  The galactic cluster Westerlund 1 contains a rich population of evolved,
massive stars, and a high binary fraction has been inferred from previous
multiwavelength observations. We use multi-epoch spectroscopy of a large sample
of early-type stars to identify new binaries and binary candidates in the
cluster. VLT/FLAMES was used to obtain spectra of ~100 OB stars over a 14-month
baseline in 2008 and 2009, supplemented with follow-up observations in 2011 and
2013, and we identify 20 new OB I--III binaries, a WN9h binary, and a WC9d
binary, greatly increasing the number of directly confirmed binary systems in
Westerlund 1, while 12 O9--9.5 Iab--III stars are identified as candidate
binaries. The 173.9 day SB1 W1030 represents the first longer-period system
identified in the cluster, while the determination of a 53.95 day period for
W44/L makes it the first Wolf-Rayet binary in Westerlund 1 with a confirmed
orbital period greater than ten days. Our results suggest the binary fraction
in the OB population is at least 40%, and may be significantly higher.
(Abridged)
