Measurements Of Temperature Fluctuations Research Articles

Development of correlation ECE system for electron temperature fluctuation measurement in LHD

Correlation-ECE (C-ECE) is a standard method for investigating turbulence driven transport. This method allows electron temperature fluctuations that contain information on turbulent transport and independent thermal noise. The turbulence feature is extracted from a correlation analysis from two close locations. The A C-ECE system is utilized on the large helical device (LHD) to measure emission within the frequency range of 74–79.6 GHz. This system employs the spectral decorrelation method and serves as a collective Thomson scattering diagnostic receiver in the LHD. The C-ECE receiver system is comprised of a filter bank system with 32 band-pass filters and a fast digitizer system operating at a sampling rate of 12.5 GHz in the intermediate frequency (IF) stage. This study presents initial experimental results on temperature fluctuation spectra in the LHD, obtained through the C-ECE system using a coherency-based analysis method. An MHD mode at 5 kHz is excited from the onset of neutral beam injection in a magnetic probe, and coherence spectra are obtained from two C-ECE receiver systems. The temperature fluctuation results are derived from the coherence spectrum after bias removal and indicate a level of approximately 3% in the frequency range of 0 to 400 kHz. Further investigations will be conducted to explore drift wave turbulence activities and reconstruct the radial profile of temperature fluctuation in the LHD using the C-ECE receiver systems.

Generation of Entropy Waves by Fully Premixed Flames in a Non-Adiabatic Combustor With Hydrogen Enrichment

Abstract Thermoacoustic combustion instability is a major concern in gas turbine combustors with hydrogen-enriched fuels. Unsteady combustion not only generates acoustic waves but it may also result in fluctuations of burnt gas temperature, referred to as entropy waves. They are convected by the mean flow through the combustor and can cause indirect combustion noise when they are accelerated at the exit. In this work, we demonstrate that entropy waves occur in a fully premixed burner due to unsteady heat transfer at the combustion chamber wall. This mechanism of entropy generation is often neglected in the literature. This work shows an additional mechanism in CH4-H2-air flames, through which entropy may be created even in the fully premixed case. This is due to differential diffusion which generates local fluctuations in equivalence and carbon-to-hydrogen ratios. An adiabatic flame temperature is defined based on these two quantities to examine the influence of differential diffusion on the generation of entropy fluctuations. The generation of entropy waves is investigated by applying system identification (SI) to time series data obtained from a broadband forced large eddy simulation (LES) coupled with a heat conduction solver. The entropy transfer function (ETF) and flame transfer function (FTF) identified with LES/SI are then compared to experimental data obtained with tunable diode laser absorption spectroscopy with wavelength modulation spectroscopy (TDLAS-WMS) for measuring temperature fluctuations, and the multimicrophone method, respectively. After validating the computational setup, the entropy frequency response is identified at various positions within the combustion chamber, and the effects of generation and convective dispersion of entropy waves are qualitatively investigated. We show that a fully premixed turbulent system may exhibit significant entropy waves caused by wall heat losses and differential diffusion of hydrogen.

Synchronized measurement of instantaneous convective heat flux and velocity fields in wall-bounded flows

This work presents an experimental setup for acquiring synchronized wall and flow field measurements in a turbulent boundary layer (TBL). Instantaneous measurements of the convective heat transfer distribution at the wall and of the flow field are carried out simultaneously, using synchronized wall-parallel planar particle image velocimetry and infrared thermography. A low-thermal-inertia heated-thin-foil sensor is embedded in the wall beneath the TBL to measure the wall temperature maps with enough temporal resolution. The unsteady energy balance of the heated foil can be solved to restore the instantaneous value of the convective heat transfer coefficient on the wall. A detailed description of the sensor design is included. Furthermore, owing to the relatively low signal-to-noise ratio of instantaneous temperature fluctuation measurements, a recipe for data processing is proposed. A study to characterize the uncertainty of the experimental setup design is also performed. The overall agreement in the correlation between wall heat transfer and velocity fields with the literature supports the validity of the proposed approach. This solution is potentially interesting for flow control purposes, where sensing is performed at the wall.

Logarithmic scaling of higher-order temperature moments in the atmospheric surface layer

A generalized logarithmic law for high-order moments of homogeneous passive scalars is proposed for turbulent boundary layers. This law is analogous to the generalized log law that has been proposed for high-order moments of the turbulent longitudinal velocity and is derived by combining the random sweeping decorrelation hypothesis with a spectral model informed by the attached eddy hypothesis. The proposed theory predicts that the high-order moments of passive scalar fluctuations within the inertial sublayer will vary logarithmically with wall-normal distance (z), and is evaluated using high frequency time-series measurements of temperature and streamwise velocity fluctuations obtained in the first meter of the atmospheric surface layer (ASL) under near-neutral thermal stratification. The logarithmic dependence with z within the inertial sublayer is observed in both the air temperature and velocity moments, with good agreement to the predictions from the proposed theory. Surprisingly, the proposed theory appears to be as, if not more, valid for transported passive scalars than for the longitudinal velocity.

Estimating inputs for dispersion modeling in mobile platform applications

Mobile monitoring platforms (MMP) are popular in air quality studies. One application of MMP is in estimating pollutant emissions from area sources. The MMP is used to measure concentrations of the relevant species at several locations around the area source, while the associated meteorological information is measured at the same time. Emissions from the area source are inferred by fitting the measured concentrations to estimates from dispersion models. These models require meteorological inputs, such as the kinematic heat flux and the surface friction velocity, that are best computed with measurements of time resolved velocity and temperature made with 3-D sonic anemometers. Because the setting up and dismantling of a 3-D sonic anemometer is not compatible with the necessary mobility of the MMP, it is useful to use alternative instrumentation and methods that provide accurate estimates of these inputs. In this study, we demonstrate such a method based on measurements of horizontal wind speed and temperature fluctuations at a single height. The method was evaluated by comparing methane emissions from a dairy manure lagoon inferred from a dispersion model that uses modeled meteorological inputs to those inferred from measurements with 3-D sonic anemometers. The emission estimates from the modeled meteorological inputs were close to those based on measurements made with 3-D sonic anemometers. We then demonstrate how this approach can be adapted for mobile platform applications by showing that winds measured using a 2-D sonic anemometer and temperature fluctuations measured with a bead thermistor, which can all be carried or mounted on a MMP, yields results that are close to those from a 3-D sonic anemometer.

Highly reliable measurement of temperature fluctuation in near-wall turbulence by a sophisticated cold-wire technique for considering the frequency response and spatial resolution

In turbulence measurement of the thermal field in a non-isothermal turbulent boundary layer, it is necessary to use a small-scale temperature sensor that can provide high spatial resolution. Thus, a fine-wire temperature sensor commonly called “cold-wire” is indispensable for capturing small-scale temperature fluctuations near the wall. However, the length-to-diameter ratio of the cold-wire need generally exceed 1000 to minimize the deterioration in dynamic response due mainly to the axial heat conduction of the thin-wire sensor. To meet such a conflicting requirement, the wire diameter of the cold-wire must be extremely thin. In the present study, we have tested experimentally the performance of several cold-wires of different geometrical features, and examined the effects of the temporal and spatial resolutions of the cold-wire on the temperature fluctuation measurements—root-mean-square (rms) values and instantaneous signal traces—in a canonical turbulent thermal boundary layer. As a result, it was found that the previously-reported response compensation technique for the cold-wire outputs enables us to realize sufficiently accurate temperature fluctuation measurement in the immediate vicinity of the wall while avoiding the deterioration in the spatial resolution of the cold-wire. Furthermore, to improve the spatial resolution of the cold-wire probe, we propose a novel temperature sensor consisting of a fine tungsten wire bent at its center to make an apex angle less than about 30 degrees and have named this sensor a “V-shaped” cold-wire. We have verified its measurement performance in reference to the results obtained by a standard cold-wire probe. As a result, it is shown that the V-shaped cold-wire naturally provides high spatial resolution especially for temperature fluctuation measurement near the wall and can take full advantage of the response compensation technique for the normal cold-wire probe.

Design of Stray Radiation Sensor for ITER ECE Diagnostic

The Electron Cyclotron Emission (ECE) diagnostic has a primary role in the measurement of electron temperature profile and electron temperature fluctuations in ITER. This diagnostic shall be exposed to significant power due to unabsorbed Electron Cyclotron Heating (ECH) power in the plasma. The expected stray power loads could be a few tens of watts, and therefore, the protection of millimetre wave components is one of the design challenges of ITER ECE diagnostic. This protection system includes sensors, a band stop notch filter, and a shutter to stop the RF stray radiation from being incident on the sensitive components. The sensors will be positioned along the ECE transmission line, and shall be used for real-time power monitoring of the stray radiation. Here, we describe a novel design of a sensor for monitoring the stray radiation power. This sensor is a Schottky Diode rectenna, known for high-power and high-speed millimetre wave detection capability. It consists of a 2x2 microstrip patch antenna array, a matching circuit, a diode, and a low pass filter. The antenna array is designed analytically and optimized in CST Microwave Studio, for wide reception angle, high gain, and low side lobe levels. Furthermore, the rectifying circuit is optimized using Agilent Advanced Design System (ADS) software to get better rectification and impedance matching of the signal, thereby improving its detection sensitivity. The ADS simulation results show that the detection sensitivity is about 1000V/W for input power of -30 dBm at 170 GHz, thereby achieving the required performance of the sensor.

Database study of turbulent electron temperature fluctuation measurements at ASDEX Upgrade

In this work, an automated method for the analysis of data from the correlation electron cyclotron emission (CECE) diagnostic is applied to discharges in the ASDEX Upgrade (AUG) tokamak. This recently developed, automated method provides an efficient means of accurately analysing large quantities of experimental turbulence data, enabling the development of the largest database of CECE measurements of tokamak plasmas to-date. The turbulence database provides the opportunity to search for large-scale trends in experimental data to improve our understanding of transport-relevant plasma turbulence. The results of physics-based investigations utilizing this turbulence database will be reported on separately from this work.

Electron temperature fluctuation measurements with Correlation Electron Cyclotron Emission in L-mode and I-mode plasmas at ASDEX Upgrade

The Correlation Electron Cyclotron Emission (CECE) diagnostic at ASDEX Upgrade (AUG) is used to investigate the features of outer core and pedestal (ρpol = 0.85-1.0) turbulence across confinement regime transitions. The I-mode confinement regime is a promising operational scenario for future fusion reactors because it features high energy confinement without high particle confinement, but the nature of the edge and pedestal turbulence in I-mode plasmas is still under investigation. The edge Weakly Coherent Mode (WCM) appears in the I-mode pedestal and may play a role in transport. In this work we explore electron temperature (Te) fluctuations in the plasma outer core and pedestal using a 24-channel high radial resolution CECE radiometer. CECE measurements provide turbulence information including the Te fluctuation amplitude, turbulent spectra, and radial localization of turbulent features. With CECE measurements we show that the WCM is localized in the pedestal region in both L-mode and I-mode and is measured in optically thick plasmas with a Te fluctuation amplitude of 2.3%. Broadband drift wave turbulence is measured in the outer core with a Te fluctuation amplitude of <1%. A second CECE system recently installed at AUG allowed for non-standard fluctuation measurements during L-mode and I-mode experiments. The second CECE system was toroidally separated from the primary system, allowing measurements of the long-range toroidal correlation of the WCM indicating its low toroidal mode number. A reflectometer sharing a line of sight with the second CECE system enabled density-temperature cross-phase (αne Te ) measurements. The WCM αne Te changes between L-mode and I-mode as the Te gradient steepens.

Intramolecular hydrogen bond-tuned thermal-responsive carbon dots and their application to abnormal body temperature imaging

A steric hindrance strategy was used to prepare intramolecular hydrogen bond–controlled thermosensitive fluorescent carbon dots (CDs) via the solvothermal treatment of o-phenylenediamine respectively with three dihydroxybenzene isomers. The CDs obtained from different isomers have very similar morphology, surfaces, and photophysical properties but exhibited different thermal sensitivities. Meanwhile, the orange-emitting CDs (p-CDs) obtained from o-phenylenediamine and p-hydroquinone exhibited an optimal thermal sensitivity of 1.1%/°C. Comprehensive experimental characterizations and theoretical calculations revealed that even a small difference in substituent locations in the phenyl ring of the precursors can considerably affect the formation of intramolecular hydrogen bonds and that the CDs with strong intramolecular hydrogen bonds exhibited poor thermosensitivity. The p-CDs were incorporated with reference CDs (B-CDs) that exhibited heating–quenching blue emission through electrostatic self-assembly to construct a dual-emission probe (p-CDs/B-CDs), which exhibited a thermal sensitivity of 2.0%/°C. Test strips based on the p-CDs/B-CDs were prepared to measure temperature fluctuations based on sensitive and instant fluorescence color evolution. Further, this fluorescent colorimetry was successfully applied to a test strip–integrated wearable wristband to measure the body temperature. This study establishes an inherent relationship between precursors and the resulting intramolecular hydrogen bonds for precisely tuning the thermal sensitivity of CDs. It also offers a visual quantitative strategy for the early warning of abnormal body temperatures.

Gravity and Cosmology in Kaniadakis Statistics: Current Status and Future Challenges.

Kaniadakis statistics is a widespread paradigm to describe complex systems in the relativistic realm. Recently, gravitational and cosmological scenarios based on Kaniadakis (κ-deformed) entropy have been considered, leading to generalized models that predict a richer phenomenology comparing to their standard Maxwell-Boltzmann counterparts. The purpose of the present effort is to explore recent advances and future challenges of Gravity and Cosmology in Kaniadakis statistics. More specifically, the first part of the work contains a review of κ-entropy implications on Holographic Dark Energy, Entropic Gravity, Black hole thermodynamics and Loop Quantum Gravity, among others. In the second part, we focus on the study of Big Bang Nucleosynthesis in Kaniadakis Cosmology. By demanding consistency between theoretical predictions of our model and observational measurements of freeze-out temperature fluctuations and primordial abundances of 4He and D, we constrain the free κ-parameter, discussing to what extent the Kaniadakis framework can provide a successful description of the observed Universe.

Entropy transfer function measurement with tunable diode laser absorption spectroscopy

Tunable diode laser absorption spectroscopy (TDLAS) with wavelength modulation spectroscopy (WMS) has been widely applied to measure the gas temperature and species concentration in combustion environments. In this work, we show the capability of TDLAS in measuring the coherent temperature fluctuations of a turbulent swirled flame. Two distributed feedback grating (DFB) lasers are used to probe the H2O absorption transitions near 7185.59 cm−1 and 6806.03 cm−1. Using WMS, the 2f/1f absorption spectra are converted into temperature at a rate of 5 kHz. The quantity of interest that we measure is the Entropy Transfer Function (ETF) which, for low Mach numbers, relates the upstream acoustic perturbation to the temperature fluctuation downstream of the flame. The ETF is obtained by taking the ratio between the measured temperature fluctuation downstream of the flame, measured with TDLAS and the upstream acoustic perturbation input, induced by loudspeakers with forcing frequency ranging from 40 to 250 Hz, reconstructed with the multi-microphone method. We show that the TDLAS-WMS technique can measure relatively low coherent temperature fluctuations as low as 5 K. It is found that the gain of ETFs of the swirling flame does not decrease monotonically with respect to the forcing frequency and exhibits a minimum response at particular frequencies depending on the operating conditions. Moreover, the ETFs for different operating conditions collapse on each other when plotted against the Strouhal number. The similarity between the measured ETFs and Flame Transfer Functions (FTFs) indicates a strong link between flame heat release rate response and the temperature fluctuation downstream of the flame. Furthermore, the measurement series demonstrate the strong capability and suitability of the TDLAS-WMS technique for entropy waves measurements, leading to the discovery of peculiar entropy responses at high frequencies.

Model marginalized constraints on neutrino properties from cosmology

We present robust, model-marginalized limits on both the total neutrino mass ($\sum m_\nu$) and abundance ($N_{\rm eff}$) to minimize the role of parameterizations, priors and models when extracting neutrino properties from cosmology. The cosmological observations we consider are CMB temperature fluctuation and polarization measurements, Supernovae Ia luminosity distances, BAO observations and determinations of the growth rate parameter from the Data Release 16 of the Sloan Digital Sky Survey IV. The degenerate neutrino mass spectrum (which implies $\sum m_\nu>0$) is weakly (moderately) preferred over the normal and inverted hierarchy possibilities, which imply the priors $\sum m_\nu>0.06$ and $\sum m_\nu>0.1$ eV respectively. Concerning the underlying cosmological model, the $\Lambda$CDM minimal scenario is almost always strongly preferred over the possible extensions explored here. The most constraining $95\%$ CL bound on the total neutrino mass in the $\Lambda$CDM+$\sum m_\nu$ picture is $\sum m_\nu< 0.087$ eV. The parameter $N_{\rm eff}$ is restricted to $3.08\pm 0.17$ ($68\%$ CL) in the $\Lambda$CDM+$N_{\rm eff}$ model. These limits barely change when considering the $\Lambda$CDM+$\sum m_\nu$+$N_{\rm eff}$ scenario. Given the robustness and the strong constraining power of the cosmological measurements employed here, the model-marginalized posteriors obtained considering a large spectra of non-minimal cosmologies are very close to the previous bounds, obtained within the $\Lambda$CDM framework in the degenerate neutrino mass spectrum. Future cosmological measurements may improve the current Bayesian evidence favouring the degenerate neutrino mass spectra, challenging therefore the consistency between cosmological neutrino mass bounds and oscillation neutrino measurements, and potentially suggesting a more complicated cosmological model and/or neutrino sector.

Temperature measurements of long sparks in air using time-resolved moiré deflectometry

This paper presents an original investigation into time-resolved moiré deflectometry (MD) for gas temperature measurements of long sparks in air. In order to perform a rigorous comparative investigation with the widely used quantitative schlieren (QS) method, we set up an orthogonal optical measurement system. The impacts of spatial resolution and exposure time on the measurement accuracy are investigated by comparing the measured radial distribution of the gas temperature and its time evolution during the same spark discharge event. It is found that the time-resolved MD with an exposure time of 1.0 μs can accurately measure the gas temperature evolution during the isobaric heating and relaxation process of long sparks. The measured results of the expansion rate of cross-section and average temperature T g confirms that the energy loss is dominated by thermal conduction during the isobaric heating and relaxation process after the extinction of discharge current. The MD can achieve a finer spatial resolution than the QS method, which is beneficial to the reconstruction of steep radial temperature distribution and the suppression of measured temperature fluctuation. Moreover, the MD can obtain a sub-microsecond exposure time by increasing the power of continuous-wave laser source, which shows its potential to capture the rapid changes in gas temperature during the fast-heating process.

Advances in physics and applications of 3D magnetic perturbations on the J-TEXT tokamak

In the last two years, three major technical improvements have been made on J-TEXT in supporting of the expanded operation regions and diagnostic capabilities. (1) The successful commission of the 105 GHz/500 kW/1 s electron cyclotron resonance heating (ECRH) system increasing the core electron temperature from 0.9 keV up to around 1.5 keV. (2) The poloidal divertor configuration with an X-point in the high-field side has been achieved. In particular, the 400 kW electron cyclotron wave has also been successfully injected into the diverted plasma. (3) A 256-channel electron cyclotron emission imaging diagnostic system and two sets of four-channel Doppler backscattering diagnostics have been successfully developed on J-TEXT, allowing detailed measurement of the electron temperature and density fluctuations for turbulence and MHD research. The locked mode (LM), especially the 2/1 LM, is one of the biggest threats to the plasma operation. Both the thresholds of 2/1 and 3/1 LM are observed to vary non-monotonically on electron density. The electrode biasing was applied successfully to unlock the LM from either a rotating or static resonant magnetic perturbation (RMP) field. In the presence of 2/1 LM, three kinds of standing wave (SW) structures have been observed to share a similar connection to the island structure, i.e. the nodes of the SWs locate around the O- or X-points of the 2/1 island. The control and mitigation of disruption is essential to the safe operation of ITER, and it has been systematically studied by applying a RMP field, massive gas injection (MGI) and shattered pellet injection on J-TEXT. When the RMP-induced 2/1 LM is larger than a critical width, the MGI shutdown process can be significantly influenced. If the phase difference between the O-point of LM and the MGI valve is +90° (or −90°), the penetration depth and the assimilation of impurities can be enhanced (or suppressed) during the pre-thermal quench (TQ) phase and result in a faster (or slower) TQ. A secondary MGI can also suppress the runaway electron (RE) generation, if the additional high-Z impurity gas arrives at the plasma edge before TQ. When the secondary MGI has been applied after the formation of the RE current plateau, the RE current can be dissipated, and the dissipation rate increases with the injected impurity quantity but saturates with a maximum of 28 MA s−1. The non-local transport is experimentally observed in the ion transport channel. The electron thermal diffusivity significantly increases with the ECRH power. Theoretical work shows that significant intrinsic current can be driven by electromagnetic turbulence, and the robust formation mechanism of the E × B staircase is identified from the Hasegawa–Wakatani system.

Collective effect of thermal plumes on temperature fluctuations in a closed Rayleigh–Bénard convection cell

We report a systematic study of the collective effect of thermal plumes on the probability density function (p.d.f.) $P(\delta T)$ of temperature fluctuations $\delta T(t)$ in turbulent Rayleigh–Bénard convection. By decomposing $\delta T(t)$ into four basic fluctuation modes associated with single and multiple warm and cold plumes and a turbulent background, we derive an analytic form of $P(\delta T)$ based on the convolutions of the five independent modes. To test the derived form of $P(\delta T)$ in the multiple-plume regions, where the thermal plumes are heavily populated, we conduct time series measurements of temperature fluctuations in two convection cells; one is a vertical thin disk and the other is an upright cylinder of aspect ratio unity. For a given normalized position in most regions of the convection cell, all of the measured p.d.f.s $P(\delta T)$ for different Rayleigh numbers fall onto a single master curve, once $\delta T$ is normalized by its root-mean-square (r.m.s.) value $\sigma _T$ . It is found that the measured $P(\delta T/\sigma _T)$ at different locations along the symmetric horizontal and vertical axes of the convection cells can all be well described by the derived form of $P(\delta T/\sigma _T)$ . The fitted values of the parameters associated with the number of plumes in multiple plume clusters and their relative strengths and degrees of intermittency are closely linked to the spatial distribution of thermal plumes and local dynamics of the large-scale circulation in a closed convection cell. Our work thus provides a unified theoretical approach for understanding scalar p.d.f.s in a turbulent field, which is very useful not only for the present study but also for the study of many turbulent mixing problems of practical interest.

Measurement of Turbulent Temperature Fluctuations by Fine-Wire Temperature Sensors with Various Shapes

In a turbulent thermal boundary layer, to accurately measure the temperature fluctuation near the wall, a thin-wire temperature sensor with high spatial resolution is indispensable for capturing small-scale temperature fluctuations in the immediate vicinity of the wall. On the other hand, in order to minimize the deterioration in the dynamic response of the thin-wire sensor, its length-to-diameter ratio need generally exceed 1000. To meet these conflicting requirements, the wire diameter of the sensor must be extremely thin. In this study, as a novel approach, we proposed a new temperature probe consisting a V-shaped thin tungsten wire, and verified its measurement accuracy by using a standard cold-wire probe as a reference. As a result, the turbulence characteristics measured in a fully-developed thermal boundary layer—r.m.s. values, power spectra, instantaneous signal traces of temperature fluctuations, etc.—show that the V-shaped thin-wire temperature sensor can improve the spatial resolution of the sensor while enabling us to take full advantage of the response compensation technique developed for the standard cold-wire probe.

Ground-based measurements of microwave brightness temperature and electric field fluctuations for clouds with a different level of electrical activity

Simultaneous measurements of the brightness temperature and short-period electric field fluctuations were carried out to reveal possible connections between the electrification rate and turbulence intensity in clouds. The measurements were conducted in Nizhny Novgorod, Russia (56°19′37″N 44°00′27″E) in 2013 and 2018. The 8 mm radiometer was used to measure the brightness temperature of thermal radiation, and the vertical component of the atmospheric electric field were carried out using an electrostatic fluxmeter. With the use of meteorological data and electric field measurements the state of analyzed events has been classified into 4 types: cloudless atmosphere and high-level clouds (Cs), cumulus clouds (Cu), cumulonimbus clouds without lightning that cause strong electrical field disturbances near the ground surface (Cb), cumulonimbus thunderstorm clouds with lightning discharges (Cb+). Detailed statistical characteristics of brightness temperature fluctuations and short-period electric field fluctuations are obtained for the first time for the indicated types of events.It is shown that measured spectral densities of the atmosphere brightness temperature and electric field fluctuations correspond well enough in the considered frequency range to the results of presented theoretical consideration. Precipitation particles in clouds can be considered herewith as passive scalar, and the movement of inhomogeneities in the particle density can be described by Kolmogorov theory. Since electric charges are located on the precipitation with small droplet and ice particles, an increase in the inhomogeneities of the water content means likely an increase in the inhomogeneities of the electric charge. For thunderclouds the estimates of the relative fluctuations of liquid water content give values of the order of tens of percent. There is a tendency towards a relative increase in brightness temperature fluctuations at high frequencies in the band around f ≈ 10−2 Hz (and possibly higher than fmax ≈ 0.05 Hz) for the sequence of cloud types Cu, Cb, Cb+.

Experimental investigation and gyrokinetic simulations of multi-scale electron heat transport in JET, AUG, TCV

Tokamaks dominated by electron heating like ITER could possibly suffer from the consequences of electron temperature gradient (ETG) mode destabilisation, which could develop a turbulent electron heat flux capable of setting an upper limit to the achievable electron temperature peaking, resulting in a degradation of the fusion performance. An effort is carried out in this paper to collect and compare the results of dedicated plasma discharges performed during the last few years at three of the major European tokamaks, TCV, AUG and JET, by analysing the electron heat transport for cases presumably compatible with ETGs relevance, given the actual theoretical understanding of these instabilities. The response of the electron temperature profiles to electron heat flux changes is experimentally investigated by performing both steady state heat flux scans and perturbative analysis by radio frequency heating modulation. The experimental results are confronted with numerical simulations, ranging from simple linear gyrokinetic (GK) or quasi-linear runs, to very computationally expensive nonlinear multi-scale GK simulations, resolving ion and electron scales at the same time. The results collected so far tend to confirm the previously emerging picture, indicating that cases with a proper balance of electron and ion heating, with similar electron and ion temperatures and sufficiently large ETG, could be compatible with a non negligible impact of ETGs on the electron heat transport. The ion heating destabilises ETGs not only by increasing the ion temperature but also thanks to the stabilisation of ion-scale turbulence by a synergy of fast ions and E × B shearing, which are in some cases associated with it. The stabilising effect of plasma impurities on ETGs is still under investigation by means of multi-scale GK simulations, and also direct experimental measurements of density and temperature fluctuations at electron scales would be needed to ultimately assess the impact of ETGs.

Most constraining cosmological neutrino mass bounds

We present here up-to-date neutrino mass limits exploiting the most recent cosmological data sets. By making use of the cosmic microwave background temperature fluctuation and polarization measurements, supernovae Ia luminosity distances, baryon acoustic oscillation observations and determinations of the growth rate parameter, we are able to set the most constraining bound to date, $\ensuremath{\sum}{m}_{\ensuremath{\nu}}&lt;0.09\text{ }\text{ }\mathrm{eV}$ at 95% C.L. This very tight limit is obtained without the assumption of any prior on the value of the Hubble constant and highly compromises the viability of the inverted mass ordering as the underlying neutrino mass pattern in nature. The results obtained here further strengthen the case for very large multitracer spectroscopic surveys as unique laboratories for cosmological relics, such as neutrinos: that would be the case of the Dark Energy Spectroscopic Instrument survey and of the Euclid mission.