The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

PRESENT STATUS OF THE KU-FEL PROJECT 2003
T. Yamazaki, H. Ohgaki, T. Kii, K. Masuda, S. Hayashi, A. Miyasako, and K. Yoshikawa
Institute of Advanced Energy, Kyoto University
Gokasho, Uji-shi, Kyoto 611-0011, Japan
A compact and economical FEL facility (KU-FEL) is
under construction at the Institute of Advanced Energy,
Kyoto University. The outline and present status of thefacility are described briefly in this paper.

bombardment effect inherent to an RF gun with athermionic cathode are underway. A 20-MW klystron anda 3-m accelerator tube have been installed and tested. A
beam transport system, vacuum system, a planar
undulator, an optical cavity are ready to be installed.

INTRODUCTIONACCELERATION SYSTEM

The purpose of the compact and economical FEL (freeelectron laser) facility (KU-FEL), which is underconstruction at our Institute is to establish linac-based
FEL technology and explore new application fields
especially in advanced energy science, e. g. researches on
bio-energy, bio-chemical reactions, and materials fornuclear fusion. For these purposes the wavelength of theFEL should span a wide wavelength region from infrared(IR) to far-infrared (FIR). A conceptual view of the KUFEL project is shown in Fig. 1. The electron beam of 20 ~40 MeV with macro-pulse length up to preferably 7 µs
will be provided by an S-band linac with a RF (radiofrequency) gun. A two stage FEL system (e. g. a MOPA
(master oscillator and power amplifier) system) is planned
for the future to enhance the output power without
deteriorating the laser quality. Generation of quasimonochromatic x rays of several keV by exploiting aFEL-Compton backscattering is also planned. An energy
recovery system is considered to save energy and reduceshielding duty. A 4.5-cell thermionic RF gun driven by a10-MW klystron (#1) has been constructed and anelectron beam has been extracted. Measurement of beamcharacteristics and quantitative study of back-Acceleration system of the KU-FEL consists of a RFgun, a 3-m accelerating tube (linac), a beam transportsystem (BTS) from the RF gun to the accelerating tube,and a BTS from the linac to the undulator. The plan viewof the present KU-FEL system is shown in Fig. 2, whereequipments with dotted lines are going to be installed inthe near future. The overall size of the whole system isabout 7 m × 3 m. Numerical simulation of the electronbeam characteristics up to the entrance of the undulator[1] and measurement of the emittance and energy spectrain front of the accelerating tube [2] are under way.

Abstract

Trigger
Generator
Modulator #1
Application
Room

Klystron #1
X-RAY
BEAM

SingalGenerator

RF Gun

FEL

Accelerator

PZT IIRF Gun

A thermionic RF gun is used as an injector because it
has features of compactness and high brightness of theoutput beam. The gun consists of a 4.5-cell cavity with a
10-MW RF driver, which provides an electron beam ofabout 4-MeV. Numerical investigation has shown that theRF gun has enough performance [3]. The parameters of
the RF gun and its RF source have been described in aprevious paper [4]. Measurement of beam characteristics
is under way. However, the back-bombardment ofelectrons limits the macro-bunch length to below a fewµsec at present. Temperature rise due tothe back-bombardment was measured
quantitatively for the first time in theModulator #2
world [5]. Evaluation of the heat due tothe back-streaming electrons has been
Klystron #2
made using the above experimental result,results of particle simulation, and a heattransport model [6]. Use of a LaB6
cathode of small diameter together with asweep magnet to deflect the backstreaming electrons seems to bepromising [7].

Undulator II

Undulator I

Amplifier

Main
Oscillator
PZT I

Figure 1: Conceptual layout of KU-FEL facility.

LinacA 3-m accelerator tube and a 20-MW
RF power source have been prepared andtested. The main parameters of the linac
have been described in a previous paper[4]. Nominal parameters of its RF source
are shown in Table 1.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

Faraday
Cup 2
B-2

Faraday
Cup 3

SC-3
CT-3

Slit
B-1

Faraday
Cup 1

SC-1
CT-1

Fig. 2 The plan view of the present KU-FEL system, where equipments with dotted lines are going to be installed in
the near future.
Table 1. Parameters of the RF source of the linac.
Klystron:
Peak Power:
Pulse Duration:
Repetition Rate:
Modulator:
Pulse Duration:
Ripple:Mitsubishi PV3030A2
20 MW
10 µsec
10 Hz
remote controlled PFN>10 µsec(flat-top)< 0.3%p-p

Signal Generator
HP8665B

delayedtrigger

CW ampA250-SMA-H

Trigger
Generator

maintrigger

Couplerphase shifter
A-B

Pulsed Amp
T146-53DDB

40dB
coupler

C-D

RF TestThe linac and its RF source have been installed.
Recently, the RF test of the system was carried out.
Figure 3 shows the circuit diagram of the RF driver andtrigger system. The macro-pulse duration of the electron
beam generated by the RF-gun can be varied remotely by
the delay module. On the other hand, the pulse duration of
the accelerator is fixed to 8-10 µs. The output pulse shape
can also be modified by adjusting the inductance remotely.
Figure 4 shows the output power of the klystron #2.
According to the specification of the PV-3030A, themaximum output power is about 28 MW with 240 kV.
However, about 15.5 MW with 240 kV was obtained in
the test measurement because the klystron was rather old.
We also measured the perveance of the klystron, which isshown in Figure 5, and found that the perveance was 1.82
µP, which is lower than its nominal value of 2.1 µP.
During the test acceleration we will use this klystron tube
for a while, and then replace it with another one.
Although we have not received permission of the finalacceleration, we have carried out numerical calculation toevaluate the electron beam parameters [1]. The

Pulsed Amp
AET-RFD-200
fixed duration

161530dB
coupler(-0.25dB)

klystronThomson modulator
TV2019modulator
60dB
coupler

14Output Power (MW)Programmable
Attenuator

klystronMitsubishi
PV3030interlock
REMOTE

131211

SG:2855.54 MHz, +6.0 dBm
Focus Coil: 9.70 A

10circulator

60dB
coupler

MonitorMonitor

60dB
coupler

Monitor

60dB
coupler

Monitor

9Monitor

8rf gunaccelerator

Figure 3 Circuit diagram of the RF driver and trigger
system.

195

200

205

210

215

220

225

230

235240Vk (kV)

Figure 4 Output power of the klystron #2 as afunction of cathode voltage.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

2.05

24.6 MeV
30.5 MeV
36.4 MeV

40
1.95

1.85

1.80
501001502002503020

1.00.80.60.4

10Vk (kV)

Figure 5 Perveance of the klystron #2 as a functionof cathode voltage.
calculation has been performed with PARMELA and theBTS parameters were calculated by TRACE3D.

FREE-ELECTRON LASER
A planar undulator and an optical cavity are ready to beinstalled after the BTS following the linac.

Undulator
A planar undulator that was used for a lasing
experiment under the collaboration of the FELI (FreeElectron Laser Research Institute) and the University ofTokyo will be used in our initial experiment. It has been
modified from a fixed gap to a variable gap for easy
handling in practical use. The main parameters of theundulator and the electron beam are listed in Table 2. The
electron-beam parameters are for typical beam energy of
36.4 MeV.
The FEL gain for electron beam energies of 24.6, 30.5,
and 36.4 MeV calculated with TDA3D code [8] areshown in figure 6. It was found after a successive
simulation that macropulse width should be longer than 3µs for FEL saturation [1].

CONCLUSIONS
Outline and present status of the KU-FEL project has
been described. Acceleration test will be begun in quite anear future after the permission of Ministry of Educationand Science.
Table 1. Parameters of the undulator and the electronbeam.
Undulator type: Halbach (permanent magnet)
Period:40 mm
Number of periods:
40
Gap:
26 – 56 mm
Peak magnetic field:
0.25 – 0.05T
K value
0.95 – 0.17
Energy:20 – 40 (36.4) MeV
Peak current:
40 A
Bunch length:
1.8 psEnergy spread:
0.40 %
Normalized emittance: εx ~ 11.3 π mm·mrad
εy ~ 10.1 π mm·mrad

0456789 10 1112 130.2

K- value

1.90Gain (%)

Parviance (µP)

2.00

Wavelength (µm)

Figure 6 Expected FEL gains.

ACKNOWLEDGEMENTS
The authors wish to thank the cooperation and advicesof Prof. A. Noda, Dr. Y. Iwashita, and Mr. Shirai of
Institute of Chemical Research, Kyoto University, Mr. K.
Yoshida of Quantum Science and Engineering Center,
Graduate School of Engineering, Kyoto University, Dr. T.
Mikado of Institute of Advanced Industrial Science andTechnology, Mr. E. Oshita of Nissin Electric, Co., and Mr.
Y. Nishinosono of Institute of Advanced Energy, Kyoto
University.

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