  We present a cryogenic ion trapping system designed for large scale quantum
simulation of spin models. Our apparatus is based on a segmented-blade ion trap
enclosed in a 4 K cryostat, which enables us to routinely trap over 100
$^{171}$Yb$^+$ ions in a linear configuration for hours due to a low background
gas pressure from differential cryo-pumping. We characterize the cryogenic
vacuum by using trapped ion crystals as a pressure gauge, measuring both
inelastic and elastic collision rates with the molecular background gas. We
demonstrate nearly equidistant ion spacing for chains of up to 44 ions using
anharmonic axial potentials. This reliable production and lifetime enhancement
of large linear ion chains will enable quantum simulation of spin models that
are intractable with classical computer modelling.
