  Electron cooling that results when a bunch of electrons overlaps a bunch of
ions , with both bunches moving at the same velocity, may be considered to be
an intrabeam scattering process. The process is similar to the usual intrabeam
scattering, where the ions scatter from each other and usually results in beam
growth. An important difference is that in electron cooling the mass of the ion
is different from and much larger than the mass of the electron. This
difference considerably complicates the intrabeam scattering theory. It
introduces a new term in the emittance growth rate, which vanishes when the
particles are identical and their masses are equal, and can give rise to
emittance cooling of the heavier particles . The term that gives rise to beam
growth for the usual intrabeam scattering is also present but is much smaller
than the cooling term when one particle is much heavier than the other. This
paper derives the results found for the emittance cooling rates due to the
scattering of the ions in the ion bunch by the electons in the electron bunch.
