Research On High Isolation Floating Grid Constant Current Power Supply For CNT Field Emission X-ray Source

Micro-focus X-ray source is one of the key components of the Micro-Computed Tomography system(Micro-CT).The parameters of the micro-focus X-ray source,such as the spot size,target power,and stability significantly affect the main spatial resolution and detection efficiency of the micro-focus CT system.Compared with traditional hot cathode micro-focus X-ray source,the carbon nanotubes(CNT)field emission cathode micro-focus X-ray source has many advantages,such as strong electron current,high power,low thermal effect,low energy consumption,and easy to realize miniaturization and high-frequency pulsed X-ray beams.It can significantly improve the image quality of the micro-CT system and it is one of the hot research areas in X-ray sources.While the power supply system is one of the key components of the CNT field emission X-ray source.Its stability and control accuracy determine the quality of the electron beam,such as the beam diameter,beam intensity,and the stability of the electron beam,which have a significant impact on the image quality.For example,when the CNT serves as the cathode of the transmission target micro-focus X-ray source electron gun,a slight oscillation of the anode voltage will seriously affect the stability of the output of the grid power.The reason is that the anode target is grounded and the grid is suspended on the anode high voltage potential.On the other hand,because the characteristic of the CNT field emission current is exponential,the slight disturbance of the voltage will cause the field emission current to fluctuate drastically,which finally affects the stability of the micro-focus X-ray source.Therefore,the developed common commercial power cannot meet the requirements of the CNT field emission cathode transmission target micro-focus X-ray source.This work was supported by the National Instruments Special Project-Development and Application of Micro-nano Structure Ultra-resolution Computer Three-Dimensional Imaging Analyzer(2013YQ030629).The purpose of this work is to develop a power source of the microfocus X-ray source of the CNT field emission cathode transmission target.In this work,the software and hardware designs of the floating grid constant current power supply system have been completed,a corresponding experimental platform has been established,and the performance of developed source has been tested.Specifically,the contents of this paper are organized as follows:(1)The research actuality of the X-ray source grid power supply has been summarized.The structure of the X-ray source under different grid power supply modes has been mentioned.To address the defect that the grid power supply of the existing CNT field emission cathode emission X-ray source which cannot achieve constant current control,a method with high isolation,suspension,and constant current control has been proposed.(2)A high isolation floating gate constant current source device has been designed.The device is composed of three parts: a 3k V high voltage output module,a constant current control module,and a control panel module.The function of the high voltage power module is to generate 0?3k V high voltage and to realize circuit isolation.The constant current source module is to realize the constant output current.The control panel module is to provide a display interface and remote control.Specifically,this work includes hardware and software designs.The hardware part includes schematic design and device selection.And the software part includes using the C8051F310 microcontroller programming to achieve panel menu display,and the mutual communication between the microcontrollers,using the TMS320F28035 to realize the functions of the circuit PWM modulation,AD conversion,constant current control and so on.Finally,the power supply can realize constant current control of 0?3k V and 0?5m A,which can be adjusted in real-time.(3)The performance of the high isolation floating gate constant current source has been tested.The ripple,stability,isolation voltage,and leakage current of the gate power supply has been tested separately.The results have shown that the power supply stability and leakage current meet the index of the requirements.This high isolation floating gate constant current source has been equipped on the micro-CT system for imaging,the results have shown that the devoleped source can help the micro-CT system to obtain a clear DR image.