In XRF wavelength dispersive sequential spectrometers, two general types of X-ray tubes are employed: end-window and side-window. In the side-window design, anode and window are grounded. This allows a large portion of high energy electrons, scattered from the target, to fall on and heat the window. The heating, which results in the loss of window strength, requires increased window thickness and shortens an X-ray tube's life cycle.
In end-window tubes, potential is reversed: cathode and window are grounded while the anode operates at a high potential. Scattered electrons are attracted back to the anode with very few striking the window. The window does not suffer from heating, and its thickness can be decreased to 125 microns. Such a window is transparent to soft radiation, which is beneficial when exciting light elements.