The BEAR was a particle beam test in space. A particle beam is a focused stream of tiny particles, such as atoms or electrons. Usually electrons.

This report details a notable particle beam experiment that happened as part of Reagan's pet money sink, the SDI. I'm trying to get ahold of the full text of this document.

O'Shea, P.G. "Linear Accelerator in the Space: The Beam Experiment Aboard Rocket." Los Alamos National Laboratory, NM. 1990. 14p. In: Linear Accelerator Conference, Albuquerque, NM, 9-14 September 1990. 
Abstract:On July 13, 1989 the BEAM experiment Aboard Rocket (BEAR) linear accelerator was successfully launched and operated in space. The flight demonstrated that a neutral hydrogen beam could be successfully propagated in an exoatmospheric environment. The accelerator, which was the result of an extensive collaboration between Los Alamos National Laboratory and industrial partners, was designed to produce a 10 mA (equivalent), 1 MeV neutral hydrogen beam in 50 (mu)s pulses at 5 Hz. The major components were a 30 keV H(sup (minus)) injector a 1 MeV radio frequency quadrupole, two 425 Mhz RF amplifiers, a gas cell neutralizer, beam optics, vacuum system and controls. The design was strongly constrained by the need for a lightweight rugged system that would survive the rigors of launch and operate autonomously. Following the flight the accelerator was recovered and operated again on the laboratory.