臺灣博碩士論文加值系統

Abstract
A micro focus x-ray tube that generates x rays with a micrometer-sized focal spot is a key device for high-resolution x-ray radiography and tomography because X rays with smaller focal spot size yield finer x-ray images with higher magnification factor. The x-ray focal spots of conventional thermionic micro-focus x ray tubes are normally less than 20 μm in size.

The major purpose of my research is to design and optimize a new micro-focus X-ray tube with a spot size on the target less than 25μm. Also, the target assembly has to withstand the high power density of an electron beam without being damaged.

During the exploring process in order to achieve the desired level of x-ray focal spot, I considered the following three steps.
The First step:
Use electronic control system on the JP-EGUN with the emitter hidden
behind the cap hole to investigate the effect of Vbias on the focal spot
size.
The Second step:
Design the gate electrode inclined to the cathode inducing a focusing
electric field on the electron beam to see if the PIRECE GUN can
considerably reduce the minimum radius of the electron beam.
The Third step:
Optimize several X-ray target parameters for the X-ray intensity and X-ray
stability.

Contents

Abstract ⅰAcknowledgements ⅱ
Part Ⅰ.)
1. Introduction 1
2. Simulation methods 3
3. Electron Motion in Static Electric Fields
3.1 Motion parallel to field 6
3.2 Relativistic velocity corrections 7
3.3 Motion perpendicular to a uniform electric field 9
3.4 Electric Lenses 10
3.5 Universal beam spread curve 11
4. Thermionic emission theory
4.1 Richardson-Dushman equation 13
4.2 Schottky effect 15
4.3 Space charge effect 16

5. JP E-GUN
5.1 Structure and operating principles 19
5.2 Effect of Ia and Va on the focal spot size 21
5.3 Experimental and theoretical results 24
6. PIERCE GUN
6.1 Pierce Electrodes 27
6.2 Effect of Dlength and Dwidth on the focal spot size 29
6.3 Effect of Ia and θ on the focal spot size 33
7. Conclusion 36

Part Ⅱ.)
1. Introduction 37
2. Simulation methods
2.1 Introduction to Monte Carlo 39
2.2 ANSYS PROGRAM 40
3. Optimization of X-ray target parameters
3.1 Effect of target thickness on X-ray intensity 42
3.2 The optimum target thickness 44
4. Thermal stability
4.1 Structure and operating principles 46
4.2 Temperature profile of the target/window assembly 49
4.3 Power loading of an X-ray target 52
4.4 Beam broadening 57
5. Conclusion 60


References 61

References
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國立清華大學物理研究所, 1999年
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