THE KEK-PF SLOW-POSITRON FACILITY AT A NEW SITE
T. Shidara, T. Kurihara, A. Shirakawa, A. Enomoto, H. Kobayashi, K. Nakahara
KEK, 1-1 Oho, Tsukuba-shi, Ibaraki-ken, 305-0801, Japan
Abstract
The KEK-PF slow-positron facility was relocated tothe 1.5-GeV point of the upgraded electron/positron
injector linac relevant to the KEKB project. A dedicatedlinac for slow-positron use is also installed utilizing theremnants of the injector linac reformation. We expect aslow-positron intensity of more than 100 millionpositrons/sec with a maximum primary beam power of 1
kW for their application in various fields of solid-statephysics.

1 INTRODUCTION
The KEK slow-positron facility, aiming at the use ofslow-positron beams (ranging from eV to keV) in various
fields of solid-state physics, was constructed. A slowpositron flux of 1x108 positrons/sec was successfully
achieved [1, 2] utilizing our 2.5-GeV electron linac [3, 4]
with a 2.0-GeV, 2-kW primary electron beam power.
Although we had opened this facility to slow-positronusers [5, 6], we had to relocate our facility relevant to theupgrade plan of the KEK 2.5-GeV linac. There are two
major goals of the upgrade [7, 8]: 1) to increase theenergy of electrons and positrons to 8 and 3.5 GeV,
respectively, and 2) to increase the bunch intensities ofpositrons by roughly one order. In accordance with thisupgrade plan, we must relocate our KEK-PF slowpositron facility to the 1.5-GeV point of the upgradedlinac (the KEKB J-linac).

2 LAYOUT OF THE RELOCATEDKEK-PF SLOW-POSITRON FACILITYThere are two primary-electron-beam sources for ourslow positron facility; the 1.5-GeV beam of the KEKB
linac and the test linac. The nominal beam power of the1.5-GeV beam is 0.75 kW (an energy of 1.5 GeV, chargeof 10 nC/pulse, a pulse length of 10 ps and a pulse
repetition rate of 50 pulse/s). A dedicated linac for slow
positron use only (the test linac) was installed utilizing
the remnants of the J-linac upgrade plan. An average
beam power of 1 kW can be expected from the test linac.
A slow-positron intensity of more than 108 positrons/sec
is easily expected in both cases.
Figure 1 shows the relocated KEK-PF slow-positron
facility, which locates at the 1.5-GeV point of the KEKB
J-linac. It comprises beam lines for the primary electron
beams, a target-moderator assembly, a slow-positron
beam-transport line and relevant assemblies.
The primary electron beam is injected into the target.
The extracted slow-positron beam is directed by a 30-m

long beam-transport line with an axial magnetic field of
100 G to an experimental area. Twelve sets of steeringcoils were installed along the slow-positron beamtransport line in order to adjust the slow-positron beam
trajectory. A high-voltage station capable of applying 60
kV was installed in order to vary the energy of thepositron beam. A device controller, combining a personal
computer and a programmable sequence controller
through optical fiber, has been adopted to control themonitors and power supplies at a high-voltage potential.
Penning-trap electrodes are also installed at this station inorder to make a dc beam from a pulsed beam.
At an experimental area, a slow-positron beam switch
system, which comprises a pair of beam deflecting coils
and two pairs of Helmholtz coils with magnetic-field
directions crossing each other, was installed. This systemenables us to direct slow-positron beams to several
experimental stations one by one without breaking thevacuum.
As for experimental equipment, a transmission-type
positron microscope, a positronium time-of-flight (TOF)
apparatus, and a 2D-ACAR (two-dimensional angularcorrelation of annihilation radiation) equipment are now
being prepared.

3 PRESENT STATUS
All components of the KEK-PF slow-positron
facility were relocated. The accelerating structures andnecessary magnets of the test linac have already been
installed in the linac tunnel.
The commissioning of the slow positron beam wasstarted from this April. We have already achieved a slowpositron intensity of more than 107 positrons/sec
utilizing the 1.5-GeV J-linac beam as its primary beamsource. Utilizing this positron beam, the 2D-ACAR
equipment was checked and adjusted.

4 FUTURE PLAN
If we reinforce its primary beam source by adding
other two accelerating units to the present test linac, wewill be able to achieve a beam power of 6 kW from theupgraded test linac. This enables us to produce more than
109 positrons/sec in our slow-positron facility.

5 SUMMARY
The KEK slow-positron facility was relocated to the
1.5-GeV point of the KEKB J-linac relevant to the KEKB
project. A dedicated linac for slow-positron use is also
installed utilizing the remnants of the KEKB J-linac309

upgrade plan. We have already achieved a slow-positron
intensity of more than 107 positrons/sec utilizing the 1.5GeV J-linac beam as its primary beam source and we
expect more than 108 positrons/sec with a maximum
primary beam power of 1 kW.

[2] T. Shidara, A. Enomoto, T. Kamitani, H. Kobayashi,
T. Kurihara, A. Shirakawa, H. Hirayama, I. Kanazawa, A.
Asami and K. Nakahara, "The KEK Slow-Positron
Source", Materials Science Forum, 175-178, 205 (1995).
[3] J. Tanaka, "Construction of the Photon Factory 2.5
GeV Injector Electron Linac", Nucl. Instr. Meth., 177,
101 (1980).
[4] I. Sato, "Accelerator Structure and Beam Transport
System for the KEK Photon Factory Injector", Nucl.
Instr. Meth., 177, 91 (1980).
[5] Y. Morinaka, Y. Nagashima, Y. Nagai, T. Hyodo, T.
Kurihara, T. Shidara and K. Nakahara, "Time-of-Flight
Spectroscopy of Positronium Emission from SiO2Surface", Materials Science Forum, 255-257, 689 (1997).
[6] eds. T. Shidara and K. Nakahara, "Construction Reportof the PF Slow-Positron Source (II)", KEK Report, 9712, (1997).
[7] "KEKB B-Factory Design Report", KEK Report, 957, (1995).
[8] eds. I. Sato, S. Anami, A. Enomoto, S. Fukuda, H.
Kobayashi and K. Nakahara, "Design Report on PF
Injector Upgrade for KEKB", KEK Report, 95-18, (1996).

ACKNOWLEDGMENTS
The authors are greatly indebted to the Director
General, Prof. H. Sugawara as well as to the staff of theKEK administration department for their encouragement
and continuous support of this slow-positron project.
They should also express their gratitude to prof. Y.
Kimura, the director of the Institute of Materials Structure
Science and to Prof. M. Kihara, the director of theAccelerator Laboratory, KEK, for their support. The staffof the KEK electron/positron linac is also gratefully
acknowledged for machine operation and support.

REFERENCES[1] A. Asami, A. Enomoto, H. Kobayashi, T. Kurihara,
K. Nakahara and T. Shidara, "A Slow-Positron Source
Project using the Photon Factory Electron Linac",
Materials Science Forum, 105-110, 1833 (1992).

,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Positron Production
Target ChamberTestLinace–Ground High Voltage
Potential Potentiale–e+nacPenningTrapApparatus

LiJ–Positron
Microscope

2D-ACAR

Experimental Area0N

2m

Positronium TOF

Figure 1. Bird's-eye view of the KEK-PF slow-positron facility.
It comprises beam lines for the primary electron beams, a target-moderator assembly, a slow-positron beamtransport line and relevant assemblies.

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