The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

Present Status of the Electron Accelerator Facility at the ETL
MIKADO Tomohisa, OHGAKI Hideaki, OHDAIRA Toshiyuki, SUZUKI Ryoichi, SEI Norihiro,
TOYOKAWA Hiroyuki, YAMADA Kawakatsu, SUGIYAMA Suguru, CHIWAKI Mitsukuni,
ONUKI Hideo, SAITO Terubumi, YAMADA Toru, SHITOMI Hiroshi,
HANE Hiroki#, OKABE Shigeo*, and YAMAZAKI Tetsuo**
Quantum Radiation Division, Electrotechnical Laboratory, Tsukuba, Ibaraki 305-8568, Japan*Okabe Keisoku Kogyosho, 1-7-13 Nozawa, Setagaya, Tokyo 154-0003, Japan**Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Shiga 611-0011, Japan

Abstract
An electron linac TELL and three storage rings, i.e.
TERAS, NIJI-II, and NIJI-IV, form the "electron accelerator
facility" of the Electrotechnical Laboratory. TELL ismainly used to produce high-intensity slow-positron beamand to fill storage rings. The research in solid-statephysics by means of slow-positrons is performed in the lowenergy experimental room and the adjoining room. Acompact storage ring NIJI-11 equipped with the Onuki-type
polarizing undulator is located in the medium-energy
experimental room. The free-electron laser (FEL) research
is under way with NIJI-IV located in the pion room; thisring often attains the world shortest record in FELwavelength. TERAS is a multi purpose storage ring.
Among a variety of experimental research programs madeat TERAS, one for generation and utilization ofmonochromatic polarized photon beam is mentioned.

1 Introduction
The electron accelerator facility of the ElectrotechnicalLaboratory (ETL) consists of an electron linac, TELL, andthree storage rings, TERAS, NIJI-11, and NIJI-IV. TELL issurrounded by five experimental rooms: low-energy
experimentalroom(L-EnRm),
medium-energy
experimental room (M-En Rm), high-energy experimentalroom (H-En Rm), pion room (P Rm), and ring room (RingRm).
TELL was constructed in 1980 [1] and wasoriginally intended to share electron beams with two or
three experimental rooms simultaneously. However, for avariety of reasons, we decided to transport electron beams
into one experimental room at one time.
Figure 1 shows the operation statistics of TELL for thelatest five fiscal years. In this figure, "Ace Rm" means thetotal hours when some experiments or maintenance works

FY 1994

FY 1995

FY 1996

FY 1997

were made inside the linac room, whereas other symbols
mean the total hours when all the accelerated electrons wereready to transport into the corresponding experimentalroom.
In the following sections, we describe several research
programs made at the electron accelerator facility.
Research projects related with the Onuki-type polarizing
undulator are presented in a little detail.

2 Slow-Positron Production
In the L-En Rm, -70-MeV electrons hit a Ta target (anelectron-to-positron converter) and generate a large amountof positrons. The positrons enter a stack of very thin W
foils (a positron moderator) and -108/s of slow positrons
emerge from the moderator. The slow-positron pulses,
whose duration is -1 f.!S and repetition rate is usually 100
pulses/s, are converted into a quasi-continuous beam by alinear storage section. The quasi-continuous beam isconverted to a pulse train of more than 105 pulses/s of slow
positrons having -100-ps width by a novel time-bunchingsystem. We use the high-intensity and very short pulses ofslow positrons to study structures of various solid materials
or thin films at surfaces, near surfaces, or interfaces bymeasuring positron lifetime spectra [2].
We alsoconstructed a neat apparatus for positron-annihilationinduced Auger-electron spectroscopy to characterize
topmost states of solids with high-resolution and high-countrate [3]. For the purpose of increasing the intensity ofslow positrons much higher, we have investigated themoderation efficiency of various materials. We found thata 6H-SiC(n) crystal is suitable as a re-moderator for a multistage brightness enhancement system [4]3 Monochromatic Polarized Photon Generation
By the use of TERAS, which is installed in theRing Rm, we generate monochromatic polarized
photon beam through the laser Compton scattering
processes. The photon beam is used for various
experimental
studies,e.g.,
nuclearphysics,
measurement of cross sections of photo-induced
reactions, construction of a novel neutron source, andso on [5].
The construction of a pilot system to generate-10-nm photons was started in Apr. 1998 in the AceRm [6]. The final target of the new project is torealize a light source for the future x-ray lithography.

FY 1998

CAccRm 13L-EnRm EIM-EnRm 13PRm .RingRm

4 Free-Electron Laser

Fig. 1 Total hours dedicated to individual experimentalrooms in the period of Apr. 1994- Mar. 1999.

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We have conducted the free-electron laser (FEL)
project with NIJI-IV in the P Rm. One of the recent

The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999---Polarization Controller

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Fig. 2

Schematic diagram of the system for microscopic imaging of CD. Circularly
polarized radiation from the undulator is reflected by a convex mirror and is focusedat the sample in 3D Piezo-driving stage by a Schwartzschild-type mirror.

!llmJ d-10-camphorsulfonic acidinstalled at NIJI-II in the M-En
Rm. The SR emitted from thePU is used for various research
fields; we describe three major
research subjects in this section.

40JO5.1
Microscopic Imaging ofCircular Dichroism

We developed a new typeof scanning microscope toobserve circular dichroism (CD)images of samples [9]. ThePU, which generates right- and·,,1030
copper grid
left-handed circularly polarized
SR alternately, was used as anilluminating light source. TheFig. 3 (a) Schematic view of sample arrangement on a copper grid (black areas
SR from the PU was focused toindicate the sample). (b) CD image of dried d-10-camphorsulfonic acidform a microbeam with the spot
films on a copper grid by subtracting the image at 230 nm from that at 275
size of less than 1 f..lm by axiallynm (white areas indicate strong CD signals of the sample on the contrary tosymmetric mirrors. The sense(a)).
of the rotation of the circularpolarization of the undulator
prominent topics of the program is that we succeeded inradiation (UR) was modulated with a frequency of -2 Hz.
lasing at 212 nm in Oct. 1998, which has been the world
Figure 2 shows schematic diagram of the CD microscope.
shortest record until very recently. The important factors
Two-dimensional CD image of thin film of d-10contributing to the lasing in the UV region such as
camphorsulfonic acid, which is one of standard samples for
improvement of the RF system and others made in NIJI-IV
the measurement of CD spectrum, was obtained by thisare reported in this symposium [7].
microscope. Figure 3 is the final CD image, which wasderived by subtracting the image signal obtained at 230 nm
5 Polarizing Undulator
from that at 275 nm.
The Onuki-type polarizing undulator (PU) [8]proposed and developed in the ETL which produces highbrilliant, quasi-monochromatic, wavelength-variable, andpolarized synchrotron radiation (SR) of any ellipticity is5.2

Optically Controlled Alignment of Liquid Crystal

Liquid crystal (LC) alignment properties on photoexposed polyimide films were studied in the UV and VUV-160-The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

is found that the present calibration results using UR for a
Si photodiode, a GaP photodiode, and a CsTe phototube
agree with the existent scale within ±4%, ±5%, and ±17%, respectively.

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Research programs using directly or indirectly electron
beam accelerated with TELL are described briefly. We
have made serious efforts to maintain and operate all theapparatus. TELL has fortunately worked very well for -20
years without replacements of key components though a lotof troubles have occurred from time to time. We keepusing the present facility to proceed the existing research
programs by fixing or repairing various components, on theone hand: We seek appropriate funds for renewing thefacility, on the other hand.
We wish to express our gratitude to Dr. Tomimasu, theformer Director of the Quantum Radiation Division, ETL
for his guidance and encouragement. The present work
was financially supported by the Science and TechnologyAgency.

\500

WAVELENGTH[nm]Fig. 4

Calibration results for Si, GaP photodiode,and CsTe phototube using monochromatized
UR based on ESR. Also shown by lines arecalibration results based on present ETL
responsivity scale.

regions using linearly polarized SR from the PU [10]. We
found that the LC alignment uniformity depends on the UVand VUV exposure conditions, especially on the SRwavelength. The photoabsorption spectrum of polyimide
films was also measured in both UV and VUV regions.
We conclude that at least two mechanisms exist in thephoto-induced alignment of LC molecules on the polyimide
films.

5.3

Concluding Remarks

Calibration of UV Detectors

Thermal detectors are often used to extend available
spectral range of established detector standards because
their responsivities are constant with wavelength.
However, the use of thermal detectors is very limited
because of their low responsivity. In order to increase
responsivity of thermal detector, its photoreceiver has to be
furnished as thin and small as possible; which results instructural fragility and small active area. As long as aconventional light source such as a quartz halogen lamp or adeuterium lamp is used, it is necessarily required that adetector used for calibration is irradiated in a large solidangle. In this case, the calibration result probably differsfrom that using a parallel beam. It was reported for Si andGaAs photodiodes that this difference becomes large in theUV and VUV regions. In order to overcome the above
problems, we decided to use UR as an intense UV radiation
source for detector calibration based on Electrical
Substitution Radiometer (ESR). We have calibrated a Si
photodiode (Hamamatsu S1337), a GaP photodiode(Hamamatsu G1963), and a CsTe phototube against a roomtemperature-operated ESR using UR monochromatized byan interference filter.
Figure 4 shows the calibration results using
monochromatized UR measured with an ESR. The present
results are compared with those based on a current ETL
responsivity scale (shown by lines) using traditional lightsources (quartz halogen lamp and deuterium lamp) and amonochromator.
The ETL responsivity scale wasestablished in the wavelength range longer than 250 nm. It

References[1]Tomimasu, T., IEEE Trans. Nucl. Sci. NS-28 (1981)
3523; Tomimasu, T., "Present Status of the 500-MeV
ETL Electron Linac 'TELL'", Proc. 4th Symp. Accel.
Sci. Techno!., Saitama, Japan (1982) 35.
[2] see, for example, Suzuki, R. et al., Jpn. J. Appl. Phys.
31 (1992) 2237.
[3] Ohdaira, T. eta!., J. Surface Analysis 5 (1999) 158.
[4] Suzuki, R. et al., Jpn. J. Appl. Phys. 37 (1998) 4636.
[5] Toyokawa, H. et a!., "Present Status of PolarizedPhoton Generation System with the Laser-ComptonBackscattering of the ETL Electron Storage RingTERAS", Proc. 11th Symp. Accel. Sci. Techno!.,Harima, Japan (1997) 110.
[6] Hane, H. et a!., "Laser Compton Scattering Using
Linac", Proc. 23rd Linear Accel. Meeting in Japan.,·Tsukuba, Japan (1998) 414.
[7] Sei, N. et a!., "Status of the Free Electron LaserExperiments with the Storage Ring NIJI-IV in 1999",
this volume.
[8] Onuki, H. et al., SPIE 2873 (1996) 90.
[9] Yamada, T. eta!., submitted to Jpn. J. Appl. Phys.
[10]Shitomi, H. et al., Jpn. J. Appl. Phys. 38 suppl. 38-1
(1999) 176.
[11] Saito, T. et al., J. Electron Spectr. Related Phenomena.
80 (1996) 397.

# On leave from SONY Corp.

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