Hot Spot Conditions Research Articles

National direct-drive program on OMEGA and the National Ignition Facility

A major advantage of the laser direct-drive (DD) approach to ignition is the increased fraction of laser drive energy coupled to the hot spot and relaxed hot-spot requirements for the peak pressure and convergence ratios relative to the indirect-drive approach at equivalent laser energy. With the goal of a successful ignition demonstration using DD, the recently established national strategy has several elements and involves multiple national and international institutions. These elements include the experimental demonstration on OMEGA cryogenic implosions of hot-spot conditions relevant for ignition at MJ-scale energies available at the National Ignition Facility (NIF) and developing an understanding of laser-plasma interactions and laser coupling using DD experiments on the NIF. DD designs require reaching central stagnation pressures in excess of 100 Gbar. The current experiments on OMEGA have achieved inferred peak pressures of 56 Gbar (Regan et al 2016 Phys. Rev. Lett. 117 025001). Extensive analysis of the cryogenic target experiments and two- and three-dimensional simulations suggest that power balance, target offset, and target quality are the main limiting factors in target performance. In addition, cross-beam energy transfer (CBET) has been identified as the main mechanism reducing laser coupling. Reaching the goal of demonstrating hydrodynamic equivalence on OMEGA includes improving laser power balance, target position, and target quality at shot time. CBET must also be significantly reduced and several strategies have been identified to address this issue.

Analyses of Low- and High-Margin Quench Propagation in the European DEMO TF Coil Winding Pack

The superconducting toroidal field (TF) coils composed of a winding pack (WP) without radial plates, encapsulated in a steel casing, are currently being studied in the framework of the EUROfusion work package magnets (WPMAG). The ENEA (Italian National Agency for New Technologies, Energy and Sustainable Economic Development) 2014 TF WP design consists of graded (Nb3Sn + NbTi), double-layer wound rectangular cable-in-conduit conductors, for which the operational as well as accidental transients must be carefully investigated. This paper presents the analysis of the quench propagation inside the TF WP proposed in 2014 by ENEA using the state-of-the-art thermal-hydraulic code 4C. Different locations are considered for the quench initiation: 1) at the maximum temperature margin $\Delta T_{\mathrm {mar}}^{\mathrm {max}}$ , resulting in the most severe hotspot condition and 2) at the minimum temperature margin $\Delta T_{\mathrm {mar}}^{\mathrm {min}}$ , to analyze the most probable event. The evolution of voltage, normal zone, hotspot temperature, and maximum pressure in the TF WP is computed comparing the results from the two cases, highlighting the role of heat diffusion inside the TF WP.

Hotspot electron temperature from x-ray continuum measurements on the NIF.

We report on measurements of the electron temperature in the hotspot of inertially confined, layered, spherical implosions on the National Ignition Facility using a differential filtering diagnostic. Measurements of the DT and DD ion temperatures using neutron time-of-flight detectors are complicated by the contribution of hot spot motion to the peak width, which produce an apparent temperature higher than the thermal temperature. The electron temperature is not sensitive to this non-thermal velocity and is thus a valuable input to interpreting the stagnated hot spot conditions. Here we show that the current differential filtering diagnostic provides insufficient temperature resolution for the hot spot temperatures of interest. We then propose a new differential filter configuration utilizing larger pinhole size to increase spectral fluence, as well as thicker filtration. This new configuration will improve measurement uncertainty by more than a factor of three, allowing for a more accurate hotspot temperature.

An ion-electron non-equilibrium model for relaxing central hot-spot ignition conditions

This paper presents an ion-electron non-equilibrium model for relaxing the central hot-spot ignition conditions in inertial confinement fusion. The model emphasizes that the hot-spot ion temperature is higher than its electron temperature, so that the hot-spot nuclear reactions are enhanced and its energy leaks from radiation bremsstrahlung and electron conduction are relatively reduced. Both the hot-spot self-heating analysis and a more comprehensive hot-spot ignition-and-burn dynamics analysis show that as compared with the commonly used equilibrium model, the ignition region would be significantly enlarged in the hot-spot R-T space. Simulations are also done using the LARED-S code to show that a tuned radiation-drive wedged-peak pulse, which creates a secondary shock, could be utilized to enhance hot-spot non-equilibrium.

Modeling and Detection of Hotspot in Shaded Photovoltaic Cells

In this paper, we address the problem of modeling the thermal behavior of photovoltaic (PV) cells undergoing a hotspot condition. In case of shading, PV cells may experience a dramatic temperature increase, with consequent reduction of the provided power. Our model has been validated against experimental data, and has highlighted a counterintuitive PV cell behavior, that should be considered to improve the energy efficiency of PV arrays. Then, we propose a hotspot detection scheme, enabling to identify the PV module that is under hotspot condition. Such a scheme can be used to avoid the permanent damage of the cells under hotspot, thus their drawback on the power efficiency of the entire PV system.

Recursive construction of output-context fuzzy systems for the condition monitoring of electrical hotspots based on infrared thermography

Infrared thermography technology is currently being used in various applications, including fault diagnosis in electrical equipment. Thermal abnormalities are diagnosed by identifying and classifying the hotspot conditions of electrical components. In this article, a new recursively constructed output-context fuzzy system is proposed to characterize the condition of electrical hotspots. An infrared camera is initially used to capture the thermal images of components with hotspots, and intensity features are extracted from each hotspot. The Recursively Constructed Fuzzy System (RCFS) is then applied to automatically realize and formulate the conditions of the thermal abnormalities. On the basis of the priority level, the hotspot conditions are categorized as normal, warning, and critical. From these three categories, the conditions can be further simplified into two categories, namely, defect (warning and critical) and normal. The proposed RCFS realizes the prominent distinctions in the output domain by using a self-organizing method. The termination of the recursive algorithm finds an effective rule base to achieve an accurate representation of the datasets. The proposed system obtains less fuzzy rules with reasonable accuracy. Our survey of 253 detected regions shows that the proposed RCFS produces 92.3% and 80% testing accuracies for classifying conditions into two and three classes, respectively. The thermographic diagnostic evaluation shows that the proposed intelligent system automatically identifies the rationally acceptable limits of hotspot conditions. Therefore, the proposed system is suitable for establishing an intelligent defect analysis system.

Influence of ultrasound power on acoustic streaming and micro-bubbles formations in a low frequency sono-reactor: Mathematical and 3D computational simulation

This paper aims at investigating the influence of ultrasound power amplitude on liquid behaviour in a low-frequency (24kHz) sono-reactor. Three types of analysis were employed: (i) mechanical analysis of micro-bubbles formation and their activities/characteristics using mathematical modelling. (ii) Numerical analysis of acoustic streaming, fluid flow pattern, volume fraction of micro-bubbles and turbulence using 3D CFD simulation. (iii) Practical analysis of fluid flow pattern and acoustic streaming under ultrasound irradiation using Particle Image Velocimetry (PIV). In mathematical modelling, a lone micro bubble generated under power ultrasound irradiation was mechanistically analysed. Its characteristics were illustrated as a function of bubble radius, internal temperature and pressure (hot spot conditions) and oscillation (pulsation) velocity. The results showed that ultrasound power significantly affected the conditions of hotspots and bubbles oscillation velocity. From the CFD results, it was observed that the total volume of the micro-bubbles increased by about 4.95% with each 100W-increase in power amplitude. Furthermore, velocity of acoustic streaming increased from 29 to 119cm/s as power increased, which was in good agreement with the PIV analysis.

Inhibition of turbulence in inertial-confinement-fusion hot spots by viscous dissipation.

Achieving ignition in inertial confinement fusion (ICF) requires the formation of a high-temperature (>10 keV) central hot spot. Turbulence has been suggested as a mechanism for degrading the hot-spot conditions by altering transport properties, introducing colder, mixed material, or reducing the conversion of radially directed kinetic energy to hot-spot heating. We show, however, that the hot spot is very viscous, and the assumption of turbulent conditions in the hot spot is incorrect. This work presents the first high-resolution, three-dimensional simulations of National Ignition Facility (NIF) implosion experiments using detailed knowledge of implosion dynamics and instability seeds and including an accurate model of physical viscosity. We find that when viscous effects are neglected, the hot spot can exhibit a turbulent kinetic energy cascade. Viscous effects, however, are significant and strongly damp small-scale velocity structures, with a hot-spot Reynolds number in the range of only 10-100.

Local Shunting in Multicrystalline Silicon Solar Cells: Distributed Electrical Simulations and Experiments

In this paper, we analyze the effect of local shunts in photovoltaic (PV) solar cells by experimental characterization and distributed electrical simulations. To this purpose, we developed a quasi-3-D distributed electrical network that is based on two-diode circuit elementary units. It allows accounting for resistive losses associated to the transport through the emitter, the fingers and the busbars, and to local defects in the semiconductor. The electrical parameters of the equivalent circuit units are calibrated according to experiments performed on multicrystalline (mc-Si) silicon solar cells, including samples that feature local shunts due to localized defects, which lead to nonuniform distribution of electrical and optical properties. The distributed electrical simulations account for the degradation of fill factor and power conversion efficiency in case of local shunting. Moreover, by combining the proposed tool with a RC thermal network it is possible to estimate the temperature distribution in a shunted solar cell. Our analysis shows how a shunted cell that operates under hot-spot conditions is subject to significant local overheating, which possibly lead to permanent PV cell damages.

Inheritance of blast resistance and identification of SSR marker associated with it in rice cultivar RDN 98-2

An F2 population was developed from a cross between rice (Oryza sativa L.) genotypes, EK 70 (highly susceptible to blast) and RDN 98-2-3-5-14 (resistant to blast), to study the inheritance of blast resistance and to identify the marker associated with resistance. The F2 population segregated in 3:1 ratio for resistance: susceptible under hot spot conditions for blast suggesting monogenic control of resistance in this population. Bulk segregant analysis conducted using a total of 25 SSR markers identified two SSRs to be polymorphic between the parents and the corresponding bulks. One of these SSR markers RM204 which has been reported to be mapped on the short arm of chromosome 6 and in close proximity of blast resistance gene/QTLs in other studies showed expected segregation ratio (1:2:1) for single gene model in the F2 population. This marker was found significantly associated with blast resistance on regression analysis. Rice is the world’s largest food crop, providing caloric needs to millions of people daily. Rice suffers attack by a large number of pests and pathogens, which under epidemic conditions, cause serious yield losses. Among these, rice blast caused byMagnaporthe grisea (Hebert) Barr. (Barr 1977), synonym M. oryzae is one of the most devastating and destructive diseases of rice worldwide. Under heavy dew, arial plant parts are affected, leaf surface becomes speckled with oval lesions and plants are liable to lodging if nodes are infected. If the panicles are infected, it also results in severe yield losses (Ou 1985). Resistance to the M. oryzae is a classic gene-for-gene system, where a major resistance gene is effective against

Modeling Angular Dependences in Land Surface Temperatures From the SEVIRI Instrument Onboard the Geostationary Meteosat Second Generation Satellites

Satellite-based estimates of land surface temperature (LST) are widely applied as an input to models. A model output is often very sensitive to error in the input data, and high-quality inputs are therefore essential. One of the main sources of errors in LST estimates is the dependence on vegetation structure and viewing and illumination geometry. Despite this, these effects are not considered in current operational LST products from neither polar-orbiting nor geostationary satellites. In this paper, we simulate the angular dependence that can be expected when estimating LST with the viewing geometry of the geostationary Meteosat Second Generation Spinning Enhanced Visible and Infrared Imager sensor across the African continent and compare it to a normalized view geometry. We use the modified geometric projection model that estimates the scene thermal infrared radiance from a surface covered by different land covers. The results show that the sun-target-sensor geometry plays a significant role in the estimated temperature, with variations strictly due to the angular configuration of more than ±3°C in some cases. On the continental scale, the average error is small except in hot-spot conditions, but large variations occur both geographically and temporally. The sun zenith angle, the amount of vegetation, and the vegetation structure are all shown to affect the magnitude of the errors. The findings highlight the need for taking the angular effects into account when applying LST estimates in models and when comparing LST estimates from different sensors or from different times, both on the daily and seasonal scale.

Thermonuclear burn characteristics of compressed deuterium-tritium microspheres

The thermonuclear burn characteristics of compressed deuterium-tritium microspheres are simulated with LARED-S code based on the isochoric and isobaric models. Two examples of the isochoric model are simulated and compared with the other present data for validating the LARED-S code. For the isobaric model, numerical results characterizing the thermonuclear burn for a broad range of initial conditions are presenteal. It is shown that the yield and burn-up fraction increase with the total fuel mass, pressure and main-fuel density. It is necessary for the hot-spot to reach temperatures up to 70 to 80 MK and areal density 3 to 4 kg· m-2 to obtain considerable fusion energy. If the main-fuel density is increased high enough, the hot-spot condition for ignition could be broadened to a lower limit. Finally, the results of the isobaric model are compared with those of the actual ignition targets simulated with the LARED-S code.

Rigorous Characterization of Resonant Hot Spot Conditions in a Stratified Tissue Model

A unified approach for determining the lossy resonance (hot-spot) conditions in a lossy stratified biological tissue model is proposed. These conditions may lead to a significant enhancement of local electromagnetic power deposition in a single layer as compared to the power dissipated in the background. Rigorous analysis of electromagnetic wave power absorption in a planar stratified tissue model renders a closed-form characterization of six possible asymptotic cases and the associated conditions and bounds on the optimal absorption in the particular layer as a function of its normalized thickness and parameters of the surrounding layers. It is shown that, even very thin and low attenuating layers (sites) of biological tissue, are capable of dissipating a very substantial amount of the incident power, subject to specific lossy resonance conditions. From a dosimetric point of view, the results obtained allow for prediction of naturally occurring spatial resonances in biological tissues on both macroscopic and microscopic scales. On the other hand, they also provide an effective mean for design and synthesis of optimally absorbing materials and tissues in therapeutic applications

A Lightweight, Robust P2P System to Handle Flash Crowds

An Internet flash crowd (also known as hot spots) is a phenomenon that results from a sudden, unpredicted increase in an on-line object's popularity. Currently, there is no efficient means within the Internet to deliver Web objects scalably under hot spot conditions to all clients that desire the object. We present peer-to-peer (P2P) randomized overlays to obviate flash-crowd symptoms (PROOFS), a simple, lightweight, P2P approach that uses randomized overlay construction and randomized, scoped searches to locate and deliver objects efficiently under heavy demand to all users that desire them. We evaluate PROOFS' robustness in environments in which clients join and leave the P2P network, as well as in environments in which clients are not always fully cooperative. Through a mix of simulation and prototype experimentation in the Internet, we show that randomized approaches like PROOFS should effectively relieve flash crowd symptoms in dynamic, limited-participation environments.

A lightweight, robust P2P system to handle flash crowds

An Internet flash crowd (also known as hot spots) is a phenomenon that results from a sudden, unpredicted increase in an on-line object's popularity. Currently, there is no efficient means within the Internet to deliver Web objects scalably under hot spot conditions to all clients that desire the object. We present peer-to-peer (P2P) randomized overlays to obviate flash-crowd symptoms (PROOFS), a simple, lightweight, P2P approach that uses randomized overlay construction and randomized, scoped searches to locate and deliver objects efficiently under heavy demand to all users that desire them. We evaluate PROOFS' robustness in environments in which clients join and leave the P2P network, as well as in environments in which clients are not always fully cooperative. Through a mix of simulation and prototype experimentation in the Internet, we show that randomized approaches like PROOFS should effectively relieve flash crowd symptoms in dynamic, limited-participation environments.

A theoretical study of parcel stability and cloud distribution in a Jovian hot spot

The Galileo probe penetrated Jupiter’s atmosphere at a hot spot, a region of unusual clarity and dryness centered at 7°N. The measured abundances of condensable species were puzzling since strong depletion of volatiles was found from 0.4 to 12 bar, far below the condensation levels. In this paper we explore in detail thermally driven dry downdraft scenarios to simulate hot spot conditions. We compare the hot spot temperature profile with that of surrounding areas to evaluate their relative buoyancy and the parcel level of descent. For the hot spot we use the vertical thermal profile and composition measured in situ by the Galileo probe, as well as the distribution of condensable species inferred by the NIMS experiment on board of the Galileo orbiter. The environment is characterized by the thermal profile measured by the Voyager 1 radio probe experiment down to 1 bar. Downward, the profile is extended adiabatically using different values for the ortho–para distribution of H 2. Different concentrations of the condensables (relative humidity from 1 to 100%) were tested for the environment using a deep value ( P>8 bar) of 1 to 4 times the solar abundance of NH 3 and 1 to 2 times for H 2O. Under these conditions, dry downdrafts can sink in Jupiter’s atmosphere to the ∼5 to 15 bar level depending on the particular values used. Conversely, in a second numerical experiment, we simulate the hot spot’s composition and temperature profiles measured by the Galileo probe using a downward dry jet entraining model. Qualitative agreement is found for different parameterizations of the entrainment rates. Furthermore, a thermochemical model predicts at the hot spot, the existence of a NH 3 cloud with a base at ∼550 mbar and an NH 4SH cloud with a base at ∼1.6 bar. Finally, the number of hot spots presented in a latitude circle could be related to the depth of the hot spot motions through the Rossby deformation radius.

Hot Spot Conditions during Cavitation in Water

Liquids irradiated with high-intensity ultrasound undergo acoustic cavitation--the formation, growth, and implosive collapse of bubbles. The energy stored during the growth of the bubble in the rarefaction phase of the acoustic field is released when the bubble violently collapses in the compression phase of the acoustic field, as acoustic noise, shock waves, chemical reactions, and the emission of light (sonoluminescence, SL). This violent collapse is predicted to generate a hot spot of thousands of Kelvin within the bubble, but, to date, there have been only a limited number of experimental measurements of the temperature of this hot spot. Although the SL of water has been studied for more than 50 years, the effective hot spot temperature during aqueous cavitation remains unresolved. Given the importance of aqueous cavitation (sonography and bioeffects of ultrasound, sonochemical remediation of aqueous pollutants, synthetic applications of sonochemistry, etc.), the authors decided to apply previous spectroscopic analysis of SL of nonaqueous liquids to aqueous solutions doped with small amounts of hydrocarbons. The authors have collected and analyzed excited-state C{sub 2} NBSL (multi-bubble sonoluminescence, light emission from the clouds of cavitating bubbles) spectra from mixtures of organic liquids in water at 20 kHz and find an effective emissionmore » temperature of 4,300 {+-} 200 K.« less

Sizing of cables in randomly-filled trays with consideration for load diversity

A method for demonstrating increased ampacity of cables in trays with loading diversity is given. Ampacity tables for sizing cables in randomly-filled cable trays are provided in NEMA WC 51-1986 based on a model developed by J. Stolpe which ensures that the maximum cable temperature does not exceed the insulation rating (typically 90/spl deg/C) under worst-case conditions. The Stolpe model intentionally disregards the reduced heating effect of deenergized or lightly-loaded cables to ensure that all possible hot spot conditions are enveloped. Other methods have been proposed to credit loading diversity in order to justify increased ampacity. However, since they involve certain assumptions about the heat distribution within the cable mass, these methods may fail to identify individual overloaded conductors. This paper describes a simple method which considers the performance of individual conductors while providing a means of increasing ampacity as a result of loading diversity.

Critical Conditions for Impact- and Shock-Induced Hot Spots in Solid Explosives

Chemical kinetic thermal decomposition models of pressed solid high explosives containing octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and triaminotrinitrobenzene (TATB), which accurately calculate the times to explosion at various initial temperatures measured in the one-dimensional time to explosion (ODTX) test, are extended to higher temperatures to predict the critical temperatures, times to explosion, and dimensions of the impact- and shock-induced hot spots that are known to control the ignition of exothermic reaction in solid explosives. The effects of hot spot geometry and surrounding temperature on the critical hot spot conditions are investigated. Since hot spot temperatures and dimensions cannot be measured experimentally, these estimated temperatures, sizes, and times required for exothermic chemical reaction provide a means to evaluate proposed physical mechanisms of hot spot formation in accident scenarios involving impact (friction and shear) and shock compression of solid explosives.

Performance analysis of single-stage, output buffer packet switches with independent batch arrivals

A theoretical framework for the analysis of an M × N, output queueing, space-division, non-blocking, packet switch with general i.i.d. batch arrivals is developed. The switch operates in a slotted time-frame with packets arriving to any of its M input ports and destined to any of its N output ports. Assuming a general traffic switching matrix, the (marginal) distribution of the queue size of packets at each of the output ports is obtained. Under FIFO service discipline, the distribution of the waiting time of packets is also obtained. Under finite buffer capacity, the loss probability of packets due to the unavailability of output buffer space is derived. Finally, the sensitivity of the performance measures of the switch under hot-spot traffic conditions is demonstrated.