R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.CHEHAB (IPNL) On behalf of I.Chaikovska (LAL), H.Guler (LAL), P.Bambade (LAL), O.Bianco (LAL), F.Plassard (LAL), X.Artru (IPNL), M.Chevallier (IPNL), J.Gao (IHEP), G.Pei (IHEP), S.Jin (IHEP), X.Li (IHEP), W.Dou(IHEP), W.Yiwei (IHEP), B.Sha (IHEP), Z.Zhou (IHEP) With collaborations from KEK and CERN R.Chehab/FCPPL/Hefei1

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS OUTLOOK * Investigations on a hybrid positron source with a granular converter * Studies on ILC final focus optics * Beam halo formation mechanisms: analysis and measurement methods * Collaboration between IN2P3 labs (LAL & IPNL) and IHEP R.Chehab/FCPPL/Hefei2

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS INTRODUCTION Investigations on positron and electron beams for future linear and circular colliders are going on at IHEP, LAL and IPNL in collaboration with other laboratories (KEK and CERN) Such investigations, based on FCPPL framework, are directed on positron sources optimization, beam halo and final focus optics. The presentation will hold on: * Positron sources using channeling radiation in oriented crystals * Special optics for the final focus * Beam halo R.Chehab/FCPPL/Hefei3

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS 1- POSITRON SOURCES USING CHANNELING The optimization of the positron source led to the choice of a hybrid scheme using an axially oriented W crystal to create an intense photon beam and an amorphous granular converter to generate the e+e- pairs. Between the two targets, a sweeping magnet is taking off the charged particles, whereas the photons, only, impinge on the converter. The converter is granular, i.e. made of small W spheres (mm size). R.Chehab/FCPPL/Hefei4

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS 1-1 TYPICAL FEATURES OF THE HYBRID SOURCE A- The sweeping magnet between the two targets taking off the charged [articles (e+, e-), only the photons are impinging on the converter. That alleviates the amount of power deposited in the converter. B- The granular converter is made of small spheres (mm diameter size) and that improves the heat dissipation (proportional to the ratio Surface/Volume of the spheres). The spheres are arranged in staggered layers with even numbers of spheres at the entrance and odd number of spheres at the exit of the converter. R.Chehab/FCPPL/Hefei5

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS 1-2 SIMULATIONS (H.Guler) The simulations have been carried out under the following hypotheses: * Incident energy (on the crystal); E= 10, 8 and 5 GeV. * W Crystal orientation: * Crystal thickness; 1 and 1.4 mm * Distance Crystal-Converter: 2 and 3 meters * Spheres radius: from 0.1 to 1.1 mm OUTPUTS: * Yield e+/e- * Deposited energy (MeV/e-) * Energy deposition density (GeV/cm3/e- R.Chehab/FCPPL/Hefei6

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS 1-3 POSITRON YIELD One important characteristics of the positron sources using channeling radiation is the soft energy of the emitted photons and, henceforth, the soft energy of the created positrons. That is interesting for the positron capture which is easier for soft positrons. Example: CLIC R.Chehab/FCPPL/Hefei7

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.Chehab/FCPPL/Hefei8 An example is given for the case of KEK beam test with E-= 8 GeV; for a 6-layer converter which represents the wished option for ILC, the deposited energy is about 300 MeV/e-. In the case of an incident energy of 10 GeV, the deposited energy increases up to 400 MeV/e Two incident electron beam rms radii are considered: 1 mm ( KEK, in red ) and 2.5 mm ( ILC & CLIC in blue) )

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.Chehab/FCPPL/Hefei9 The heat load in the converter may give rise to mechanical stresses, leading to the breaking of the converter as observed for the SLC target. It is important, henceforth, to get the energy deposition density in the converter and to know its maximum value (PEDD)

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS 1-5 TABLE OF YIELD, DEPOSITED ENERGIES AND PEDD FOR CLIC, ILC AND KEK-TEST Project Total Yield Incident Energy layers number Dep. Energy PEDD * N+/N- GeV MeV/e- GeV/cm3/e- ILC ILC KEK KEK CLIC CLIC * The PEDD is calculated in central spheres of 1.1 mm radius at the converter exit Publication: X.Artru et al. Investigations on a hybrid positron source with a granular converter: to be published this year in NIMB R.Chehab/FCPPL/Hefei10

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.Chehab/FCPPL/Hefei11 TEST ON THE KEK BEAM 4 granular converters have been built at LAL-Orsay in order to be tested at KEK in a hybrid mode configuration (A thin crystal provides the channeling radiation and the photons are converted in e+e- pairs in the granular converter).

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.Chehab/FCPPL/Hefei12

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.Chehab/FCPPL/Hefei13 Thermocouples MEASUREMENTS AT KEK: YIELD and Temperature rise Thermocouples with small area have been glued on some spheres of the exit face of the converter. As they are distributed laterally, in X and Y axes, they will provide the lateral distribution of the temperatures, from which calculations will give the deposited energies. Energy deposition density for E-=8 GeV Thermocouples on the exit face of the converter

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS 2- FINAL FOCUS OPTICS In order to prevent the beam size dilution by the final doublet, due to the chromaticity, it is important to bring chromaticity corrections through local sextupoles attached to the final doublets. A dispersion is created upstream through a bending magnet. The principle of the adopted optics is: - to widen the horizontal beam size  x and reduce the vertical size  y - to keep the product  y.  x almost unchanged to preserve the luminosity - to limit the beamsstrahlung losses (increasing  x ) As the decrease of  y may increase the hour glass effect, it would be interesting to decrease bunch length to mitigate this effect. Moreover, an interesting way is also to use flatter beams. The results of the computations made on this basis are given on the following slide. Ref: D.Wang et al Study of alternative ILC final focus optical configurations : NIMA 781 (2015)14-19 R.Chehab/FCPPL/Hefei14

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.Chehab/FCPPL/Hefei15 ILC FINAL FOCUS OPTICS

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS 3-BEAM HALO ON ATF: Calculations and Measurements  The beam halo which has a large lateral extension provokes background and should be controlled  3 sources for beam halo: - Beam-gas-scattering  elastic scattering on the residual gas atoms - Beam-gas bremsstrahlung  the e- are deflected by the electric field of the atomic nucleus  photon emission - Intra beam scattering (IBS)  Multiple small-angle Coulomb collisions between particles in the beam. Analytical calculations and simulations (CMAD) are used. CMAD allows ATF equilibrium emittances to be computed in presence of IBS. Publication: D.Wang et al. Analytical estimation of ATF beam halo distribution : Chinese Physics C Vol.38 No 12 (2014) R.Chehab/FCPPL/Hefei16

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.Chehab/FCPPL/Hefei17 Beam Halo: beam-gas scattering : calculations Similar expressions are obtained for the vertical distribution (y). The important parameters are: Θ= θ min /  ’ 0 ( where θ min is depending on  and Z and  ’ 0 is angular beam size) and N , collision probability of e- with gas during one damping time X in units of 

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.Chehab/FCPPL/Hefei Measurements on ATF extraction line (WS) Beam-gas bremsstrahlung: calculations and Measurements rms values Measurements were operated using Wire Scanners: Ion pumps (IP) were on and off

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.Chehab/FCPPL/Hefei19 IBS: Calculations have been operated to determine the IBS induced beam distributions for the vertical and longitudinal distributions (D.Wang et al. Chinese Physics C 38 No12(2014) ) Comparisons between the 3 sources of beam halo shows the predominance of beam-gas scattering on vertical beam distributions whereas the longitudinal distributions are more sensitive to beam-gas bremsstrahlung.

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.Chehab/FCPPL/Hefei20 IBS: Simulation with CMAD (contribution from Theo Demma) and Measurements Measurements on ATF (SR & Laser wire) and on extraction line (WS)

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS R.Chehab/FCPPL/Hefei21 IBS: Simulation with CMAD ( contribution from Theo Demma) and Measurements Measurements on ATF ring (b) and extraction line (a) (a) (b)

R&D ON POSITRON AND ELECTRON BEAMS FOR FUTURE COLLIDERS SUMMARY & CONCLUSIONS * R&D on positron sources The simulations on a hybrid positron source using channeling radiation and a granular converter brought promising expectations for this option for future linear colliders as ILC or CLIC. Moreover, an experiment is foreseen at KEK next summer, at closest time and will bring informations on the energy deposition from which stresses in the converter may be inferred. These studies are associating IHEP, LAL and IPNL and also KEK and a CERN physicist expert on targets (P.Sievers). Colleagues from IHEP are directly involved in the studies associated to the reliability of the targets. Exchanges between french and chinese laboratories will be very useful to develop these studies. * R&D on beam dynamics * Continuation of the collaboration on the final focus system for ILC and CLIC - Check the possibility of bunch compression to make shorter bunches for ILC - Propose/study new optics with flat bunches within the official ILC-TDR optics (for different energies) - keep abreast of current study on ATF2, the ultra-low β y optics, using very flat beam (10 times β x, half or even quarter β y ) which is quite similar to our ILC proposal and may be, an experimental verification of it. * Continuation of the collaboration on ATF halo study - connect the calculation results with the simulations (include our halo model analytically in CMAD) - compare with experimental measurements in the ATF extraction line using either OTR or YAG screens (Naito) * Halo propagation, collimation and measurement along ATF2 so far pursued by LAL and IFIC; also IHEP group may be involved. R.Chehab/FCPPL/Hefei22