ROBERT CHEHAB (IPNL/IN2P3/CNRS AND UNIVERSITE LYON 1) ON BEHALF OF ILC_IHEP_IPNL_POSITRON SOURCE GROUP ON BEHALF OF POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC R.Chehab/FCPPL2012/Orsay-Saclay 1

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC THE PROJECT This project is based on a relatively new kind of positron source using the intense radiation emitted by high energy (some GeV) electrons channeled along a crystal axis. Only the photons generated in the crystal are impinging on the amorphous converter. The charged particles coming from the crystal are swept off.  the energy density is lowered in the amorphous. The lateral dimensions of the photon beam is increased between the crystal and the amorphous: that contributes also to lower the energy density. It is then possible to have a Peak Energy Deposition Density (PEDD) lower than the limit of 35 J/g. [defined after SLC target breakdown]  CLIC choice R.Chehab/FCPPL2012/Orsay-Saclay2

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC WORKS MADE IN 2011: The hybrid source has been selected by CERN as the CLIC baseline. Its use for ILC required additional investigations due to the very high pulse intensity in ILC. These efforts have mainly concerned the activities of the PhD student Chenghai XU in LAL-Orsay, this year. So, the main activities on the item have been: * Optimization of the amorphous target to withstand the ILC beam * Optimization of the capture system * Transport of the positrons in the Pre-accelerator linac  The first point has been especially developed in collaboration with CERN (Peter Sievers) R.Chehab/FCPPL2012/Orsay-Saclay3

POSITRON SOURCES FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC OPTIMIZATION OF THE AMORPHOUS TARGET IN THE HYBRID SCHEME: TOWARDS A GRANULAR CONVERTER As already pointed out (see P.Pugnat, P.Sievers) [J.Phys.G.Nucl.Part.Phys.29 (2003) ] a granular converter made of small spheres of ~ mm radius offers the advantages of presenting a relatively high [surface/volume] ratio which is interesting for the power dissipation. The spheres are arranged in staggered rows. A comparison has been carried out between the granular and the compact targets concerning the yield and deposited energy. R.Chehab/FCPPL2012/Orsay-Saclay4

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC COMPARISON BETWEEN GRANULAR AND COMPACT TARGETS R.Chehab/FCPPL2012/Orsay-Saclay5

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC SIMULATIONS WITH THE HYBRID SOURCE CRYSTAL EFFECTS  VMS program. Pair creation  GEANT4 PHOTONS AT ENTRANCE OF GRANULAR TARGET R.Chehab/FCPPL2012/Orsay-Saclay6 (a) x-y distribution (b) marginal y distribution

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC SIMULATIONS:  THE POSITRONS FROM GRANULAR TARGET POSITRONS AT TARGET EXIT Total yield: 12.5 e+/e- R.Chehab/FCPPL2012/Orsay-Saclay7

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC SIMULATIONS: THE DEPOSITED ENERGY The Energy Deposition Density For a 10 GeV e- beam Impinging on a 1 mm Crystal is shown. The maximum (PEDD) reaches 1.8 GeV/cm3/e- at the Converter exit. R.Chehab/FCPPL2012/Orsay-Saclay8

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC THE CASE OF ILC The ILC beam pulse (1300 bunches; e-/bunch) is very intense; putting a target in the beam would be possible if; - we use a multi-target system, the nominal beam being chopped in N parts with N targets - the nominal beam pulse is transformed in many short pulses, to withstand the high power/pulse and a rotating target system allows significant decrease of the average power on one target The latter system is chosen. Before the target, the beam pulse is transformed in several short beam pulses. R.Chehab/FCPPL2012/Orsay-Saclay9

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC ILC BEAM TRANSFORMATION BEFORE THE TARGET The beam pulse is transformed following the scheme proposed by T. Omori. Minitrains of 100 bunches each are produced with a frequency of 300 Hz. There are 13 minitrains in a macropulse. So the charge Per minitrain is about e- and is of e-/macropulse. The macropulse width is of 40 ms allowing 160 ms for the damping in a 5 Hz repetition frequency. R.Chehab/FCPPL2012/Orsay-Saclay10

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC HEAT DISSIPATION IN THE HYBRID SOURCE TARGETS 1- THE CRYSTAL The crystal is receiving heat load and submitted to PEDD: it must be cooled. A solution is, in order to lower the heat load on the crystal, to put 5 crystals on a holder with a transverse displacement; this is matching with the 5 Hz repetition frequency. R.Chehab/FCPPL2012/Orsay-Saclay11

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC THE GRANULAR AMORPHOUS TARGET: A ROTATING WHEEL Characteristics of the wheel: * Diameter: 58 cm * Rim velocity: 3.25 m/s * Rotation: 1.78 Hz or 107 r.p.m. Heat dissipation: * Each sphere is hit every 5 turns(2.8s) * Average power to dissipate: 10 kW * He 1 MPa; v e  10m/s (entrance velocity of He) R.Chehab/FCPPL2012/Orsay-Saclay12

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC * THE PENDULUM # the target: 13 cm for 13 Minitrains (1 cm diameter for each) # the target holder is moving at 3m/s over ± 7.5 degrees # the in-beam duration is 40 ms for the 13 minitrains; The off-beam duration is 160 ms allowing inversion direction of the motion. R.Chehab/FCPPL2012/Orsay-Saclay13

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC PROBLEMS STILL TO SOLVE: * EDDY CURRENTS : simulations and tests would be useful; with the reduced velocity (~3m/s) this problem is alleviated w.r.t. undulator baseline * RADIATION DAMAGES IN THE CRYSTAL: the fluence for which no damage was observed was e-/cm 2 A test of damages with a long irradiation might be considered in order to determine the damage threshold R.Chehab/FCPPL2012/Orsay-Saclay14

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC SUMMARY AND CONCLUSIONS * Considering an hybrid positron source with a high photon yield from channeling radiation in a crystal and granular amorphous converter with interesting properties for power dissipation, it has been possible to describe a possible solution for the ILC. Such unpolarized source requires; - a few GeV (10) incident electron beam - a transformation of the ILC nominal beam structure before the target; the nominal structure is given back after the Damping ring. - cooling systems for the crystal and the amorphous granular target; these systems require moderate rotating velocities. Such solution has been selected for the CLIC project as baseline R.Chehab/FCPPL2012/Orsay-Saclay15

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC THE EXCHANGES FRANCE-CHINA (in our program) * A student from IHEP: Chenghai XU is ending his PhD preparation. He will defend his PhD next May at Beijing in a co-tutelle framework. His PhD research was done during 2 years at LAL with 2 fellowships: : CAS fellowship : EIFFEL fellowship. * Visits to China; Robert Chehab in april 2011 at Jinan and Beijing. R.Chehab/FCPPL2012/Orsay-Saclay16

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC. PUBLICATIONS; * Positron sources using channeling: A promising device for linear colliders X. Artru(1), I. Chaikovska(2), R. Chehab(1)( ∗ ), M. Chevallier(1),O. Dadoun(2), K. Furukawa(3), T. Kamitani(3), T. Omori(3), G. Pei(4),F. Poirier(2), L. Rinolfi(5), M. Satoh(3), V. M. Strakhovenko(6),T. Sugimura(3), T. Suwada(3), T. Takahashi(7), K. Umemori(3), J. Urakawa(3),A. Variola(2), A. Vivoli(5) and C. Xu(2)(4) (1) IPNL/IN2P3/CNRS and Universit´e Lyon Villeurbanne, France (2) LAL/IN2P3/CNRS and Universit´e Paris-Sud Orsay, France (3) KEK - Tsukuba-shi, Ibaraki-ken, , Japan (4) IHEP/CAS - Beijing, China (5) CERN - Geneva, Switzerland (6) BINP Novosibirsk, Russia (7) Hiroshima University - Hiroshima, Japan Published in IL NUOVO CIMENTO C 34 N.4 (July-August 2011) POSIPOL: From polarized and unpolarized photons to positrons R. Chehab( ∗ ) on behalf of POSIPOL Collaboration IPNL/IN2P3/CNRS and Universit´e Lyon 1 - Villeurbanne, France Published in IL NUOVO CIMENTO C 34 N.4 (July-August 2011) R.Chehab/FCPPL2012/Orsay-Saclay17

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC PUBLICATIONS * A positron source using an axially oriented crystal associated to a granular amorphous converter C.Xu (LAL & IHEP), R.Chehab (IPNL0, P.Sievers (CERN), X.Artru (IPNL), M.Chevallier (IPNL), O.Dadoun (LAL). G.Pei(IHEP), V.Strakhovenko (BINP), A.Variola (LAL) Accepted for publication in Chinese Physics C * Participation to workshops and conferences A granular conversion target for the hybrid positron source P.Sievers (CERN), X.Artru, R.Chehab, M.Chevallier (IPNL-Lyon), O.Dadoun, A.Variola (LAL), C.Xu (LAL & IHEP), V.M.Strakhovenko (BINP-Novosibirsk) Proceedings of POSIPOL 2011 workshop in Review of Accelerator science and Technology (Wei Gai Ed.) A granular converter for a positron source using channeling R.Chehab, X.Artru, M.Chevallier (IPNL), O.Dadoun, A.Variola (LAL), C.Xu (LAL and IHEP), P.Sievers (CERN), V.Strakhovenko (BINP-Novosibirsk) LCWS 2011, Granada (Spain), September 2011 Positrons for linear colliders: generation and capture R.Chehab (IPNL-Lyon) on behalf of the ILC_IHEP_IPNL_PositronSource group. Talk at FCPPL11, Jinan (China), April 2011 R.Chehab/FCPPL2012/Orsay-Saclay18

POSITRONS FOR LINEAR COLLIDERS: AN HYBRID SOURCE FOR ILC PERSPECTIVES In the close future, the research activity will focus on: - the optimization of the positron beam transport up to the DR for ILC - the study of radiation damages in the crystal with a possible test to determine the threshold. - an observation of the thermal effects in an hybrid positron source with granular converter (to discuss with KEK colleagues) - some applications of the studies carried out for the linear colliders to BEPCC positron source. R.Chehab/FCPPL2012/Orsay-Saclay19