Ultrafast X-ray Imaging Research Articles

High Speed Imaging Study of the Dynamics of Ultrasonic Bubbles at a Liquid-Solid Interface

High speed imaging, including the ultrafast synchrotron X-ray imaging facility at the beamline 32-ID-B of the Advanced Photon Source (APS), was used to study in-situ (1) the dynamics of ultrasonic bubbles inside a water suspension with an acoustic field of varied pressure; and (2) the interaction of a pulsing bubble at a primary dendrite arm tip inside a succinonitrile-1wt% camphor organic transparent alloy. A simple finite element based model was developed to simulate the stress distribution inside the dendrite due to the pulsing of the ultrasonic bubble, providing more evidence for understanding quantitatively the ultrasonic wave induced dendrite fragmentation phenomenon.

Scale effect on unsteady cloud cavitation

No experiment was conducted, yet, to investigate the scale effects on the dynamics of developed cavitating flow with periodical cloud shedding. The present study was motivated by the unclear results obtained from the experiments in a Venturi-type section that was scaled down 10 times for the purpose of measurements by ultra-fast X-ray imaging (Coutier-Delgosha et al. 2009). Cavitation in the original size scale section (Stutz and Reboud in Exp Fluids 23:191–198, 1997, Exp Fluids 29:545–552 2000) always displays unsteady cloud separation. However, when the geometry was scaled down, the cavitation became quasi steady although some oscillations still existed. To investigate this phenomenon more in detail, experiments were conducted in six geometrically similar Venturi test sections where either width or height or both were scaled. Various types of instabilities are obtained, from simple oscillations of the sheet cavity length to large vapor cloud shedding when the size of the test section is increased. It confirms that small scale has a significant influence on cavitation. Especially the height of the test section plays a major role in the dynamics of the re-entrant jet that drives the periodical shedding observed at large scale. Results suggest that the sheet cavity becomes stabile when the section is scaled down to a certain point because re-entrant jet cannot fully develop.

Size limits the formation of liquid jets during bubble bursting

A bubble reaching an air–liquid interface usually bursts and forms a liquid jet. Jetting is relevant to climate and health as it is a source of aerosol droplets from breaking waves. Jetting has been observed for large bubbles with radii of R≫100 μm. However, few studies have been devoted to small bubbles (R<100 μm) despite the entrainment of a large number of such bubbles in sea water. Here we show that jet formation is inhibited by bubble size; a jet is not formed during bursting for bubbles smaller than a critical size. Using ultrafast X-ray and optical imaging methods, we build a phase diagram for jetting and the absence of jetting. Our results demonstrate that jetting in bubble bursting is analogous to pinching-off in liquid coalescence. The coalescence mechanism for bubble bursting may be useful in preventing jet formation in industry and improving climate models concerning aerosol production.

Recent Advances in the Development of X-Ray Cameras Inserted Inside a Pressurized Box for LMJ Plasma Diagnostics

For the first plasma diagnostics to be deployed at the Laser Megajoule (LMJ), the Commissariat à l'Energie Atomique (CEA) is developing ultrafast x-ray imaging cameras to analyze spatial and temporal evolution of laser-plasma interaction parameters. These cameras, which operate in the target chamber vacuum, are composed of a one-dimensional (1-D) streak or a two-dimensional (2-D) gated detector, power supply units, control electronic modules, and a charge-coupled device (CCD) readout system. In order to optimize their definition and to ensure easy maintenance, these cameras are packaged inside a hermetically sealed chamber comprised of a pressurized box (air box), which also enable the electronics to operate at atmospheric pressure and provide protection of the camera against the harsh operating environment induced by fluxes of neutrons, x-rays and gamma rays, and electromagnetic radiations. This paper introduces the work led by CEA concerning the development of the air box which integrates the x-ray streak and framing cameras for the first LMJ plasma diagnostics experiments, with regard to the integration and operational constraints of the facility.

Intense High-Contrast FemtosecondK-Shell X-Ray Source from Laser-Driven Ar Clusters

Bright Ar quasimonochromatic K-shell x ray with very little background has been generated using an Ar clustering gas jet target irradiated with a 30 fs ultrahigh-contrast laser, with a measured flux of 2.2×10(11) photons/J into 4π. This intense x-ray source critically depends on the laser contrast and intensity. The optimization of source output with interaction length is addressed. Simulations point to a nonlinear resonant mechanism of electron heating during the early stage of laser interaction, resulting in enhanced x-ray emission. The x-ray pulse duration is expected to be only 10 fs, opening the possibility for single-shot ultrafast keV x-ray imaging applications.

High contrast femtosecond laser-driven intense hard X-ray source for imaging application

In this report we address the current situation of laser-driven hard X-ray sources for imaging applications, especially the saturation of X-ray conversion efficiency and the serious impact upon imaging quality. By employing high contrast laser pulses, the conversion efficiency to X-rays from solid foil targets is improved and the structure of the spectrum can be optimized with respect to imaging applications. In addition, bright Ar K-shell X-rays with very little continuum background have been generated by irradiating, with an ultra-high contrast laser, a target of Ar gas clusters created by a gas jet. These improvements show great potential for single-shot ultrafast X-ray imaging.

Synchrotron ultra-fast X-ray imaging of a cavitating flow in a Venturi profile

Cavitation consists of successive vaporization and condensation processes in a liquid flow, due to a large pressure decrease usually associated with sudden flow acceleration. This phenomenon occurs typically in pumps and naval propellers, on the blades’ suction side and/or in periphery of the rotor. It is associated with performance decrease, blade erosion, vibrations that may lead to damage, and noise due to vapor collapse close to the solid walls. Therefore, a general understanding of the mechanisms that govern flow vaporization and condensation is of the utmost importance to reduce or at least to control these effects. A major issue is to estimate velocity fields in both phases, i.e. liquid and vapor. These combined measurements are missing in the literature. We propose a method of ultra-fast X-ray imaging to cope this lack. This method is based on X-ray absorption and phase-contrast enhancement. This technique can simultaneously measure the flow velocities of both liquid and vapor phases at kHz frequency. For the X-ray measurements, a dedicated Venturi shape canal has been designed for the experiments. The design is based on a known two-phase flows hydraulic set-up. The studied cavitation occurs downstream from the Venturi profile. The experiments were carried out at the Advanced Photon Source (APS) at Argonne National Laboratory. These experiments have confirmed the advantages of ultra-fast X-ray imaging for the visualization of liquid–vapor interfaces. Also, the feasibility of estimating velocity field in the flow is acknowledged.

Monochromatic x-ray sampling streak imager for fast-ignitor plasma observation

Ultrafast two-dimensional (2D) x-ray imaging is required to investigate the dynamics of fast-heated core plasma in inertial confinement fusion research. A novel x-ray imager, consisting of two toroidally bent Bragg crystals and an ultrafast 2D x-ray imaging camera, has been demonstrated. Sequential and 2D monochromatic x-ray images of laser-imploded core plasma were obtained with a temporal resolution of 20 ps, a spatial resolution of 31 mum, and a spectral resolution of over 200, simultaneously.

A sagittally focusing double-multilayer monochromator for ultrafast X-ray imaging applications

The development of a sagittally focusing double-multilayer monochromator is reported, which produces a spatially extended wide-bandpass X-ray beam from an intense synchrotron bending-magnet source at the Advanced Photon Source, for ultrafast X-ray radiography and tomography applications. This monochromator consists of two W/B(4)C multilayers with a 25 A period coated on Si single-crystal substrates. The second multilayer is mounted on a sagittally focusing bender, which can dynamically change the bending radius of the multilayer in order to condense and focus the beam to various points along the beamline. With this new apparatus, it becomes possible to adjust the X-ray beam size to best match the area detector size and the object size to facilitate more efficient data collection using ultrafast X-ray radiography and tomography.

Ultrafast x-ray imaging with sliced sampling streak cameras

The ultrafast imaging methods in sliced sampling streak cameras are investigated. It is shown that the sampling-image x-ray streak camera has potential advantages in highly time-resolved and space-resolved imaging for imploded core plasmas. An optimized sampling method is presented to acquire two-dimensional spatial resolutions ⩽10μm and temporal resolution ∼10ps, within a field of view ∼100μm and a time range ∼100ps.

Potential impact of an X-ray free electron laser on structural biology

Recent developments in X-ray source technology provide new opportunities for both the rapid imaging of macromolecules in three dimensions, and the observation of short-lived structural intermediates in light-sensitive macromolecules. Pioneering time-resolved X-ray diffraction studies on macromolecules have laid the foundations for similar studies on increasingly complex macromolecular systems at developing X-ray sources. In addition, the increased peak brilliance expected from an X-ray free electron laser source opens the possibility of new imaging technologies for determining X-ray structures from systems which do not readily yield well-diffracting crystals. Here we review the potential impact of extreme brilliance free electron laser X-ray sources on structural biology. We both sketch the biological case for sub-picosecond X-ray studies of light-sensitive proteins and describe the new imaging possibilities which will emerge through ultrafast X-ray imaging. A central issue is that of X-ray-induced radiation damage on macromolecular samples, and the advantages in this context of working in the femtosecond regime, are discussed.

高分解能プラズマ X 線計測の最前線 2.レーザープラズマの時空同時分解分光画像計測 2.1 画像サンプリングを用いたレーザープラズマの高時間空間分解画像計測

We have developed a wide variety of one- (1D) and two-dimensional (2D) image sampling techniques coupled with x-ray streak cameras for ultrafast x-ray imaging. As 1D sampling, a multi-image x-ray streak camera (MIXS) was developed and successfully utilized for diagnosing the uniformity and heating process of laser-imploded core plasmas with time and space resolutions of 10 ps (equivalent to 1011 frames/sec) and 10 µm, respectively. Two types of spectroscopic application of the MIXS have been developed. One is multi-channel MIXS (McMIXS), which has various spectral responses for time-resolved 2D temperature measurement. The other is monochromatic MIXS (M-MIXS), useful for temperature, density, and material mixing measurement, in which monochromatic images made with Bragg crystal are coupled to MIXS. 2D image sampling on an x-ray streak camera (2D-SIXS) has also been developed. Such ultrafast x-ray imaging is of great importance for diagnosing laser-produced plasmas such as imploded core plasma of inertial confinement fusion and ultrashort-laser-irradiated plasma.

Ultra-fast 2-dimensional X-ray imaging with a 10-ps resolution for use in laser fusion research

2-dimensional x-ray imaging of the laser fusion target is now possible with 10-ps temporal resolution by using recently developed multi-imaging x-ray streak (MIXS) technique. Structures in the x-ray image of the laser-imploded core, symmetry and size, were found to be rapidly changing with 10-ps time scale.

マルチイメージX線ストリークカメラを用いた超高時間分解2次元X線画像計測法によるレーザー核融合プラズマの研究 : 情報入力,情報ディスプレイ

マルチイメージX線ストリークカメラを用いた超高時間分解2次元X線画像計測法によるレーザー核融合プラズマの研究 : 情報入力,情報ディスプレイ

Ultrafast secondary emission X-ray imaging detectors: A possible application to TRD

Fist high accuracy, X-ray imaging at high photon flux can be achieved when coupling thin solid convertors to gaseous electron multipliers, operating at low gas pressures. Secondary electrons emitted from the convertor foil are multiplied in several successive amplification elements. The obvious advantages of solid X-ray convertors, as compared to gaseous conversion, are the production of parallax-free images and the fast (subnanosecond) response. These X-ray detectors have many potential applications in basic and applied research. Of particular interest is the possibility of an efficient and ultrafast high resolution imaging of transition radiation (TR), with a reduced d E/d x background. We present experimental results on the operation of secondary emission X-ray (SEX) detectors, their detection efficiency, localization and time resolution. The experimental work is accompanied by mathematical modelling and computer simulation of transition radiation detectors (TRDs) based on CsI TR convertors.