Lizhi Sheng

Novel space communication technology based on modulated x-ray source

A novel space communication method is presented in this paper based on X-ray photons. As a result of its short wavelength and great penetrability, X-ray has no attenuation for transmission in space when its photon energy is more than 10keV (λ<0.1nm). Thus a communication technology of long distance signal transmission in space can be achieved with smaller volume, lower weight and lower power. Therefore, X-ray communication (XCOM) is especially valuable to the deep space missions, which will be able to realize higher data rates, smaller SWAP than with RF and laser communications. Using X-ray photons as information carrier will not only be a good complement to laser and RF communications, but will also have unique applications when RF and laser signals are not available like the spacecraft’s re-entering to the earth. High-speed modulation and high-sensitivity detection of X-rays are two major technical issues which should be addressed in order for the X-ray communication to take place. A Grid-controlled Modulated X-ray tube (GMXT) is proposed and developed as X-ray transmitter. One or more specially designed grid electrodes are added to the traditional X-ray tube to modulate the electrons. The communication signal is coded and applied to the modulated grid electrode, and then the corresponding X-ray signals are generated and sent out. X-ray detector based on micro-channel plate(MCP) is used as communication receiver because of its high temporal resolution. An audio communication experiment system based on XCOM is setup in laboratory including the X-ray transmitter and the receiver. X-ray communication is successfully demonstrated and the communication speed reaches 64 kilobits per second in a vacuum tube of 6 meters long. As a new concept of space communication, X-ray communication will have more important scientific significance and application prospects when technologies for X-ray modulation and detection are further developed.

X-ray photon-counting detector based on a micro-channel plate for pulsar navigation

The pulse time of arrival (TOA) is a determining parameter for accurate timing and positioning in X-ray pulsar navigation. The pulse TOA can be calculated by comparing the measured arrival time with the predicted arrival time of the X-ray pulse for pulsar. In this study, in order to research the measurement of pulse arrival time, an experimental system is set up. The experimental system comprises a simulator of the X-ray pulsar, an X-ray detector, a time-measurement system, and a data-processing system. An X-ray detector base is proposed on the basis of the micro-channel plate (MCP), which is sensitive to soft X-ray in the 1–10 keV band. The MCP-based detector, the structure and principle of the experimental system, and results of the pulse profile are described in detail. In addition, a discussion of the effects of different X-ray pulse periods and the quantum efficiency of the detector on pulse-profile signal-to-noise ratio (SNR) is presented. Experimental results reveal that the SNR of the measured pulse profile becomes enhanced as the quantum efficiency of the detector increases. The SNR of the pulse profile is higher when the period of the pulse is smaller at the same integral.

Selection of MCP for array X-ray pulsar navigation detector

According to the demands of an array detector in the X-ray pulsar navigation system for Micro-channel Plate (MCP), a selection method for the MCP was explored. Four key parameters for the selection of MCPs, the uniformity of gain, impedance matching, dark count rate and the gain coefficient were determined. Based on the four key parameters, corresponding experiments were designed and the selection process of MCPs was set out. The amplitudes and counting rates of MCPs selected by proposed method were tested. The tested results show that the relative error of each detection unit is not identical. When a single channel anode is used, the ranges of the maximum relative error Δ1i and minimum relative error Δ2i of the amplitudes for output signals from the ith anode are 7%-13.5% and 3%-6.7%, respectively, and when a four-channel anode is used, Δ1i and Δ2i are 7.8% and 3.1%, respectively. Moreover, the relative error between the anode count rate n1+n2+n3+n4 from the single channel and N from the four-channel shared anode is 4.38%, less than 10%. Obtained results indicate that the MCPs with good performance have been effectively chosen by the proposed selection method. ©, 2015, Chinese Academy of Sciences. All right reserved.

Continuous measurement of the arrival times of x-ray photon sequence

In order to record x-ray pulse profile for x-ray pulsar-based navigation and timing, this paper presents a continuous, high-precision method for measuring arrival times of photon sequence with a common starting point. In this method, a high stability atomic clock is counted to measure the coarse time of arrival photon. A high resolution time-to-digital converter is used to measure the fine time of arrival photon. The coarse times and the fine times are recorded continuously and then transferred to computer memory by way of memory switch. The pulse profile is obtained by a special data processing method. A special circuit was developed and a low-level x-ray pulse profile measurement experiment system was setup. The arrival times of x-ray photon sequence can be consecutively recorded with a time resolution of 500 ps and the profile of x-ray pulse was constructed. The data also can be used for analysis by many other methods, such as statistical distribution of photon events per time interval, statistical distribution of time interval between two photon events, photon counting histogram, autocorrelation and higher order autocorrelation.

Research of nested X-ray concentrator for future X-ray timing astronomy

X-ray grazing incidence optics are widely used in X-ray astronomy, especially for imaging payloads Wolter optics are the most workhorse. However, as there are two cascaded mirrors in Wolter type, the efficiency is quite low after two reflections. In this paper a kind of nested conical concentrator is developed with only one reflection to concentrate the X-ray photons and obtain the timing information. The mirror length is 200mm, the mirror foils cover from 38.8 to 100mm in diameter. D263T glass of 0.3mm thickness is used as mirror substrate with Iridium film deposited in order to improve the X-ray reflection. The D263T glass is slumped at 580°C with precisely machined and polished mold. 3D printed resin serves as upper mold for glass cutting. The quality of mirror substrate is mainly determined by the surface of forming mandrel. As the surface roughness is quite important for X-ray reflection, after deposition it is tested with interferometer and AFM, and the roughness is 0.6nm. Mirror integration based on visible light is built, and the conical mirrors are assembled and adjusted by real time monitoring for the focal point of visible light. With the monochromic X-ray source, the concentrator efficiency is tested as 38%@1.49keV, 20%@4.51keV. The focal point is Φ8.2mm in Xray, with 80% of its energy encircled in a 4mm width. This kind of X-ray concentrator could be used in X-ray navigation, X-ray communication and other X-ray timing astronomy.

Nested grazing incidence optics for x ray detection

Grazing incidence optics (GIO) is the most important compound in an x-ray detection system; it is used to concentrate the x-ray photons from outer space. A nested planar GIO for x-ray concentration is designed and developed by authors in this paper; planar segments are used as the reflection mirror instead of curved segments because of the simple process and low cost. After the complex assembling process with a special metal supporter, a final circle light spot of was obtained in the visible light testing experiment of GIO; the effective area of 1710.51 mm2@1 keV and 530 mm2@8 keV is obtained in the x-ray testing experiment with the GIO-SDD combination, which is supposed to be a concentrating detector in xray detection systems.

Gird-control electron gun with multiple focusing electrode

An electron gun with multiple focus system was designed, and a smaller beam spot was obtained in the computer simulation technology. The different cathode emission models would be actived when different voltage was load on the gird electrode, and which affects the number of electrons emitted from cathode significantly, the number of electrons would increase and decrease under the Schottky emission and Rejecting;field emission mode. When voltage of focusing electrodes is U1:U2:U3:U4:U5=5:8:15:70:100, the spot size of 160 mm at the distance of 10 m was acquired in the electron gun model.

Multilayer nested X-ray focusing optical device

Aiming at the demand on X-ray pulsar navigation and X-ray space communication, the multilayer nested X-ray focusing optical device is developed and tested. Theoretical design of focusing lenses is carried out according to the principle of grazing incidence, and key parameters of the focusing lenses are determined. The materials of focusing lenses and the preparation technologies such as the coating process are discussed. The performance parameters of the focusing lenses are tested respectively under the conditions of visible light and X-ray. The results show that the spot diameter of visible light is 14 mm, the spot diameter of X-ray is 20 mm, and the focusing efficiency is 30.2%. The effective area is 2400 mm2in a 10 m vacuum pipe when the photon energy is 1.5 keV.

Decoding algorithms for improving the imaging performance of Vernier anode readout

The Long Slit Spectrograph is one of instruments onboard The World Space Observatory-Ultraviolet. Both the FUV (102-1700nm) and NUV (160-320nm) channels of LSS choose micro-channel plates (MCP) detector with anode readout in the focal plane. The MCP detectors with anode readout are typically used to provide photon counting imaging. According to the desired performance of LSS, the Vernier anode may be the optimum readout scheme. The Vernier anode is famous for its high spatial resolution, however, the original decode algorithms of the Vernier anode is susceptible to wrongly decode, when the charge acquisition is not precise enough and the footprint size of charge cloud collected by Vernier anode is not small enough and eventually results in the deterioration of photon counting image. In this paper, the causes leading to image deterioration is analyzed. The least-squares method was used to calculate the phase value to correct imaging distortions caused by charge measurement accuracy. The area ratio of each electrode covered by charge cloud is accurately calculated to improving the imaging results. The corrected algorithms are verified by experimental results and the results show that the correction methods can obviously improve the quality of the original photon counting image.

Temporal resolution of x-ray detector for pulsar navigation

Pulsar navigation is a promising new technique for space exploration because of its autonomous and deep space capability. Since the baseline of pulsar navigation approach is to observe the X rays (0.2~20keV) emitted from pulsars, a compact high temporal resolution X-ray detector is needed. In this paper an micro-channel plate(MCP) photon counting detector sensitive to X-rays is proposed. The detection system consists of a CsI photocathode, a 50mm diameter micro-channel plate (MCP) stack, a collection anode, a preamplifier, a constant fraction discriminator(CFD) and data acquisition(DAQ). The incident X-rays photons are absorbed by CsI and converted to photoelectrons, the electrons are multiplied by MCP and collected by the anode. Anode output signal is a fast pulse which need to be amplified by preamplifier and then fed to CFD circuit and DAQ for a precise timing. The total temporal resolution (ΔT) of the entire detection system could be determined by ▵tD, the intrinsic temporal resolution of cathode-MCP-anode, and ▵E the resolution of electronic system including preamplifier and CFD. The resolution of the detection system is tested to be 18.4ns in experiment.