A_RD_6: Study and optimization of the power deposition density in new positron targets Masanori Satoh (Accelerator Laboratory, KEK) On behalf of collaborators: D. Dauvergne, R. Chehab, X. Artru, M. Chevallier, A.Variola, P. Rudnycky, T. Suwada, K. Furukawa, T. Kamitani, K. Umemori, and F. Miyahara 2014 Joint Workshop of the France-Japan (TYL/FJPPL) and France-Korea (FKPPL) Particle Physics Laboratories, France, Bordeaux, May 26-28, 2014.

A_RD_6: Study and optimization of the power deposition density in new positron targets Contents Introduction New Positron Production Target: Granular W Target Development of Granular W targets Objectives Applications to CLIC and ILC Experimental Setup at KEK e-/e+ injector linac Collaborators Summary 2

A_RD_6: Study and optimization of the power deposition density in new positron targets Introduction High-intensity positron sources are required for future linear colliders (CLIC and ILC). Conventional methods using amorphous heavy metals limit to increase the intensity of primary electron beams due to the heat load on the target. In the muon collider and neutrino factories projects, a similar situation is met with powerful proton beams impinging on targets to produce pions decaying into muons and then into neutrinos. New method using the granular target is one of the bright schemes for high-intensity e+ production. 3

A_RD_6: Study and optimization of the power deposition density in new positron targets Introduction (cont’d) Beam energy density per area (GeV*10^12/mm^2) Num. of e- pulses exposed (10^6) Survived target Cracked target

A_RD_6: Study and optimization of the power deposition density in new positron targets Introduction (cont’d) A bunch train is separated into 3 sparse trains by the RF separator. Each trains hit one of the three target - capture section system They are merged by another RF deflector. Need a large space and cost. More simple system is better. From

A_RD_6: Study and optimization of the power deposition density in new positron targets Introduction (cont’d) The activity on positron sources is directed to hybrid sources using a crystal-radiator and an amorphous converter with sweeping off of the charged particles upstream of the converter. Such scheme is the baseline for CLIC positron source. 6 X.Artru et al., “Polarized and unpolarized positron sources for electron-positron colliders”, NIM B 266 (2008)

A_RD_6: Study and optimization of the power deposition density in new positron targets 7 As already pointed out (P. Pugnat, P. Sievers, J. Phys. G. Nucl. Part. Phys. 29 (2003) ). 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. New Positron Production Target: Granular W Target

A_RD_6: Study and optimization of the power deposition density in new positron targets Simulations have been operated with 2 programs: VMS (V. Strakhovenko) and FOT (X. Artru); both were associated to GEANT4. Their results are in good agreement. Compact and granular targets give almost the same total yield as seen on the table resulting from the simulations of C. Xu (PhD). Simulation result (granular and compact target)

A_RD_6: Study and optimization of the power deposition density in new positron targets Development of Granular W targets Tungsten spheres with 2.2 mm diameter have been realized by a French company and delivered to LAL, last year. These balls are made mainly of W (95%) with small amounts of Cu and Ni. The targets are made with staggered layers. The first layer has 10x10 spheres, the next one has 9x9 spheres. Four granular tungsten targets w/ different number of layers have been already manufactured (2, 4, 6, and 8 layers). 9

A_RD_6: Study and optimization of the power deposition density in new positron targets Objectives Obtain the information about PEDD (peak energy deposition density) of granular target by beam test. 10

A_RD_6: Study and optimization of the power deposition density in new positron targets Objectives (cont’d) 11 The expected measurements are concerning the temperature rise in the spheres using thermocouples. In a future stage, use of infrared cameras should give complementary information. The thermocouples w/ diameter of 70  m can will be glued to the spheres (w/ Ag paste). The distribution of the thermocouples (> 5, if possible) can provide view of the temperature distribution in the transverse plane of the exit surface. Thermocouples

A_RD_6: Study and optimization of the power deposition density in new positron targets Expected power and temperature rise 12 Electron beam: 7 GeV, 1 nC/bunch, 50 Hz Incident photon beam transverse profile is foreseen with a Demarquest screen. (expected: 1 mm FWHM). /bunch Hybrid-granular positron source: granular w/ 6-layers is assumed.

A_RD_6: Study and optimization of the power deposition density in new positron targets Expected power and temperature rise (cont’d) Only the 6 layers case is presented; for the KEK test, also 2, 4, and 8 layers will be tested. A beam time duration of 1 s will lead to a temperature rise of 30  K in the 6-layeres converter. Thus, the beam will be stopped after 1 s allowing the converter to cool down before sending another burst (50 bunches) during 1 s. The application for ILC should consider cooling and rotation; solutions with rotating wheel or pendulum were already described. The data corresponding to the Hybrid-Granular solution could be compared with the Truly Conventional one. 13

A_RD_6: Study and optimization of the power deposition density in new positron targets Applications to CLIC and ILC 14 CLICILC Incident beam energy 5 GeV10 GeV W crystal thickness 1.4 mm1 mm W amorphous target thickness 10 mm8 mm Beam power deposition crystal/amorphous 0.2/7.5 kW0.17/10 kW PEDD crystal/amorphous 7/15 J/g5.8/30 (*) J/g (*) per mini-train of 100 bunches.

A_RD_6: Study and optimization of the power deposition density in new positron targets Experimental setup --- KEK e-/e+ Injector Linac Under upgrade for SuperKEKB project –High intensity bunch charge and low emittance beam –Maximum beam energy: 7 GeV Beam repetition: up to 50 Hz (variable) Bunch charge: 5 nC (up to double bunches w/ interval of 96 ns)

A_RD_6: Study and optimization of the power deposition density in new positron targets Bunch charge history (new rf gun) 0.58 nC 5.6 nC

A_RD_6: Study and optimization of the power deposition density in new positron targets Experimental setup (cont’d) Beam test will be carried out at KEK injector linac 3 rd SY. Crystalline target is mounted on the 2-axis goniometer. Analyzing magnet, collimators, and detector are in a vacuum (10^-3 Torr). Geometrical acceptance of the detector is 0.22 msr. 17 Sweeping magnet Analyzing magnet, collimator, and detector Crystalline W target Granular W target e- to PF to SKB e-/e+, PF- AR

A_RD_6: Study and optimization of the power deposition density in new positron targets Members Members French GroupJapanese Group NameTitleLab./Organis.NameTitleLab/Organis. Leader: D. DauvergneProf. IPNL Leader: M. SatohAssoc. Prof. KEK R. ChehabDr.IPNL T. SuwadaAssoc. Prof. KEK X. ArtruProf.IPNL K. Furukawa Prof.KEK M. ChevallierProf.IPNL T. KamitaniProf.KEK A.Variola Dr. LAL K. UmemoriAssoc. Prof. KEK P. RudnyckyTech.LAL F. MiyaharaAssist. Prof. KEK I.ChaikovskaDr.LAL 18 Collaboration of P. Sievers from CERN and S. Jin from IHEP-Beijing.

A_RD_6: Study and optimization of the power deposition density in new positron targets Funding Requests 19

A_RD_6: Study and optimization of the power deposition density in new positron targets Summary Status: –Measure temperature rise of new granular W target. –Beam test will be conducted at test beam line in KEK e-/e+ injector linac. –New granular W targets of 2, 4, 6 and 8 layers have been manufactured at LAL and delivered at KEK. –Experimental beam line, goniometer, detector, and so on are ready. In preparation: –Simulation study by GEANT4 and ANSYS. –e- beam (7 GeV, 1 nC, 50 Hz) is now under development by new rf gun. –Gluing thermocouple to granular target (9 points or at least 5 in each) is now under preparation. 20