JAERI-Conf 95-021

PB48

OPERATION OF LINAC BASED FELs IN IR- AND VISIBLE-RANGEAT THE FELl
Tomimasu, T., Saeki, K. t 1 , Miyauchi, Y., Oshita, E., Okuma, S., Wakita, K.,
Kobayashi, A. t 2 , Suzuki, T., Zako, A., Nishihara, S., Koga, A., Wakisaka K.,Tongu, E., Nagai, A. and Yasumoto, M. *Free Electron Laser Research Institute, Inc. (FEU)4547-44, Tsuda, Hirakata, Osaka 573-01, japan* Osaka National Research Institute1-8-31, Midorigaoka, Ikeda City, Osaka 563, japan
Abstract
Two infrared free electron lasers (FELs) facilities covering the wavelength range of 1-20 ,u m are opened for
FEL users in this October. We are also challenging 0.3 ,u m-FEL oscillations using a 2.68m undulator (A u=4cm)
installed at the 160-MeV beam line of the FELl linac with a thermionic gun. A 0.52- ,u m spontaneous radiationof 0.1W has been observed using a 145-MeV electron beam and the undulator.
INTRODUCTION
The Free Electron Laser Research Institute, Inc.
(FELl) has been established in March 1991 and hasachieved first lasings at infrared- and visible-range
using an S-hand 80-MeV electron linac with athermionic gun driven by a 500-ps, 22.3125-MHz grid
pulser in Oct. 31, 1994 and Feb. 28, 1995,
respectively, in a year from the start of the machine
installation [1 ]. At the FELl there are three freeelectron laser (FEL) facilities installed along by thebeam line of an S-band 160-MeV linac, as shown inFig. 1. The linac and these FEL facilities are locatedin the accelerator room on the ground floor.
The FEL beam becomes rather thick and round due
to hole coupling and is delivered to the diagnostics
room and eight user's stations on the third floor
through the evacuated pipeline, and is further delivered
through a simultaneous FEL beam sharing system [2]from the diagnostics room to eight user's stations.
The FELl 160-MeV linac, the S-type BT line 3[3] and the FEL facility 3 (covering from 0.3 .U m to1.2 ,u m) are in the commissioning stage.
We are trying to achieve UV-range FEL
oscillations using the FELl Iinac with the thermionicgun, taking the advantage of the thermionic gun's
superior performances such as long-life, easy
operation, and low-cost, in addition to some attempts
on low emittance beam acceleration of the order of 107rmm • mrad in the 6-MeV injector [4].

IR- AND VISIBLE-FELs AT THE FELlFirst lasing at 5.5 .U m was achieved using the FEL
facility 1 composed of a 2-m long planar undulator(A u=3.4cm) [5] and a 6.72-m optical cavity [6]installed at the 30-MeV BT line of the FELl Iinac inOct. 31, 1994. The FEL beam can be delivered froma 0.5-mm aperture in the upstream mirror of theoptical cavity to the diagnostic room through a 50-mlong evacuated pipeline as shown in Fig. 1.
First lasings at 1.88 .U m and 0.63 ,u m was achieved
using the FEL facility 2 composed of a 3-m long
planar undulator (A u=3.8cm) and a 6.72-m opticalcavity installed at the 80-MeV BT line of the FELllinac in Feb. 27 and 28, 1995. The FEL beam can bedelivered from a 0.5-mm aperture in the upstream
mirror of the optical cavity to the diagnostics room
through a 40-m long evacuated pipeline.
The characteristics of the linac beams, theundulators used in these oscillations and lasing areshown in ref. [1].
Fig. 2 shows average FEL powers as a functin ofwavelength at a 0.5-mm aperture in the upstream
mirror of the optical cavity. A spectral range of thefacility 1, between 5 and 22 .U m, is covered using threeelectron energy values: 32, 26 and 20MeV. A spectral
range of the facility 2, between 1 and 6 .U m, is also
covered using four electron energy values: 78, 62, 50
and 40MeV. The present maximum average power isPresent address: t 1 Matsushita Electric Industrial Co., Ltd.: 2-7, Matsuba-cho, Kadoma City, Osaka 571, Japant 2 Kobe Steel, Ltd.,: 1-5-5, Takatsuka-dai, Nishi-ku, Kobe 651-22, Japan-383-JAERI-Conf 95-021

0.14W at 7.5 f1 m at the 0.5-mm aperture in theupstream mirror of the FEL facility 1 for 4000
micropulses/s. The FEL micropulse duration is notmeasured yet but estimated to be 10 ps from theelectron bunch measurement with a streak camera.
The peak power is calculated from an average power,
the micropulse duration and the number of micropulsesin the FEL macropulses. The peak powers of the FEL
facility 2 are about 2MW and 0.45MW at 1.88 f1 m and0.63 f1 m, respectively, at the 0.5-mm aperture in theupstream mirror.
The peak power of the facility 1 reaches up to 70%of the theoretical limit EIP/(4eN), where E is theelectron energy (MeV), Ip is peak current (A), e theelectron charge, and N is the number of periods of theundulator. The present intracavity peak power isabout 0.7GW at 7.5 f1 m. Therefore, the average
power of 0.5W will be obtained by using the mirror
aperture of 1mm ¢ and should be 4W at a highmicropulse repetition rate of 178.5MHz of the 500-ps
grid pulser. Considering the fact that the electron
beam diameter is 1mm and the optical beam waist is
2.5-5.4mm for the wavelength A FEL=4.8-22.7 11m,
the peak power as well as the average power will beimproved at wavelengths longer than 10 f1 m ·bychanging the mirror curvature. Furthermore, both will
be improved at these wavelengths by changing theaperture from 0.5mm to 1mm, since the transparencyof FELs declines at these wavelengths.
On the other hand, a 2-MW peak power of thefacility 2 is a seventh of the expected value but this isdue to a small filling factor between the low emittancebeam whose diameter is less than 0.5mm and a
1.5-mm waist of the stored FEL beam at 1.88 f1 m.
Red color beam were observed on the third
harmonics at 1.88- f1 m oscillation and on the fifth
harmonics at 3.1- f1 m oscillation.

[8]. A modulator for the klystron 1VA88R uses
MOS-FET modules [9]. However, a modulator for
the klystron E3729 consists 4 parallel networks of 24capacitors and 24 variable reactors, and it has aline-switch of an optical thyristor stack. The flatnessof our klystron modulator for E3729 is 0.067% at 2411 s duration [10] . An rf-ageing for new four
accelerating waveguides of the high energy section wasstarted in June.
The FEL facility 3 including a 2.68-m undulator(A u=4.0cm, N=67, Krnax=l.9, gap length;;:;18mm)[11]
and an optical cavity (Lc=6.72m) was installed in July.
The optical cavity 3 is the Fabry-Perot cavity
which consists of two mirror vacuum chambers. Eachchamber has a rotating type mirror holder
accommodating eight mirrors. One mirror position isempty and used for alignments of the optical cavity
line and the five OTR beam profile monitors. The
cavity mirror is controlled with a resolution of 0.1 f1 m
or 10 f1 rad. To cover wide wavelength range from 0.3
f1 m to 1.2 f1 m, seven dielectric multilayer mirrors for
IR-, visible-, and ultraviolet-range are installed.
A calculated small signal gain of this undulator is
7.8% per pass for a 0.3- f1 m spontaneous radiation
using a 160-MeV, 50-A electron beam when the Kparameter is 0.95 [12,13]. The net gain is estimated tobe larger than 7.3%, considering that an extraction
factor of a dielectric multilayer mirror is 0.4% and themirror loss per roundtrip of the spontaneous radiation
is 0.1 %. Figure 3 shows a 0.52- f1 m spontaneous
macropulse shape measured with a Si-photodetector(Si-APD C5331-04, HAMAMATSU PHOTONICS
Inc.) and an electron current pulse measured with abutton monitor [14].
The peak power of thespontaneous radiation is about 0.1W on August 18,
1995.

CONCLUSIONSCHALLENGE AT ULTRAVIOLET-RANGE FEL
The 160-MeV linac consists of the 6-MeV injector[4] and seven ETL type accelerating waveguides [7] asshown in Fig. 1. These accelerating waveguides are oflinearly narrowed iris type to prevent beam blow up(BBU) effects at high peak current acceleration. The
length of the linac including bending sections of twoS-type BT systems for two IR-FEL facilities is 46m.
An rf system for linac based FELs requires rf
sources with long pulse duration and high stability.
Our rf sources are a klystron (1 VA88R) for the714-MHz prebuncher and two klystrons (E3729,24MW for 24- f1 s flat top pulses per each) for thebuncher and seven accelerating waveguides. The latterklystrons are modified for a 24- f1 s pulse operation

IR- and visible-range FELs are delivered to thediagnostic room and eight user's stations through theevacuated pipelines and simultaneous beam sharing
systems. The FEU 160-MeV linac and the FEL
facility 3 including the 2.68-m undulator and the6.72-m optical cavity are in the commissioning stage.
References[1] T. Tomimasu, et al., Proc. PAC'95 (DALAS, May1-5, 1995) FAA30[2] S. Okuma, et al., Proc. FEL'95 (BNL, Aug.
21-25, 1995)[3] Y. Miyauchi, et al., Proc. 9th Symp. on
Accelerator Science and Technology, KEK,
Aug 25-27, 1993, p.175-384-JAERI-Conf 95-021[4] T. Tomimasu, et al., Nucl. lnstr. Meth., A358
(1995) ABSll[5] A. Kobayashi, et al., Proc. 6th Int'l Symp. on
Advanced Nuclear Energy Res. (JAERI,March 23-25, 1994) p.589.
[6] K. Saeki, et al., Nucl. lnstr. Meth., A358 (1995)
ABS56[7] T. Tomimasu, IEEE Trans., NS-28, No. 3, 3523
(1981)[8] Y. Morii, et al., Ref. 3, p.l75[9] S. Abe, et al., Proc. 19th Linear Accelerator
Meeting, JAERI, Japan, July 20-22, 1994, p.225[10] E. Oshita, et al., Proc. PAC'95 (DALLAS, May1-5, 1995) TAQ35[11] Y. Miyauchi, et al., Proc. FEL'95 (BNL, Aug.
21-25, 1995)[12] G. Dattoli, et al., IEEE J. Quantum Electron,
QE-20 (1984) 637[13] D. A. Jaroszynski, et al., Nucl. lnstr. Meth., A318(1992) 582.
[14] A. Zako, et al., Proc. 1995 Annual Meeting ofthe Atomic Energy Society of Japan (TIT,March 28-30, 1995) p.326

FEL Facility 151" m-221" m

FEL Facility2
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0.52-/1 m spontaneous macropulse and current pulse