Pulse Forming Network Conceptual Design for the Proposed PS Multi-Turn Extraction System

A five-turn continuous extraction system is currently used to transfer the proton beam from the CERN Proton Synchrotron (PS) to the Super Proton Synchrotron (SPS). The present approach, which is based on cutting the filament beam into 5 slices using an electrostatic septum, causes inherent losses of about 15% of the extracted beam and non optimal betatronic matching for the different slices in the receiving machine. This will be an even more serious drawback when the beam intensity needs to be increased for the CERN Neutrinos to Gran Sasso (CNGS) facility. To overcome this, a novel multi-turn extraction (MTE) scheme has been proposed, where the beam is separated, prior to extraction, into a central beam core and four islands by means of elements such as sextupoles and octupoles. Each beamlet is ejected using fast kickers and a magnetic septum. For the MTE kickers, two new pulse generators are required, each containing a lumped element Pulse Forming Network (PFN) of 12.5 Omega, 80 kV and 10.5 mus. For cost reasons, it is envisaged to re-use existing 15 Omega transmission line kicker magnets. The PFN characteristic impedance deliberately mismatches that of the magnets to allow a higher maximum available kick. The PFN design has been optimized such that undesirable side-effects of the impedance mismatch, on kick rise-time and flat-top, remain within acceptable limits. The conceptual design for the MTE PFN is presented.