Spectroscopic observations of opacity in JET He discharges

On October 24, 2021, the Chinese government unveiled a guiding document about state-level work to achieve carbon peaking and carbon neutrality goals under a new development philosophy, laying out key targets and measures for upcoming decades. The documment, titled “Working Guidance For Carbon Dioxide Peaking and Carbon Neutrality In Fully And Faithful Implementation Of The New Development Philosophy.” stated that China's carbon dioxide emissions per unit GDP would have dropped by 18% from the level in 2020 by 2025 and by more than 68% from the level in 2005 by 2030. Fusion energy, as an environment-friendly and intrinsically safe energy source with an abundant fuel supply, is considered an effective low-carbon ultimate solution. Fusion research has been conducted for 60 years, and has been demonstrated that magnetic confinement controlled fusion is very effective magnetic confinement fusion research has progressed significantly over the years. Generally, it is believed in the magnetic confinement fusion plasma community that the next pivotal step in magnetic confinement fusion plasma research is to create burning plasma, where the dominant method of heating plasmas is alpha particle self-sustaining heating. The research aims to understand the underlying physics of the confinement, heating, and instability of burning plasma and to explore the technologies associated with the power-producing fusion reactor. In future burning plasmas, multiple mode-number instabilities are very important but complicated physics issues because of the employment of strong power auxiliary heating schemes. Compared with the time-consuming large-scale computer simulation, the machine learning can bring an advantage for the investigations concerning multiple mode-number instabilities, especially in predictions compared to the time-consuming large-scale computer simulation.

Collisional-radiative model for the visible spectrum of W26+ ions

The only method for assessing the fusion power throughput of a deuterium-tritium (DT) reactor presently relies on determining the absolute number of 14MeV neutrons produced in the DT plasma. An independent method, developed and investigated during the recent DT campaign at the Joint European Torus, is based on the absolute counting of 17MeV gamma rays produced by the competing T(D, γ)5He reaction that features a very weak branching ratio (about 3-6 × 10-6) when compared to the main T(D,n)4He reaction. The state-of-the-art spectrometer used for gamma-ray measurements in magnetic confinement fusion plasmas is LaBr3(Ce) scintillator detectors, although they require significant neutron shielding to extract a relatively weak gamma-ray signal from a much more abundant neutron field. A better approach relies on a gamma-ray detector that is intrinsically insensitive to neutrons. We have advanced the design of a gamma-ray counter based on the Cherenkov effect for gamma-rays whose energy exceeds 11MeV, optimized to work in the neutron-rich environment of a steady-state, magnetically confined fusion plasma device. The gamma-rays interact with an aluminum window and extract electrons that move into the radiator emitting photons via the Cherenkov effect. Since the Cherenkov light consists of few photons (25 on average) in the far UV band (100-200nm), a pre-amplifier is required to transport the photons to the neutron-shielded location, which may be a few meters away, where the readout elements of the detector, either a silicon or standard photomultiplier tube, are placed. The present work focuses on the development of a scintillating GEM (Gas Electron Multiplier) based pre-amplifier that acts as a Cherenkov photon pre-amplifier and wavelength shifter. This paper presents the result of a set of Garfield++ simulations developed to find the optimal GEM working parameters. A photon gain of 100 is obtained by biasing a single GEM foil to 1kV.

Astrophysical and fusion plasmas share significant similarities, particularly in their ubiquitous turbulence, coherent structures, and self-organization. This paper focuses on magnetic confinement fusion plasmas, emphasizing their inherently non-equilibrium nature and the use of non-perturbative statistical approaches to quantify them. The statistical properties of fusion plasmas often deviate from Gaussian distributions, rendering low-order moments—such as means and standard deviations—inadequate for fully characterizing turbulence and its impact. The low-to-high confinement (L–H) transition, a key plasma bifurcation leading to improved confinement, is examined as a stochastic bifurcation, where the transition occurs probabilistically for a given input power. Probability density function methods help reveal how hidden variables influence the power threshold. Additionally, information theory is employed to uncover nonlinear plasma interactions, including self-regulation and causality.

Doppler-free two-photon excitation of fluorescence may be used to measure the deuterium/tritium fuel mix in magnetic confinement fusion plasmas. Two atomic transition schemes of the hydrogen isotopes come into question for this purpose: (I) excitation of the first excited energy level (n=2) and observation of Lyman-α, (II) excitation of the second excited energy level (n=3) and observation of Balmer-α. Comparison of the two schemes indicates that both may have their merits in particular situations. Due to lack of information about the future laser characteristics achievable for scheme II, the detailed performance of this scheme cannot yet be definitely assessed.

Radio-frequency (rf) waves can penetrate fusion plasmas and deposit energy and momentum through collisionless mechanisms, resulting in plasma heating and, in some cases, current drive and flow drive. The advantage of this noninductive current drive is that a tokamak-type fusion reactor can be operated at a steady state. Meanwhile, an appropriate profile of plasma current and a significant plasma flow are important in stabilizing magnetohydrodynamics instabilities and realizing and sustaining high-performance confinement regimes. Therefore, rf current drive and flow drive are important in research on the physics of magnetic confinement fusion plasma. This paper presents the elementary physics of wave-particle interactions in plasmas, reviews the present status and challenges of research on rf current drive and flow drive, and suggests possible research strategies. Several problems are highlighted. These include the intrinsic relation of resonant absorption to the reduction of rf current drive efficiency in high-density plasmas; the existence/feasibility of a nonresonant drive scheme; the possibility of increasing the drive efficiency within the resonant mechanism; the direct and indirect effects of rf waves in flow drive, especially the generalized ponderomotive force generated by rf waves; and nonlinear processes during the coupling and propagation of waves, such as parametric decay instabilities, and their possible effects on current drive and flow drive.

This paper describes the possible application of VUV free-electron lasers to probe the role of neutral particles in magnetic confinement fusion plasmas.

Understanding surface instability in magnetized fusion plasma supports the appropriate implementation and handling of liquid metal as plasma facing components (PFCs) in future fusion reactors. A Lagrange equation describing a viscous liquid surface deformation in a magnetized plasma is derived using Rayleigh’s method. Its solution justifies the general instability criterion and helps in characterizing the key interactions driving such instability under fusion conditions. Surface tension and gravity, especially with the poloidal angles of the lower part of a plasma chamber, mainly stabilize the liquid surface at small and large disturbance wavelengths, respectively. The sheath electric field and the external tangential magnetic field cause the liquid surface to disintegrate at an intermediate wavelength. Practically, a magnetic confinement fusion (MCF) device requires a strong magnetic field for confinement. The study suggests that such a strong field dominates the rest and governs instability. In addition, this implies that the configuration of a static planar free liquid surface is difficult to adopt as a candidate for handling the liquid metal as PFCs in next step MCF devices.

view Abstract Citations (10) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Distribution of Radiation from Relativistically Expanding Radio Sources De Young, D. S. Abstract The distribution of synchrotron radiation in a relativistically expanding source is considered as seen by a distant observer. A variety of initial conditions, optical depths, and geometries are examined, including sources of constant energy input, blast waves, and jets. It is found that double or core-and-halo sources with apparent expansion velocities in excess of the velocity of light can result from natural geometries and actual expansion rates less than c. The results are compared with observations of 3C 279, 3C 273, and 3C 120, all of which exhibit possible "superrelativistic" expansions. Publication: The Astrophysical Journal Pub Date: November 1972 DOI: 10.1086/151734 Bibcode: 1972ApJ...177..573D full text sources ADS |

Highly charged ions play a crucial role in magnetic fusion plasmas. These plasmas are excellent sources for producing highly charged ions and copious amounts of radiation for studying their atomic properties. These studies include calibration of density diagnostics, x-ray production by charge exchange, line identifications and accurate wavelength measurements, and benchmark data for ionization balance calculations. Studies of magnetic fusion plasmas also consume a large amount of atomic data, especially in order to develop new spectral diagnostics. Examples we give are the need for highly accurate wavelengths as references for measurements of bulk plasma motion, the need for accurate line excitation rates that encompass both electron-impact excitation and indirect line formation processes, for accurate position and resonance strength information of dielectronic recombination satellite lines that may broaden or shift diagnostic lines or that may provide electron temperature information, and the need for accurate ionization balance calculations. We show that the highly charged ions of several elements are of special current interest to magnetic fusion, notably highly charged ions of argon, iron, krypton, xenon, and foremost of tungsten. The electron temperatures thought to be achievable in the near future may produce W70+ ions and possibly ions with even higher charge states. This means that all but a few of the most highly charged ions are of potential interest as plasma diagnostics or are available for basic research.

This paper presents the status of the HL-2A tokamak and its auxiliary systems, and the highlights of the experiments on magnetic fusion plasma in HL-2A. In particular, China’s first high confinement mode (H-mode) operation has been achieved on this device which is an important milestone in the history of magnetic fusion research in China. Due to its good accessibility, innovative fueling technologies and many advanced diagnostics with high spatiotemporal resolution, an amount of key issues on magnetic fusion plasma have been investigated and a series of innovative achievements have been obtained. They will provide important scientific and technical basis for ITER operation and design of future fusion DEMO.

At present, magnetic confinement fusion devices rely solely on absolute neutron counting as a direct way of measuring fusion power. Absolute counting of deuterium-tritium gamma rays could provide the secondary neutron-independent technique required for the validation of scientific results and as a licensing tool for future power plants. However, this approach necessitates an accurate determination of the gamma-ray-to-neutron branching ratio. The gamma-ray-to-neutron branching ratio for the deuterium-tritium reaction ^{3}H(^{2}H,γ)^{5}He/^{3}H(^{2}H,n)^{4}He was determined in magnetic confinement fusion plasmas at the Joint European Torus in predominantly deuterium beam heated plasmas. The branching ratio was found to be equal to (2.4±0.5)×10^{-5} over the deuterium energy range of (80±20) keV. This accurate determination of the deuterium-tritium branching ratio paves the way for a direct and neutron-independent measurement of fusion power in magnetic confinement fusion reactors, based on the absolute counting of deuterium-tritium gamma rays.

High resolution (λ∕Δλ ∼ 10 000) 1D imaging x-ray spectroscopy using a spherically bent crystal and a 2D hybrid pixel array detector is used world wide for Doppler measurements of ion-temperature and plasma flow-velocity profiles in magnetic confinement fusion plasmas. Meter sized plasmas are diagnosed with cm spatial resolution and 10 ms time resolution. This concept can also be used as a diagnostic of small sources, such as inertial confinement fusion plasmas and targets on x-ray light source beam lines, with spatial resolution of micrometers, as demonstrated by laboratory experiments using a 250-μm (55)Fe source, and by ray-tracing calculations. Throughput calculations agree with measurements, and predict detector counts in the range 10(-8)-10(-6) times source x-rays, depending on crystal reflectivity and spectrometer geometry. Results of the lab demonstrations, application of the technique to the National Ignition Facility (NIF), and predictions of performance on NIF will be presented.

In the dynamic environment of burning, thermonuclear deuterium-tritium plasmas, diagnosing the time-resolved neutron energy spectrum is of critical importance. Strategies exist for this diagnosis in magnetic confinement fusion plasmas, which presently have a lifetime of ∼1012 longer than inertial confinement fusion (ICF) plasmas. Here, we present a novel concept for a simple, precise, and scale-able diagnostic to measure time-resolved neutron spectra in ICF plasmas. The concept leverages general tomographic reconstruction techniques adapted to time-of-flight parameter space, and then employs an updated Monte Carlo algorithm and National Ignition Facility-relevant constraints to reconstruct the time-evolving neutron energy spectrum. Reconstructed spectra of the primary 14.028MeV nDT peak are in good agreement with the exact synthetic spectra. The technique is also used to reconstruct the time-evolving downscattered spectrum, although the present implementation shows significantly more error.

This study reports a 37-year long record of direct beam spectral irradiance measurements made in Athens, Greece. An analysis of aerosol effects on the spectral distribution of solar radiation through effective optical depths, are presented. Thus, spectrally resolved aerosol optical depths were calculated and analyzed for the period 1954–1990. Summertime aerosol optical depths were found to be larger than winter values, while their seasonal variations were related to varying weather conditions throughout the year. The interrelationships between effective optical depths were found to be linear and were related strongly to microphysics of aerosol loading in the atmosphere. For the period 1962–1983 as wavelength exponentα0 values ranged between 0.76–1.14 the spectrally resolved optical depths were found to increase markedly with respect to remaining periods 1954–1961 and 1984–1990 in whichα0 values ranged between 1.16–1.39. A minimum in aerosol optical depths, believed to be near background levels, was reached during period 1954–1957, while there was some indication that both optical depths continued to decrease reaching background levels at the end of the study period. From the long-term variation of aerosol effective optical depths some interesting information on the time evolution of air quality in Athens was gained. In addition, their frequency distribution, temporal daily variations and some remarks on photosynthetically active radiation for plant development, are presented and discussed.