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