  The TP3-WFS (Two Pupil Plane Positions Wavefront Sensor) is, to the best of
the authors' knowledge, the first physical implementation of the geometrical
wavefront reconstruction algorithm that has been tested in a telescope as part
of an actual AO-enabled instrument. The main advantage of this algorithm is
that it theoretically provides a fairly good reconstruction accuracy even under
very low levels of light, in the order of a few hundreds of photons. This paper
presents the first control-related results obtained at the William Herschel
Telescope (WHT). Such results demonstrate the feasibility of this novel WFS as
part of a real-time AO control loop.
