  GASTOF (Gas Time-of-Flight) detector is a Cherenkov detector proposed for
very precise (10--20 ps) arrival time measurements of forward protons at some
420 m from the central detectors of CMS and ATLAS. Such an excellent time
resolution will allow by z-by-timing technique for precise measurement of the
z-coordinate of the event vertex in exclusive production at the LHC, when two
colliding protons are scattered at very small angles. In the paper we present
first GASTOF prototype, simulations of its performance as well as first tests
using a cosmic muon telescope.
