Pulse Field Emission CT X Ray Tube

X ray is widely used in medical computed tomography(CT)image detection and process nondestructive testing.As the core component of X-ray radioscopy system,thermal cathode X-ray tubes have some obvious disadvantages such as high working temperature,low current density and slow start-up speed.In particular,in medical CT imaging applications,X-ray tubes are often required to have small focal spots,large current density,quick response,quick photo-taking,low dose of X-ray radiation.Carbon nanotube field emission source,as a kind of cold cathode electron emission source,is considered as the core cathode materials that can overcome the shortcomings of the traditional thermal cathode and replace it as X-ray tube.CT system based on carbon nanotube X-ray tube can realize pulse emission,high-speed photograph,the characteristics of low dose.However,there are obvious shortcoming when carbon nanotube used as emitters.For example,the current stability is poor,and easy to be burned.Moreover,field emission generally requires a relatively strong electric field on the cathode surface,usually in a grid manner.One method is inner gate which is difficult to be prepared and it is easy to occur short circuit.The external grid structure can effectively avoid the inner gate defect,but the external gate intercepts the electron seriously,resulting in the grid heating deformation.These deficiencies greatly affect the application and promotion of carbon nanotube emission X-ray tubes.In this paper,in order to improve the reliability of carbon nanotube field emission cathode,microwave plasma CVD method was used to grow carbon nanotube field emission arrays to obtain high emission current density in large with improved the.At the same time,this paper optimizes the structure of an X-ray tube electron gun,which achieves a high compression ratio and has a good focusing property while greatly reducing the number of electronic intercepts.This paper mainly has the following three aspects:1.A new electron gun for carbon nanotube based X-ray tubes designed,in which a shadow grid structure was used to avoid the gird intercepting electrons efficiently.And a double focus electrodes were used to obtain very small electron spot,the design results can meet the requirements of high resolution CT system;2.The carbon nanotube arrays were fabricated by MW-PCVD large area cathode array realized high current density of more than 2A/cm~2.3.According to the design high-power pulse X ray tube was successfully prepared,and high-resolution CT images were achieved successfully.