| With ever-increasing space activities and space missions on a global scale,communication frequency resources are becoming less and less.It is urgent to explore new communication mode.So X-ray communication,called “Next-Generation Communications”,has extensive application prospect.It can be used in complex space environments on account of good directivity,low transmitting power,distant transmission distance,fine confidentiality.As the critical component of the space x-ray communication,modulated x-ray source's modulation rate and focal spot size have a direct impact on communication rate and distance.So it is significant to develop a modulated x-ray source,with functions of low power consumption,miniature size,small focal spot and high modulation rate,for demonstrating x-ray communication and finally realizing inter-satellite communication.This thesis is aimed at developing a vacuum-sealed transmission-type micro-beam modulated x-ray source and more details about theoretical analysis,modeling and simulation,tackling of key technologies,special technology exploration,prototype fabrication and testing can be found in the next section.The low voltage modulation of the modulated x-ray source,range from-0.6V to +0.6V,is obtained by electron motion simulation using SIMION software.And the modulation voltage amplitude is reduced by an order of magnitude,wherefore it is easy to achieve high-frequency modulation and sequently enhance x-ray communication rate.Then 150?m focal spot size is acquired by means of simulating and optimizing three electrostatic electrodes,which breaks the technical bottlenecks that it's difficult to focus into micron focal spot for hot cathodes and lays the foundation for the space long-distance x-ray communication.Using the simulation of MCNP software,optimized target thicknesses are obtained in different target materials and different electron energies,which improves the x-ray intensity of reflective-type anode target and increases the x-ray modulation frequency.In order to change the current situation of undesirability of the coventional chemical coating or vacuum coating process,crafts of cleaning,replacement zinc layer and high vacuum ion sputtering of beryllium are explored.One time tube sealing and exhausting technique of vacuum interrupters should be make use for reference in full vacuum seal of the modulated x-ray source and the vacuum degree of the tube is higher than 10-3Pa.Finally,the prototype has been fabricated and grid pulse modulation and amplitude modulation of the modulated x-ray source have been demonstrated successfully.Compared with the previous modulated x-ray source,the innovative results of this paper are mainly reflected in the following four aspects: the low-voltage modulation technology of the grid electrode,range from-0.6V to 0.6V,is tackled and it is probable of the x-ray high-frequency modulation;three electrostatic focusing electrodes are used to improve the focusing ability of electron beam and,moreover,the micro-focal spot of 150?m is achieved;the full high-vacuum seal of several components in the modulated x-ray source is finished and the vacuum degree remains higher that 10-3Pa for more than two years;in addition,it is discovered unexpectedly that high frequency pulses loaded on the grid electrode have significant impact on the x-ray intensity.The modulated x-ray source is composed of the hot cathode,the grid electrode,three electrostatic focusing electrodes and the transmission-type anode target.As the newest vacuum-sealed modulated x-ray source based on hot cathode,it can provide technical support for demonstrating long distance and high speed space x-ray communication in our country. |
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