Positron-Production Experiment Using 8-GeV ChannelingElectrons in a Crystal-Tungsten Target
T.Suwada, S.Anami, A.Enomoto, K.Furukawa, K.Kakihara, T.Kamitani,Y.Ogawa,S.Ohsawa, T.Oogoe
Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), 1-1 Oho,Tsukuba, Ibaraki 305-0801, Japan
H.OkunoInstitute of Particle and Nuclear Studies, High Energy Accelerator Research
Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
T.Fujita, K.Umemori, K.Yoshida
Hiroshima Synchrotron Radiation Center, Hiroshima University, 2-313 Kagamiyama,
Higashi-Hiroshima 739-8526, Japan
R.Hamatsu, K.Sasahara
Department of Physics, Tokyo Metropolitan University, 1-1 Minami-Ohsawa, Hachiojishi, Tokyo 192-0397, Japan
V.Ababiy, A.P.Potylitsin, I.E.Vnukov
Nuclear Physics Institute, Tomsk Polytechnic University, 634050, P.O.Box 25, Tomsk,Russia
SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Motivation
V High-intensity positron sources are required forfuture linear colliders and B-factories.
V Conventional methods using amorphous heavy
metals limit to increase the intensity of primaryelectron beams due to the heat load on the target.
V New method using the processes of coherent
bremsstrahlung (CB) and channeling radiation(CR) is one of the bright schemes for highintensity e+ sources.
SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Motivation (cont.)
V Theoretically unified treatment taking into accountboth processes of CR and CB has not yet been
established on the simulation.
V More experimental data are expected to clearly
understand the elementary physical processes of
the CR and CB, and they are also required todevelop the design of a real-type positron source.

SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Historical View of Our ExperimentMonth/Year

Accelerator

Energy [GeV]

Positron Target [mm]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]0.6, 0.8, 1

Wc [0.4, 1.2, 2.2],
GaAs [0.36], Diamond[1.1]

Sep, Oct/2000

KEK Tsukuba,

8

Electron Linac
Apr/2001

KEK Tsukuba,
Electron Linac

Wc [2.2],
Wc [2.2]+Wa [5, 10, 15]

8

Wc [2.2], Wc [9]Wc [9]+Wa [2, 4]

SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Channeling Radiation &Coherent Bremsstrahlung
Physical processes for the channeling radiation andcoherent bremsstrahlung
CrystalNucleusBeam
Critical Angle of
Channeling Radiation

ChannelChanneling Radiation

F c=(2U0/Eb)1/2~0.43mrad@Eb=8GeV
U0:Potential Energy of a Channel
Eb:Beam Energy
Coherent Bremsstrahlung
SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

New Positron Production Scheme

SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Experimental Setup
Beam

Rotational Axes of
the Goniometer

Lead-Glass Calorimeter
Acrylic Cherenkov Counter

V Axis
H AxisLead-Block Shields

Collimator(40mmf)
Collimator(30mmf)
8-GeV e- Beam

Target/Goniometere+e-eVacuum Window
Screen Monitor
Wall-Current Monitor

e+60oCollimators(20mmf)Magnetic Spectrometer

SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Linac Beam Line & Experimental Setup

SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Experimental Condition
Electron Beam:• Beam Energy = 8 GeV• Angular Spread ~72 mrad (Horizontal), ~15 mrad (Vertical)• Transverse Beam Size ~1 mm (FWHM) in diameter• Beam Charge = 0.2 nC/bunch• Bunch Length (Single Bunch) ~10 ps (FWHM)• Beam Repetition = 2Hz
Angular Spread of the Electron Beam at the Positron Target• F ~ 0.1 mrad < Fc (due to multiple scattering by a vacuumwindow(100mm-thick SUS))
Critical Angle for the Channeling Condition at the Positron Target• Fc ~ 0.43 mrad @8GeV (Linhard Angle)
SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Experimental Condition (cont.)
Positron-Production Targets:• Crystal Tungsten Target : 2.2mm and 9mm thickness• Amorphous Tungsten Target : 2mm and 4mm thick (for the purpose ofhybrid targets)• Amorphous Tungsten Target: 3-18mm (3mm step) thickness (for thee+ production yield calibration)
Detected Momentum Range• Pe+ <30 MeV/cPositron Detectors•Lead-Glass Calorimeter and Acrylic Cherenkov Counter
Beam Monitors•Wall-current monitor for the beam-charge measurement
and screen monitor for the beam-profile measurement
SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Experimental Results:
Rocking Curves (Crystal Axis <111>) for
2.2mmt and 9mmt Wcs
44On Axis

(a)

3.5

2.2mm-thick Wc(b)3.59mm-thick Wc
On Axis+Pe =20MeV/c

Pe =20MeV/c

3

Relative Positron Yield[arbitrary unit]

Relative Positron Yield[arbitrary unit]+

2.5

FWHM=9.0 mrad

2Off Axis

1.5
10.5

32.5

FWHM=39.2 mrad

Off Axis

2
1.5
10.5

0-60-40-20020

Rotational Angle [mrad]

40600-60-40-2002040

Rotational Angle [mrad]

SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

60

Experimental Results:
Momentum dependence of the Positron-Yield
Enhancement (=PYon-axis/ PYoff-axis)
Momentum

Enhancement

Enhancement[MeV/c](2.2mm Wc)(9mm Wc)10

6.6 ± 0.1

1.9 ± 0.1

15

6.1 ± 0.1

1.7 ± 0.120

5.1 ± 0.1

1.7 ± 0.1

SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Experimental Results:
Momentum dependence of the PositronYield Enhancement (=PYon-axis/ PYoff-axis)

SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Experimental Results:
Positron Yields vs. Target Thickness
Positron-Production Efficiency (%)

0.08+

Pe =20MeV/c0.07
0.06

9mm-thick Wc

9mm-thick Wc+ 2mm-thick Wa
9mm-thick Wc+ 4mm-thick Wa

0.05
0.04
0.03

2.2mm-thick Wc

0.02
0.01
005101520

W Thickness [mm]SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Experimental Results: Simulation check foramorphous W targets using the EGS4 code
0.05

Positron-Production Efficiency (%)

P=20MeV/c0.04

P=15MeV/c0.03P=10MeV/c
0.02

0.01

005101520W Thickness [mm]SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

Experimental Results:Experiment vs. Simulation
542.2mm-thick Wc
Pe+=20MeV/c

Simulation
Experiment

3.5

Relative Positron Yield[arbitrary unit]

Relative Positron Yield[arbitrary unit]

432Simulation
Experiment

9mm-thick Wc
Pe+=20MeV/c32.5

21

1.5

0-40-20020

Rotational Angle [mrad]401-40-20020

Rotational Angle [mrad]

SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)

40

Conclusionsº Positron production experiment has been successfully
performed at the KEKB 8-GeV electron linac.
º Enhancement (En) and momentum dependence of the e+ yieldfrom 8-GeV channeling electrons• En=5.1 ±0.1 (2.2mmt Wc), 1.7 ±0.1 (9mmt Wc)@Pe+=20MeV/c• the enhancement decreases as the target thickness increases.
• the positron yield of the 9mmt crystal W is slightly larger than thatof a 15mmt amorphous W.
• the result of the momentum dependence indicates that as themomentum becomes low, the enhancement is getting larger.
º The present simulation results can not agree with the experiment.
More sophisticated simulation code is under development.
SAST01@Osaka University, Osaka, October 29-31, 2001 Tsuyoshi Suwada (tsuyoshi.suwada@kek.jp)