  We present a design for an atomic synchrotron consisting of 40 hybrid
magnetic hexapole lenses arranged in a circle. We show that for realistic
parameters, hydrogen atoms with a velocity up to 600 m/s can be stored in a
1-meter diameter ring, which implies that the atoms can be injected in the ring
directly from a pulsed supersonic beam source. This ring can be used to study
collisions between stored hydrogen atoms and molecular beams of many different
atoms and molecules. The advantage of using a synchrotron is two-fold: (i) the
collision partners move in the same direction as the stored atoms, resulting in
a small relative velocity and thus a low collision energy, and (ii) by storing
atoms for many round-trips, the sensitivity to collisions is enhanced by a
factor of 100-1000. In the proposed ring, the cross-sections for collisions
between hydrogen, the most abundant atom in the universe, with any atom or
molecule that can be put in a beam, including He, H$_2$, CO, ammonia and OH can
be measured at energies below 100 K. We discuss the possibility to use optical
transitions to load hydrogen atoms into the ring without influencing the atoms
that are already stored. In this way it will be possible to reach high
densities of stored hydrogen atoms.
