CERN Accelerating science

Preprint
Report number	CERN-OPEN-2010-017 ; CLIC-Note-817
Title	The CLIC electron and positron polarized sources
Author(s)	Rinolfi, Louis (CERN) ; Brachmann, Axel (SLAC) ; Bulyak, Eugene (NSC/KIPT) ; Chehab, Robert (IPNL) ; Dadoun, Olivier (LAL) ; Gai, Wei (ANL) ; Gladkikh, Peter (NSC/KIPT) ; Kamitani, Takuya (KEK, Tsukuba) ; Kuriki, Masao (Hiroshima University) ; Liu, Wanming (ANL) ; Maryuama, Takashi (SLAC) ; Omori, Tsunehiko (KEK, Tsukuba) ; Poelker, Matt (JLAB) ; Sheppard, John (SLAC) ; Urakawa, Junji (KEK, Tsukuba) ; Variola, Alessandro (LAL) ; Vivoli, Alessandro (CERN) ; Yakimenko, Vitaly (Brookhaven) ; Zhou, Feng (SLAC) ; Zimmermann, Frank (CERN)
Publication	2010
Imprint	08 Jan 2010
Number of pages	8
Subject category	Accelerators and Storage Rings
Accelerator/Facility, Experiment	CLIC ; CTF3
Abstract	The CLIC polarized electron source is based on a DC gun where the photocathode is illuminated by a laser beam. Each micro-bunch has a charge of 6x109 e−, a width of 100 ps and a repetition rate of 2 GHz. A peak current of 10 A in the micro-bunch is a challenge for the surface charge limit of the photo-cathode. Two options are feasible to generate the 2 GHz e− bunch train: 100 ps micro-bunches can be extracted from the photo-cathode either by a 2 GHz laser system or by generating a macro-bunch using a  200 ns laser pulse and a subsequent RF bunching system to produce the appropriate micro-bunch structure. Recent results obtained by SLAC, for the latter case, are presented. The polarized positron source is based on a positron production scheme in which polarized photons are produced by a laser Compton scattering process. The resulting circularly-polarized gamma photons are sent onto a target, producing pairs of longitudinally polarized electrons and positrons. The Compton backscattering process occurs either in a Compton ring, where a 1 GeV electron beam interacts with circularly-polarized photons in an optical resonator or in a 1.8 GeV Compton Energy Recovery Linac (ERL) or in a 6 GeV Linac with several optical cavities. The undulator scheme is also studied. The nominal CLIC e+ bunch population is 6.7x109 particles per bunch at 200 MeV. The tradeoff between e+ yield and level of polarization is an important topic. The overal l scheme for both polarized electron and positron beams is described.
Other source	Inspire
Submitted by	[email protected]