic CTS model under HL-3 operating parameters. Compared with the least squares with nuisance parameters (LSN), the machine-learning approach demonstrates markedly improved robustness and accuracy, maintaining an R 2 of 0.985 with 10% Gaussian noise. Extending to 2D, the velocity distribution is represented as an image and reduced in dimensionality through principal component analysis (PCA), with additional soft constraints applied in both coefficient and pixel spaces to preserve physical consistency. Benchmarking against the 1D baseline model, HSPCE shows that the higher structural similarity (SSIM) and lower normalized root mean square error (NRMSE) with different Gaussian noise, with 0.930 and 0.043 at noise level of 0.1 respectively. Further analysis indicates that the fraction of fast ions plays an important role in enabling the network to extract reliable fast-ion information, with higher fractions yielding clearer reconstructions and reduced uncertainty. Overall, the proposed framework suggests that neural networks offer a promising and robust approach for improving the interpretability and reliability of fast-ion diagnostics based on CTS in magnetically confined plasmas.

We report observations of strong electron temperature profile stiffness in high poloidal beta ( βp∼2) plasmas on EAST for the first time. Key features of this regime include: (1) Negligible contributions to stored energy and electron temperature from additional auxilliary heating power; and (2) a rapid increase of core broad-band turbulence ( kθρs∼1−5, f∼0−2000kHz) monitored by collective Thomson scattering (CTS) diagnostic system. Notably, no significant increase in impurities or MHD activities are observed during this process. This strong stiffness can be interpreted as a nonlinear increase in turbulent thermal flux when temperature gradients exceed a critical threshold. Gyro-kinetic simulations show that trapped electron mode is responsible for the enhanced broad-band turbulence observed in the core. The experimental electron heat fluxes are well matched by the nonlinear electromagnetic simulations for the high heating power case, whereas larger discrepancies between the simulations and experiments are observed for the low heating power case. This finding highlights the advantages of using CTS to detect microturbulence in the core of high-density plasmas, allowing for immediate identification of profile stiffness induced by turbulence.

Isolated multi-MeV $\\gamma$ -rays with attosecond duration, high collimation and beam angular momentum (BAM) may find many interesting applications in nuclear physics, astrophysics, etc. Here, we propose a scheme to generate such $\\gamma$ -rays via nonlinear Thomson scattering of a rotating relativistic electron sheet driven by a few-cycle twisted laser pulse interacting with a micro-droplet target. Our model clarifies the laser intensity threshold and carrier-envelope phase effect on the generation of the isolated electron sheet. Three-dimensional numerical simulations demonstrate the $\\gamma$ -ray emission with 320 attoseconds duration and peak brilliance of $9.3\\times 10^{24}$ photons s ^{-1}$ mrad ^{-2}$ mm ^{-2}$ per 0.1 $\\%$ bandwidth at 4.3 MeV. The $\\gamma$ -ray beam carries a large BAM of $2.8 \\times 10^{16}\\mathrm{\\hslash}$ , which arises from the efficient BAM transfer from the rotating electron sheet, subsequently leading to a unique angular distribution. This work should promote the experimental investigation of nonlinear Thomson scattering of rotating electron sheets in large laser facilities.

To comprehensively study the physical properties of inductively coupled plasma (ICP), a finite element method (FEM) simulation model of ICP is developed using the well-established COMSOL software. To benchmark the validation of the FEM model, two key physical parameters, the electron density and the electron temperature of the ICP plasma, are precisely measured by the state-of-the-art laser Thomson scattering diagnostic approach. For low-pressure plasma such as ICP, the local pressure in the generator tube is difficult to measure directly. The local gas pressure in the ICP tube has been calibrated by comparing the experimental and simulation results of the maximum electron density. And on this basis, the electron density and electron temperature of ICP under the same gas pressure and absorbed power have been compared by experiments and simulations. The good agreement between the experimental and simulation data of these two key physical parameters fully verifies the validity of the ICP FEM simulation model. The experimental verification of the ICP FEM simulation model lays a foundation for further study of the distribution of various physical quantities and their variation with pressure and absorption power, which is beneficial for improving the level of ICP-related processes.

We investigate the dynamics of electrons initially counter-propagating to an ultra-fast ultra-intense near-infrared laser pulse using a model for radiation reaction based on the classical Landau–Lifshitz–Hartemann equation. The electrons, with initial energies of 1 GeV, interact with laser fields of up to 1023 W/cm2. The radiation reaction effects slow down the electrons and significantly alter their trajectories, leading to distinctive Thomson scattering spectra and radiation patterns. It is proposed to use such spectra, which include contributions from harmonic and Doppler-shifted radiation, as a tool to measure laser intensity at focus. We discuss the feasibility of this approach for state-of-the-art and near-future laser technologies. We propose using Thomson scattering to measure the impact of radiation reaction on electron dynamics, thereby providing experimental scenarios for validating our model. This work aims to contribute to the understanding of electron behavior in ultra-intense laser fields and the role of radiation reaction in such extreme conditions. The specific properties of Thomson scattering associated with radiation reaction, shown to be dominant at the intensities of interest here, are highlighted and proposed as a diagnostic tool, both for this phenomenon itself and for laser characterization in a non-intrusive way.

This article delves into the generation and modulation process of X-rays as high-energy photon sources. Using the principles of classical electrodynamics, this study enables nonrelativistic short pulse lasers to collide with high-energy electrons while the collision center is away from the focal point. This scattering method may produce X-rays with good collimation and monochromaticity, and it progressively approaches inverse Thomson scattering. We studied and analyzed the effects of different electron characteristics and laser parameter settings on the high-energy angular distribution and spectrum of X-rays, especially the setting of the collision center and initial electron velocity, as well as the setting of laser intensity and pulse width. Linear polarized laser pulses with relativistic intensity can generate discrete supercontinuum X-rays with spectral distortion. In addition, the relationships between electronic and laser properties and radiation energy were also studied. Our research can provide valuable insights for manipulating collimated or distorted, monochromatic, or tunable X-rays, as well as understanding their properties.