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

2. 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, May 2012, Le L.P.C., Clermond-Ferrand, France

3. 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 photo-production from a long helical undulator to generate positrons.
A crystal-assisted positron source with a hybrid target would be another approach for the ILC, and this new scheme has been adopted as 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, May 2012, Le L.P.C., Clermond-Ferrand, France

4. An atomic undulator for the generation of unpolarized positrons for CLIC and ILC
An hybrid source using an atomic undulator (first proposition for a crystal source, Proceedings of PAC, Chicago, 1989)
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 GeV
R. Chehab, POSIPOL2010, KEK, June2010
Tsuyoshi Suwada/KEKB Linac
FJPPL Workshop 2012, May 2012, Le L.P.C., Clermond-Ferrand, France

5. New hybrid target scheme for positron production
THE HYBRID SCHEME FOR FUTURE LINEAR COLLIDERS
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
[R.Chehab, V.M.Strakhovenko, A.Variola]
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, POSIPOL2010, KEK, June2010
Tsuyoshi Suwada/KEKB Linac
FJPPL Workshop 2012, May 2012, Le L.P.C., Clermond-Ferrand, France

6. 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 GEANT4. The new program will be used for extended
simulations and for the KEKB experiment (data analysis).
O. Dadoun, POSIPOL2010, KEK, June2010
Tsuyoshi Suwada/KEKB Linac
FJPPL Workshop 2012, May 2012, Le L.P.C., Clermond-Ferrand, France

7. Experimental status at KEK
The purpose is the experimental evaluation for the hybrid-target scheme.
Particularly, to estimate the positron-production efficiency,
and to evaluate the heat load on a hybrid target.
The positron-production experiments based on a hybrid target has been continued with 8-GeV e- beam at KEK and the systematic studies were carried out on the positron-production efficiency in 2010.
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-GeV e- beam due to the Tohoku heavy earthquake.
Tsuyoshi Suwada/KEKB Linac
FJPPL Workshop 2012, May 2012, Le L.P.C., Clermond-Ferrand, France

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

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

10. This is the beginning of the earthquake (11 Mar.2011).
Long (~3 minutes) and strong (6 lower in Japanese scale)
earthquake we never experienced!
KEK
Tohoku area
hypocenter
~0.2 s (~5 Hz)
K-Netによる加速度の観測
(防災科学技術研究所提供）
342.9 gal
328.8 gal
Tsukuba
Tsukidate
Tsuyoshi Suwada/KEKB Linac
FJPPL Workshop 2012, May 2012, Le L.P.C., Clermond-Ferrand, France

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

12. Experimental Setup based on the hybrid target scheme
amorphous W
8 mm
18 mm
8GeV e-
Sweeping Magnet
0.96T 0.75m
Analyzing magnet
5 ~ 30MeV
1mm thick
W crystal
Tsuyoshi Suwada/KEKB Linac
FJPPL Workshop 2012, May 2012, Le L.P.C., Clermond-Ferrand, France

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

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

15. Experimental scheme Hybrid scheme Conventional scheme e- 8GeV γ
positrons from
the target
momentum
analyzed
Amorphous W
sweep mag
1mm-thick W Crystal
on axis (aligned to the beam)
off axis (not aligned to the beam)
temperature
at the end of
the targets by
thermocouples
and infrared camera
Amorphous W
e- 8GeV
amorphous Ws 1.75, 3.5, 5.25, 8, 18mm
Tsuyoshi Suwada/KEKB Linac
FJPPL Workshop 2012, May 2012, Le L.P.C., Clermond-Ferrand, France

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

17. Positron yield measurement
Ee- = 8GeV,
Pe+ = 20MeV
e+ detected [a.u]
amorphous W thickness [mm]
Need more simulations for analyzing the magnet collimator , detector
to evaluate e+ yields
Tsuyoshi Suwada/KEKB Linac
FJPPL Workshop 2012, May 2012, Le L.P.C., Clermond-Ferrand, France

18. Temperature Measurement with 8-GeV e- beam
Temperature of the 8mm amorphous W
target for the hybrid case
Beam charge ~1nC/bunch, 25Hz
Preliminary
Temperature (degree Celsius)
ΔT~32 degree
Base temp. 23.3deg.
Time from Beam On (Minutes)
Tsuyoshi Suwada/KEKB Linac
FJPPL Workshop 2012, May 2012, Le L.P.C., Clermond-Ferrand, France

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

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

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

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

23. Summary
The systematic study on positron-production efficiency has been successfully carried out with 8-GeV e- beam at KEK.
Test measurements for the thermocouple array detector have been preliminary conducted to evaluate the pulse-by-pulse temperature rise with 3-GeV 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 in progress, and after the suitable recovery in this September, we will restart our experiments as soon as possible.
Tsuyoshi Suwada/KEKB Linac
FJPPL Workshop 2012, May 2012, Le L.P.C., Clermond-Ferrand, France