Phase-contrast imaging using X-ray sources with high spatial coherence is an emerging tool in biology and material science. Much of this research is being done using large synchrotron facilities or relatively low-flux microfocus X-ray tubes. An alternative high-flux, ultra-short and high-spatial-coherence table-top X-ray source based on betatron motions of electrons in laser wakefield accelerators has the promise to produce high quality images. In previous phase-contrast imaging studies with betatron sources, single-exposure images with a spatial resolution of 6–70 μ m were reported by using large-scale laser systems (60–200 TW). Furthermore, images obtained with multiple exposures tended to have a reduced contrast and resolution due to the shot-to-shot fluctuations. In this article, we demonstrate that a highly stable multiple-exposure betatron source, with an effective average source size of 5 μ m, photon number and pointing jitters of <5% and spectral fluctuation of <10%, can be obtained by utilizing ionization injection in pure nitrogen plasma using a 30–40 TW laser. Using this source, high quality phase-contrast images of biological specimens with a 5- μ m resolution are obtained for the first time. This work shows a way for the application of high resolution phase-contrast imaging with stable betatron sources using modest power, high repetition-rate lasers.

A non-intrusive x-ray transmission video based method for measuring local concentrations of one phase dispersed or emulsified in another, on-line and without sampling, is described using illustrative examples. The method involves passing a polychromatic x-ray beam through a multiphase fluid/slurry contained in an x-ray transparent or translucent vessel. The leading dimensions for the unit cell for local concentration measurements are the cross-sectional area of a single pixel (magnification dependent) and the length of the path followed by the x-ray beam through the vessel (vessel dependent). Measurement frequency is dictated by the data acquisition system or the video format employed-typically thirty measurements per second. X-ray transmission radiography is sensitive to small density differences. For example, in a prototype apparatus, the water content in a water-in-oil emulsion/ dispersion is readily measured to within 5000 ppm. The water þ nano scale silica particle content in a water þ silica in oil emulsion/dispersion has a comparable uncertainty unless the particles aggregate or disaggregate in which case the uncertainty jumps to 5 wt%. The resolution limit for nano scale silica particles, with mean diameters less than 40 nm, in water is 2 wt%. However, the technique is more sensitive to larger particles. The vessel employed maybe made from any x-ray transparent or translucent material such as glass, aluminum, beryllium, etc. Potential applications for the technique include both batch and continuous processes drawn from diverse application areas such as the food, environmental and phase separation sciences, as well as in the energy sector. Technique limitations and the role SAXS can play in addressing them are also discussed.

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In order to realize stable, reliable, and high-precision motion control of the satellite-borne data transmission antenna, a FPGAbased motion controller is designed and achieved. The controller receives commands through the RS-422 asynchronous transmission serial port and performs speed planning autonomously. The controller also performs closed-loop position control with the collected resolver angle and controls two antennas synchronously or independently in a subdivision driving method. The controller is firstly designed using the hardware description language VHDL, simulated in ModelSim software. Then, it is connected to the stepping motors through the LMD18200H bridge chip by using aerospace-grade FPGA, controlling the data transmission antennas to regulate the angle, go to zero-position, or stop rotation. The simulation and experiment results show that the design can control the antennas accurately and stably. The accuracy of angle regulation reaches 0.0085°under the condition of 64 subdivisions and 100 : 1 reduction ratio.

Single shot gamma-induced positron annihilation spectroscopy (GiPS) based on a laser wakefield accelerator is proposed. In this spectroscopy, a large number of gamma rays generated by laser-wakefield accelerated electrons are injected into a sample in a very short time (&lt;2 ps), and the positron lifetime is detected by measuring the time profile of the annihilation radiation (511 keV gamma ray) from the sample. The processes including gamma-ray production, shielding, annihilation generation, and annihilation detection were simulated by using the Monte Carlo method. The results show that up to 1010 gamma rays with a duration of 1.4 ps can be produced per shot with a 45 TW laser system. A Cherenkov radiator PbF2 was used to detect the annihilation radiation, and its optimal thickness of 15 mm was obtained. A whole process simulation with optimized parameters was conducted. A low statistical fluctuation lifetime spectrum can be produced, which confirms the feasibility of single shot GiPS with a typical 45 TW laser system.