Energy Release Dynamics Research Articles

Dynamics of energy release in a nuclear reactor core

Dynamics of energy release in a nuclear reactor core

Dynamics of Energy Release in a Nuclear-Reactor Core

Dynamics of Energy Release in a Nuclear-Reactor Core

Effect of hydroxyl radical precursor addition on LTC-affected detonation in DME–$$\hbox {O}_{{2}}$$–$$\hbox {CO}_{{2}}$$ mixtures

The effects of hydrogen peroxide ( $$\hbox {H}_{2}\hbox {O}_{2}$$ ) and tert-butyl hydroperoxide (TBHP), both hydroxyl radical precursors, on the characteristic length-scales of low-temperature-chemistry-affected (LTC-affected) detonation propagating in dimethyl-ether–oxygen–carbon-dioxide (DME– $$\hbox {O} _{2}$$ – $$\hbox {CO}_{2}$$ ) mixtures were investigated using the Zeldovich–von Neumann–Doring model. A three-step energy release is observed when the $$\hbox {CO}_{2}$$ content is above a critical value, with and without $$\hbox {H}_{2}\hbox {O}_{2}$$ or TBHP addition. The effect of these two additives on the energy release dynamics and chemical kinetics has been analyzed in detail. The $$\hbox {H}_{2}\hbox {O} _{2}$$ addition induces a similar reduction of the different induction zone lengths, as well as an increase of the energy release rate. The addition of TBHP induces both a thermal and a chemical effect. Thermally, since the effective equivalence ratios of the mixtures are higher, higher Mach numbers and higher von Neumann temperatures are achieved. Chemically, an “LTC chain propagation loop” leads to a significant decrease of the induction zone length along with a substantial increase of the energy release rate, especially for the first stage of energy release. Hence, TBHP seems to be a promising additive for experimentally observing LTC-affected detonation with multi-stage energy release.

Neutron data field in a fission reactor core with fusion neutron source at pulse-periodic operation

Results are presented on the distinctive features of the energy release dynamics in the hybrid thorium reactor operating in combination with the neutron source based on the extended magnetic mirror trap. In the reactor core configuration under study, the high-temperature plasma column is formed in a pulse-periodic mode. At a certain duty cycle (pulse ratio) of the plasma column formation, it can be expected that the fission “wave” will be formed diverging from the axial region of the system and propagating in the radial direction in the fuel assembly (blanket). Under such conditions, in order to correct the resulting offset of the energy release distribution, it is necessary to optimize the fuel composition of the assembly in order to obtain the most appropriate radial distributions of physical parameters. The studies are carried out on the basis of the full-scale model of the reactor core, in which the axial region is modified: the extended magnetic mirror trap operating as a source of fusion neutrons is installed in the reactor core axial region.

Excitation of the global correlation wavefield by large earthquakes

SUMMARY Recorded globally, cross-correlated ground-motion time-series of the coda of large earthquakes enable the construction of a 2-D representation of correlation lapse time and inter-receiver distance—a global correlogram. A better understanding of how the features present in a correlogram are generated can revolutionize the characterization of planetary interiors. Here, we investigated correlograms based on individual large earthquakes and identified 12 events from the past decade with a multitude of prominent and some ‘exotic’ features in the first 3 hr following correlation origin. We found that the type of the source mechanism and energy-release dynamics are the key influencers responsible for individual correlograms equal in quality to a stack of hundreds of correlograms. A single event is sufficient in creating a correlogram resembling previous correlograms constructed from a large number of events, which reinforces the notion that the earthquake coda-correlation features are not ‘reconstructed’ body waves. Numerical simulations of the correlation wavefield can thus be based on exceptional-quality events, becoming more computationally affordable. Here, we explain more than 60 features of the global coda-correlogram, which presents the most extensive catalogue to date.

Effect of oxygen atom precursors addition on LTC-affected detonation in $${\hbox {DME}}{-}{\hbox {O}}_{2}{-}{\hbox {CO}}_{2}$$ mixtures

The effects of ozone $$({\hbox {O}}_{3})$$ or nitrogen dioxide $$({\hbox {NO}}_{2})$$ as oxygen atom precursors on the characteristic length-scales of low-temperature chemistry (LTC)-affected detonation propagating in dimethyl $${\hbox {ether}}{-}{\hbox {O}}_{2}{-}{\hbox {CO}}_{2}$$ mixtures were investigated using the Zeldovich–von Neumann–Doring model. The effect of these two additives on the energy release dynamics and chemical kinetics was analyzed. Under some conditions, up to three steps of energy release were observed. Ozone strengthens the LTC which results in a decrease in the induction zone length along with an increase of the energy release rate. The addition of $${\hbox {NO}}_{2}$$ provides chemical pathways which lead to a bypass of the intermediate-temperature chemistry and a decrease in the separation distance between the first and the second steps of energy release. An increase of the energy release rate is also observed for the two first peaks. Among the two additives tested, ozone appears as the most promising to experimentally observe LTC-affected detonation with multi-stage energy release.

Detonation propagation along percolating cluster in composite explosives

The detonation performance of melt-cast plastic-bonded explosives (PBXs) based on high melting explosive octogen (HMX) was studied in the paper. It has been found that the detonation velocity strongly depends from the dispersion distribution of HMX particles: it changes from 7800 to 8700 m/s. We explain this by the possibility of detonation propagation in PBX through different mechanisms, including detonation front propagation along a percolating cluster formed by filler particles. Thus, varying the particle size distribution can bring about one detonation mechanism or another and hence control the energy release dynamics of melt-cast PBXs to attain high efficiency in practice. Experimental results confirm the assumptions.

Comparison of post-detonation combustion in explosives incorporating aluminum nanoparticles: Influence of the passivation layer

Aluminum nanoparticles and explosive formulations that incorporate them have been a subject of ongoing interest due to the potential of aluminum particles to dramatically increase energy content relative to conventional organic explosives. We have used time-resolved atomic and molecular emission spectroscopy to monitor the combustion of aluminum nanoparticles within the overall chemical dynamics of post-detonation fireballs. We have studied the energy release dynamics of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) charges incorporating three types of aluminum nanoparticles: commercial oxide-passivated nanoparticles, oleic acid-capped aluminum nanoparticles (AlOA), and nanoparticles in which the oxide shell of the particle has been functionalized with an acrylic monomer and copolymerized into a fluorinated acrylic matrix (AlFA). The results indicate that the commercial nanoparticles and the AlFA nanoparticles are oxidized at a similar rate, while the AlOA nanoparticles combust more quickly. This is most likely due to the fact that the commercial nano-Al and the AlFA particles are both oxide-passivated, while the AlOA particles are protected by an organic shell that is more easily compromised than an oxide layer. The peak fireball temperatures for RDX charges containing 20 wt. % of commercial nano-Al, AlFA, or AlOA were ∼3900 K, ∼3400 K, and ∼4500 K, respectively.

NON-THERMAL RESPONSE OF THE CORONA TO THE MAGNETIC FLUX DISPERSAL IN THE PHOTOSPHERE OF A DECAYING ACTIVE REGION

We analyzed Solar Dynamics Observatory line-of-sight magnetograms for a decaying NOAA active region (AR) 11451 along with co-temporal Extreme-Ultraviolet Imaging Spectrometer (EIS) data from the Hinode spacecraft. The photosphere was studied via time variations of the turbulent magnetic diffusivity coefficient, η(t), and the magnetic power spectrum index, α, through analysis of magnetogram data from the Helioseismic and Magnetic Imager (HMI). These measure the intensity of the random motions of magnetic elements and the state of turbulence of the magnetic field, respectively. The time changes of the non-thermal energy release in the corona was explored via histogram analysis of the non-thermal velocity, vnt, in order to highlight the largest values at each time, which may indicate an increase in energy release in the corona. We used the 10% upper range of the histogram of vnt (which we called Vuppnt) of the coronal spectral line of Fe xii 195 Å. A 2 day time interval was analyzed from HMI data, along with the EIS data for the same field of view. Our main findings are the following. (1) The magnetic turbulent diffusion coefficient, η(t), precedes the upper range of the vnt with the time lag of approximately 2 hr and the cross-correlation coefficient of 0.76. (2) The power-law index, α, of the magnetic power spectrum precedes Vuppnt with a time lag of approximately 3 hr and the cross-correlation coefficient of 0.5. The data show that the magnetic flux dispersal in the photosphere is relevant to non-thermal energy release dynamics in the above corona. The results are consistent with the nanoflare mechanism of the coronal heating, due to the time lags being consistent with the process of heating and cooling the loops heated by nanoflares.

Dynamic responses of reactive metallic structures under thermal and mechanical ignitions

Abstract

The Effects of Stoichiometry and Sample Density on Combustion Dynamics and Initiation Energy of Al/Fe2O3 Metastable Interstitial Composites

The effect of the stoichiometry (i.e., the Al/Fe ratio) and the compressed density of the sample on the dynamics of energy release from a series of Al/Fe2O3 metastable intersitital composites (MIC) were investigated. The reaction was initiated photothermally with a single 8 ns pulse of the 1064 nm fundamental of a Nd:YAG laser. The reaction dynamics were measured by using time-resolved spectroscopy of the light emitted from the igniting and deflagrating material. Two fundamental parameters are measured by this approach: the time to initiation and the duration of the deflagration. The effect of Al particle size on these parameters shows that they attain a minimum value at 100 nm, Al with 120 and 50 nm both having longer initiation and deflagration times. The amount of active Al metal relative to the amount of oxide explains this trend as the Al particle size decreases. As the Al/Fe ratio was varied from stoichiometric (1:1 Al:Fe) to slightly fuel rich (1.5:1) there is a significant decrease in the initiati...

Parameters of the Magnetic Flux inside Coronal Holes

The parameters of the magnetic flux distribution inside low-latitude coronal holes (CHs) were analyzed. A statistical study of 44 CHs based on Solar and Heliospheric Observatory (SOHO)/MDI full disk magnetograms and SOHO/EIT 284 Å images showed that the density of the net magnetic flux, B net, does not correlate with the associated solar wind speeds, V x . Both the area and net flux of CHs correlate with the solar wind speed and the corresponding spatial Pearson correlation coefficients are 0.75 and 0.71, respectively. A possible explanation for the low correlation between B net and V x is proposed. The observed non-correlation might be rooted in the structural complexity of the magnetic field. As a measure of the complexity of the magnetic field, the filling factor, f(r), was calculated as a function of spatial scales. In CHs, f(r) was found to be nearly constant at scales above 2 Mm, which indicates a monofractal structural organization and smooth temporal evolution. The magnitude of the filling factor is 0.04 from the Hinode SOT/SP data and 0.07 from the MDI/HR data. The Hinode data show that at scales smaller than 2 Mm, the filling factor decreases rapidly, which means a multifractal structure and highly intermittent, burst-like energy release regime. The absence of the necessary complexity in CH magnetic fields at scales above 2 Mm seems to be the most plausible reason why the net magnetic flux density does not seem to be related to the solar wind speed: the energy release dynamics, needed for solar wind acceleration, appears to occur at small scales below 1 Mm.

Measurement of apparent temperature in post-detonation fireballs using atomic emission spectroscopy

The energy release dynamics of explosives are of ongoing interest, but the short timescales involved often limit the measurements that can be made during these processes. We have used atomic emission spectroscopy to measure the temperature of fireballs resulting from detonation of charges of Hexahydro-1,3,5-trinitro-1,3,5-triazine doped with barium nitrate. The time-averaged emission spectra indicate an apparent temperature of ∼3000 K, in good agreement with theoretical predictions. The technique demonstrated herein should be applicable to time-resolved studies, including those on detonation timescales.

Scale‐free and scale‐dependent modes of energy release dynamics in the nighttime magnetosphere

Based on a spatiotemporal analysis of POLAR UVI images, we show for the first time that energy, power, area and lifetime probability distributions of electron precipitation events in the nighttime auroral oval have a significant latitudinal dependence. The low‐latitude group of the events contains a distinct subpopulation of strong auroral disturbances violating the uniform power‐law behavior reported in previous publications, while the high latitude group is described by nearly perfect power‐law statistics over the entire range of scales studied, in agreement with earlier findings. The results obtained indicate that the inner and outer portions of the plasma sheet may be characterized by substantially different scaling regimes of bursty energy dissipation suggestive of different universality classes and/or driving conditions associated with multiscale turbulence in these regions.

Photothermal Initiation of Hybrid Organic/Inorganic Metastable Interstitial Composites: Synergistic Effects on the Dynamics of Energy Release

The organic high-energy material pentaerythritol tetranitrate (PETN) was incorporated at low concentrations into Al (100 nm)/Fe(2)O(3) metastable intersitital composites (MIC) to form a hybrid organic/inorganic high-energy material. Studies of the dynamics of energy release were carried out by initiating the reaction photothermally with a single 8 ns pulse of the 1064 nm fundamental of a Nd:YAG laser. The reaction dynamics were measured using time-resolved spectroscopy of the light emitted from the deflagrating material. Two parameters were measured: the time to initiation and the duration of the deflagration. The presence of small amounts of PETN (16 mg/g of MIC) results in a dramatic decrease in the initiation time. This is attributed to a contribution to the temperature of the reacting system from the combustion of the PETN that, at lower loadings, appears to follow an Arrhenius dependence. The presence of PETN was also found to reduce the energy density required for single-pulse photothermal initiation by an order of magnitude, suggesting that hybrid materials such as this may be engineered to optimize their use as an efficient photodetonation medium.

Dynamics of energy release in a low-voltage pulsed arc in air

The influence of the discharge conditions on the dynamics of energy release is considered for pulsed arcs in air at initial pressures from 105 to 8×105 Pa and a low-voltage capacitor voltage of up to 400 V. A novel method for determining the resistance of the discharge channel in the final stage of a spark discharge is proposed. The method is applied to estimating the discharge channel parameters.

Method for generating a low-voltage pulsed arc in gas: Study of the influence of the circuit parameters

A novel method for generating a pulsed arc in gas is considered. The method can be used in devices in which rapid and efficient heating of the working gaseous medium is required. Electric circuits for generating pulsed arcs are analyzed. For the chosen discharge circuit, the dynamics of energy release in the column of a pulsed arc is experimentally investigated. Methods for estimating the discharge circuit parameters are proposed. Results of estimating these parameters in an existing experimental device are presented.

Zipf–Mandelbrot scaling law for world track records

World track records (WTR) can be fitted with a Zipf–Mandelbrot scaling law. Metabolic energy balances are used to describe the energy release dynamics during a race. It is shown that several hierarchical relaxation processes related to metabolic mechanisms can explain the power-law behavior of WTR.

Evidence for self-organized criticality in human epileptic hippocampus.

Self-organized criticality (SOC) is a property of complex dynamic systems that evolve to a critical state, capable of producing scale-free energy fluctuations. A characteristic feature of dynamical systems exhibiting SOC is the power-law probability distributions that describe the dynamics of energy release. We show experimental evidence for SOC in the epileptic focus of seven patients with medication-resistant temporal lobe epilepsy. In the epileptic focus the probability density of pathological energy fluctuations and the time between these energy fluctuations scale as (energy) and (time), respectively. The power-laws characterizing the probability distributions from these patients are consistent with computer simulations of integrate-and-fire oscillator networks that have been reported recently. These findings provide insight into the neuronal dynamics of epileptic hippocampus and suggest a mechanism for interictal epileptiform fluctuations. The presence of SOC in human epileptic hippocampus may provide a method for identifying the network involved in seizure generation.

Fractal approach in modelling of earthquakes

A model for an earthquake simulation is proposed with the use of a fractal approach. Multiple generation and coalescence of shear faults in stochastic brittle media (modelled as a 2d lattice) are considered to be a source of seismicity. Dynamics of local failure events are governed by accumulation of shear defects, described in terms of continuum damage mechanics. Fractal tree structure is used as an analogue for a stress redistribution process. Energy release, caused by the non-uniform failure, is studied for a non-conservative case. Effect of various types of rocks' properties stochasticity on energy release dynamics is analysed with a utilization of multifractal formalism. The latter is shown to be an additional method for seismicity characterization.