Zhurong Cao

Three-dimensional particle-in-cell simulation on gain saturation effect of microchannel plate

We present here the results of the simulation work, using the three-dimensional particle-in-cell method, on the performance of the lead glass microchannel plate under saturated state. We calculated the electron cascade process with different DC bias voltages under both self-consistent condition and non-self-consistent condition. The comparative results have demonstrated that the strong self-consistent field can suppress the cascade process and make the microchannel plate saturated. The simulation results were also compared to the experimental data and good agreement was obtained. The simulation results also show that the electron multiplication process in the channel is accompanied by the buildup process of positive charges in the channel wall. Though the interactions among the secondary electron cloud in the channel, the positive charges in the channel wall, and the external acceleration field can make the electron-surface collision more frequent, the collision energy will be inevitably reduced, thus the electron gain will also be reduced.

Large-field high-resolution Kirkpatrick–Baez amélioré-Kirkpatrick–Baez mixed microscope for multi-keV time-resolved x-ray imaging diagnostics of laser plasma

Abstract. A large-field high-resolution x-ray microscope was developed for multi-keV time-resolved x-ray imaging diagnostics of laser plasma at the Shenguang-III prototype facility. The microscope consists of Kirkpatrick–Baez amélioré (KBA) bimirrors and a KB single mirror corresponding to the imaging and temporal directions of a streak camera, respectively. KBA bimirrors coated with an Ir single layer were used to obtain high spatial resolutions within the millimeter-range field of view, and a KB mirror coated with Cr/C multilayers was used to obtain a specific spectral resolution around 4.3 keV. This study describes details of the microscope with regard to its optical design, mirror coatings, and assembly method. The experimental imaging results of the grid with 3 to 5 μm spatial resolution are also shown.

Influence of target geometry on the ion temperature of laser-produced plasmas

Thomson scattering measurements of laser-produced plasmas have been performed with a 4ω probe beam in Shenguang II laser facility. Three kinds of the targets are irradiated with 3ω laser beams: disc target, curved target, and void hohlraum. Thomson scattering spectra are quite different with the different targets. The two ion-acoustic resonance peaks become much broader when a curved target or a hohlraum is irradiated. The experimental results show that the target geometry has a strong influence on the ion temperature of the laser-produced plasmas. The ion temperature could be about several ten keV in the plasma produced with curved target or hohlraum.

Calibration of the linear response range of x-ray imaging plates and their reader based on image grayscale values.

X-ray imaging plates are one of the most important X-ray imaging detectors and are widely used in inertial-confinement fusion experiments. However, their linear response range, which is the foundation of their quantitative data analysis, has not been sufficiently deeply investigated. In this work, we develop an X-ray fluorescer calibration system and carefully explore the linear response range of X-ray imaging plates. For the first time, nearly the entire grayscale range of the X-ray imaging plate linear response-7819-64 879 in the range of 0-65 535-has been observed. Further, we discuss the uncertainties involved in the calibration process. This work demonstrates the excellent linear response qualities of X-ray imaging plates and provides a significant foundation for expanding their quantitative applied range.

Development of high resolution dual-energy KBA microscope with large field of view for RT-instability diagnostics at SG-III facility

High resolution X-ray diagnosis is a significant method for obtaining ablation-front and trajectory measurements targeting Rayleigh-Taylor (RT)-instability growth in initial confinement fusion (ICF) experiments. In this paper, a novel Kirkpatrick-Baez-type structure, as a kind of essential X-ray micro-imaging apparatus, has been developed that realizes a large field of view (FOV) and images with high resolution and energy response. Zoned multilayer coating technology is applied to the Kirkpatrick-Baez mirrors to transmit two specific quasi-monochromatic light through the same mirror and enables a compact dual-channel structure. This microscope has been assembled in the laboratory and later implemented at the Chinese SG-III laser facility. The characterization results show that this imaging system can achieve a good spatial resolution of 5 µm in a large FOV of 500 µm, while maintaining a strong monochromatic performance with bandwidth of 0.5 keV at 2.5 keV and 4.3 keV respectively.

Realization of a flat-response photocathode for x-ray streak cameras.

We present a novel photocathode which can make x-ray streak cameras to be of a flat spectral response in the x-ray energy range of 0.1-5 keV. The photocathode consists of two layers of gold foils with optimized thickness ratio and structures. The photocathode was calibrated, and it is shown that a flat spectral response has been achieved.

Note: New method for high-space-resolving hotspot electron temperature measurements on Shenguang-III prototype

High-space-resolving information of hotspot electron temperature is a foundation for further research on physical processes of implosion in inertial confinement fusion. This work proposed a novel high-space-resolving electron temperature detector, which is based on the bremsstrahlung radiation mechanism of the implosion hotspot and uses two-channel Kirkpatrick-Baez microscopes. In this novel detector, an optical quasi-coaxis method was used to eliminate the strong impact of the view field difference on the high space resolution and correctness of the electron temperature diagnosis, and a compound KB microscope method was proposed to reduce the number of spherical reflectors and save space.

Development of an x-ray eight-image Kirkpatrick–Baez diagnostic system for China’s laser fusion facility

This article presents the development of an x-ray eight-image Kirkpatrick-Baez diagnostic system to be used at Chinas Shenguang-III (SG-III) laser facility in aspects of the optical design, multilayers, and online/offline tests. Six pieces of concave spherical substrates are used for constituting a special optical structure. Dual-periodic tungsten/carbon (W/C) multilayers are used for high reflectivity and large angular bandwidth of ∼0.1°. The global spatial resolution is ∼5  μm in the ±100  μm range. The schemes of system installation, transport, collimation, and image acquisition at Chinas SG-III facility are also discussed.

Design of KB complex type microscope for ICF x-ray diagnostics

In the field of target diagnostics for Initial Confinement Fusion experiment, high resolution X-ray imaging system is seriously necessary to record the evolution details of target ablation-front disturbance at different energy points of backlight conditions. Kirkpatrick-Baez mirror is a wide used imaging system to achieve a large efficient field of view with high spatial resolution and energy transmitting capability. In this paper, we designed a novel type of reflective microscope based on Kirkpatrick-Baez structure, and this system can achieve 5μm spatial resolution at 600μm field of view specific energy point in one dimension.

Kirkpatrick-Baez microscope with spherical multilayer mirrors around 2.5keV photon energy

A Kirkpatrick-Baez (KB) x-ray microscope has been developed for the diagnostics of inertial confinement fusion (ICF). The KB microscope system works around 2.5keV with the magnification of 20. It consists of two spherical multilayer mirrors. The grazing angle is 3.575° at 2.5keV. The influence of the slope error of optical components and the alignment errors is simulated by SHADOW software. The mechanical structure which can perform fine tuning is designed. Experiment result with Manson x-ray source shows that the spatial resolution of the system is about 3-4μm over a field of view of 200μm.