Research on a new crystalassisted positron source for

Research on a new crystal-assisted positron source for the ILC A_R&D_06 proposal T. Suwada (tsuyoshi. suwada@kek. jp) Accelerator Laboratory, KEK Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 1

Collaboration Japanese Group K. Furukawa, T. Kamitani, T. Omori, M. Satoh, T. Suwada, J. Urakawa, Accelerator Laboratory, KEK K. Umemori, IMSS, KEK T. Takahashi, S. Kawada, Y. Uesugi, Hiroshima University French Group A. Variola, O. Dadoun, F. Poirier, I. Chaikovska, LAL-Orsay R. Chehab, X. Artru, M. Chevallier, IPNL-Lyon with collaboration of V. Strakhovenko , BINP-Novosibirsk Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 2

Introduction • It is a challenge task to construct a dedicated and also robust positron source towards the next generation of e+e- linear colliders. • The present RDR-based ILC e+ (positron) source uses photoproduction from a long helical undulator to generate positrons. • A crystal-assisted positron source would be another approach to ILC. Successful tests on a positron source using channeling radiation in crystals were performed at CERN (WA 103) and KEK. An hybrid scheme based on the separation between the crystal-radiator and the amorphous converter has been adopted for the CLIC positron source. • We propose that the feasibility studies based on this new scheme need to be conducted under powerful collaboration between France and Japan. Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 3

An atomic undulator for the generation of unpolarized positrons for CLIC and ILC l An hybrid source using an atomic undulator (first proposition for a crystal source, Proceedings of PAC, Chicago, 1989) l R. Chehab, A. Artru, F. Couchot, A. R. Nyaiesh, F. Richard Simulations of a hybrid source made of Ge or Si crystals as radiators and amorphous W as converters: For Ge and Si crystals oriented on <110> axis and 1 cm thick, we had e+ accepted yields of 0. 5 to 0. 6 e+/e- for 0. 5 Xo thick converter and 1. 2 to 1. 3 e+/e- for 1 Xo thick; the incident e- energy is 20 Ge. V R. Chehab, POSIPOL 2010, KEK, June 2010 Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 4

New hybrid target scheme for positron production l THE HYBRID SCHEME FOR FUTURE LINEAR COLLIDERS l Assuming thin crystal target and, hence, moderate heating in it and in order to lower the amount of energy deposited in the amorphous target and also the PEDD, the following scheme has been proposed by l [R. Chehab, V. M. Strakhovenko, A. Variola] l This new scheme is the basis of the present common research between France and Japan. Magnet Putting a drift between the 2 targets allows sweeping off the charged particles coming from the crystal; only the ϒ impinge on the amorphous target R. Chehab, POSIPOL 2010, KEK, June 2010 Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 5

Development of simulation code at LAL-Orsay + X. Artru simulation The present work is consisting in the combination of X. Artru’s program on channeling with GEANT 4. The new program will be used for extended simulations and for the KEKB experiment (data analysis). O. Dadoun, POSIPOL 2010, KEK, June 2010 Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 6

Experimental status at KEK l The purpose is the experimental evaluation for the hybridtarget scheme. – Particularly, to estimate the positron-production efficiency, – and to evaluate the heat load on a hybrid target. l The positron-production experiments based on a hybrid target has been continued with 8 -Ge. V e- beam at KEK and the systematic studies were carried out on the positron-production efficiency in 2010. l The experiments on the heat load with a hybrid target has been continued from 2011, and however, they have been carried out as only a test experiment with 3 -Ge. V e- beam due to the Tohoku heavy earthquake. Tsuyoshi Suwada/KEKB Linac. FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 7

Experimental site at KEKB LINAC Switchyard KEKB Linac 8 -Ge. V　e- beam 1 nc/bunch upto 25 Hz single bunch Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 8

Site Set up at the KEK Linac Looking up from Down stream Max. Ee-=8 Ge. V Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 9

This is the beginning of the earthquake (11 Mar. 2011). Long (~3 minutes) and strong (6 lower in Japanese scale) earthquake we never experienced! ~0. 2 s (~5 Hz) Tohoku area KEK hypocenter Tsukuba 328. 8 gal 342. 9 gal Tsukidate K-Netによる加速度の観測 (防災科学技術研究所提供） Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 10

Drop-down of a quadrupole triplet and the recovery work is in progress! Beamline Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 11

Experimental Setup based on the hybrid target scheme 8 Ge. V e- Sweeping Magnet 1 mm thick 0. 96 T 0. 75 m W crystal Tsuyoshi Suwada/KEKB Linac amorphous W 8 mm 18 mm Analyzing magnet 5 ~ 30 Me. V FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond. Ferrand, France 12

pictures Sweeping magnet e- 8 Ge V W Crystal on the goniometer Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 13

pictures amorphous thermocoupoles attached back end targets movable stage Tsuyoshi Suwada/KEKB Linac Amorphous Ws mounted on a linear stage FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 14

Experimental scheme l Hybrid scheme e- 8 Ge. V sweep mag γ Amorphous W 1 mm-thick W Crystal on axis (aligned to the beam) off axis (not aligned to the beam) l Conventional scheme Amorphous W e- 8 Ge. V amorphous Ws 1. 75, 3. 5, 5. 25, 8, 18 mm Tsuyoshi Suwada/KEKB Linac positrons from the target momentum analyzed temperature at the end of the targets by thermocouples and infrared camera FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 15

Rocking curve measurement Amorphous W 8 -GV e- sweep magnet positron yield (arb. unit) 8 mm rotation in ver. plain Fitting function for the rocking curve y r a n i m i l re Crystal W on a goniometer factor 3 enhancement [mrad] P angle of crystal　axis<111> w. r. t. beam (mrad) Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 16

Positron yield measurement Ee- = 8 Ge. V, Pe+ = 20 Me. V e+ detected [a. u] 15 Conventional Hybrid ON axis 10 Hybrid OFF axis 5 0 0 5 10 15 amorphous W thickness [mm] Need more simulations for analyzing the magnet collimator , detector to evaluate e+ yields Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 17

Temperature (degree Celsius) Temperature Measurement with 8 -Ge. V ebeam Temperature of the 8 mm amorphous W target for the hybrid case Beam charge ~1 n. C/bunch, 25 Hz y r a e r P n i il m ΔT~32 degree Base temp. 23. 3 deg. Time from Beam On (Minutes) Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France

T at equilibrium (deg. ) (measured) Temp. rise vs. total energy deposit Temperature at equilibrium has information for total energy deposit except for 18 mm hybrid conventional hybrid　on axis hybrid off axis 18 mm target thickness is larger than shower maximum 8 mm (simulation)

Development of a thermocouple array to measure temperature rise of the target Thermocouple array fixed at the back plane of amorphous target Thermocouple 1 mm x 1 mm to fast data logger read temperature each 10 ms temperature at equilibrium total energy deposit bunch by bunch temperature variation 9 thermocouples are fixed on the target with use of silver paste PEDD information by thermocouple Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 20

Test results on pulse-by-pulse Temp. rise measurement (3 -Ge. V e- beam) (1) The pulse-by-pulse temp. measurement has been successfully performed at the rep. rate of 1 Hz. (2) A clear signal was obtained 1秒 from each thermocouple. 3 -Ge. V e- single-bunch beam is directly hitting at the center of target. 2 mm 1℃ 1 mm 1 s Clear temp. signal trace with a data logger has been obtained in a test measurement. FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, Tsuyoshi Suwada/KEKB Linac France 21

AN HYBRID TARGET TEST WITH GRANULAR CONVERTER l POSIBLE DEVELOPMENTS ON THE HYBRID SOURCE l In order to lower the heat load on the amorphous converter a particular shape for the amorphous converter was chosen. A granular converter made of small spheres (Φ= 2 mm) has been investigated following the works of P. Sievers et al. on a target dedicated to a neutrino factory. The application for a positron source has been developed in the Ph. D thesis of Chenghai XU from IHEP/Beijing , at LAL-Orsay. In such a scheme, the heat dissipation is improved. Different models have been studied and their merits concerning the e+ yield, the energy deposition and the PEDD (Peak Energy Density Distribution) , compared. As an example, for a granular converter made of 864 spheres of 2 mm diameter we get a total yield of 12. 5 e+/e-, an energy deposition of 446 me. V/e- and a PEDD less than 2 Ge. V/cm 3/e-, somewhat better in terms of energy deposition than a compact converter giving the same yield. Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 22

An Hybrid target test with a granular converter l l l l PRESENTATION OF THE GRANULAR CONVERTER The granular converter made of staggered rows has been considered and its main features described (cf. article in Chinese Physics C) The best way of cooling being use of a He gas jet which removes the heat passing Between the spheres. To fulfill the requirements of ILC yield, 3 staggered rows (6 layers) of W spheres (Φ=2 mm) have been chosen (864 spheres). Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 23

AN HYBRID SOURCE TEST WITH A GRANULAR CONVERTER A granular converter might be thermally controlled with thermocouples and infrared cameras (see slides 20 &21). A comparison with a compact converter giving the same yield can, then, be operated. In a first step, the granular converter as the compact one will not be cooled during the test. thermocouples Two firms have been contacted and are able to produce W spheres; 2 mm diameter will be considered. This test will be done in collaboration with IHEP/Beijing and CERN Tsuyoshi Suwada/KEKB Linac photons FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 24

Funding requests in 2012 From French group Euro/unit Nb of units Total (Euro) Ph. D Student stay in France 1000/month 3 months 3000 Visit to Japan (2 visits) 150/day 10 days 3000 Travels (2) 1000 2 travels 2000 Total 8000 From Japan group k. Yen/unit Nb of units Total (k. Yen) Travel (3 persons) 750 1 travels 750 Visit to France(3 persons) 60/day 10 days 600 Total Tsuyoshi Suwada/KEKB Linac 1350 FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 25

Summary • The systematic study on positron-production efficiency is in progress with 8 -Ge. V e- beam at KEK. • Test measurements with thermocouple array detector have been preliminary conducted to evaluate pulse-by-pulse temperature rise with 3 -Ge. V e- beam. • The systematic simulations to estimate the detector acceptance are in progress with a new simulation code taking into account crystal effect. • Due to unfortunate heavy earthquake, the recovery work of the KEKB linac is vigorously in progress. • The perspective of testing an hybrid e+ source with a granular converter can open promising solutions for ILC. Tsuyoshi Suwada/KEKB Linac FJPPL Workshop 2012, 28 -29 May 2012, Le L. P. C. , Clermond-Ferrand, France 26