  Antiprotons in Fermilab's Recycler ring are cooled by a 4.3 MeV, 0.1 - 0.5 A
DC electron beam (as well as by a stochastic cooling system). The unique
combination of the relativistic energy ({\gamma} = 9.49), an Ampere - range DC
beam, and a relatively weak focusing makes the cooling efficiency particularly
sensitive to ion neutralization. A capability to clear ions was recently
implemented by way of interrupting the electron beam for 1-30 \mus with a
repetition rate of up to 40 Hz. The cooling properties of the electron beam
were analyzed with drag rate measurements and showed that accumulated ions
significantly affect the beam optics. For a beam current of 0.3 A, the
longitudinal cooling rate was increased by factor of ~2 when ions were removed.
