High Peak Flux Research Articles

Directed pulsed neutron source generation from inverse kinematic reactions driven by intense lasers

Neutron production driven by intense lasers utilizing inverse kinematic reactions is explored self-consistently by a combination of particle-in-cell simulations for laser-driven ion acceleration and Monte Carlo nuclear reaction simulations for neutron production. It is proposed that laser-driven light-sail acceleration from ultrathin lithium foils can provide an energetic lithium-ion beam as the projectile bombarding a light hydrocarbon target with sufficiently high flux for the inverse p(Li7,n) reaction to be efficiently achieved. Three-dimensional self-consistent simulations show that a forward-directed pulsed neutron source with ultrashort pulse duration 3 ns, small divergence angle 26°, and extremely high peak flux 3 × 1014n/(cm2⋅s) can be produced by petawatt lasers at intensities of 1021 W/cm2. These results indicate that a laser-driven neutron source based on inverse kinematics has promise as a novel compact pulsed neutron generator for practical applications, since the it can operate in a safe and repetitive way with almost no undesirable radiation.

Searching for Radio Outflows from M31* with VLBI Observations

As one of the nearest and most dormant supermassive black holes (SMBHs), M31* provides a rare but promising opportunity for studying the physics of black hole accretion and feedback at the quiescent state. Previous Karl G. Jansky Very Large Array (VLA) observations with an arcsecond resolution have detected M31* as a compact radio source over centimeter wavelengths, but the steep radio spectrum suggests optically thin synchrotron radiation from an outflow driven by a hot accretion flow onto the SMBH. Aiming to probe the putative radio outflow, we conducted milliarcsecond-resolution very long baseline interferometric (VLBI) observations of M31* in 2016, primarily at 5 GHz and combining the Very Long Baseline Array, Tianma 65 m, and Shanghai 25 m radio telescopes. Despite the unprecedented simultaneous resolution and sensitivity achieved, no significant (≳3σ) signal is detected at the putative position of M31* given an rms level of 5.9 μJy beam−1, thus ruling out a pointlike source with a peak flux density comparable to that (∼30 μJy beam−1) measured by the VLA observations taken in 2012. We disfavor the possibility that M31* has substantially faded since 2012, in view that a 2017 VLA observation successfully detected M31* at a historically high peak flux density (∼75 μJy beam−1 at 6 GHz). Instead, the nondetection of the VLBI observations is best interpreted as the arcsecond-scale core being resolved out at the milliarcsecond scale, suggesting an intrinsic size of M31* at 5 GHz larger than ∼300 times the Schwarzschild radius. Such extended radio emission may originate from a hot wind driven by the weakly accreting SMBH.

High deuteron and neutron yields from the interaction of a petawatt laser with a cryogenic deuterium jet

A compact high-flux, short-pulse neutron source would have applications from nuclear astrophysics to cancer therapy. Laser-driven neutron sources can achieve fluxes much higher than spallation and reactor neutron sources by reducing the volume and time in which the neutron-producing reactions occur by orders of magnitude. We report progress towards an efficient laser-driven neutron source in experiments with a cryogenic deuterium jet on the Texas Petawatt laser. Neutrons were produced both by laser-accelerated multi-MeV deuterons colliding with Be and mixed metallic catchers and by d (d,n)3He fusion reactions within the jet. We observed deuteron yields of 1013/shot in quasi-Maxwellian distributions carrying ∼8−10% of the input laser energy. We obtained neutron yields greater than 1010/shot and found indications of a deuteron-deuteron fusion neutron source with high peak flux (>1022 cm−2 s−1). The estimated fusion neutron yield in our experiment is one order of magnitude higher than any previous laser-induced dd fusion reaction. Though many technical challenges will have to be overcome to convert this proof-of-principle experiment into a consistent ultra-high flux neutron source, the neutron fluxes achieved here suggest laser-driven neutron sources can support laboratory study of the rapid neutron-capture process, which is otherwise thought to occur only in astrophysical sites such as core-collapse supernova, and binary neutron star mergers.

Collimated gamma beams with high peak flux driven by laser-accelerated electrons

Abstract Laser-accelerated electrons are promising in producing gamma-photon beams of high peak flux for the study of nuclear photonics, obtaining copious positrons and exploring photon–photon interaction in vacuum. We report on the experimental generation of brilliant gamma-ray beams with not only high photon yield but also low divergence, based on picosecond laser-accelerated electrons. The 120 J 1 ps laser pulse drives self-modulated wakefield acceleration in a high-density gas jet and generates tens-of-MeV electrons with 26 nC and divergence as small as $1.51{}^{\circ}$ . These collimated electrons produce gamma-ray photons through bremsstrahlung radiation when transversing a high-Z solid target. We design a high-energy-resolution Compton-scattering spectrometer and find that a total photon number of $2.2\times {10}^9$ is captured within an acceptance angle of $1.1{}^{\circ}$ for photon energies up to $16\;\mathrm{MeV}$ . Comparison between the experimental results and Monte Carlo simulations illustrates that the photon beam inherits the small divergence from electrons, corresponding to a total photon number of $2.2\times {10}^{11}$ and a divergence of $7.73{}^{\circ}$ .

Exploring efficiency limits for molten-salt and sodium external cylindrical receivers for third-generation concentrating solar power

Third-generation concentrating solar-thermal power (CSP) systems are proposed which aim to halve the cost of electricity from CSP. This work demonstrates that a transition from state-of-the-art cylindrical molten nitrate salt receivers with a peak concentrated solar flux of 1MW/m2 and a heliostat field optical error of 3mrad to future cylindrical sodium receivers with a peak flux of 1.8MW/m2 and a heliostat field optical error of 1mrad could enable the exergy output of CSP receivers to be increased significantly, by 25% at design point, while keeping the general system design very similar. This comparison is conducted on a large dataset established with a detailed field and receiver energy balance model considering field aiming, peak receiver flux and hydrodynamics. It is based on design point simulations, and is independent from cost considerations. At high temperatures, the optimal configurations achieve their gains only with very accurate heliostats and when the peak flux is increased, while at low temperatures, there is nothing to be gained from very high peak flux limits on external tubular receivers. This underscores the critical importance of high heliostat accuracy for high-temperature CSP systems design. For the third-generation, high-temperature (740 °C) sodium receiver configuration considered, it is found that the upper limit to thermal–optical efficiency of optimised receivers at design-point is around 88 %.

A flexibly controllable high-flux solar simulator for concentrated solar energy research from extreme magnitudes to uniform distributions

High-flux solar simulator (HFSS) is a useful lab-scale equipment for material, device, and prototype characterizations and testing via creating stable and controllable irradiation environments close to real solar concentrators. This study presents the design, building, and characterization of a flexibly controllable 40 kWe HFSS consisted of 4 × 10 kWe radiation modules at SUSTech enabling applications from photothermal to photoelectrochemical devices. A cylindrical reflector was designed at the focal plane as the optical homogenizer for generating uniform flux profiles for concentrated photovoltaic and photoelectrochemical applications. Both indirect and direct calibration methods were performed, compared, and correlated. The measured results are shown a record high peak flux of 41.43 MW m−2, summing over all four lamps without the homogenizer, which is 91% higher than the highest value reported in the literature. The average flux and total power in a circular target with a radius of 50 mm are 2.25 MW m−2 and 17.57 kW, respectively, showing a high electricity-to-radiation efficiency of 43.93%. When adding the homogenizer, the total uniformity of the system was tripled. Highly uniform region with non-uniformity of only 1.76% can be identified meeting the ASTM class A standard in terms of spatial non-uniformity. In addition to solar thermal/thermochemical applications, this newly built HFSS enables applications in concentrated solar photovoltaics and photoelectrochemical devices and beyond.

Anomalous nature of outbursts of black hole candidate 4U 1630−472

ABSTRACT The Galactic black hole candidate (BHC) 4U 1630−472 has gone through several outbursts (13 to be particular) in the last two and a half decades starting from the RXTE era till date. Like the outbursts of other transient BHCs, the outbursts of this source show variations in duration, peak numbers, highest peak flux, etc. However, unlike other soft X-ray transients, this source showed outbursts of two types, such as normal and super. The normal outbursts of duration ∼100−200 d are observed with an average recurrence or quiescence period of ∼500 d. The super outbursts of duration ∼1.5−2.5 yr, consist of more than one normal outburst and one mega outburst. We make an effort to separate the flux contributions of the normal and mega components from the super outbursts, and try to understand the nature of evolution of both types (normal and mega) of outbursts, based on the quiescent period prior to the outbursts. Archival data of RXTE or ASM from 1996 January to 2011 June, and MAXI or GSC from 2009 August to 2020 July are used for our study. Based on the variations of various properties of both the normal and mega outbursts, we think that this BHC is a special source which may contain two companions. Two companions might be responsible for two types of outbursts.

Design and experimental study of a 30 kWe adjustable solar simulator delivering high and uniform flux

• A 30 kWe high-flux simulator with controllable solar-like irradiation is designed. • A non-coaxial ellipsoidal reflector is specifically designed to homogenize the flux. • The maximum radiant power of 9.534 kW and peak flux of 8.568 MW·m −2 are achieved. • The system efficiency of 26.22–31.78% is reached under different input power. To make a good compromise between the flux uniformity and the high peak flux of the light spot, a new high-flux solar simulator (HFSS) with the continuously adjustable input power of 6–30 kWe was designed and studied in this paper. In the design, three 10 kWe xenon arc lamps, which can provide good solar-like irradiation, were selected as the light sources, and the lamps were reasonably arranged in the HFSS to achieve the high peak flux. Meanwhile, a kind of non-coaxial ellipsoidal reflector was specifically designed to concentrate the irradiation of each lamp and reduce the flux non-uniformity of the light spot. After the design and construction, an indirect measurement method was employed to determine the performance of the HFSS. Firstly, error analysis of the method indicatesd that the measured errors of the flux and the accumulated power are 7.9% and 8.0%, respectively, which are reasonable and acceptable. Then, sensitivity analysis of photo quantity recommended that the average greyscale of light spot obtained from 10 raw photos are accurate enough for data processing. Finally, the measuring results demonstrated that the flux distributions of the individual lamp and the HFSS both show good uniformity. As the input power of the HFSS increases from 6 kWe to 30 kWe, the system efficiency increases from 26.22% to 31.78%. The corresponding accumulated power within a 100 mm diameter light spot increases from 1.573 kW to 9.534 kW, and the peak flux reaches 1.709 MW·m −2 to 8.568 MW·m −2 under different input power. The good flux uniformity and the highest peak flux of 8.568 MW·m −2 indicated that this HFSS can satisfy the requirement of indoor CSP experiments. The contradiction between high flux and good flux uniformity was solved effectively, and the performance of the HFSS was boosted significantly. Therefore, the designed HFSS can be suitable and practical for the CSP experiments.

Discovery of the Black Hole X-Ray Binary Transient MAXI J1348–630

Abstract We report the first half-year monitoring of the new Galactic black hole candidate MAXI J1348–630, discovered on 2019 January 26 with the Gas Slit Camera on board the Monitor of All-sky X-ray Image (MAXI). During the monitoring period, the source exhibited two outburst peaks, where the first peak flux (at T = 14 days from the discovery of T = 0) was ∼4 Crab (2–20 keV) and the second one (at T = 132 days) was ∼0.4 Crab (2–20 keV). The source exhibited distinct spectral transitions between the high/soft and low/hard states and an apparent “q”-shape curve on the hardness-intensity diagram, both of which are well-known characteristics of black hole binaries (BHBs). Compared to other bright black hole transients, MAXI J1348–630 is characterized by its low disk temperature (∼0.75 keV at the maximum) and high peak flux in the high/soft state. The low peak temperature leads to a large innermost radius that is identified as the innermost stable circular orbit, determined by the black hole mass and spin. Assuming the empirical relation between the soft-to-hard transition luminosity (L trans) and the Eddington luminosity (L Edd), L trans/L Edd ≈ 0.02, and a face-on disk around a non-spinning black hole, the source distance and the black hole mass are estimated to be D ≈ 4 kpc and , respectively. The black hole is more massive if the disk is inclined and the black hole is spinning. These results suggest that MAXI J1348–630 may host a relatively massive black hole among the known BHBs in our Galaxy.

What Determines Solar Flares Producing Interplanetary Type III Radio Bursts?

Abstract Energetic electrons accelerated by solar flares often give rise to type III radio bursts at a broad wave band and even interplanetary type III bursts (IT3) if the wavelength extends to a decameter–kilometer. In this Letter, we investigate the probability of the flares that produce IT3, based on the sample of 2272 flares above M-class observed from 1996 to 2016. It is found that only 49.6% of the flares are detected to be accompanied with IT3. The duration, peak flux, and fluence of the flares with and without IT3 both present power-law distributions in the frequency domain, but the corresponding spectral indices for the former (2.06 ± 0.17, 2.04 ± 0.18, and 1.55 ± 0.09) are obviously smaller than that for the latter (2.82 ± 0.22, 2.51 ± 0.19, and 2.40 ± 0.09), showing that the flares with IT3 have longer durations and higher peak fluxes. We further examine the relevance of coronal mass ejections (CMEs) to the two groups of flares. It is found that 58% (655 of 1127) of the flares with IT3 but only 19% (200 of 1078) of the flares without IT3 are associated with CMEs, and that the associated CMEs for the flares with IT3 are inclined to be wider and faster. This indicates that CMEs may also play a role in producing IT3, speculatively facilitating the escape of accelerated electrons from the low corona to the interplanetary space.

Forecast of Major Solar X-Ray Flare Flux Profiles Using Novel Deep Learning Models

Abstract In this Letter, we present the application of a couple of novel deep learning models to the forecast of major solar X-ray flare flux profiles. These models are based on a sequence-to-sequence framework using long short-term memory cell and an attention mechanism. For this, we use Geostationary Operational Environmental Satellite 10 X-ray flux data from 1998 August to 2006 April. Seven hundred sixty events are used for training and 85 for testing. The models forecast 30 minutes of X-ray flux profiles during the rise phase of the solar flare with a minute time cadence. We evaluate the models using the 10-fold cross-validation and rms error (RMSE) based on flux profiles and RMSE based on its peak flux. For comparison we consider two simple deep learning models and four conventional regression models. Major results of this study are as follows. First, we successfully apply our deep learning models to the forecast of solar flare X-ray flux profiles, without any preprocessing to extract features from data. Second, our proposed models outperform the other models. Third, our models achieve better performance for forecasting X-ray flux profiles with low-peak fluxes than those with high-peak fluxes. Fourth, our models successfully predict flare duration with high correlations for both all cases and cases at peak times. Our study indicates that our deep learning models can be useful for forecasting time-series data in astronomy and space weather, even for impulsive events such as major flares.

Very high energy proton peak flux model

Solar energetic particles (SEPs) pose a serious radiation hazard to spacecraft and astronauts. The highest energy SEPs are a significant threat even in heavily shielded applications. We present a new probabilistic model of very high energy differential peak proton fluxes. The model is based on GOES/HEPAD observations between 1986 and 2018, i.e., covering very nearly three complete solar cycles. The SEP event list for the model was defined using a statistical criterion derived by setting the possibility of false detection of an event to 1%. The peak flux distributions were calculated for the interpolated energies 405 MeV, 500 MeV and 620 MeV, and modelled with exponentially cut off power law functions. The HEPAD data were cleaned and corrected using a “bow-tie” method which is based on the response functions of the HEPAD channels P8–P10 found in the instrument calibration reports. The results of the model are available to the Space Weather community as a web-based tool at the ESA’s Space Situational Awareness Programme Space Weather Service Network.

A two-parameter aiming strategy to reduce and flatten the flux map in solar power tower plants

In surrounding solar power tower plants, the collector field is designed with all the heliostats pointing to the cylindrical receiver equator to obtain maximum intercept. However, in commercial plants, the addition of thousands of energy spots at the same receiver level causes an excessively high peak heat flux of about 2 MW/m2. Therefore, this peak flux should be almost halved to avoid receiver problems due to creep and fatigue effects. The single-parameter aiming strategy (Vant-Hull, 2002) has already shown its ability to divide this high peak flux into two lower peaks; it consists in moving the hot spots up and down from the equator, in alternative heliostat rows, to create symmetric flux maps although they are clearly not very homogeneously distributed along the receiver height. In this work, a slight variation of the single-parameter aim strategy, simply proposing two aim parameters, has been successfully tested for a commercial solar power tower plant with a regular layout. The new two-parameter aiming strategy achieves not only reasonable peak flux values, but also an acceptably flattened flux profile and a slight reduction in spillage compared with the single-parameter strategy.

Feasibility study of a new concept of solar external receiver: Variable velocity receiver

The deployment of new solar power tower plants mainly depends on becoming cost-competitive with traditional forms of electricity generation. The solar field represents around 40% of the solar power tower investment cost, thus the cost reduction of such subsystems is mandatory to achieve that goal. This reduction could be done by increasing the solar flux intercepted by the receiver, which would increase the peak flux. Therefore, new concepts of solar receivers are required to accommodate such high peak flux.The proposed receiver, which withstands high peak flux, consists on a Traditional External Tubular Receiver (TETR) equipped with valves that allow the division of each panel of the receiver in two independent panels, increasing the velocity of the heat transfer fluid in specific zones of the receiver. This receiver configuration, named Variable Velocity Receiver (VVR), avoids tube overheating. Moreover, this novel receiver allows more concentrated aiming strategies, which increases the optical efficiency of the solar field and permits to reduce the number of heliostats in the field. Given a specific generation capacity, the size of the solar field required by a VVR is 12.5% smaller in comparison to a TETR.Such efficiency improvement has a negligible effect in tube mechanical stresses; even though pressure drop and parasitic consumption of the power plant increase. This new receiver configuration also gains hours of operation, even in winter: in hours with low solar irradiance all the panels can be split in two, increasing the number of passes and the velocity of the heat transfer fluid and accomplishing the transition from laminar to turbulent regime. Therefore, this receiver is able to reduce the levelized cost of energy.

Effect of the variation of the gating system on the magnetic properties of injection molded pole-oriented rings

Abstract The demand for contactless and wear-free sensor systems for the measurement of different physical values, such as angle, position, or speed has increased over the past years and opened up new application areas for magnetically sensitive sensors. Polymer bonded magnets can be used as signal transmitters in these sensor applications. In general, a high precision and good repeatability of the magnetic field is required, whereas in particular, a high peak flux density and accurate pole length of each pole is demanded for precise measurement. These polymer bonded magnets can be produced economically using the injection molding process with an integrated magnetization of the particles, such that a second magnetization step is unnecessary. This article addresses the influences of the gating system on the magnetic properties of multipolar bonded rings. Further, the particle orientation as well as filler content at different locations, and along the pathway are investigated. It was evaluated that the gating system significantly influences the pole length accuracy, as well as the peak flux density. However, differences in the filler orientation and content cannot be analyzed quantitatively.

Influences on the Magnetic Properties of Injection Molded Multipolar Rings

Abstract Polymer bonded magnets with a multipolar structure can be economically produced using the injection molding process for applications such as electric drives or sensor modules. Depending on the specific application, certain requirements of the multipolar bonded magnets, such as a high peak flux density or accurate pole length of each pole, must be assured. The multipolar magnetic structure of the parts can be applied during the injection molding process by incorporating a magnetic field inside the mold. Thus, the hard magnetic particles are oriented and magnetized directly in the injection molding process. The final properties of the multipolar molded magnets are affected by different parameters, such as the magnetic compound, the mold design and the processing parameters. This paper addresses the effects processing parameters have during the injection molding process. Additionally, the role the filler volume content plays with the properties of pole-oriented molded multipolar rings is also investigated. In particular, the magnetic characteristics, such as the maximum radial flux density, the pole length and the rate of the course of the flux density, were investigated. Further, the orientation of the particles and the influence of the varied parameters on the geometry of the rings were analyzed. It was found that the varied parameters do not significantly influence the accuracy of the pole length. The slope of the flux density curve is influenced by the peak maxima and varies slightly due to the high peak flux densities.

Nitrous Oxide Emissions and Carbon Sequestration in Turfgrass: Effects of Irrigation and Nitrogen Fertilization (Year 1)

In this study, annual nitrous oxide (N2O) emissions were greatest in urea and least in untreated (no N) among treatments. Differences were negligible due to irrigation treatment. Irrigation levels may be decreased further in the final year to induce slight stress on the low irrigation treatment. All fertilizer treatments maintained acceptable quality, however the controlled-release fertilizer resulted in more consistent visual quality ratings compared to urea and untreated. Urea fertilizer had higher peak fluxes after fertilization and overall annual emissions than polymer-coated N-fertilizer. Thus, controlled released N fertilizers, such as polymer-coated urea, in turfgrass systems could potentially help mitigate N2O emissions.

Ultrashort Pulsed Neutron Source

We report on a novel compact laser-driven neutron source with an unprecedented short pulse duration (<50 ps) and high peak flux (>10(18) n/cm(2)/s), an order of magnitude higher than any existing source. In our experiments, high-energy electron jets are generated from thin (<3 μm) plastic targets irradiated by a petawatt laser. These intense electron beams are employed to generate neutrons from a metal converter. Our method opens venues for enhancing neutron radiography contrast and for creating astrophysical conditions of heavy element synthesis in the laboratory.

Emission reduction of 1,3-dichloropropene by soil amendment with biochar.

Soil fumigation is an important treatment in the production chain of fruit and vegetable crops, but fumigant emissions contribute to air pollution. Biochar as a soil amendment has shown the potential to reduce organic pollutants, including pesticides, in soils through adsorption and other physicochemical reactions. A laboratory column study was performed to determine the effects of soil applications of biochar for reducing emissions of the fumigant 1,3-dichloropropene (1,3-D). The experimental treatments comprised of unamended and amended with biochar at doses of 0, 0.5, 1, 2, and 5% (w/w) in the top 5 cm soil layer. The unamended treatment resulted in the highest emission peak flux at 48 to 66 μg m s. Among the biochar amendment treatments, the highest peak flux (0.83 μg m s) was found in the biochar 0.5% treatment. The total emission loss was 35.7 to 40.2% of applied for the unamended treatment and <0.1 to 2.9% for the biochar-amendment treatments. A germination bioassay with cucumber seeds showed that ≥7 d of aeration would be needed to avoid phytotoxicity before replanting in biochar-containing fumigated soil. The results indicate that treatments with 0.5% or more biochar amendment reduced emission peak flux by >99.8% and showed total 1,3-D emission loss by >92% compared with that without biochar. The amendment of surface soil with biochar shows a great potential for reducing fumigant emissions.

GRB 120711A: an intense INTEGRAL burst with long-lasting softγ-ray emission and a powerful optical flash

A long and intense gamma-ray burst (GRB) was detected by INTEGRAL on July 11 2012 with a duration of ~115s and fluence of 2.8x10^-4 erg cm^-2 in the 20 keV-8 MeV energy range. GRB 120711A was at z~1.405 and produced soft gamma-ray emission (>20 keV) for at least ~10 ks after the trigger. The GRB was observed by several ground-based telescopes that detected a powerful optical flash peaking at an R-band brightness of ~11.5 mag at ~126 s after the trigger. We present a comprehensive temporal and spectral analysis of the long-lasting soft gamma-ray emission detected in the 20-200 keV band with INTEGRAL, the Fermi/LAT post-GRB detection above 100 MeV, the soft X-ray afterglow from XMM-Newton, Chandra, and Swift and the optical/NIR detections from Watcher, Skynet, GROND, and REM. We modelled the long-lasting soft gamma-ray emission using the standard afterglow scenario, which indicates a forward shock origin. The combination of data extending from the NIR to GeV energies suggest that the emission is produced by a broken power-law spectrum consistent with synchrotron radiation. The afterglow is well modelled using a stratified wind-like environment with a density profile k~1.2, suggesting a massive star progenitor (i.e. Wolf-Rayet). The analysis of the reverse and forward shock emission reveals an initial Lorentz factor of ~120-340, a jet half-opening angle of ~2deg-5deg, and a baryon load of ~10^-5-10^-6 Msun consistent with the expectations of the fireball model when the emission is highly relativistic. Long-lasting soft gamma-ray emission from other INTEGRAL GRBs with high peak fluxes, such as GRB 041219A, was not detected, suggesting that a combination of high Lorentz factor, emission above 100 MeV, and possibly a powerful reverse shock are required. Similar long-lasting soft gamma-ray emission has recently been observed from the nearby and extremely bright Fermi/LAT burst GRB 130427A.