The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

ELECTRO N ACCELERATOR FACILITY AT THE AISTMIKADO Tomohisat, YAMADAKa wakatsu, OHGAKI Hideaki, OHDAIRA Toshiyuki,
SUZUKI Ryoichi, SEI Norihiro, TOYOKAWA Hiroyuki, NOGUCHI Tsutomu,
CHIWAKI Mitsukuni, SUGIYAMA Suguru, OGAWA Hiroshi, and YASUMOTO Masato
Photonics Research Institute, National Institute of Advanced Industrial Science and Technology
1-1-1 Umezono, Tsukuba, lbaraki 305-8568, Japan.
OKABE Shigeo, Okabe Keisoku Kogyosho, 1-7-13 Nozawa, Setagaya, Tokyo 154-0003, Japan.

Abstract
The electron linac TELL at the National Institute ofAdvanced Industrial Science and Technology (formerlyknown as the Electrotechnical Laboratory) was in"ready-to-operate" mode for 2,000 and 1,300 hours infiscal year 1999 and 2000, respectively. One of therecent topics attained in research programs using slowpositron beam is that we showed the feasibility ofcontrolling the dielectric constant of ihin films byadjusting low-frequency power in plasma-enhanced
chemical vapor deposition processes. We constructed aradiography system using high-energy x rays producedwith laser-Compton scattering processes at TERAS.
Various improvements have been made at NIJI-IV toaccomplish oscillation of free electron lasers in thevacuum ultraviolet region.

1 INTRODUC TION
Laboratories and institutes attached to the Agency ofIndustrial Science and Technology, Ministry of International Trade and Industry, were united to one instituteon April 1st, 2001. The reorganized institute is named
the National Institute of Advanced Industrial Science andTechnology (AIST).
The electron linac TELL is

2 RESEARCH PROGRAMS USING TELL
In this section, we describe several research programs
made wiih the electron accelerator facility at the AIST.

250h200h

managed mainly by the Photonics Research Institute withthe assistance by the Metrology Institute of Japan, AIST.
TELL is used to produce high-intensity slow-positron
beam and to fill three storage rings, viz., TERAS, NIJI-11,
and NIJJ-IV. Solid-state physics using slow-positron
beam is studied in the low-energy experimental room (LEn. Rm). The storage ring NIJI-11 is located in themedium-energy experimental room (M-En. Rm) and isequipped wiih the Onuki-type polarizing undulator. The
storage ring NIJI-IV solely dedicated to the free-electron
laser (FEL) experiments is in ihe pion experimental room(P Rm). One more storage ring TERAS, which has
worked since 1981, is in the ring room (Ring Rm).
The operation statistics of TELL for the latest two
fiscal years (FY's) is shown in Fig. 1. In this figure,"Ace. Rm" means the total hours when experiments ormaintenance works were made inside the linac room,
whereas other symbols mean ihe total hours when all theaccelerated electron beams were ready to transport into
the corresponding experimental room. Total hours in FY
2000 was about 1,300 hours whereas that in FY 1999
was about 2,000 hours. This decrement in FY 2000 wasmainly caused by a series of engineering works to renew
cooling-water system of TELL.

+-2.1 Positron Lifetime Spectroscopy

150h100h+-SOhII II

Oh

Apr. 1999

IIIAcc.Rm

Oct. 1999.L-Fn.Rm

Apr. 2000

ElM-En.Rm

Oct. 2000

ElPRm·Ring~

Figure 1: Total hours dedicated to eachexperimental room from April 1999 toMarch2001.
tmikado.tomohisa@aist.go.jp

In the L-En. Rm, we generate -108 slow positrons/s byusing -70-MeV electrons bombarding a Ta target and aW-foil moderator. We constructed a facility for thepositron annihilation lifetime spectroscopy (PALS). ThePALS technique is suitable to detect nondestructively
open volume type defects in a solid material. By the useof the PALS system, we measured lifetime distributionof positrons and ortho-positronium (o-Ps) in lowdielectric-constant films. The samples were hexamethyldisiloxane-based thin films formed by plasma-enhanced
chemical vapor deposition (PECVD) with dualfrequency power sources [1]. Figure 2 shows thelifetime distributions of positrons in the films at anincident energy of 3 keV. As clearly shown in Fig. 2, all
the lifetime distributions have long-lived components
being caused by o-Ps pick-off annihilation.

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10°

BL3-3~PECVDiilt;&lii!t11$1l~

BL4 Lithography,~~ *\1150 nm
HMDSO 50 cc/min
N20 200 cc/min
He 400 cc/min
375"0 1.5 Torr
RF(13.56 MHz) 250 W
LF(380 kHz) 0-100 W•10-1.L,'\LIGATERAS:{\ 10-2.....
~e:~c

300-800 MeV
300mA-R

10-3: (Beam position monitor):(Vertical compensation magnet)

100W

10-4

020

1030

406050

gamma-raystandardi,zation

il!f~~~J (j- /t.P)

RadiographofTH571A

1.0-r-------------------,4.5~-----------·-----~ 0.6-x·~·i

0.4 / .

00.2

1m 2m

Figure 4: Plan view of storage ring TERAS.

Figure 2: Positron lifetime distributions for thehexamethyldisiloxane-based thin films formedby dual-frequency PECVD.

J o.a' \L_L___j04.0 ....
c:~c:

3.5(10 MeV)

8()

3.0 ~~Q)Qj

0· - - - - -...- - - - • 2 . 5

0.0-!----.---.--~--r-..--~-......---,.----.--+2.0

020

40

60

80

100

LF power (W)Figure 3: Cavity volume (triangles) anddielectric constant (circles) vs. LF power ofthe PECVD process.

Figure 5: Photograph and transmission typeradiographs of RF tetrode TH571A.

Figure 3 shows the dependence of the cavity volumeand dielectric constant upon the low-frequency (LF)
power. The figure indicates that the LF power makes thecavity volume smaller; i.e., the LF power compresses thefilm structure. As a result, the dielectric constantincreases. This means that we can control the dielectric
constant by adjusting LF power in PECVD processes.

2.2 Laser-Compton Backscattered Photons
Figure 4 shows the plan view of the storage ring
TERAS. A research project to produce monochromatic
photon beam through laser-Compton scattering (LCS)
processes was started at the position marked as 11 LCS-1 11in Fig. 4 [2]. The facility has been upgraded gradually togenerate completely polarized high-energy photons up to-106 photons/s in the energy range of 1 to 40 MeV [3).
At present, the location LCS-1 is dedicated to the highenergy gamma-ray standardization project. Therefore,
the experimental area should meet the regulations for
ISO 17025 and it became difficult to perform variousexperiments other than standardization program in theLCS-1 area.
We have constructed a new site labelled as 11 LCS-3 11 inFig. 4 for LCS experiments. Recently, we examine thephoton radiography by the use of LCS photons [4].
Figure 5 shows the photograph and transmission-typeradiographs of a tetrode TH571A: The tetrode is used toamplify the 172-MHz RF power to accelerate electrons
revolving in TERAS. The photon energy was 10 MeV
and the scanned area was 100 x 70 mm2 • The
radiographs were taken with two different scanningspeeds. The preliminary experiments prove that the LCS
photon radiography is really applicable to observe insideof opaque materials.

2.3 Free Electron Laser Research
As previously reported, the compact storage ring NIJIIV solely dedicated to the FEL research has been
improved by installing sextupole-quadrupole-sextupole
magnets in all of the short straight sections and by-203-

The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

medical diagnostics, x-ray microscopy, solid-statephysics, materials science, and so on. In this project, weplan to generate hard x rays through LCS processes; thesource of photons colliding with high-energy electrons isFEL. The x-ray energy is 0.1-1 MeV and the wavelengthof the FEL is about 10 !!ill. Therefore, a new optical
klystron was designed. Figure 7 shows the upper half ofthe klystron whose total length is about 3.7 m [7].
Manufacturing of the klystron is under way.

3 ACKNOWLEDGMENTS
We wish to express our thanks to Dr. Kobayashi Naoto,
the Director of the Photonics Research Institute, AIST,and Dr. Tomimasu Takio and Dr. Yamazaki Tetsuo, theformer Directors of the Quantum Radiation Division,ETL, for their guidance, encouragement, and cooperation. The management and maintenance of TELL
are financially supported by the Ministry of Education,
Culture, Sports, Science and Technology (the formerScience and Technology Agency).

Figure 6: Preliminary design of low impedancevacuum chamber at bending magnets for NIH-IV.

4 REFERENCES

Figure 7: Drawing of upper half of optical
klystron for infrared FEL in "FEL-X project."renewing RF cavity [5]. After that, we renewed thepower source of accelerating RF power. Due to theupgrading of the RF system mentioned above, the RF
power being fed into the cavity increased from 1 kW to 4
kW; thus the peak electron density in a bunch increasedby -30% than before.
High impedance of the vacuum chamber forming thering has been remained a serious problem for NIJI-IV,
because it results in anomalous bunch lengthening
through longitudinal RF instability. Very recently, we
replaced vacuum chambers with low impedance ones
except for those at the optical klystron and at the septum
magnet. Figure 6 shows an example of low impedancechamber to be inserted at six bending magnets; thefabricated one was slightly modified. A calculation tells
us that the FEL gain increases more than 10% with theaverage electron current stored in NIH-IV above 10 rnA;
which leads us to the vacuum ultraviolet FEL [6].
At present, we have two major projects with NIH-IV:
one is to shorten the FEL wavelength toward 150 nm, orin the vacuum ultraviolet region, and the other is to lasein the infrared region. The latter is named "FEL-Xproject"; which is expected to be a powerful tool in[1] Suzuki Ryoichi et al., "Pore Characteristics of LowDielectric-Constant Films Grown by PlasmaEnhanced Chemical Vapor Deposition Studied byPositron Annihilation Lifetime Spectroscopy," Jpn. J.
Appl. Phys. 40 (2001) L414.
[2] Yamazaki Tetsuo et al., "Generation of QuasiMonochromatic Photon Beams from Compton
Backscattered Laser Light at ETL Storage Ring,"
IEEE Trans. Nucl. Sci. NS32 (1985) 3406.
[3] Ohgaki Hideaki et a/., "Generation and Applicationof Laser-Compton Gamma-Ray at ETL," Nucl.
Instrum. Methods A455 (2000) 54.
[4] Toyokawa Hiroyuki et al., "Laser-Compton Photon
Radiography for Nondestructive Test of Bulk
Materials," to be appeared in Proc. Int. Syrup. Opt.
Sci. Technol. (Jul.-Aug. 2001, San Diego).
[5] Sei Norihiro et al., "Improvement of the Beam
Quality by Chromaticity Correction for WavelengthShortening in the NIH-IV FEL," Nucl. Instrum.
Methods A429 (1999) 185; "Improvement of the RF
System in the Storage Ring NIJI-IV for VUV Free
Electron Lasers," ibid. A445 (2000) 437.
[6] Yamada Kawakatsu et al., "Characteristics of theNIJI-IV FEL System -Toward Lasing down to 150
nm Using a Compact Storage Ring," to be appearedin Nucl. Instrum. Methods A (Proc. 22nd Int. Free
Electron Laser Conf.).
[7] Sei Norihiro et al., "Design of an Insertion Device forthe FEL-X Project," to be appeared in Nucl. lnstrum.
Methods A (Proc. 22nd Int. Free Electron LaserConf.).

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