Design of TiO_{2} nanotube based X-ray tube with single focusing electrode

We studied in details the effect of various X-ray tube parameters (cathode size, anode size, anode - lens distance, etc.) on TiO_{2} nanotube field emission electron-beam focal spot size (FSS) and lens voltages for a single electrode lens system. The simulations were performed using commercially available SIMION 8.1 software. A wide range of parameters was simulated to determine conditions when FSS and lens focusing voltage had minimum values. In particular, the dependence of FSS and lens voltages on cathode size (d_{S}) was studied for different size lens apertures (d_{L}) and different anode voltages. The cathode size d_{S} was varied in the range from 0.1 mm to d_{L}; the d_{L} was changed from 4 to 24 mm in 4 mm increments. The simulations were performed for two different V_{A} values 60 kV and 120 kV. It was found that for 20 mm and 24 mm diameter lens apertures the maximum cathode size when the resulting FSS was not greater than 1600 μm (the focal spot size in clinical X-ray CT) were 17.5 mm and 16.2 mm, respectively. The lens voltages V_{f} corresponding to 17.5 mm and 16.2 mm cathode size in 20 mm and 24 mm aperture diameter x-ray tubes are 1850 V and -1550 V, respectively.