Reseach On Electrostatic Self-focusing Lanthanum Hexaboride X-ray Source

High power, high current density, fine focus X-ray sources are widely used in the field of industrial nondestructive testing, medical imaging, security technology etc. With the development of X-ray imaging system, the demands for small, low power consumption, high quality X-ray source are more and more urgently. Synchrotron Radiation, laser plasma source and electron beam ion trap can produce high-density X-ray. But these methods are complicated, expensive and high costs. Therefore, the design of high current density, small size, low power X-ray source by using the traditional electron-beam bombardment method has significant meaning in improving the spatial resolution and reducing the equipment cost. In this research we design a X-ray source for cranial CT scan and the main research content and results including:1. To reduce the size of high power X-ray tube, we design a fixed anode structure in replace of the rotating anode. To avoid the leads of focusing electrode, we design a single focusing electrode with trapezoidal focusing groove.2. To reduce power density of the fixed anode, we use Lanthanum hexaboride cathode in replace of the traditional Tungsten cathode to design the electron emitting structure of the X-ray tube. The size of the cathode which is working under pulse current is 4.5mm×0.8mm. Thermionic emission test shows that at 1500℃, 2500 V anode voltage, the anode current is 65 mA and the emission stability is good.3. To improve the efficiency and uniformity of the electron beam and generate 1mm×1mm X-ray spot, we use electron beam simulation software(EBS) to stimulate the structure of X-ray source. After computer stimulation and theoretical discussion, select the appropriate parameters such as electrode structure electrode spacing and voltage. Results show that 97.76 mA electron beam current is produced and the spot size is 0.997 mm×0.988 mm at the voltage of 120 kV.4. To complete the design electron emission system of the X-ray source by following the stimulation results, we design the clamping type cathode with graphite heater and other cathode structures such as cathode cover, cathode support and insulating ceramics and complete the assembling of electron emitting system. X-ray tube has been constructed in experiment based simulated model after optimized.5. The test of the X-ray tube shows that at 1150℃, 20 kV, anode current is 10 mA, and the focal spot size is 1.2mm×1.1mm. And at 120 kV, good X-ray tube switching performance is obtained.