Positron-production experiment using
Diamond and Si crystals in the KEKB
8-GeV injector linac

T.Suwada (tsuyoshi.suwada@kek.jp)
Accelerator Laboratory, KEKCollaboration
S.Anami, A.Enomoto, K.Furukawa, K.Kakihara,
T.Kamitani,Y.Ogawa, S.Ohsawa, T.Oogoe, M.Satoh,T.Sugimura, T.Suwada and K.Yoshida
Accelerator Laboratory, KEK
H.Okuno,Institute of Particle and Nuclear Studies, KEK
K.Umemori,Institute of Materials Structure Science, KEK
R.Hamatsu, J.Hara
Physics Department, Tokyo Metropolitan University
V.Ababiy, A.P.Potylitsin, I.E.Vnukov,NPI, Tomsk Polytechnic University
R.Chehab,LAL, IN2P3-CNRS, Universite de Paris-Sud
KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Motivationz High-intensity positron sources are required
for future linear colliders and B-factories.
z Conventional methods using amorphousheavy metals limit to increase the intensity ofprimary electron beams due to the heat loadon the target.
z New method using the processes of coherent
bremsstrahlung (CB) and channelingradiation (CR) is one of the bright schemes
for high-intensity e+ production.
KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Introductionz New method utilizing a crystal target wasproposed by Chehab, et al. In 1989.
(R. Chehab, et al., PAC’89, Chicago, IL, USA,Mar. 1989, p.283)
z Yoshida, et al., demonstrated a clear
enhancement of the e+ yield in a tungsten
crystal target using a 1.2-GeV electron beam.
(K. Yoshida, et al., Phys. Rev. Lett. 80, 1437,1998)
KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Introduction (cont’d)z A series of e+ production experiments basedon the new scheme has been continued,⇒by Yoshida(Hiroshima/KEK), et al.,using 1.2-GeV e- beam of the ES at KEK-Tana branch,3-GeV e- beam at e+ station, and e- beam(<8GeV) atthe end station of the KEKB injector linac.

⇒by Chehab(LAL), et al.,using 5-40 GeV secondary e- beam at CERN-SPS.

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Introduction (cont’d)z Theoretically unified treatment taking into
account both processes of CR and CB has not
yet been established on the simulation.
z More experimental data are expected toclearly understand the elementary physicalprocesses of the CR and CB, and they arealso required to develop the design of a realtype positron source.

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Historical View of the KEK Experiments
Month/Year
May/1997

KEK Tanashi, ES

1.2

Crystal W (Wc) [1.2]Apr, Jun/1998

KEK Tsukuba,3

Wc [1.7]

Electron Linac
Nov/1998

KEK Tanashi, ES+ Amor. W (Wa) [7]
Wc [0.4, 1.2, 2.2],

0.6, 0.8, 1GaAs [0.36], Diamond[1.1]
Sep, Oct/2000

KEK Tsukuba,8

Wc [2.2]+Wa [5, 10, 15]Electron Linac
Apr/2001

KEK Tsukuba,

Wc [2.2],

8Wc [2.2], Wc [9]Electron Linac
Sep/2001

KEK Tsukuba,

Wc [9]+Wa [2, 4]
8Combined targets(Wc +Wa)

Electron Linac
Jan/2002

KEK Tsukuba,

4

KEK Tsukuba,

Wc [2.2], Wc [5.3], Wc [9]Combined targets(Wc +Wa)

Electron Linac
Aug-Sep/2002

Wc [2.2], Wc [5.3], Wc [9]8Electron Linac

Si <110> 2.6, 30, 48
Diamond <110> 4.57
Combined (Si/Dia.+Wa)

Dec/2002

KEK Tsukuba,
Electron Linac

8Si <110> 10, 30, 48
Diamond <110> 4.57
Combined (Si/Dia.+Wa)

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Channeling Radiation & Coherent
Bremsstrahlung Processes
Physical processes for the channeling radiation andcoherent bremsstrahlung
CrystalNucleus

ChannelBeam
Critical Angle ofChanneling Radiation

Channeling Radiation

F c=(2U0/Eb)1/2~0.43mrad@Eb=8GeV
U0:Potential Energy of a Channel
Eb:Beam Energy

Coherent Bremsstrahlung
KEK Linac/
Tsuyoshi Suwadae+ Production Mini-Workshop@KEK,
17/Jan,2003

New Positron Production Schemes

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Experimental Setup
Goniometer

Positron Detectors
Lead-Glass Cherenkov Calorimeter
Lucite Cherenkov Detector{V
e- BeamTarget

Lead Shield+H+X-+A

e++Target
e- Beam

Wall-Current Monitor

KEK Linac/
Tsuyoshi Suwada

Screen Monitor

e+eVacuum Chamber
Analyzer Magnet

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Linac Beam Line at the 3rd switch yard

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,17/Jan,2003

Experimental Setup (cont’d):Photo pictureof a crystal target on a goniometer

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Experimental Setup (cont’d):Photo pictureof crystal & amorphous targets

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Experimental Setup (cont’d):Positron
spectrometer

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Acceptance of the Positron Spectrometer
Pe+Acceptance (∆P∆Ω)(MeV/c)(10-4 x (MeV/c)•sr)

51.08 ± 0.03

102.47 ± 0.07

153.80 ± 0.1

204.81 ± 0.12

KEK Linac/Tsuyoshi Suwadaz The acceptance (∆P∆Ω) was obtained byusing the simulation
code (GEANT3).
z Typical acceptance
Momentum:∆P/P=2.4% (FWHM)&
Geometrical:∆Ω=1msr
at Pe+=20MeV/c.

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Experimental Condition
Electron Beam:• Beam Energy = 8 GeV• Angular Spread ~22 µrad (H), ~44 µrad (V)• Transverse Beam Size ~0.8mm (FWHM) in diameter• Beam Charge = 0.1 nC/bunch• Bunch Length (Single Bunch) ~9 ps (FWHM)• Beam Repetition = 25Hz
Angular Spread of the Electron Beam at the Positron Target• Φ ~ 55 µrad < Φc (due to multiple scattering by a beam-extraction
vacuum window(30µm-thick SUS))
Critical Angle for the Channeling Condition at the Positron Target
Linhard Crytical Angles• Φc ~ 170µrad @8 GeV for Silicon Crystal• Φc ~ 130µrad @8 GeV for Diamond Crystal

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Experimental Condition (cont.)
Positron-Production Targets:• Crystal Silicon Target : 2.55, 9.9, 29.9 and 48.15mm thickness• Crystal Diamond Target : 4.57mm thickness• Amorphous Tungsten Target: 3-18mm (3mm step) thickness (forthe purpose of hybrid targets and for the e+ production yieldcalibration)
Detected Momentum Range:• 10 MeV/c ≤ Pe+ ≤ 30 MeV/c
Positron Detectors•Lead-Glass Calorimeter:Measurement of total energy of e+•Acrylic Cherenkov Counter:Measurement of number of e+
Beam Monitors•Wall-current monitor for the electron beam-charge measurement•Screen monitor for the beam-profile measurement

KEK Linac/Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,17/Jan,2003

Experimental Results:
2-Dimensional Axis Scan for 5mm-thick Diamond
Crystal at Ee-=8 GeV (Pe+=20MeV/c)

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Experimental Results:
2-Dimensional Axis Scan for 30-mm thick Si
Crystal at Ee-=8 GeV (Pe+=20MeV/c)

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Experimental Results:
Rocking Curves (Axis <110>) for 5mm-thick
Diamond and 30mm-thick Si Crystals at Ee-=8GeV (Pe+=20MeV/c)

KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Experimental Results:
Variations in the width of the rocking-curve peakfor Ee-=8 GeV (Pe+=20MeV/c)σ)[mrad]Rocking-Curve Peak Width (1σ2Preliminary

Si Crystal
Diamond Crystal+Pe =20MeV/c
1.5

10.5

00

0.1

0.2

0.3

X
KEK Linac/
Tsuyoshi Suwada

0.4

0.5

0e+ Production Mini-Workshop@KEK,
17/Jan,2003

0.6

Experimental Results:
Variations in the enhancement (Ne+@peak/ Ne+@base)of the e+ yield at Ee-=8 GeV (Pe+=20MeV/c)
Crystal Thickness vs. Enhancement
20PreliminarySiliconDiamond16+

Enhancemnet

Pe =20MeV/c
128400.1

0.20.3X
KEK Linac/
Tsuyoshi Suwada

0.40.50e+ Production Mini-Workshop@KEK,
17/Jan,2003

0.6

Experimental Results:
Positron momentum dependence for the e+ yieldenhancement at Ee-=8 GeV
Positron Momentum Dependence
25Preliminary+
Pe =20MeV/c

1 0mm Si
3 0mm Si50mm Si5mm Diamond

Enhancement

2015105051015202530+

Pe [MeV/c]
KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

35

Experimental Results:
Variations of the e+ production yield for theamorphous tungstens and off-axis crystal targets
at Ee-=8 GeV (Pe+=20MeV/c)++

Normalized e Yield from Off-Axis Combined Target

Normalized e Yield from W Target

400

400

Preliminary+350

Pe =20MeV/c

Positron Yield [Arbitrary Unit]

Positron Yield [Arbitrary Unit]

Preliminary
300
250200Normalization

15010mmSi30mmSi50mmSi5mmDiamond

100
50350+Pe =20MeV/c

300
250
200
15010mmSi30mmSi50mmSi5mmDiamond

100
50000510152001W Thickness [mm]
KEK Linac/Tsuyoshi Suwadae+ Production Mini-Workshop@KEK,
17/Jan,2003

23X

4056Experimental Results:
variations of the e+ production yield for the onaxis crystal targets at Ee-=8 GeV (Pe+=20MeV/c)+Normalized e Yield from On-Axis Combined Target
400

Positron Yield [Arbitrary Unit]

Preliminary
350+Pe =20MeV/c

300
250
200
15010mmSi30mmSi50mmSi5mmDiamond
W Base e+ Yield

100
5000123X

KEK Linac/Tsuyoshi Suwada

40e+ Production Mini-Workshop@KEK,
17/Jan,2003

56Experimental Results:
Variations of the e+ production enhancement forthe crystal targets at Ee-=8 GeV (Pe+=20MeV/c)
Thickness (in Total) vs.Enhancement
20Preliminary+Pe =20MeV/c

Enhancement

152 .2mmWCrystal
5.3mmWCrystal
9mmWCrystal
Reference

10500123X

KEK Linac/
Tsuyoshi Suwada

40e+ Production Mini-Workshop@KEK,
17/Jan,2003

56

Experimental Results:
Crystal effects for the Diamond and Si crystal
targets at Ee-=8 GeV (Pe+=20MeV/c)
Crystal Effect6iliconiamond+Pe =20MeV/c

5.5at Shower Maximum

0Thickness[X ] of a Combined Target

Preliminary

5Thickness at Shower Maximum (W base)

4.54

Palabora Fitting

3.5

300.1

0.2

0.3

X
KEK Linac/
Tsuyoshi Suwada

00.4e+ Production Mini-Workshop@KEK,
17/Jan,2003

0.50.6

Experimental Results:
Multiple Scattering Effect of the Vacuum
Windows Using the Diamond crystal at Ee-=8GeV (Pe+=20MeV/c)
Multiple Scattering Effect
5mm Diamond Crystal

120Width[mm]Enhancement

Enhancement

150.8

0.7
100.6

Preliminary+
Pe =20MeV/c
500.1

0.2

0.3

0.4

0.5

0.5
0.6

Thickness of Vacuum Window (SUS304) [mm]
KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Rocking-Curve Peak Width [mm]0.9Conclusions♠Positron production experiment using Diamond andSilicon crystal targets has been successfully performedat the KEKB 8-GeV electron linac.
♠Rocking curves⇒ The obtained widths of the rocking-curve peak islarger than the critical angle,⇒ and broaden with the thickness of the crystal target.
⇒ These broad width of the rocking curves indicate that
coherent bremsstrahlung is the predominant process
over the channeling radiation process in this energyregion.
⇒ The increase of the peak width depending on thetarget thickness may come from the multiple
scattering of the incident electrons in the target.
KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003

Conclusions (cont’d)♠Enhancement (En) and momentum dependence of the e+ yieldfor the crystal target alone from 8-GeV channeling electrons at a e+
momentum of 20MeV/c⇒ En= 9.3 ±0.5 (9.9-mmSi), 9.9 ±0.5 (29.9-mmSi),⇒ En= 6.4 ±0.3 (48.15-mmSi), 16 ±0.8 (4.57-mmDiamond)• The enhancement is much reduced with an increase of the total target
thickness.
• No crystal effect enhances the e+ yield at the target thickness larger than
~4.2 X0 in total.
•The e+ yields with Pe+=20MeV/c at Ee-=8GeV were almost the same level
as the maximum e+ yield obtained for the amorphous tungsten target.

♠New scheme using the combined crystal target indicates that heatload in the amorphous tungsten part of the target could beconsiderably reduced due to a small amount of the energy loss intotal.
⇒ It is of great benefit to apply such a crystal target to a high-intensity e+source required for high-luminosity e+e- colliders and B-fatories.
KEK Linac/
Tsuyoshi Suwada

e+ Production Mini-Workshop@KEK,
17/Jan,2003