Bunches of particles circulate around the Cornell Electron Storage Ring (CESR) at nearly the speed of light. Each one centimeter-long bunch consists of some billions of particles. In a blink of an eye the bunch of particles has traveled around the 768m circumference ring nearly 1,000,000 times.
The particles in the bunch emit photons as they speed around the ring. The photon emission heats up the particles in the bunch, where the hot particles expand and spread out. An otherwise bright beam is made dimmer, compromising its effectiveness as a tool for research.