ILC POSITRON SOURCE - IHEP-IN2P3 COLLABORATION-

1. ILC POSITRON SOURCE- IHEP-IN2P3 COLLABORATION- G.PEI, J.GAO, X.Li, Z.ZHOU (IHEP/Beijing/China) X.ARTRU, R.CHEHAB, M.CHEVALLIER (IPNL/IN2P3/Lyon/France), V.M.STRAKHOVENKO (Visitor from BINP at IPNL) A.VARIOLA, A.VIVOLI, F.ZOMER (LAL/IN2P3/Orsay/France) presented by R.Chehab R.Chehab/FCPPL Workshop, January 2008, Marseille

2. ILC POSITRON SOURCE- IHEP-IN2P3 COLLABORATION- • INTRODUCTION • The positron source is one of the crucial elements of the ILC. There is a strong interest on polarized positrons and, among the different possibilities, we have chosen to study the so-called Compton Source using the collision of a circularly polarized laser with an electron beam in the GeV energy range. For unpolarized positrons the recent promising results, at CERN and KEK, on crystal positron sources, using the strong enhancement in photon production in aligned crystals due to channeling, made us study this kind of source as the starting solution for which the Compton source is taken as an upgrade. For the two kinds of sources, the capture, acceleration and emittance preservation are considered. R.Chehab/FCPPL Workshop, January 2008, Marseille

3. ILC POSITRON SOURCE- IHEP-IN2P3 COLLABORATION- • PLAN • *The Compton Source • * Capture and Transport of the positrons • * Emittance (Longitudinal & Transverse) preservation • * The crystal positron source • * Collaboration status and perspectives R.Chehab/FCPPL Workshop, January 2008, Marseille

4. Compton cavities ILC POSITRON SOURCE-IHEP-IN2P3 COLLABORATION • THE “COMPTON” SOURCE • The lay-out is represented: an Energy Recovery Linac (ERL) provides the energetic e- (1 to 2 GeV) colliding with circularly polarized photons from Nd:Yag laser. Capture is made with AMD (Adiabatic Matching Device) and pre-acceleration (150 MeV) with warm L-Band sections. The main e+ linac is a superconducting L-Band R.Chehab/FCPPL Workshop, January 2008, Marseille

5. ILC POSITRON SOURCE- IHEP-IN2P3 COLLABORATION • PHOTONS AND POSITRONS (“Compton “source ) • Simulations made with CAIN (Compton process) and EGS4 (pair production) provide 6-D emittances and polarization. Positrons:Polarization/Energy Photons:Polarization/Energy R.Chehab/FCPPL Workshop, January 2008, Marseille

6. ILC POSITRON SOURCE- IHEP-IN2P3 COLLABORATION • CAPTURE AND PRE-ACCELERATION (“Compton”source) • An AMD is put after a W target (~0.4Xo) with a magnetic field tapering from 6 to 0.5 Tesla on 50 cm. Adiabatic transformation of the phase space is represented below: pT pT aperture aperture The e+ transverse momentum is reduced to 3 MeV/c and Transverse size expanded to accelerator aperture ~20 mm. Simulations made with PARMELA confirmed that R.Chehab/FCPPL Workshop, January 2008, Marseille

7. ILC POSITRON SOURCE- IHEP-IN2P3 COLLABORATION • EMITTANCE PRESERVATION ( “Compton” Source) • The geometrical transverse emittance is reduced with acceleration. The longitudinal emittance must be reduced before injection in the Damping Ring which has limited acceptance. Bunch lengthening after the target is the main contribution (spiralization in magnetic fields, differences in velocities); a bunch compression mustbe provided. A magnetic chicane provided the compression shown (simulations with PARMELA) : R.Chehab/FCPPL Workshop, January 2008, Marseille

8. ILC POSITRON SOURCE- IHEP-IN2P3 COLLABORATION • CRYSTAL POSITRON SOURCE • Enhancement of photon production by channeled electrons in crystals provides a powerful source of photons, which materialized, give an intense e+ source. Pair production may occur in the same crystal or, preferably, in amorphous converters put after. Such solution is represented below (a distance of 2 meters is chosen corresponding to precise simulations): this set of 2 targets substitutes the Compton cavities in the lay-out. R.Chehab/FCPPL Workshop, January 2008, Marseille

9. ILC POSITRON SOURCE- IHEP-IN2P3 COLLABORATION • ADVANTAGES OF A CRYSTAL SOURCE • YIELD: the yield obtained with 8 mm thick W crystals (or 4 Xtal+4 Am.) fit with ILC requirements (cf CERN experiment) • DEPOSITED POWER: due to faster development of the showers in crystals w.r.t. amorphous, there is less deposited power in equivalent targets (giving same total yield) => see X.Artru et al: PRST-AB 6 (2003) 091003 • PEDD: the Peak Energy Deposited Density, responsible of important thermal gradients leading to target destruction (see SLC target) can be advantageously handled in an hybrid scheme (see figure). As a consequence, the number of targets can be drastically reduced. • RADIATION RESISTANCE: a test made at SLAC with a W crystal showed no damages up to a fluence of 2.1018e-/mm2 • RELIABILITY: a W crystal 10.5 mm thick is installed since july 2006 on KEKB linac and serves as the positron source without diminution in the yield. R.Chehab/FCPPL Workshop, January 2008, Marseille

10. ILC POSITRON SOURCE- IHEP-IN2P3 COLLABORATION • COLLABORATION STATUS • 1)The works made separately concerned: • # Generation of polarized positrons in thin amorphous targets by polarized g-rays. {use of CAIN +EGS4 (and GEANT4) by LAL-IPNL and GEANT4 by IHEP) • # Capture and transport of the positrons (PARMELA by LAL) • # Generation of positrons due to intense g production in crystals with channeling • 2) Visits to IHEP by 2 french collaborators during CCAST ILC in Nov. 2007; discussions prepared the incoming programme R.Chehab/FCPPL Workshop, January 2008, Marseille

11. ILC POSITRON SOURCE- IHEP-IN2P3 COLLABORATION • PERSPECTIVES • # Collaborations with crossed simulations made on the generation of polarized positrons • # Optimization of the capture and transport parameters for the emitted positrons; work sharing is considered concerning the longitudinal and transverse phase spaces. • # Welcome of a PhD student from IHEP in LAL/IPNL; the student would be situated in Orsay with frequent visits to IPN-Lyon. A co-direction for the thesis is wished. R.Chehab/FCPPL Workshop, January 2008, Marseille