1. R.Chehab/FCPPL2010/Lyon1 AN HYBRID POSITRON SOURCE FOR ILC -Collaboration IN2P3-IHEP, with BINP, KEK, Hiroshima-U, CERN- X.Artru, R.Chehab, M.Chevallier (IPNL, France) O.Dadoun, P.Lepercq, F.Poirier, A.Variola (LAL, France) V.M.Strakhovenko (BINP, Russia) T.Kamitani, T.Omori, T.Suwada, J.Urakawa (KEK, Japan) T.Takahashi (Hiroshima) G.Pei, C.Xu (IHEP, Beijing) L.Rinolfi, A.Vivoli (CERN) Presented by R.Chehab

2. R.Chehab/FCPPL2010/Lyon2 AN HYBRID POSITRON SOURCE FOR ILC IN2P3-IHEP-BINP-KEK-Hiroshima-U-CERN INTRODUCTION Since the last FCPPL meeting the main common activity on e+ sources between the groups of the two institutes, with straight collaboration with BINP/Novosibirsk, KEK, Hiroshima University and CERN has been concerning hybrid positron sources using channeling radiation in crystals. Such a scheme has been studied aiming to get an enough e+ yield at the IP with a 6-D emittance matched to the DR injection and above all, a minimum energy deposition and minimum PEDD (Peak Energy Deposition Density). Such scheme being able to lead to the use of a unique target in some cases or simplifying the target system at least in others. We present here, the solutions studied for CLIC (briefly) and ILC.

3. R.Chehab/FCPPL2010/Lyon3 AN HYBRID POSITRON SOURCE FOR ILC AN HYBRID POSITRON SOURCE USING CHANNELING R.Chehab, V.M.Strakhovenko, A.Variola The photons from the crystal are impinging on the amorphous target; the e- and e+ can be swept off or partially sent to the amorphous target. The distance L is taken from 1.5 to 4m. On the presented simulations, L=2 m.

4. R.Chehab/FCPPL2010/Lyon4 AN HYBRID POSITRON SOURCE FOR ILC The hybrid e+ source using channeling High energy e- (some GeV) impinging at glancing angles to the main axes of an oriented crystal radiate a large number of soft photons (some tens of MeV, typically) ; this is much more than with ordinary bremsstrahlung in amorphous targets of the same material and thickness; it works like an atomic undulator Successful experiments at CERN (WA103) and KEK If we separate the photon radiator from the e+ converter and use only the photons (and eventually part of the e+, e-) coming out from the crystal, we may lower considerably the level of PEDD. A practical consequence is the possibility in some cases of using 1- target system, only. Studies on conventional e+ sources at KEK are also carried out to minimize the effects of heating (PEDD,..) => Such hybrid system has been chosen for the CLIC unpolarized e+ source baseline.

5. R.Chehab/FCPPL2010/Lyon5 AN HYBRID POSITRON SOURCE FOR ILC CLIC: ACCEPTED POSITRON YIELD [matching system + longitudinal constraint] * For an incident e- beam with s = 1 mm => h = 1 e+/e- * For an incident e- beam with s = 2.5 mm => h = 0.9 e+/e- PEDD Assuming an incident e- pulse of 2.34 1012 e-, we have : CRYSTAL AMORPHOUS PEDD/e- PEDD/total PEDD/e- PEDD/total (GeV/cm3/e-) J/g (GeV/cm3/e-) J/g s=1mm 2 38 2.5 48.5 s=2.5mm 0.35 6.8 0.8 15.5 An entirely amorphous target, 9 mm thick, with the same incident e- beam would have provided the same accepted yield and a PEDD of 150 J/g (s=1mm) or 40 J/g (s=2.5 mm). This shows the advantages of an hybrid scheme leading to a unique target with a PEDD < 35 J/g using an e- beam with s= 2.5 mm.

6. R.Chehab/FCPPL2010/Lyon6 AN HYBRID POSITRON SOURCE FOR ILC IS SUCH SYSTEM APPLICABLE FOR ILC ? The main problem: very high beam intensity which could destroy the targets. To avoid this difficulty, we may think about a modification of the beam structure before the target to lower the number of particles per pulse which is one of the main parameters for the PEDD. The separation between pulses is determined in order to allow the thermal shock wave to damp. After e+ production capture and acceleration the DR restores the nominal time distribution. Two solutions are considered: - the 300 Hz (T.Omori, KEK) - the 45kHz/5Hz (A.Variola, LAL)

7. R.Chehab/FCPPL2010/Lyon7 AN HYBRID POSITRON SOURCE FOR ILC We present here some simulations concerning the hybrid positron source with results on the yield, emittance, energy distribution, capture,.. Two incident energies will be considered: 8 and 10 GeV. The crystal thickness will be 1mm and the amorphous target thickness will be taken between 6 and 10 mm. The distance between the crystal-radiator and the amorphous-converter will be chosen between 2 and 3 meters to allow enough place for a sweeping magnet. The simulations use the results of Strakhovenko’s code with GEANT4 (O.Dadoun)

8. R.Chehab/FCPPL2010/Lyon8 AN HYBRID POSITRON SOURCE FOR ILC THE PHOTON BEAM Energy spectrum and transverse distribution E-=8 GeV

9. R.Chehab/FCPPL2010/Lyon9 AN HYBRID POSITRON SOURCE FOR ILC THE PHOTON BEAM: Energy spectrum & transverse distribution (E-=10 GeV)

10. R.Chehab/FCPPL2010/Lyon10 AN HYBRID POSITRON SOURCE FOR ILC The positron beam [E- = 10 GeV] Transverse emittance distribution (at target (blue) and at AMD exit (red)

11. R.Chehab/FCPPL2010/Lyon11 AN HYBRID POSITRON SOURCE FOR ILC The positron beam [E-= 10 GeV]. Energy spectrum at the target and at the exit of AMD The AMD acts as a low energy filter Target AMD

12. R.Chehab/FCPPL2010/Lyon12 AN HYBRID POSITRON SOURCE FOR ILC DEPOSITED ENERGY The incident e- beam is at 10 GeV; the total deposited energy in a 8 mm target is ~ 500 MeV/e-; 10000 e- have been simulated

13. R.Chehab/FCPPL2010/Lyon13 AN HYBRID POSITRON SOURCE FOR ILC ENERGY DEPOSITION DENSITY : E- = 10 GeV L(Xtal)= 1 mm; L(amorphous)= 10 mm; L= 2m PEDD  2.7 GeV/cm 3 /e- The rms e- radius is 2.5 mm

14. R.Chehab/FCPPL2010/Lyon14 AN HYBRID POSITRON SOURCE FOR ILC ENERGY DEPOSITION DENSITY : E- = 10 GeV L(Xtal)=1 mm, L(Amorphous)= 8 mm; L= 2 m PEDD  2.11 GeV/cm 3 /e-

15. R.Chehab/FCPPL2010/Lyon15 AN HYBRID POSITRON SOURCE FOR ILC The positron beam: the yield (t am = 8 mm) Target AMD end Accel (150 MeV) E-=8 GeV 11 3.7 2.3 E-=10GeV 13.4 4.7 2.9 The distance between the two targets is 2 meters The solenoid at B=0.5 Tesla extends over the accelerated part The accepted yields present enough margin to realize 1e+/e- at IP.

16. R.Chehab/FCPPL2010/Lyon16 AN HYBRID POSITRON SOURCE FOR ILC ENERGY DEPOSITED, THERMAL GRADIENT PEDD AND SHOCK WAVES After the breaking of the SLC e+ target analyses and tests have been undertaken (LLNL, LANL, SLAC). Particularly, the timescales of the different phenomena were determined. It came out that the stress level due to the temperature gradient was lower than the instantaneous shock (see Vinod Bharawadj). The timescale of the shock wave is of some  s ; so if we spread out the initial ILC pulse in order to have short pulses separated by intervals of microsecond level, a solution can be available. Two schemes will be presented: * the 300 Hz (KEK) * the 45kHz (LAL)

17. R.Chehab/FCPPL2010/Lyon17 AN HYBRID POSITRON SOURCE FOR ILC

18. R.Chehab/FCPPL2010/Lyon18 AN HYBRID POSITRON SOURCE FOR ILC The 45 kHz scheme; micropulse duration: 22.14  s

19. R.Chehab/FCPPL2010/Lyon19 AN HYBRID POSITRON SOURCE FOR ILC SOME PRELIMINARY CONCLUSIONS Two alternative solutions of hybrid targets using channeling radiation in oriented crystals are under consideration for ILC. Due to the large pulse intensity of ILC, a rotating target is to be considered in the 2 cases, as for the undulator case. 1) The hybrid sources present enough margin for the positron yield at IP 2) With respect to the undulator scheme they present the advantage of reduced PEDD with more moderate values of the rotating target velocity. As an example, the 300 Hz solution has a rotating target with 30 less velocity than for the undulator case, whereas the 45 kHz solution has 3 times less velocity 3) Comparing the 2 hybrid schemes, if the rotation velocity is much lower for the 300 Hz scheme, the PEDD and time sharing between pulse duration and relaxing time is better for the 45 kHz. Anyway, an optimization procedure is being carried out in order to reach a very satisfying solution.

20. R.Chehab/FCPPL2010/Lyon20 AN HYBRID POSITRON SOURCE FOR ILC COLLABORATION IN2P3-IHEP FOR e+ SOURCES FOR LC A PhD student ( XU Chenghai) is at LAL since November 2009 with a CAS fellowship. He is spending the 1 st year of his PhD: the subject is concerning the hybrid e+ source. He just obtained an EIFFEL fellowship for 10 months; so, he will spend almost 2 years at LAL. He is in the positron group (6 persons) A post-doc from IHEP ( ZHOU Zusheng) is expected for next september; he will have a stay of 1.5 month and will work in the Accelerator Department of LAL. His subject concerns the e- sources. The wishes is to continue to welcome a post-doc from IHEP for next year and to allow mutual visits between the 2 institutes in order to strengthen the collaboration.