Electron Cooling Experiments at Fermilab

A 115 MeV proton beam has been successfully cooled in the Electron Cooling Ring at Fermilab. Initial experiments have measured the longitudinal drag force, transverse damping rate, and equilibrium beam size. The proton beam was cooled by a factor of ~50 in momentum spread in 5 sec, and by a factor of 3 in transverse size in 15 sec. Long term losses were consistent with single scattering from residual gas, with lifetime ~1000 sec. Using the measured electron beam temperature Te= 0.8(2) eV, the observed cooling agrees well with expectations from cooling theory.