Framing Camera Research Articles

Assessing the energy release characteristics during the middle detonation reaction stage of aluminized explosives

Afterburning behind the detonation front of an aluminized explosive releases energy on the millisecond timescale, which prolong the release of detonation energy and the energy release at different stages also shows significant differences. However, at present, there are few effective methods for evaluating the energy release characteristics of the middle reaction stage of such explosives, which can have a duration of tens to hundreds of microseconds. The present work demonstrates an approach to assessing the mid-stage of an aluminized explosive detonation based on a water push test employing a high degree of confinement. In this method, the explosive is contained in a steel cylinder having one end closed that is installed at the bottom of a transparent water tank. Upon detonation, the gaseous products expand in one direction while forcing water ahead of them. The resulting underwater shock wave and the interface between the gas phase products and the water are tracked using an ultra-high-speed framing and streak camera. The shock wave velocity in water and the expansion work performed by the gaseous detonation products were calculated to assess the energy release characteristics of aluminized explosives such as CL-20 and RDX in the middle stage of the detonation reaction. During the middle stage of the detonation process of these aluminized explosives, the aluminum reaction reduced the attenuation of shock waves and increased the work performed by gas phase products. A higher aluminum content increased the energy output while the presence of oxidants slowed the energy release rate. This work demonstrates an effective means of evaluating the performance of aluminized explosives.

Four-framed X-ray imaging crystal spectrometer for time-resolved laser plasma diagnostics

X-ray imaging crystal spectrometers with high spectral and spatial resolutions are the important diagnostic tools for acquiring high-quality plasma information in the study of laser–matter interactions. In this paper we propose a new multi-channel imaging crystal spectrometer with coupling X-ray framing camera to record the dynamic evolution of a laser-induced plasma: a four-channel imaging mica crystal spectrometer with a spatial resolution of 40–60 μm for diagnosing the aluminum (Al) plasma targets was developed. Calibration experiments revealed that the spectral resolution is higher than 1700 at Al Kα3 characteristic lines (1496.4eV). Further, we established an aiming method based on the positioning ball and two monitoring CCDs. The optical design, mechanical design, and experimental measurements of the four-channel imaging mica crystal spectrometer are discussed.

Energy-Efficient Spiking Segmenter for Frame and Event-Based Images.

Semantic segmentation predicts dense pixel-wise semantic labels, which is crucial for autonomous environment perception systems. For applications on mobile devices, current research focuses on energy-efficient segmenters for both frame and event-based cameras. However, there is currently no artificial neural network (ANN) that can perform efficient segmentation on both types of images. This paper introduces spiking neural network (SNN, a bionic model that is energy-efficient when implemented on neuromorphic hardware) and develops a Spiking Context Guided Network (Spiking CGNet) with substantially lower energy consumption and comparable performance for both frame and event-based images. First, this paper proposes a spiking context guided block that can extract local features and context information with spike computations. On this basis, the directly-trained SCGNet-S and SCGNet-L are established for both frame and event-based images. Our method is verified on the frame-based dataset Cityscapes and the event-based dataset DDD17. On the Cityscapes dataset, SCGNet-S achieves comparable results to ANN CGNet with 4.85 × energy efficiency. On the DDD17 dataset, Spiking CGNet outperforms other spiking segmenters by a large margin.

Bright Na‐Carbonate Exposures Reveal Recent, Widespread Mobilization of Material in Ceres' Shallow Subsurface

AbstractStriking exposures of Na‐carbonate‐bearing bright materials are found in Ahuna Mons and the central landforms of Occator and other impact craters on Ceres; however, most bright materials on its surface occur as excavated material on the rims and walls of impact craters. The source of the widespread excavated Na‐carbonate is uncertain. We map the distribution and extent of rim/wall Na‐carbonate with Dawn's Visible and Infrared Imaging Spectrometer and Dawn Framing Camera. We find a strong spatial correlation between domes and shallow subsurface Na‐carbonate deposits, suggesting that they form by the same or related processes. Using Monte Carlo impact models, we constrain the timing of emplacement of the shallow subsurface Na‐carbonate to be within the last ∼1 Ga and probably within the last few hundred Ma. We examine the likelihood that the Na‐carbonate was mobilized from Ceres' deep interior and the plausibility of brine upwelling or solid‐state processes. We demonstrate that a combination of processes, including diapirism driven by Rayleigh‐Taylor instabilities and solid‐state deformation due to differential loading, could mobilize Na‐carbonate‐bearing ices to the shallow subsurface without requiring the recent presence of brines.

Hybrid CMOS detectors for high-speed X-ray imaging.

Hybrid CMOS (hCMOS) x-ray framing cameras are a new and powerful detector option for experiments in the fields of Inertial Confinement Fusion (ICF) and High Energy Density Physics (HEDP). These digital cameras capture multiple images along a single line-of-sight with a time resolution as short as 1.5ns and with high quantum efficiency. To manage the high data rate, an image sequence is acquired in a short burst of time and subsequently read out on a much longer time scale. The technology is well suited for operating in high radiation environments, including fusion ignition experiments. Diagnostics using hCMOS cameras are now deployed in experiments on major laser and pulsed-power ICF facilities around the world. Continued advances in microelectronics technologies will enable faster and more capable detectors well into the future. This paper reviews this detector technology with a focus on application to ICF and HEDP experiments.

Multi-Stage Network for Event-Based Video Deblurring with Residual Hint Attention

Video deblurring aims at removing the motion blur caused by the movement of objects or camera shake. Traditional video deblurring methods have mainly focused on frame-based deblurring, which takes only blurry frames as the input to produce sharp frames. However, frame-based deblurring has shown poor picture quality in challenging cases of video restoration where severely blurred frames are provided as the input. To overcome this issue, recent studies have begun to explore the event-based approach, which uses the event sequence captured by an event camera for motion deblurring. Event cameras have several advantages compared to conventional frame cameras. Among these advantages, event cameras have a low latency in imaging data acquisition (0.001 ms for event cameras vs. 10 ms for frame cameras). Hence, event data can be acquired at a high acquisition rate (up to one microsecond). This means that the event sequence contains more accurate motion information than video frames. Additionally, event data can be acquired with less motion blur. Due to these advantages, the use of event data is highly beneficial for achieving improvements in the quality of deblurred frames. Accordingly, the results of event-based video deblurring are superior to those of frame-based deblurring methods, even for severely blurred video frames. However, the direct use of event data can often generate visual artifacts in the final output frame (e.g., image noise and incorrect textures), because event data intrinsically contain insufficient textures and event noise. To tackle this issue in event-based deblurring, we propose a two-stage coarse-refinement network by adding a frame-based refinement stage that utilizes all the available frames with more abundant textures to further improve the picture quality of the first-stage coarse output. Specifically, a coarse intermediate frame is estimated by performing event-based video deblurring in the first-stage network. A residual hint attention (RHA) module is also proposed to extract useful attention information from the coarse output and all the available frames. This module connects the first and second stages and effectively guides the frame-based refinement of the coarse output. The final deblurred frame is then obtained by refining the coarse output using the residual hint attention and all the available frame information in the second-stage network. We validated the deblurring performance of the proposed network on the GoPro synthetic dataset (33 videos and 4702 frames) and the HQF real dataset (11 videos and 2212 frames). Compared to the state-of-the-art method (D2Net), we achieved a performance improvement of 1 dB in PSNR and 0.05 in SSIM on the GoPro dataset, and an improvement of 1.7 dB in PSNR and 0.03 in SSIM on the HQF dataset.

Stability of breakdown phenomenon in N2, SF6, and their mixture under impulse voltages

In the self-breakdown experiment, it is demonstrated that the breakdown stability of 15% SF6/N2 was higher than that of pure SF6 and N2 in the non-uniform field under negative impulse voltages. In this paper, the stable breakdown phenomenon of the gas mixture is studied at the nanosecond scale. The corona process and streamer process of these three gases are investigated by using a high-speed framing camera. The stabilized corona and the abnormal streamer phenomena observed in the gas mixture discharge have a relation to the stable breakdown phenomenon. The stabilized corona is supposed to be the main reason that obstructs the development of negative steamer and stabilizes the supply of photons to the anode. Furthermore, the captured images of the streamer process in the gas mixture show that there is a negative ion sheath between the electrodes. The sheath keeps the corona stabilized near the cathode tip. In addition, photons emitted by the stabilized corona can ionize neutral particles near the anode. The generated photoelectrons and positive ions accumulate near the anode surface. The positive streamer occurs once the accumulation number reaches a certain value. In addition, the photon emission intensity and stability also have an influence on the stability of the positive streamer.

Fragment plume diagnostics for cryogenic pellet shattering studies: Development and first experimental results

Shattered pellet injection is the baseline technology for the ITER Disruption Mitigation System (DMS) [1]. ITER DMS requires the use of large, 28.5 × 57 mm (diameter x length) cryogenic pellets, made of hydrogen, neon, or a mixture of those gasses and accelerated to several hundred m/s velocity. Beside the production, acceleration and transfer of such ITER-size pellets, the characterization of the shattering is one of the main task of the ITER DMS Support Laboratory at center of Energy Research as part of the ITER DMS Task Force program to validate the design choices of the DMS [2]. For this purpose, a fragment plume diagnostic chamber and two optical diagnostics using fast framing cameras, namely the laser curtain at two distances from the shattering head and a shattering observation were designed and implemented. Preliminary experiments for different pellet material and velocities at 20⁰ and 30⁰ shattering angle showed a strong pellets sublimation during shattering process. The fragments seem to slide along the shattering plate, no significant total reflection was detected. No qualitative difference between 20⁰ and 30⁰ shattering angle was observed, but clear differences for different materials and or pellet speeds.

Real-Time Hetero-Stereo Matching for Event and Frame Camera With Aligned Events Using Maximum Shift Distance

Event cameras can show better performance than frame cameras in challenging scenarios, such as fast-moving environments or high-dynamic-range scenes. However, it is still difficult for event cameras to replace frame cameras in non-challenging normal scenarios. In order to leverage the advantages of both cameras, we conduct a study for the heterogeneous stereo camera system which employs both an event and a frame camera. The proposed system estimates the semi-dense disparity in real-time by matching heterogeneous data of an event and a frame camera in stereo. We propose an accurate, intuitive and efficient way to align events with 6-DOF camera motion, by suggesting the maximum shift distance method. The aligned event image shows high similarity to the edge image of the frame camera. The proposed method can estimate poses of an event camera and depth of events in a few frames, which can speed up the initialization of the event camera system. We verified our algorithm in the DSEC dataset. The proposed hetero-stereo matching outperformed other methods. For real-time operation, we implemented our code using parallel computation with CUDA and release our code open source:

Simulation of the SGEMP Response Inside the Cavity With Aperture

In laser inertial confinement fusion facilities, the X-ray streak cameras and framing cameras are shielded by the structure of a cavity with aperture. The cavity is illuminated by the compound radiation environment composed of X-rays and electromagnetic pulses (EMPs). A complex EMP environment is generated by the multiphysical field interaction, which excites intense system-generated EMP (SGEMP) interference. Two cases are simulated to demonstrate the characteristics of the coupling field of external SGEMP and the complex EMP environment. The planes of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$z$ </tex-math></inline-formula> = 2.5 cm and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$z$ </tex-math></inline-formula> = 20 cm are selected to represent the area near and away from the aperture, respectively. The electric fields located at several positions along the axis or radius are output to depict the spatial distributions. The electric field waveform varies a lot and its peak keeps decreasing when away from the center of aperture. Finally, the waveform comparisons of the two cases indicate that the coupling field provides the governing contribution to the complex EMP environment.

A Residual Learning Approach to Deblur and Generate High Frame Rate Video With an Event Camera

Event cameras are bio-inspired cameras that can measure the intensity change asynchronously with high temporal resolution. One of the advantages of event cameras is that they suffer less from motion blur than traditional frame cameras when recording daily scenes with fast-moving objects. In this paper, we formulate the deblurring task on traditional cameras directed by events to be a residual learning one, and propose corresponding network architectures for effective learning of deblurring and high frame rate video generation tasks. We first train a modified U-Net network to restore a sharp image from a blurry image using the corresponding events. Then we train another similar network by replacing the downsampling blocks with blocks of the convolutional long short-term memory (Conv-LSTM) to recurrently generate high frame rate video using the restored sharp image and part of the events. Benefitting from the blur-free events and the proposed learning strategy, the experimental results show that the proposed method outperforms state-of-the-art methods for generating sharp images and high frame rate videos.

Improvement of Temporal Uniformity of Pulse-Dilation Framing Camera Using Pulse Superposition Technique

Improvement of Temporal Uniformity of Pulse-Dilation Framing Camera Using Pulse Superposition Technique

Dynamic characteristics of axial load bi-stable energy harvester with piezoelectric polyvinylidene fluoride film

In this paper, a nonlinear bi-stable energy harvester with a bulking beam is proposed. Its bi-stable characteristics can be realized by the structure. The characteristics of the piezoelectric energy harvester are tested under different conditions. In the experiment, high speed framing camera is used to capture the details of movement. It is found that similar characteristics occur at low frequency and high frequency, but the principles are not the same. The vibration amplitude is insufficient former when the frequency is low. Under high frequency conditions, the system is hindered by the reverse excitation when the system is about to enter the second steady state due to insufficient response time. In the experiment, the axial load is measured by the length of the buckling beam and the electronic scale. It is found that the axial load has great influence on the vibration amplitude of the harvester. The results show that the harvester changes from inter-well vibration to intra-well vibration when axial load changes from 0.4 N to 1.5 N. The inter-well vibration of the harvester occurs when the acceleration is 3.5 g, the vibration frequency is 15 Hz and the axial load is 0.4 N.

Diagnosing low-mode (ℓ < 6) and mid-mode (6 ≤ ℓ ≤ 60) asymmetries in the post-stagnation phase of laser-direct-drive deuterium-tritium cryogenic implosions on OMEGA.

Low- and mid-mode perturbations are possible candidates for performance limitations in cryogenic direct-drive implosions on the OMEGA laser at the Laboratory of Laser Energetics. Simulations with a 3D hydrocode demonstrated that hotspot imagers do not show evidence of the shell breakup in the dense fuel. However, these same simulations revealed that the low- and mid-mode perturbations in the dense fuel could be diagnosed more easily in the post-stagnation phase of the implosion by analyzing the peak in the x-ray emission limb at the coronal-fuel interface than before or at the stagnation phase. In experiments, the asymmetries are inferred from gated images of the x-ray emission of the implosion by using a 16-pinhole array imager filtered to record x-ray energies >800eV and an x-ray framing camera with 40-ps time integration and 20-μm spatial resolution. A modal analysis is applied to the spatial distribution of the x-ray emission from deuterium and tritium cryogenic implosions on OMEGA recorded after the bang time to diagnose the low- and mid-mode asymmetries, and to study the effect that the beam-to-target ratio (Rb/Rt) has on the shell integrity.

Visual Identification-Based Spark Recognition System

With the development of artificial intelligence, image recognition has seen wider adoption. Here, a novel paradigm image recognition system is proposed for detection of fires owing to the compression of lithium-ion batteries at recycling facilities. The proposed system uses deep learning method. The SparkEye system is proposed, focusing on the early detection of fires as sparks, and is combined with a sprinkler system, to minimize fire-related losses at affected facilities. Approximately 30,000 images (resolution, 800 × 600 pixels) were used for training the system to &gt;90% detection accuracy. To fulfil the demand for dust control at recycling facilities, air and frame camera protection methods were incorporated into the system. Based on the test data and realistic workplace feedback, the best placements of the SparkEye fire detectors were crushers, conveyors, and garbage pits.

Investigation for the movement of the laser entrance hole and bubble plasmas in laser-driven hohlraum

In indirect-drive hohlraum, the heated plasmas from the laser entrance hole (LEH) and bubbles blow radially inward with time, which plays an important role in the evolution of hohlraum plasmas. Previously, the boundary of the LEH and bubble plasmas is measured using time-integrated x-ray images or x-ray images at several discrete moments. A new experiment is conducted to study the continuous temporal behaviors of the LEH and bubble plasmas, which utilizes a gas-filled hohlraum truncated on one side. Compared experiments are performed with 3 different LEH diameters (1.0 mm, 1.2 mm, and 1.4 mm). An x-ray streak camera (XSC) is employed for the first time to diagnose the continuous temporal x-ray images of the LEH and bubble plasmas, which are also measured by an x-ray framing camera (XFC) at several discrete moments. The XSC and the XFC are combined for the first time and give coincident results for the movement of the LEH and bubble plasmas. In addition, 2 sets of flat-response x-ray diode (FXRD) measure the total x-ray flux from both the LEH and the open end and thus give the radiation temperature (Tr) in the hohlraum. The Tr from the LEH end shows a visual increase compared with that from the open end, due to the LEH closure, which is coincident with the temporal x-ray images. This work presents more precise and detailed description for the continuous movement of the LEH and bubble plasmas, which is beneficial to optimize our radiation hydrodynamic code and hohlraum design for ignition.

Study of the electrothermal and MHD instabilities in exploding cylindrical foil liner

An experimental and numerical study of the plasma instabilities in an electrical exploding cylindrical Al liner is reported. The Al liner 3 mm in diameter and 10 μm in thickness is exploded at the Qin-1 facility (450 ns, 400 kA). Various diagnostics, such as multi-frame laser shadowgraphy, an x-ray framing camera, and an x-ray backlighting system are developed. The different imaging systems are sensitive to plasma of different areal densities based on the comparison between the experiments and simulation, which reveal the dynamics of the exploding liner in more detail. The laser shadow images show the low-density plasma (∼1–2 × 10−4 g cm−2) at the edge of the liner, and both the amplitude and wavelength of the plasma instabilities increase over time, which are considered to be magnetohydrodynamic (MHD) instabilities rather than electrothermal instabilities. During the ablation of the liner, quasi-periodic azimuthally correlated striations are directly observed in extreme ultraviolet (EUV) self-emission images. Meanwhile, the vertical filaments, which are electrothermal instabilities for plasma under the condition of ∂η/∂T < 0, are also observed in EUV self-emission images. The x-ray backlighting images of the exploding liner are obtained by placing an X-pinch load on the current-return path to serve as an x-ray point source (∼1 ns, ∼10 μm). The x-ray backlighting results show the behavior of the high-density plasma (∼1.89 × 10−3 g cm−2), which includes the transition from electrothermal to MHD instabilities. Finally, we realized a 2D MHD simulation of the exploding liner under experimental conditions, which shows good agreement with the results of the experimental perturbation.

Simulation of the temporal resolution uniformity of a dilation framing camera.

The temporal resolution uniformity of a time-dilation framing camera is studied, and the ideal photocathode (PC) pulse curve is determined, while the temporal magnification factor is kept constant. To obtain the ideal curve, a series of linear pulses with the same slope are superposed. The variance in the temporal resolution and the number of linear pulses required are compared, while the superposition results with different slopes are used as the PC voltage. As the slope of the linear pulses decreases, the variance decreases, which means that the uniformity of the temporal resolution is improved, but the number of linear pulses required increases. In this study, linear pulses with a slope of 1V/ps are superposed. Nine linear pulses with a front edge time of 200ps, amplitude of 200V, and flat top time of 1ns are superimposed to approximate the ideal PC pulse curve with a constant temporal magnification factor of 10; the trigger times of the pulses are 0, 0, 0, 185, 200, 350, 450, 605, and 790ps. When the superposition result is applied as the PC voltage and the measured signal is synchronized to the PC pulse at 128ps-1ns, the temporal resolution error is within 5%.

Geology and colour of Kupalo crater on Ceres

Kupalo is a ∼4 ​Ma old, 26-km diameter impact crater on dwarf planet Ceres, which exhibits extensive areas of bright bluish material. Here we describe, for the first time, the geology of Kupalo on a regional and local scale in detail, based on Dawn Framing Camera (FC) imagery. We find the crater has a complex geology consistent with a brittle and heterogeneous crust in this area. Through analyses of the FC colour data, we identify a correlation between the geologic units and the spectral variations, which can be explained by a mixture of subsurface materials in response to the impact. The brightest sites of Kupalo, located at the upper west wall and the central ridge, show similar FC colour and spectral IR data, which suggest that the bright material in these locations likely has the same origin. To explain the distribution of the bright bluish material in the crater and its vicinity, we propose two scenarios for the structure of the upper Cerean crust. Both require deep-seated brine or salt reservoirs, possibly connected to a brine ocean at the crust-mantle transition. • Geology of Kupalo suggests that Ceres' crust is rather heterogeneous (69). • Mixture of impacted subsurface materials explains correlation of spectra and geology (84). • Bright material in Kupalo would have originally been deposited at a depth of ∼3 ​km (82). • The brightest exposures are linked to subsurface reservoirs of hydrated carbonates (82).

Diagnosing X-pinch and cylindrical wire array Z-pinch with an all-optical framing camera on the “QiangGuang-I” facility

An all-optical framing camera has been established on the 1-MA “QiangGuang-I” facility for investigating the imploding dynamics of the X-pinch and the cylindrical wire array Z-pinch. This camera measures the photons flux distribution by detecting the photon-induced refractive index changes in the InP semiconductor with a probe laser beam. The InP-based imaging sensor with a 100 nm thick Al film and a 10 μm thick gold transmission grating of 20 μm spatial period was fabricated based on the lithography method. Two sequential frames with 1.5 ns time resolution and 13 ns inter frame separation time can be recorded in one single shot. Framing images indicating the plasma generation and dissipation of the X-pinch and the cylindrical wire array Z-pinch have been obtained, showing that this framing camera is a promising technique for investigating the mechanisms of the Z-pinch and other high energy density physics.