Many people mistaken "particle accelerators" to be the same as "particle colliders" and lump them with particle/high energy physics. This is of course a mistake. While particle accelerators certainly is a major component of any particle physics experiment, its use is not just restricted to such an area. Any facility that needs a beam of charged particles requires a particle accelerator. This can range from synchrotron facilities all the way to your doctor's office. Synchrotron centers require the injection of electrons into a circular storage ring. The electron bunches must be of high "quality", i.e. a small range of energy and a small emittance so that they don't deteriorate while going around the ring. Doctors offices require a compact accelerator to produce x-rays (google "medical accelerator"). Some of these x-ray sources may even be used at airports to scan your bags!
There is a further, direct use of accelerators for medical purposes, as in using the beam itself for therapy. This article describes one such example where it is used to fight cancer.