End-window transmission-target X-ray tubes are designed for very close anode-to-sample coupling for compact portable XRF instruments. Several recent improvements have been achieved to make these tubes considerably brighter, with better output stability and even smaller size and lower power consumption for handheld instrumentation.
Areas of the tube that have been improved include the anode, the cathode, and the high-voltage power supply. 1) The anode can be a sputtered film on the inside of the X-ray window. Densified films of a more uniform thickness provide higher X-ray output and more consistent performance from tube to tube. 2) Changes in the anode geometry have resulted in reduced spectral contamination from metal parts in the anode. 3) The electron beam position on the anode is primarily influenced by the filament placement relative to the cathode optic. Using finite-element analysis (FEA) charged-particle beam modeling software it was possible to design an improved cathode optic with significantly better electron beam performance. This results in higher electron density on the target and a more stable beam position. 4) Finally, innovations in the high-voltage power supply have resulted in significant reductions in size and weight in this component. New power supply designs also require significantly less input power than the earlier designs. The combination of these improvements results in miniature X-ray tubes with higher flux, lower spectral contamination, more stable X-ray beams, smaller and lighter packages, and lower overall power consumption.