  Arcus is a concept for a probe class mission to deliver high-resolution FUV
and X-ray spectroscopy. For X-rays, it combines cost-effective silicon pore
optics (SPO) with high-throughput critical-angle transmission (CAT) gratings to
achieve $R> 3000$ in a bandpass from 12-50 Angstroem. We show in detail how the
X-ray and the UV spectrographs (XRS and UVS) on Arcus will be aligned to each
other. For XRS we present ray-tracing studies to derive performance
characteristics such as the spectral resolving power and effective area, study
the effect of misalignments on the performance, and conclude that most
tolerances can be achieved with mechanical means alone. We also present an
estimate of the expected on-orbit background.
