Radiative Power Losses Research Articles

Soft x-ray tomography on the high field spherical tokamak ST40.

As part of its roadmap to developing commercial fusion plants, Tokamak Energy Ltd. operates the high field spherical tokamak ST40. Studies on this device will help to expand the high field spherical tokamak physics basis by characterizing confinement and the fusion triple product. In support of this, bolometers and broadband and x-ray sensitive diodes can provide information on key energy loss mechanisms of the plasma. These mechanisms include core magnetohydrodynamic activity that deteriorates confinement, such as sawtooth crashes that can be used to characterize relaxations in the q-profile. In addition, combinations of these diagnostics can be used to infer the total radiated power losses and plasma composition. Here, we present results from a new, midplane, tangential, Be-filtered diode with 16 channels spanning the radial extent of the plasma. The system is shown to resolve magnetohydrodynamic instabilities (up to 100kHz) and be able to provide radiation profiles through tomography. The tomographic inversion routine is compared against other diagnostics on ST40 and provides emissivity measurements across a variety of operating scenarios. Finally, we look ahead to implementing multiple soft x-ray cameras on ST40 and the improvements this will have on the diagnostic capabilities.

Impact of fuel dilution on Lawson parameter by considering relativistic correction of radiation loss in toroidal magnetic configuration

In this paper, the ignition boundary and height of the saddle point as the lowest heating power on the way to ignition for D-3He toroidal magnetic configuration are derived. Fusion fuel cycle involving deuterium and helium-3, along with side reactions is considered. The effect of fuel dilution, incorporating synchrotron radiation and bremsstrahlung power loss with relativistic correction on ignition criteria, is investigated. The results were compared by considering the classical state of bremsstrahlung power. It is found that the height of the saddle point is increased with increasing the ratio of the proton particle density to the fuel deuteron density. The ignition regime shrinks and the minimum value of the Lawson parameter for the breakeven condition and ignition boundaries is reduced due to fuel dilution.

Atomic structure, electron-impact excitation and collisional-radiative modelling for Ar II

The spectra from singly ionized argon Ar II has significant diagnostic capability in the characterization and modelling of both magnetically-confined fusion and astrophysical plasmas. The literature has several pre-existing data sets for Ar+ but this paper presents the results from 3 new atomic structure and electron-impact scattering models in order to better constrain the differences in atomic data and how they impact well-known plasma diagnostics. Several independent atomic structure methodologies are employed to calculate the energy levels and transition probabilities for each model. The first approach employs a relativistic Dirac–Coulomb Hamiltonian model, the second approach uses a semi-relativistic Breit–Pauli Hamiltonian with the mass-velocity, Darwin and spin–orbit corrections, and in a third case an ICFT approach. Three atomic structure models provide a foundation for Dirac R-matrix, a semi-relativistic ICFT (Intermediate Coupling Frame Transformation) and a Breit–Pauli R-Matrix with Pseudostates (BPRMPS) calculation. Synthetic spectra utilizing these three data sets are compared against measurements taken at the Compact Toroidal Hybrid (CTH) stellarator, and the total radiative power loss is also benchmarked against previous calculations.

Preliminary design of an AXUV photodiode-based bolometer camera for MT-I spherical tokamak

The MT-I is a spherical tokamak at the Pakistan Tokamak Plasma Research Institute, and has a major radius of 15 cm and a minor radius of 9 cm. This paper presents the design and computational analysis of the Absolute eXtreme Ultra-Violet (AXUV) photodiode-based bolometer camera, which will be used for the first time in the MT-I tokamak. The bolometer camera contains a single array of 16 AXUV photodiodes placed behind an aperture to compute the line of sight (LOS) and field of view (FOV) of the system. This array is located at the midplane of the vessel, which provides a radial resolution of about 16 mm. The individual FOV of each photodiode and the collective FOV of the array are 4.1° and ±34.5°, respectively. The impurity densities and their cooling rates for elements like carbon, oxygen, and iron are used to compute the plasma emissivity distribution, the power incident on the photodiode array, and signal-to-noise ratio (SNR) analysis. The analysis reveals that the radiated power loss is about 10 % of the ohmic heating input power. The geometrical etendue falls within the range of 2.2 × 10−5 to 3.2 × 10−5 Sr cm2. The bolometer exhibits a frequency response bandwidth of 10 kHz, and its temporal resolution is around 0.1 milliseconds.

Calculation and prediction of divertor detachment via impurity seeding by using one-dimensional model

Abstract Achieving the divertor detachment helps to alleviate excessive heat load and sputtering problems on the target plates, thereby prolonging the lifetime of divertor components for fusion devices. In order to provide a rapid but relatively reliable prediction of plasma parameters along the flux tube for future devices design, a one-dimensional (1D) modeling code for the impurity seeded detached divertor operational point has been developed based on the Python language, which is a fluid model based on the previous work.[1] The experimental observation of the onset of divertor detachment by neon (Ne) and argon (Ar) seeding in EAST is well reproduced by using the 1D modeling code. The comparison of the 1D modeling and 2D simulation by SOLPS-ITER code for CFETR detachment operation with Ne and Ar seeding also shows good consistency. The predictions of the radiative power loss and requirement of the corresponding impurity concentration for achieving divertor detachment via different impurity seeding for the high heating power scenarios on EAST and CFETR Phase II by the 1D model are also presented. Based on the predictions, the optimized parameter space for divertor detachment operation on EAST and CFETR has also been determined. Such a simple but reliable 1D model can provide a reasonable parameter inputs for a detailed and accurate analysis by 2D or 3D modeling tools through rapid parameter scanning.

Comparison of partial and deep energy detachment behaviors with Ar seeding on EAST new corner slot divertor

It is necessary for future fusion reactor to reduce the heat fluxes on the entire divertor target, especially if view of long pulse high performance operation. In recent EAST experiments, partial energy detachment without confinement degradation, and deep energy detachment with protection of the entire divertor target have both been confirmed on EAST corner slot divertor by argon (Ar) seeding, which can provide reference for the divertor protection on future fusion reactors. In the deep energy detachment state, the electron temperature T et along entire lower outer divertor target decreases to less than 10 eV and heat fluxes are also strongly mitigated with peak heat flux reduction of more than 90%. Compared to the attached state, there is a moderate confinement degradation with H 98,y2 from ∼1 to ∼0.9 because of Ar radiation in the core region. This confinement degradation can be avoided in the partial energy detachment state, where the radiative power losses in the core are reduced. The experiment and SOLPS-ITER simulation results show that there is no decrease of particle flux js on the divertor target in the partial energy detachment state because the momentum loss in the SOL region is not strong enough. With increasing Ar seeding, there is a js decrease in the deep energy detachment state. The increases of momentum and power losses in the SOL region, and the decrease of upstream pressure all contribute to the js reduction.

Resonant interaction between runaway electrons and the toroidal magnetic field ripple in TCV

This work explains the anomalously high runaway electron (RE) pitch angles inferred in the flat-top of dedicated Tokamak à Configuration Variable (TCV) experiments. Kinetic modelling shows that the resonant interaction between the gyromotion of the electrons and the toroidal magnetic field ripple will give rise to strong pitch angle scattering in TCV. The resulting increase in synchrotron radiation power losses acts as a RE energy barrier. These observations are tested experimentally by a magnetic field ramp-down, which gradually reduces the resonant parallel momentum at which the REs interact with the ripple. Resulting changes in synchrotron emission geometry and intensity are observed using three multi-spectral camera imaging systems, viewing the RE beam at distinct spatial angles in multiple wavelength ranges. Experimental reconstructions of the RE distribution in momentum- and real-space are consistent with kinetic model predictions.

The role of plasma–atom and molecule interactions on power & particle balance during detachment on the MAST Upgrade Super-X divertor

This paper shows first quantitative analysis of the detachment processes in the MAST Upgrade Super-X divertor (SXD). We identify an unprecedented impact of plasma-molecular interactions involving molecular ions (likely D2+ ), resulting in strong ion sinks (Molecular Activated Recombination—MAR), leading to a reduction of ion target flux. The MAR ion sinks exceed the divertor ion sources before electron-ion recombination (EIR) starts to occur, suggesting that significant ionisation occurs outside of the divertor chamber. In the EIR region, Te≪0.2 eV is observed and MAR remains significant in these deep detached phases. The total ion sink strength demonstrates the capability for particle (ion) exhaust in the Super-X Configuration. Molecular Activated Dissociation is the dominant volumetric neutral atom creation process can lead to an electron cooling of 20% of PSOL . The measured total radiative power losses in the divertor chamber are consistent with inferred hydrogenic radiative power losses. This suggests that intrinsic divertor impurity radiation, despite the carbon walls, is minor in the divertor chamber. This contrasts previous TCV results, which may be associated with enhanced plasma-neutral interactions and reduced chemical erosion in the detached, tightly baffled SXD. The above observations have also been observed in higher heat flux (narrower SOL width) type I ELMy H-mode discharges. This provides evidence that the characterisation in this paper may be general.

Investigations of Single-Mode Optical Fiber Microbending Properties

This research is devoted to the study of the properties of the microbending of an optical fiber. It is shown that an increase in the diameter of a microbend at a constant force in the area of its formation led to an increase in the power of optical radiation output from the fiber in the area of the microbend. It has been established that the smallest value of the optical radiation power branched in the microbending region and the smallest value of the radiation power loss at the microbending for the entire range of wavelengths under study is observed for the G657 optical fiber. The largest value of the radiation power branched off in the microbending region and the largest value of the radiation power loss at the microbending for the entire range of wavelengths under study is observed for the G655 optical fiber. The results of the article can be used in systems for protecting information transmitted over fiber-optic communication lines.

Fusion Gain and Triple Product for the Sheared-Flow-Stabilized Z Pinch

Fusion gain Q and triple product nTτ are derived for the sheared-flow-stabilized (SFS) Z pinch by including the input power associated with driving the plasma flow and the additional advective loss of thermal energy. Plasma impurities contribute to radiative power losses and to thermal power losses by increasing the electron population. The presence of impurities increases the required plasma parameters, characterized by the triple product, to achieve fusion gain. The analysis is applied to deuterium-tritium (D-T) fusion, though the methodology can be extended to other reactions. Since D-T fusion produces an alpha particle, the possibility exists of magnetically confining the alpha with sufficiently high magnetic fields, which are self-generated by the plasma pinch current. Confined alpha particles can heat the D-T fusion fuel, reduce the needed input power, and thereby amplify the fusion gain. However, ignition (Q→∞) does not occur since the axial plasma flow must be externally driven. The impacts of alpha heating and impurity losses are considered on the fusion performance of the SFS Z pinch. Requirements, assumptions, and limitations are described that would justify a determination of “D-T equivalent Q=1 conditions” in a D-D plasma. A minimum set of experimental measurements of plasma parameters is specified that can be compared to a plasma parameter map to facilitate a “Q=1” claim, where Q is defined by instantaneous values of fusion power and input power. Corroborating measurements are also discussed that would further support extrapolation of plasma and fusion performance to D-T operation.

Integrated simulation analysis of the HL-2M high-parameter hybrid scenario

On the basis of the OMFIT integrated simulation platform and the parameters of the HL-2M device, a hybrid scenario with a typical safety factor q profile is simulated using the joint injection method of neutral beam and electron cyclotron wave with a normalized toroidal beta (β N) of 2.39. At the same time, by analyzing the effect of impurity concentration (Z eff) and pedestal density (n e,ped) on confinement, a higher parameters hybrid scenario is obtained, with β N reaching 3.118. The research results indicate that the turbulent stabilization effect caused by Z eff gradually decreases from strong to weak with the increase of Z eff, whereas the radiation power loss increases linearly as Z eff increases. Consequently, there exists an optimal Z eff value for optimal confinement. In addition, it is found that the optimal Z eff value decreases with the increase of n e,ped. The research results are crucial for the HL-2M device to accomplish the 1 MA advanced scenario discharge target, and they serve as a reference for future impurity seeding experiments.

Multi-fluid and dynamic simulation of tungsten impurity in tokamak boundary plasma

Accumulation of tungsten (W) in core is a serious challenge for achieving high-performance plasmas in future tokamak reactors, thus W impurity transport is a highly concerned topic in the tokamak physics researches. Multi-fluid model and kinetic model are the numerical tools widely used for investigating and/or predicting impurity behaviors in the boundary of tokamak plasma. Generally, the applicability of multi-fluid model for impurity transport modeling requires that the collision mean-free-path should be smaller than the gradient scale lengths of particles, which may not be always satisfied. It is performed and comparatively investigated to evaluate the applicability of multi-fluid model for W impurity transport modeling, multi-fluid (SOLPS-ITER) modeling and kinetic (DIVIMP) modeling of W impurity transport in the edge of high-confinement plasma in Experimental Advanced Superconducting Tokamak (EAST) during neon impurity seeding. It is found that low-charge-state W ions are mainly located in the divertor region near the target plate where plasma collisionality is relatively high due to the relatively low/high local plasma temperature/density. Hence, the fluid assumption for transport of lowly-charged W ions can be well satisfied. Consequently, the density of lowly-charged W ions predicted by SOLPS-ITER and that calculated by DIVIMP are almost similar. Owing to the fact that the density of highly-charged W ions is relatively low and these particles mainly exist in the upstream (e.g. the main SOL and core) where plasma collisionality is relatively low, the fluid approximation cannot be well satisfied. However, the total W impurity density calculated by the kinetic code DIVIMP and the multi-fluid model SOLPS-ITER are found to be in agreement with each other within a factor of 1.5 for the simulation cases presented in this contribution. Besides, the multi-fluid simulation with bundled charge state model has also been performed, the obtained results are compared with those from the multi-fluid modeling with W ions treated as 74 fluids. It is revealed that in simulation cases with neon impurity seeding and with divertor plasmas in high-recycling or partially detached regimes, the bundling scheme, which is commonly used for saving the computation cost in multi-fluid modeling, tends to overestimate the average charge state of W ions and thus tends to underestimate the radiation power loss, especially in the divertor region. Consequently, under the circumstance that W impurity radiation dominates the radiative power loss in divertor region, plasma temperature/density can be largely overestimated/underestimated, leading to the underestimation of W ion ionization source and W impurity density. Moreover, simulation results demonstrate that W accumulation in core can decrease effectively during divertor detachment promoted by neon seeding.

Extreme Electron Acceleration with Fixed Radiation Energy.

We examine the extreme situation of radiation from an electron that is asymptotically accelerated to the speed of light, resulting in finite emission energy. The analytic solution explicitly demonstrates the difference between radiation power loss and kinetic power loss (null).

Efficient data acquisition and training of collisional-radiative model artificial neural network surrogates through adaptive parameter space sampling

Effective plasma transport modeling of magnetically confined fusion devices relies on having an accurate understanding of the ion composition and radiative power losses of the plasma. Generally, these quantities can be obtained from solutions of a collisional-radiative (CR) model at each time step within a plasma transport simulation. However, even compact, approximate CR models can be computationally onerous to evaluate, and in-situ evaluation of these models within a larger plasma transport code can lead to a rigid bottleneck. As a way to bypass this bottleneck, we propose deploying artificial neural network (ANN) surrogates to allow rapid evaluation of the necessary plasma quantities. However, one issue with training an accurate ANN surrogate is the reliance on a sufficiently large and representative training and validation data set, which can be time-consuming to generate. In this work we explore a data-driven active learning and training routine to allow autonomous adaptive sampling of the problem parameter space to ensure a sufficiently large and meaningful set of training data is assembled for the network training. As a result, we can demonstrate approximately order-of-magnitude savings in required training data samples to produce an accurate surrogate.

Analytical coupled vibro-acoustic modeling of tensioned membrane backed by the rectangular cavity

This paper proposes a unified approach to establish the analytical vibro-acoustic coupled model consisting of the tensioned membrane and the closed cavity. A 2-D Fourier cosine series with auxiliary functions is used to derive the displacement of the membrane structure. The sound pressure inside the cavity is expressed as a 3-D Fourier series with additional terms by the method of wave acoustics. Then, the vibro-acoustic coupled model between the membrane and the closed cavity is established based on the Hamilton's principle, which is suitable for different boundary conditions. The program developed by this method can be used to study the sound radiation power and sound transmission loss of coupled systems with various parameters. To demonstrate the accuracy of the proposed method, the free and forced responses of the coupled model are compared with results obtained by finite element method. The membrane with general boundary conditions is well investigated. Besides, the acoustic characteristics of the coupled model are analyzed by adjusting membrane thickness, membrane tension, cavity depth, membrane mounting position and source position, including sound radiation power and sound transmission loss. And the findings have been interpreted appropriately.

Analytical Calculation of Maximum Radiated Power and Surface Wave Loss of Printed Antennas on Thick Anisotropic Substrates

A new approximation for the Green's function of a grounded anisotropic dielectric slab is proposed to obtain closed-form analytical expressions for the maximum radiated power of a short printed dipole on an anisotropic substrate. The corresponding surface wave power can also be accurately estimated as a root of a cubic polynomial which makes it possible to compute radiation efficiency due to surface wave loss analytically.

Development of a MEMS hotplate-based photoacoustic CO2 sensor

Instead of the conventional use of micro-electro-mechanical system (MEMS) hotplate for metal oxide semiconductor (MOS) or nondispersive infrared (NDIR) gas sensing, it was used for photoacoustic (PA) gas sensing. A low-cost MEMS microphone was used for the development of this MEMS hotplate PA carbon dioxide (CO2) sensor. To the knowledge of the authors, this is the first time that a MEMS hotplate and a MEMS microphone are combined for use in gas sensing with high modulation frequency. NDIR sensors use much more expensive photodetectors compared to the MEMS microphone used in this work. The MEMS hotplate and MEMS microphone have the desired characteristics of low power consumption, small size and low cost. The hotplate as a blackbody is a good infrared emitter which is suitable for CO2 detection around the 4.26 µm absorption band. Despite the significant radiation power loss due to high modulation frequency, the remaining/reduced power radiation power was still sufficient to excite CO2 molecules for PA signal generation. Temperature analysis on the sensor showed that PA signal decreases with an increase in temperature, which implies that compensation must be provided for such temperature effects. This work provides alternative optical gas sensing that is comparatively inexpensive compared to the conventional NDIR sensors and by using components that can be easily mass-produced, thereby making a valuable contribution to the fight against air pollution and global warming.

Tungsten divertor plasma simulation with bundled charge state model by SOLPS-ITER on EAST

Research was originally carried out to evaluate plasma performance with a tungsten (W) divertor on EAST using the bundled charge state model by the coupled multi-fluid plasma and kinetic neutral code SOLPS-ITER. This work focuses on the comparisons of several bundled charge state models of W and the all W ion model in low and high recycling divertor operational regimes. It is found that bundled charge state models have a pronounced effect on the reduction of computational time and computer memory and provide an improved marked code speed by a factor of more than five. In the low recycling regime, compared to the full W charge state model, the differences in the plasma parameters at both divertor targets are within 15% for different bundling schemes. In the high recycling regime, no significant difference between bundled charge state models and the all charge state model is observed due to the very low W concentration (∼10−6). It, therefore, indicates that bundled charge state models of W can describe divertor parameters well to a considerable degree. Besides, the errors of tungsten concentration (CW) and the effective ion charge number (Zeff) at the outer mid-plane for bundled models are within 40% inside the separatrix. At the same time, highly resolved bundled models with more than 20 W fluids can describe the radiation power loss consistently within 50% as compared with the all charge state model, while it varies greatly from one aggressively bundled model to the other, especially for core radiation, which is strongly related to the bundling schemes for relatively high charge states.

A novel hydrogenic spectroscopic technique for inferring the role of plasma–molecule interaction on power and particle balance during detached conditions

Detachment, an important mechanism for reducing target heat deposition, is achieved through reductions in power, particle and momentum; which are induced through plasma–atom and plasma–molecule interactions. Experimental research in how those reactions precisely contribute to detachment is limited. Both plasma–atom as well as plasma–molecule interactions can result in excited hydrogen atoms which emit atomic line emission. In this work, we investigate a new Balmer Spectroscopy technique for Plasma–Molecule Interaction—BaSPMI. This first disentangles the Balmer line emission from the various plasma–atom and plasma–molecule interactions and secondly quantifies their contributions to particle (ionisation and recombination) and power balance (radiative power losses). Its performance is verified using synthetic diagnostic techniques of both attached and detached TCV and MAST-U SOLPS-ITER simulations. We find that H 2 plasma chemistry involving and/or H − can substantially elevate the Hα emission during detachment, which we show is an important precursor for Molecular Activated Recombination. An example illustration analysis of the full BaSPMI technique shows that the hydrogenic line series, even Lyα as well as the medium-n Balmer lines, can be significantly influenced by plasma–molecule interactions by tens ofpercent. That has important implications for using atomic hydrogen spectroscopy for diagnosing divertor plasmas.

Radiative recombination data for low-charged tungsten ions: IV. W[formula omitted]W[formula omitted

The radiative recombination and photoionization cross sections as well as the radiative recombination rate coefficients and the radiated power loss rate coefficients are presented for the low-charged tungsten ions from W3+ to W13+. The data are essential to diagnostic and modeling the divertor plasmas impurities in the ITER tokamak because tungsten has been resolved to use as a plasma-facing material. Partial cross sections and rates are given for the ground and excited electron states with principal quantum numbers n≤10 and orbital momenta ℓ≤4 in the wide energy range. Relativistic calculations have been performed taking into account all significant multipoles of the radiative field. Electron wave functions have been found by the Dirac–Fock method. The relativistic Maxwell–Jüttner distribution of continuum electrons has been used in calculations of radiative recombination and radiated power loss rates. Photoionization cross sections have been fitted by an analytical expression with five fit parameters. Peculiarities of behavior of the cross sections and rates for low-charged ions as well as ensuing problems of the cross section fitting are considered. The radiative recombination rates are compared with other recent calculations for the low-charged tungsten ions.