How does a microfocus X-ray tube work?
In an evacuated tube electrons are emitted from a heated filament and are accelerated towards the anode by the potential difference UACC. Electrons enter through a hole in the anode into a magnetic lens which focuses the electron beam to a small spot of a few microns in diameter on the massive tungsten target (directional tube).
In the tungsten the electronis are abruptly decelerated whereby X-rays are generated. The focal spot represents a very small X-ray source which enables sharpest imaging with micrometer resolution. Latest nanofocus tubes (transmission tube) achieve a detail detectability down to 200 nanometers (0.2 microns) by using multiple electron lenses. The electron beam current is controlled by the bias voltage UG via the Wehnelt electrode („grid“).
Research and Development at University of Michigan