High Energy Electron Radiography Research Articles

Observation and mitigation of image distortion in high-energy electron radiography

Observation and mitigation of image distortion in high-energy electron radiography

Multi-parameters optimization and matching analysis simulation studies of the linac for high-energy electron radiography

The electron linear accelerator, dedicated for high-energy electron radiography (HEER) experimental studies, was developed by the Institute of Modern Physics (IMP), Chinese Academy of Sciences (CAS). At present, some HEER experiments have been carried out in the operation stage and further requirements are put forward for lower beam emittance, lower energy spread and better uniformity at the exit of LINAC to enhance radiography quality. This paper uses the General Particle Tracer (GPT) code to perform global optimization studies based on the current beam line setup. The beam injection angle of alpha magnet and the model of the beam scraper are re-optimized. The influence of each factor on the beam parameters is comprehensively considered, and especially the influence of the space charge effect was analyzed by simulation studies. In order to suppress the deterioration of the beam quality in the alpha magnet, this paper take the lead in researching the relationship of the transverse phase space characteristics and the emittance growth and summarizes the rules for beam matching at the alpha magnet. The detailed simulation and analysis studies are presented in this paper.

Demonstration of high energy electron radiography with sub-micron spatial resolution

As a new scheme, High Energy Electron Radiography (HEER) was considered as an effective diagnostic tool in the mesoscale sciences due to its high spatial temporal resolution and large area density diagnostic range. Some improvements were implemented to achieve high spatial resolution using a 50 MeV electron beam in Lanzhou, China. These included improving the uniformity of the beam transverse distribution, optimizing the energy spread and increasing the magnet lens magnification. Then the HEER image was collected by a CCD camera with image processing program and in-situ spatial resolution optimization adjustment program. To the best of our knowledge, the achieved spatial resolution of 0.8 μm constitutes a world record. The details of this experiment are described in this publication.

Tunable Plasma Linearizer for Compensation of Nonlinear Energy Chirp

The removal of undesired nonlinear time-energy correlation (energy chirp) present in relativistic electron beams is crucial for many accelerator-based scientific applications, such as free-electron lasers, high-energy electron radiography, and MeV ultrafast electron microscopy. Here, we propose and demonstrate that a low-density plasma section can be used as a passive ``linearizer'' to significantly compensate for the nonlinear energy chirp imprinted on a beam by the curvature of the radio-frequency field in a conventional accelerator. Physically, the passage of the beam through the plasma excites a strong quasi-cosinoidal longitudinal decelerating wakefield that acts to mitigate the beam's nonlinear energy chirp by superimposing a reverse chirp on the beam. Time-resolved phase-space measurements, combined with high-fidelity three-dimensional particle-in-cell simulations show that the longitudinal phase space of the beam core is almost completely linearized, leading to a fourfold reduction of the beam overall energy spread from $0.148\mathrm{%}$ to $0.036\mathrm{%}$ (FWHM).

Experimental demonstration of three-dimensional high energy electron radiography

High energy electron radiography (HEER) proposed first for real-time high spatial and temporal resolution diagnosis of warm dense matter (WDM) and inertial confinement fusion (ICF) has proved experimentally feasible for mesoscale sciences diagnosis. Until now, the spatial resolution of the images close to 1 μm has been reached experimentally which is better than that of X-rays and neutron radiography. However, traditional HEER obtains two-dimensional images which cannot accurately present the three-dimensional structure of the sample. To further improve the capability of HEER to diagnose and obtain the internal information of samples, three-dimensional high energy electron radiography (TDHEER) was put forward by combining HEER with three-dimensional (3D) reconstruction tomography technology. The validity and usage of the TDHEER method have been confirmed through simulation of the fully 3D diagnostic of static mesoscale sample. This paper focuses mainly on the experimental demonstration of the 3D high energy electron radiography. The feasibility of TDHEER is for the first time confirmed by the results achieved with different 3D reconstruction algorithms. The 3D reconstruction algorithms, analytical algorithm-filtered back projection (FBP), iterative algorithms-algebraic reconstruction technique (ART), and simultaneous algebraic reconstruction technique (SART) are used here. In this experiment, the less projected data are used, so it takes the less time to obtain two-dimensional (2D) HEER images and the reconstruction. In order to spend the time as little as possible and obtain the satisfactory quality of reconstruction result, there are three groups of projected image sets, 180, 36 and 18, acquired in our experiment. When all three algorithms are adopted in 180 projected images, the reconstructed images show that all three algorithms FBP, ART and SART are feasible for TDHEER. The different reconstructed slice images of the sample in <i>X-</i>, <i>Y-</i>, and <i>Z-</i> direction clearly show the detailed structure of the sample. The images reconstructed by ART and SART algorithm are equivalent. Comparing with ART and SART, the reconstruction results by FBP can show more details, but there are some artifacts. Because the 36 2D HEER images fail to satisfy the Nyquist sampling theory, the analytic algorithm FBP is not used. Taking the result of FBP reconstructed by 180 images as a standard reference to compare the result of ART with the results of SART, the images reconstructed by the SART algorithm are closer to the original images. Testing 18 images, the results of the ART and SART both have lots of artifacts but the SART algorithm spends less time in reconstruction. As fewer projected images are used, more artifacts are found in the reconstructed images. Therefore, it is advantageous to combine the SART algorithm with 36 HEER projected images, which obtains high-quality reconstruction images and spends less time. The feasibility of TDHEER is confirmed experimentally for the first time and all three dimensions of the sample structures are obtained. Of the three different 3D reconstruction algorithms, the SART algorithm is the most suitable for reconstructing the few-view images. The TDHEER technology will extend HEER’s application fields, especially for mesoscale sciences.

Ultrafast High-Energy Electron Radiography Application in Magnetic Field Delicate Structure Measurement

Transient electromagnetic field plays very important roles in the evolution of high-energy-density matter or laser plasma. Now, a new design is proposed in this paper to diagnose the transient magnetic field, using relativistic electron bunch as a probe based on high-energy electron radiography. And based on this scheme, the continuous distribution of magnetic strength field can be snapshotted. For 1 mm thick quadrupole magnet model measured by 50 MeV probe electron beams, the simulation result indicates that this diagnosis has spatial resolution better than 4 microns and high measurement accuracy for strong magnetic strength and high magnetic gradient field no matter whether the magnetic interaction is focusing or defocusing for the range from -510 T∗μm to 510 T∗μm.

Visualizing the melting processes in ultrashort intense laser triggered gold mesh with high energy electron radiography

High-energy electron radiography (HEER) is a promising diagnostic tool for high-energy-density physics, as an alternative to tools such as X/γ-ray shadowgraphy and high-energy proton radiography. Impressive progress has been made in the development and application of HEER in the past few years, and its potential for high-resolution imaging of static opaque objects has been proved. In this study, by taking advantage of the short pulse duration and tunable time structure of high-energy electron probes, time-resolved imaging measurements of high-energy-density gold irradiated by ultrashort intense laser pulses are performed. Phenomena at different time scales from picoseconds to microseconds are observed, thus proving the feasibility of this technique for imaging of static and dynamic objects.

Three-Dimensional High-Energy Electron Radiography Method for Static Mesoscale Samples Diagnostics

In this paper, we propose a new method for static mesoscale sample diagnosis using three-dimensional radiography with high-energy electron radiography (HEER). The principle of three-dimensional high-energy electron radiography (TDHEER) is elucidated, and the feasibility of this method is confirmed by start-to-end simulation results. TDHEER is realized by combining HEER with the three-dimensional reconstruction method, by which more information about the samples can be attained, especially regarding the samples’ internal structures. With our study, the internal structures and the three-dimensional positions of the spherical sample are determined with a ~3 μm resolution. We believe that this new method enhances the HEER diagnostic capability and extends its application potential in mesoscale sciences.

Demonstration of Single-Shot High-Quality Cascaded High-Energy-Electron Radiography using Compact Imaging Lenses Based on Permanent-Magnet Quadrupoles

High-energy electron radiography is an emerging technique for imaging matter at high energy densities ($i.e.$ under extreme temperature and pressure) with high spatiotemporal resolution, but its development is hindered by the technical difficulty of creating advanced electron optics. This study explores the combination of state-of-the-art high-brightness electron sources with an innovative cascaded imaging system to make progress on the problem. Interestingly, the energy spread of the electron source seems to be the main obstacle to further improvement of the resolving power of this technology.

Design and simulation of a LINAC for high energy electron radiography research

We designed an electron linear accelerator (LINAC) for High Energy Electron Radiography (HEER) studies, which consists of two different guns, either a thermionic cathode or a photocathode RF gun, for diagnosing different targets. In this paper, we present the simulation studies and optimization of the LINAC based on an S-band thermionic RF gun. The LINAC is capable of generating sub-picosecond electron pulses with low energy spread (0.13%) and large micro-bunch charge (143 pC). The beam dynamics of the LINAC is studied and optimized by different beam dynamics simulation codes. The entrance hole induced field distortion in the alpha magnet is also reported. The space charge effects are studied by the General Particle Tracer (GPT) code. The results showed that the space charge forces had a significant influence on beam dynamics in such a low energy LINAC.

Generation of uniform transverse beam distributions for high-energy electron radiography

AbstractHigh-energy electron radiography (HEER) has been proposed for time-resolved imaging of materials, high-energy density matter, and for inertial confinement fusion. The areal-density resolution, determined by the image intensity information is critical for these types of diagnostics. Preliminary experimental studies for different materials with the same thickness and the same areal-density target have been imaged and analyzed. Although there are some discrepancies between experimental and theory analysis, the results show that the density distribution can indeed be attained from HEER. The reason for the discrepancies has been investigated and indicates the importance of the uniformity in the transverse distribution beam illuminating the target. Furthermore, the method for generating a uniform transverse distribution beam using octupole magnets was studied and verified by simulations. The simulations also confirm that the octupole field does not affect the angle-position correlation in the center part beam, a critical requirement for the imaging lens. A more practical method for HEER using collimators and octupoles for generating more uniform beams is also described. Detailed experimental results and simulation studies are presented in this paper.

Areal density and spatial resolution of high energy electron radiography**Project supported by the National Natural Science Foundation of China (Grant Nos. 11435015 and 11505251), the Ministry of Science and Technology of China (Grant No. 2016YFE0104900), and the Chinese Academy of Sciences (Grant Nos. 28Y740010 and 113462KYSB20160036).

Ultrafast imaging tools are of great importance for determining the dynamic density distribution in high energy density (HED) matter. In this work, we designed a high energy electron radiography (HEER) system based on a linear electron accelerator to evaluate its capability for imaging HED matter. 40 MeV electron beams were used to image an aluminum target to study the density resolution and spatial resolution of HEER. The results demonstrate a spatial resolution of tens of micrometers. The interaction of the beams with the target and the beam transport of the transmitted electrons are further simulated with EGS5 and PARMELA codes, with the results showing good agreement with the experimental resolution. Furthermore, the experiment can be improved by adding an aperture at the Fourier plane.

Warm dense matter research at HIAF

The research activities on warm dense matter driven by intense heavy ion beams at the new project High Intensity heavy-ion Accelerator Facility (HIAF) are presented. The ion beam parameters and the simulated accessible state of matter at HIAF are introduced, respectively. The progresses of the developed diagnostics for warm dense matter research including high energy electron radiography, multiple-channel pyrometer, in-situ energy loss and charge state of ion detector are briefly introduced.

Design and simulation study of ultra-fast beam bunches split for three orthogonal planes high-energy electron dynamic radiography

AbstractHere a compact three orthogonal planes high-energy electron radiography system was proposed. One of the critical technologies, the ultra-fast beam bunches split from the bunch train are studied. The separated bunches could be transported to the three orthogonal planes of the target for dynamic radiography diagnostics. The key elements of the ultra-fast bunches split system are transverse deflecting cavity (TDC) and the twin septum magnet (TSM). The principle of TDC and TSM are briefly introduced. An example of the beam bunches split system for test experiment (40 MeV electron beam) with TDC and TSM is designed and studied by particle-tracking simulation and it confirms this method is valid and feasible. Especially with TSM, a compact three orthogonal planes radiography system can be realized. The evolution of the beam parameters along the beam line from simulation are investigated. The detailed design of the beam split system and beam dynamics simulation study are presented in this paper.

High-energy electron radiography of microstructures in a dense material

This study presents experimental and numerical results for the high-energy electron-beam radiography of two types of microstructures in a dense material. A copper step target with 1- and 4-mm-thick steps is irradiated by an electron beam with an energy of 150 MeV. A and structure with 285 mu m width was observed in 4-mu m step target experiment, as indicated by the valley to peak feature at the 4-mm step boundary caused by multiple scattering. In a gap-target experiment, the rate of increase of the penetrant-electron counts with a gap width of 500-900 mu m grows from 1.5 to 2.5 times the background counts. Consequently, the width of the gaps can be approximately deduced from the ratio of the penetrant-electron counts combined with the value. The features observed in the experiment are reproduced by a Monte Carlo-FLUKE code with parameters similar to those used experimentally.

An accelerator scenario for a hard X-ray free electron laser combined with high energy electron radiography**Supported by China Academy of Engineering Physics (2014A0402016) and Institute of Fluid Physics (SFZ20140201)

In order to study the dynamic response of the material and the physical mechanism of fluid dynamics, an accelerator scenario which can be applied to both hard X-ray free electron laser and high energy electron radiography is proposed. This accelerator is mainly composed of a 12 GeV linac, an undulator branch and an eRad beamline. In order to characterize a sample’s dynamic behavior in situ and real-time with XFEL and eRad simultaneously, the linac should be capable of accelerating the two kinds of beam within the same operation mode. Combining in-vacuum and tapering techniques, the undulator branch can produce more than 1011 photons per pulse in 0.1% bandwidth at 42 keV. Finally, an eRad amplifying beamline with 1:10 ratio is proposed as an important complementary tool for the wider view field and density identification ability.

High energy electron radiography system design and simulation study of beam angle-position correlation and aperture effect on the images

A beam line dedicated to high-energy electron radiography experimental research with linear achromat and imaging lens systems has been designed. The field of view requirement on the target and the beam angle-position correlation correction can be achieved by fine-tuning the fields of the quadrupoles used in the achromat in combination with already existing six quadrupoles before the achromat. The radiography system is designed by fully considering the space limitation of the laboratory and the beam diagnostics devices. Two kinds of imaging lens system, a quadruplet and an octuplet system are integrated into one beam line with the same object plane and image plane but with different magnification factor. The beam angle-position correlation on the target required by the imaging lens system and the aperture effect on the images are studied with particle tracking simulation. It is shown that the aperture position is also correlated to the beam angle-position on the target. With matched beam on the target, corresponding aperture position and suitable aperture radius, clear pictures can be imaged by both lens systems. The aperture is very important for the imaging. The details of the beam optical requirements, optimized parameters and the simulation results are presented.

High energy electron radiography scheme with high spatial and temporal resolution in three dimension based on a e-LINAC

AbstractWe present a scheme of electron beam radiography to dynamically diagnose the high energy density (HED) matter in three orthogonal directions simultaneously based on electron Linear Accelerator. The dynamic target information such as, its profile and density could be obtained through imaging the scattered electron beam passing through the target. Using an electron bunch train with flexible time structure, a very high temporal evolution could be achieved. In this proposed scheme, it is possible to obtain 1010 frames/second in one experimental event, and the temporal resolution can go up to 1 ps, spatial resolution to 1 µm. Successful demonstration of this concept will have a major impact for both future inertial confinement fusion science and HED physics research.

Image blur in high energy electron radiography

Image blur in high energy electron radiography

Imaging with penetrating radiation for the study of small dynamic physical processes

AbstractSince Roentgen's discovery of X rays in the late 1800s the use of penetrating radiation to form images has become a part of our everyday life as well as providing a useful tool for the scientific study of processes that have been previously impossible to measure. This can include the study of processes that are too deeply embedded in opaque materials for direct observation, or that occur on a length or time scale smaller than otherwise can be easily measured. As technologies to generate penetrating radiation and quickly collect images have matured, new techniques have emerged to measure processes that have been hidden for many years. One example is advances in flash radiography using charged particles as radiographic probes, including proton radiography and electron radiography. Recently the successful commissioning of proton microscope systems has provided remarkable improvements in spatial resolution. These techniques are being implemented for applications with electron radiography. With the evolution of these new techniques comes the opportunity to choose the probe that provides the maximum information for the desired measurement. This paper describes these new imaging techniques, predicts the capabilities of high-energy electron radiography, and provides a guide for identifying the optimal probe for a wide range of measurements.