Bolometric Measurements Research Articles

Improved weighted sum estimation of total radiated power at W7-X

AbstractAs magnetic confinement devices move toward higher fusion powers, moderating the heat load to the plasma-facing components becomes increasingly challenging. Efficient power dissipation can be achieved through control of the plasma radiation. However, defining a reliable proxy for the total radiated power is particularly challenging for non-axisymmetric devices such as stellarators. To address this problem, the radiated power can be estimated through a sum of the individual line-integrated bolometer measurements with weights properly calculated to account for the three-dimensional magnetic geometry. The present contribution aims to apply this weighted sum approach to Wendelstein 7-X (W7-X) and quantitatively validate it. First, we generate synthetic radiated power phantoms with characteristic W7-X radiation features to derive a set of optimized line-of-sight weights. Then, we test the weights on mock-ups and EMC3-EIRENE radiation patterns, including acquisition and analysis errors such as random noise fluctuations, camera misalignments, and field errors. Compared to other methods, the optimized weighted sum technique exhibited the best performance in all the presented synthetic test cases. When applied to experimental bolometer data, the optimized weights provided a proxy that is both reliable and real-time capable. Further validation is foreseen for the next experimental campaign.

High-n Rydberg transition spectroscopy for heavy impurity transport studies in W7-X (invited).

Here, we present a novel spectroscopy approach to investigate impurity transport by analyzing line-radiation following high-n Rydberg transitions. While high-n Rydberg states of impurity ions are unlikely to be populated via impact excitation, they can be accessed by charge exchange (CX) reactions along the neutral beams in high-temperature plasmas. Hence, localized radiation of highly ionized impurities, free of passive contributions, can be observed at multiple wavelengths in the visible range. For the analysis and modeling of the observed Rydberg transitions, a technique for calculating effective emission coefficients is presented that can well reproduce the energy dependence seen in datasets available on the OPEN-ADAS database. By using the rate coefficients and comparing modeling results with the new high-n Rydberg CX measurements, impurity transport coefficients are determined with well-documented 2σ confidence intervals for the first time. This demonstrates that high-n Rydberg spectroscopy provides important constraints on the determination of impurity transport coefficients. By additionally considering Bolometer measurements, which provide constraints on the overall impurity emissivity and, therefore, impurity densities, error bars can be reduced even further.

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In rotating 3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^3$$\\end{document}He superfluids, the Kelvin–Helmholtz (KH) instability of the AB interface has been found to follow the theoretical model above 0.4Tc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.4 \\, T_\ extrm{c}$$\\end{document}. A deviation from this dependence has been assumed possible at the lowest temperatures. Our NMR and thermal bolometer measurements down to 0.2Tc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.2 \\, T_\ extrm{c}$$\\end{document} show that the critical KH rotation velocity follows the extrapolation from higher temperatures. We interpret this to mean that the KH instability is a bulk phenomenon and is not compromised by interactions with the wall of the rotating container, although weak pinning of the interface to the wall is observed during slow sweeping of the magnetic field. The KH measurement provides the only so far existing determination of the interfacial surface tension at temperatures down to 0.2Tc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.2 \\, T_\ extrm{c}$$\\end{document} as a function of pressure.

Effects of neutral gas pressure on calibration parameters of resistive bolometer sensors in fusion devices.

Ambient pressure may influence the thermal path between the absorber and heat sink of resistive bolometers and thus impact the calibration parameters. This effect is investigated for metal resistive bolometer sensors as used in bolometer diagnostics on fusion experiments. Measurements in the test facility IBOVAC indicate that pressure has no effect up to 10-3 mbar. However, a significant change in the cooling time constant is observed for pressures above 10-2 mbar, a reduction up to a factor of three at 1mbar. The measurements performed in N2 and He atmospheres and simulations in H2 indicate no difference between the results from different gas species up to 10-3 mbar and less than 10 % up to 0.1mbar. A model based on the thermal conductivity of the surrounding gas combined with the geometry of the sensor holder successfully demonstrates that the additional cooling path through the gas, which may vary between the measurement and reference absorbers, can explain the measurement results. Applying the model to the geometry of a sensor holder designed for port-mounted bolometer cameras in ITER led to design modifications that should help reduce the impact of high environmental pressures on the bolometer measurements. Similarly, it can be assumed that applying the model to the geometries and sensors of operating bolometer diagnostics can help correct the measurements and improve the understanding of plasma radiation in the case of high pressures at the location of bolometer sensors.

A systematic investigation of radiation collapse for disruption avoidance and prevention on JET tokamak

To produce fusion reactions efficiently, thermonuclear plasmas have to reach extremely high temperatures, which is incompatible with their coming into contact with material surfaces. Confinement of plasmas using magnetic fields has progressed significantly in the last years, particularly in the tokamak configuration. Unfortunately, all tokamak devices, and particularly metallic ones, are plagued by catastrophic events called disruptions. Many disruptions are preceded by anomalies in the radiation patterns, particularly in ITER-relevant scenarios. These specific forms of radiation emission either directly cause or reveal the approaching collapse of the configuration. Detecting the localization of these radiation anomalies in real time requires an innovative and specific elaboration of bolometric measurements, confirmed by visible cameras and the inversion of sophisticated tomographic algorithms. The information derived from these measurements can be interpreted in terms of local power balances, which suggest a new quantity, the radiated power divided by the plasma internal energy, to determine the criticality of the plasma state. Combined with robust indicators of the temperature profile shape, the identified anomalous radiation patterns allow determination of the sequence of macroscopic events leading to disruptions. A systematic analysis of JET campaigns at high power in deuterium, full tritium, and DT, for a total of almost 2000 discharges, proves the effectiveness of the approach. The warning times are such that, depending on the radiation anomaly and the available actuators, the control system of future devices is expected to provide enough notice to enable deployment of effective prevention and avoidance strategies.

ZnO-based scintillating bolometers: new prospects to study double beta decay of 64Zn

The first detailed study on the performance of a ZnO-based cryogenic scintillating bolometer as a detector to search for rare processes in zinc isotopes was carried out. A 7.2 g ZnO low-temperature detector, containing more than 80% of zinc in its mass, exhibits good energy resolution of baseline noise 1.0–2.7 keV FWHM at various working temperatures resulting in a low-energy threshold for the experiment, 2.0–6.0 keV. The light yield for β/γ events was measured as 1.5(3) keV/MeV, while it varies for α particles in the range of 0.2–3.0 keV/MeV. The detector demonstrates an effective identification of β/γ events from α events using time-properties of only heat signals. The radiopurity of the ZnO crystal was evaluated using the Inductively Coupled Plasma Mass Spectrometry, an ultra-low-background High Purity Ge γ-spectrometer, and bolometric measurements. Only limits were set at the level of 𝒪(1–100) mBq/kg on activities of 40K, 137Cs and daughter nuclides from the U/Th natural decay chains. The total internal α-activity was measured as 22(2) mBq/kg, with a major contribution caused by 6(1) mBq/kg of 232Th and 12(2) mBq/kg of 234U. Limits on double beta decay (DBD) processes in ^64Zn and 70Zn isotopes were set on the level of 𝒪(1017–1018) yr for various decay modes, profiting from 271 h of acquired background data in the above-ground lab. This study shows a good potential for ZnO-based scintillating bolometers to search for DBD processes of Zn isotopes, especially in 64Zn, with the most prominent spectral features at ∼ 10–20 keV, like the two-neutrino double electron capture. A 10 kg-scale experiment can reach the experimental sensitivity at the level of 𝒪(1024) yr.

Gaussian Process Tomography at ASDEX Upgrade with Magnetic Equilibrium Information and Nonstationary Kernels

This paper explores the application of Gaussian process tomography (GPT) to the bolometer diagnostic at ASDEX Upgrade. Previous work is extended by nonstationary Cartesian kernels and kernels that incorporate magnetic equilibrium information. With the help of existing tomograms from actual shots, a set of hyperparameters working well on a broad range of bolometer measurements is found. While other tomography methods usually rely on additional information like the magnetic equilibrium, those are not required by the GPT method, and it is shown that the method presented here can produce good results without additional information. In addition, the real-time capability of this approach is successfully demonstrated by computing tomograms for 10s of bolometer data in under 5s. This is possible without providing additional information besides bolometer measurements and enables the possibility of real-time reactor control for the future.

Bolometer tomography on Wendelstein 7-X for study of radiation asymmetry

The algorithm for bolometer tomography at Wendelstein 7-X (W7-X) has been recently improved using a novel regularization functional, based on relative gradient smoothing of the sought radiation profile. It has been validated using radiation patterns provided by 3D modeling under real plasma conditions as phantoms and then applied to bolometer measurements performed during the first divertor operation phase of W7-X. The following results are presented: (1) edge-localized 2D radiation patterns with clearly resolved magnetic island radiation structures, (2) an up-down asymmetry in the impurity radiation that is not captured by the 3D edge plasma transport modeling, (3) reversal of the asymmetry with reversed magnetic field direction. Further analysis reveals a poloidal variation of the emissivity in the outer confined plasma region with a field-direction dependent asymmetry, also supported by the soft x-ray measurements. This asymmetry is considered to be related to asymmetric impurity distributions, driven by the pronounced ion-impurity friction force at the plasma edge where the collisionality of the W7-X plasma is sufficiently high to develop impurity asymmetry as predicted by neoclassical theory of parallel impurity transport.

Constraints on cosmological parameters from gamma-ray burst peak photon energy and bolometric fluence measurements and other data

ABSTRACT We use measurements of the peak photon energy and bolometric fluence of 119 gamma-ray bursts (GRBs) extending over the redshift range of 0.3399 ≤ z ≤ 8.2 to simultaneously determine cosmological and Amati relation parameters in six different cosmological models. The resulting Amati relation parameters are almost identical in all six cosmological models, thus validating the use of the Amati relation in standardizing these GRBs. The GRB data cosmological parameter constraints are consistent with, but significantly less restrictive than, those obtained from a joint analysis of baryon acoustic oscillation and Hubble parameter measurements.

Correction for Neutral Pressure-Driven Signal in Radiated Power Measurements on Proto-MPEX

A pinhole camera using four-channel resistive bolometers was designed and implemented on the Prototype Material Plasma Exposure eXperiment (Proto-MPEX) to measure the plasma radiated power. Quantification of the radiated power is required for comprehensive power balance assessments but faces unique challenges on linear plasma devices due to weak absolute signal, compared to typical use in toroidal fusion plasmas, and high neutral pressure changes. Around 1 mTorr, the pressure-driven signal contribution was shown to overwhelm the radiated power signal in Proto-MPEX, found to be ~3 μW. Since the pressure-driven signals could not be predicted from first principle arguments, the signals were corrected using empirical models that take two experimental pressure measurements and the raw bolometer signal to reveal the radiated power signals. Four “gas-only” Proto-MPEX shots were taken, without the radio frequency (rf) plasma discharge, to train, optimize, and validate empirical models. The data included two pressure measurements at different locations along with the bolometer signal. Multiple models were tested; partial least-squares regression with a cross correlation method to account for the time offset in the pressure measurements provided the best combination of accuracy and stability. The model was validated to have a modeling error of 0.0036 V, which was lower than 10% of the expected radiated power signal. The model was tested on a different “gas-only” shot with a complete time-series data. For plasma operation shots, the corrected bolometer measurements were compared with an absolute extreme ultraviolet photodiode measurement and similarities and differences are discussed.

Long-Range Distributed Solar Irradiance Sensing Using Optical Fibers.

Until recently, the amount of solar irradiance reaching the Earth surface was considered to be a steady value over the years. However, there is increasing observational evidence showing that this quantity undergoes substantial variations over time, which need to be addressed in different scenarios ranging from climate change to solar energy applications. With the growing interest in developing solar energy technology with enhanced efficiency and optimized management, the monitoring of solar irradiance at the ground level is now considered to be a fundamental input in the pursuit of that goal. Here, we propose the first fiber-based distributed sensor able of monitoring ground solar irradiance in real time, with meter scale spatial resolutions over distances of several tens of kilometers (up to 100 km). The technique is based on an optical fiber reflectometry technique (CP-ϕOTDR), which enables real time and long-range high-sensitivity bolometric measurements of solar radiance with a single optical fiber cable and a single interrogator unit. The method is explained and analyzed theoretically. A validation of the method is proposed using a solar simulator irradiating standard optical fibers, where we demonstrate the ability to detect and quantify solar irradiance with less than a 0.1 W/m2 resolution.

Bolometer measurements of the radiated power and estimates of the effective ion charge Zeff on the Keda Torus eXperiment

We have measured the power radiated by the plasma in the Keda Torus eXperiment (KTX) using a 20-channel AXUV bolometer. The bolometer has a frequency response bandwidth of 40 kHz, spatial resolution better than 40 mm, and overlap between adjacent channels of about 20%. For an ultra-low q discharge, the radiated power obtained from the bolometer measurements is about 8.0% of the ohmic heating input power. In addition, together with the Hα-emission data, we have used the bolometer data to calculate the effective ion charge Zeff profile, which proves to agree well with a plasma-resistivity calculation and which is hollow in the central region of a poloidal cross-section of the KTX.

Determination of the tolerable impurity concentrations in a fusion reactor using a consistent set of cooling factors

In the present work, the tolerable impurity level and composition for a reactor plasma using several sets of model assumptions are evaluated. Special care was taken to evaluate a comprehensive and consistent set of atomic data for 35 different elements, such that the impurity level for various elements may be studied as a function of their nuclear charge. The data set may not only be useful for the presented work or for system codes which design fusion reactors, but also for interpretation of bolometric measurements. Additionally, the predictions of the spectral distribution of the radiated power is of high quality such that soft x-ray broadband measurements may be interpreted.In the present work the data is used for predicting the radiated power in a reactor plasma, using a 0D, several variants of a 0.5D model and a realistic 1D ASTRA modelling of a DEMO plasma, i.e. the EU DEMO1 2015 design. The maximal or appropriate impurity content of a reactor plasma for all models can be determined, such that the predictions from a simplistic 0D model can be compared to less simplistic models and a proper reactor simulation. These comparisons suggest that with the simplistic models the impurity content may be estimated within a factor of about 1.5, independent of the realization of the reactor plasma. At the same time this study underlines the sensitivity of the reactor performance on the impurity mixture and especially of the He content of the plasma. Additionally, an extended 0.5D model is presented which is able to predict variations of the fusion yield Q and the He concentration, when both is known for a reference scenario. These predictions prove to be of high accuracy when compared to the 1D ASTRA modelling and thus, allow the net impact of an increased dilution and a simlutaneous temperature rise at constant plasma pressure to be evaluated. Furthermore, the parameter space is scanned with more than 105 model reactor plasmas demonstrating that the use of a low-Z impurity diminishes the possibility of an economical feasible reactor plasma. The main results of the parameter scan are made available via scaling formulae.

Impurity transport in T-10 plasmas with ohmic heating

Impurity transport in the T-10 tokamak plasma with ohmic heating is studied in this paper. The values of various impurities densities, measured with the use of passive spectral diagnostics in the visible (Zeff), active charge exchange measurements (He, C, O), and integral bolometric measurements with absolute extreme ultraviolet detectors (Fe, W) are shown. The experimental data show that accumulation level is growing with impurity nuclear charge and determined by the parameter , which is common for all sorts of impurities. Accumulation process is determined by neoclassical processes and begins with the increase of impurity content in the plasma and ends with the formation of density profiles more peaked than the ne(r). In discharges with low γ anomalous transport completely dominates. So it prevents the impurity accumulation and flattens their density profiles down to the ne(r). These observations correlates with measured negative (positive) plasma potential in discharges with high γ (low γ). 1D modelling using ASTRA and STRAHL transport codes is performed to describe the behaviour of impurities in a wide range of T-10 ohmic regimes. It is shown that the coefficients of anomalous transport Dan and Van established in Krupin et al (1983 Sov. J. Plasma Phys. 9 529–36) and Krupin et al (1985 12th EPS Conf. on Plasma Physics) by describing the density dynamics of injected argon and potassium ions are applicable for the modelling of the He, C, O, W impurity density profiles and their sources. The analysis of the obtained results allows us to state the existence of a common dependence of the anomalous transport for all ions (impurities and deuterons) on the discharge parameters in the T-10 ohmic regimes.

The luminosities of cool supergiants in the Magellanic Clouds, and the Humphreys–Davidson limit revisited

The empirical upper luminosity boundary $L_{\rm max}$ of cool supergiants, often referred to as the Humphreys-Davidson limit, is thought to encode information on the general mass-loss behaviour of massive stars. Further, it delineates the boundary at which single stars will end their lives stripped of their hydrogen-rich envelope, which in turn is a key factor in the relative rates of Type-II to Type-Ibc supernovae from single star channels. In this paper we have revisited the issue of $L_{\rm max}$ by studying the luminosity distributions of cool supergiants (SGs) in the Large and Small Magellanic Clouds (LMC/SMC). We assemble samples of cool SGs in each galaxy which are highly-complete above $\log L/L_{\odot}$=5.0, and determine their spectral energy distributions from the optical to the mid-infrared using modern multi-wavelength survey data. We show that in both cases $L_{\rm max}$ appears to be lower than previously quoted, and is in the region of $\log L/L_{\odot}$=5.5. There is no evidence for $L_{\rm max}$ being higher in the SMC than in the LMC, as would be expected if metallicity-dependent winds were the dominant factor in the stripping of stellar envelopes. We also show that $L_{\rm max}$ aligns with the lowest luminosity of single nitrogen-rich Wolf-Rayet stars, indicating of a change in evolutionary sequence for stars above a critical mass. From population synthesis analysis we show that the Geneva evolutionary models greatly over-predict the numbers of cool SGs in the SMC. We also argue that the trend of earlier average spectral types of cool SGs in lower metallicity environments represents a genuine shift to hotter temperatures. Finally, we use our new bolometric luminosity measurements to provide updated bolometric corrections for cool supergiants.

Interferometric diameters of five evolved intermediate-mass planet-hosting stars measured with PAVO at the CHARA Array

Debate over the planet occurrence rates around intermediate-mass stars has hinged on the accurate determination of masses of evolved stars, and has been exacerbated by a paucity of reliable, directly-measured fundamental properties for these stars. We present long-baseline optical interferometry of five evolved intermediate-mass ($\sim\,1.5\,\mathrm{M}_\odot$) planet-hosting stars using the PAVO beam combiner at the CHARA Array, which we combine with bolometric flux measurements and parallaxes to determine their radii and effective temperatures. We measured the radii and effective temperatures of 6 Lyncis ($5.12\pm0.16\,\mathrm{R}_\odot$, $4949\pm58\,\mathrm{K}$), 24 Sextantis ($5.49\pm0.18\,\mathrm{R}_\odot$, $4908\pm65\,\mathrm{K}$), $\kappa$ Coronae Borealis ($4.77\pm0.07\,\mathrm{R}_\odot$, $4870\pm47\,\mathrm{K}$), HR 6817 ($4.45\pm0.08\,\mathrm{R}_\odot$, $5013\pm59\,\mathrm{K}$), and HR 8641 ($4.91\pm0.12\,\mathrm{R}_\odot$, $4950\pm68\,\mathrm{K}$). We find disagreements of typically 15 per cent in angular diameter and $\sim$200 K in temperature compared to interferometric measurements in the literature, yet good agreement with spectroscopic and photometric temperatures, concluding that the previous interferometric measurements may have been affected by systematic errors exceeding their formal uncertainties. Modelling based on BaSTI isochrones using various sets of asteroseismic, spectroscopic, and interferometric constraints tends to favour slightly ($\sim$15 per cent) lower masses than generally reported in the literature.

Evaluation of Photopolymerization Kinetics by Means of Transmittance Measurements

Polymeric resins are widely used for dental reconstruction, and most resins use camphorquinone as activator of the polymerization reaction, through the absorption of light at a defined wavelength range (from 400 nm to 460 nm). During the photopolymerization curing, transparency of these resins changes and transmittance variation can be detected by photodiode and bolometer measurements. This change can be used as an index of the reaction rate, and the kinetic parameter k (reaction rate) can be evaluated from transmittance data by means of nonlinear regression. The relation between k and the light intensity impinging on the resin sample can thus be obtained. In the present work, tests were carried out using the resin Enamel Plus HFO GE2. Results reveal the presence of two different polymerization reactions at two different intensity ranges. The obtained k values were used to predict the most suited curing times for different light intensities. The proposed methodology can be applied to different dental reconstruction materials, provided that the material is partially transparent and that its transparency changes during the polymerization reaction.

The projected background for the CUORE experiment

The Cryogenic Underground Observatory for Rare Events (CUORE) is designed to search for neutrinoless double beta decay of ^{130}Te with an array of 988 TeO_2 bolometers operating at temperatures around 10 mK. The experiment is currently being commissioned in Hall A of Laboratori Nazionali del Gran Sasso, Italy. The goal of CUORE is to reach a 90% C.L. exclusion sensitivity on the ^{130}Te decay half-life of 9 times 10^{25} years after 5 years of data taking. The main issue to be addressed to accomplish this aim is the rate of background events in the region of interest, which must not be higher than 10^{-2} counts/keV/kg/year. We developed a detailed Monte Carlo simulation, based on results from a campaign of material screening, radioassays, and bolometric measurements, to evaluate the expected background. This was used over the years to guide the construction strategies of the experiment and we use it here to project a background model for CUORE. In this paper we report the results of our study and our expectations for the background rate in the energy region where the peak signature of neutrinoless double beta decay of ^{130}Te is expected.

Improvement in the Accuracy of Flux Measurement of Radio Sources by Exploiting an Arithmetic Pattern in Photon Bunching Noise

Abstract A hierarchy of statistics of increasing sophistication and accuracy is proposed to exploit an interesting and fundamental arithmetic structure in the photon bunching noise of incoherent light of large photon occupation number, with the purpose of suppressing the noise and rendering a more reliable and unbiased measurement of the light intensity. The method does not require any new hardware, rather it operates at the software level with the help of high-precision computers to reprocess the intensity time series of the incident light to create a new series with smaller bunching noise coherence length. The ultimate accuracy improvement of this method of flux measurement is limited by the timing resolution of the detector and the photon occupation number of the beam (the higher the photon number the better the performance). The principal application is accuracy improvement in the signal-limited bolometric flux measurement of a radio source.

ArchPbMoO4 scintillating bolometer as detector to searches for the neutrinoless double beta decay of 100Mo

The archPbMoO4 scintillating crystal has been produced from archaeological lead for the first time. The advanced technique for deep purification of lead against chemical impurities was used resulting in 99.9995% purity level of final material. The archPbMoO4 crystal was characterized by means of cryogenics bolometric measurements and demonstrates excellent performances as a scintillating bolometer. The energy resolution (0.3% at 1462 keV of 40K), the high light yield (5.2 keV/MeV for γs, and 1.2 keV/MeV for α particles) and the highly efficient particle identification achieved with this detector, representing the high quality of the crystal. As a final proof for the feasibility of the archPbMoO4 crystal as a promising detector to search for the neutrinoless double β-decay of 100Mo, the crystal should be produced using the LTG Czochralski technique to prevent the possible contamination during the crystal growth and to increase the production yield.