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.
