Development and Test of High Resolution Cavity BPMs for the CLIC Main Beam Linac

The main beam of the Compact LInear Collider (CLIC) requires the beam trajectory to be measured with 50 nm spatial resolution. It also requires a time resolution capable of making position measurements of the head and tail of the 156 ns long CLIC bunch train, for use in dispersion free steering based on an energy chirp applied along the train. For this purpose, a stainless steel 15 GHz cavity BPM prototype has been manufactured, installed at the CLIC Test Facility (CTF3) and tested with beam. An improved design has been fabricated from copper. We discuss results from the two types of the prototype pickups, both from laboratory tests and from beam tests. We also cover the development of the new downconverter electronics.