Electrostatic Focusing Lens Module With Large Focusing Capability in Carbon Nanotube Emitter-Based X-Ray Sources

We fabricated and analyzed an electrostatic focusing lens (FL) module comprising a micro-FL with many holes near the gate and a macro-FL of single aperture toward the anode for carbon nanotube (CNT) emitter-based X-ray sources. The micro-FL suppresses the divergence of the electron beams whereas the macro-FL governs the shape of the beam bundle. The FL module can be controlled over a wide range of gate and anode voltages while maintaining the focal spot. We achieved a small focal spot of 300 $\mu \text{m}$ from CNT emitter dot arrays of 10 mm $\times 1.6$ mm with line pairs of 3 lp/mm maintained for different anode voltages.