Proceedings of the 22nd Linear A ccelerator Meeting in Japan

PP-21
COMMISSIONING OF FEU FACttHY 5 COVERING THE WAVELENGTH FROM 50 TO lOO^mS. Nishihara1}，S. Okuma2)，K Wakita3) ，丁. Takii, A Koga4)，A Nagai and 丁. Tomimasu

Free E kcbvn Laser Research Institute, Inc. (FEU)
2-9-5, TsudchYamate，Hirakata, Osaka 573-01, JapanABSTRACT
The F EU fa d lify 5 (50-100}im) o f the com pactfacility, including a 224~m long im diilator ( h i = 8 o?% N=28) and a 5.04m long opticalcodify, w as installed a t iJie 2G M eV beam line o f f c 20-M eV S-band linac Milh an RF-gLm in the Laser Instnm ient Room in M arch 1996.
An FEL beam w ill be delw evd jiv m 1he upstream optical cavity to 1he Laser E xperinientd R oan ivviig h a vipelim . The operation o f iheca iip a ctfa cility m cltidng fin d R F a^ng w as begun in M ay' and ihe bean acceleration M'as started in the m iddle o f Jime.

The beam a o rm to f 150-200 mA w as obtcdned jiv m ihe linac in the m iddle o f O ctober and the spontaneous emission w as m easured in iie end o f October.
The FEL osdlM m experim ent is continued.

Table 1 FELI f a c ilit y 5 systan parameters
The ¥K 1 f a c ilit y 5 is an RF linac based f a c ilit ydesigned to extend our FEL ^ p lica tio n s to sanicoiductor

Electrai beam

devices at the far-infrared wavelengths fran 50 to 100 ji

Macropulse lm gth

4 -5 /zsm[l].

This paper w ill review the design, coistruction andMacropulse repetition rate10 Hzstatus.

The distinguishing characteristics of the FEL

f a c ilit y 5 are the use of a thermiaiic-cathode RF gun, aMicropulse length

3_5ps

Micropulse r e p e titim rate

2856 MHzPV3020 k lystrai driven by a l Of i s modulator with a FRi ofBeam energy

18 MeVtwo parallel by 24 sectors, and a 2.24 m long， 28 periods

Hfecropalse current

150-200

NdFeB Halbach undulator.

The design woik of the FELI

f a c ilit y 5 was began in 1995，and the syston was in stalled

Ihdiilator

m the presort s it e in March 1996.

PeriodSince th m , the svstan

has been under caitinuous improvenent.

Spontaneousenissian was f ir s t ly observed in October 1996.

8 an

Number of periods

28

Gap

30-150 mn

K—value

1~2.3

2 Descrqitkm of the madiine performance
The goieral layout of FELI f a c ilit y o is shown in Fig.

Optical cavity

1 . The system parameters are showi in Table 1 . TheseCavity length

5.04 mvalues are presait operating values.

Operating wavelength50-100Mirror ra a n upstream

2.662 m2.662 mdown streamMirror reflectance99 %Raylei^i lm gth0.6 m

2.1

The thermionic RF gun
As an injector, the RF gun c o is is ts of two parts, thegun cavity and tiie aljiia magnet.

The electrons are

emitted by a 3 mn diameter LaB 6 cathode.

They areaccelerated across a 3 an gap by the RF fie ld in the cavity.
Presait a d d r ess;1)Mitsubishi E lectric Corporation, Conmunication Equipoeit Works, E i a i 丄：nishiha@cew.melcaco.jp
2) Toshiba Corporation, 3)Daihai Corporatin, 4) Mitsubishi tfeavy Industries, LtdThe electrms emerge from the cavity thra^i steering andtriple quadrupole magnets and tbm pass throu^i the aljiia

after the accelerator

magnet.

sectimThis magnet selects most of the electrons in s o d baiergy range, and bunches tbm for injecti<xi into theaccelerator.

|before the accelerator

Since the electroi energy is not very hi由，J sectiai

the aoerging bundles will lengthen as they pass throu^i thedrift sectiais before and after the alfiia magnet.

The， い 丨 附 腿 *i B f c 一 を 面

alfiia magnet is configured to have a positive m i m t i m
caDpressiai factor,

and tte debunching of the drift

sectiais must caEpeisated by the overbunching in themagnet.

V: 200rrWdiv.

Fg. 2

H: 2^s/div.

Electron beam maaDpulses before and after theaooelerator section^ince the diumsioi of the alfiia magnet and thelaigth of the drift sections are fixed,

in order toincrease its bundling effect we must increase the electrai
energy anerging fran the gun cavity while increasing the2.4 The beam transport line
Along the electrai beam line, seven screei miitors aremagnetic field to keep the electron path undianged in theprepared

The electrai beam size and positioi are alwaysmagnet.

This indicated that electron bunches werenmitored and controlled to pass throu^i the center ofcxmpressed to a few picosaxnds at the artrance of theaccelerator section using screen monitors installed at theinlet and outlet of accelerator section.

linear accelerator.
It is known that the badc-booterdmait effect could
cause beam currart to increase witnin macropulse.

This

Further, using

five screai monitors installed in the S-type BT line for
the FEL facility，the beam size and position are adjusted

beam is gmerally not suitable for acce丄era.ti<xi because ofalong axis so as to pass throu^i the carter of a narrow

beam loading.

vacuum chanber inserted into the undulator. The systen ofThis is the main reasoi we do not use theffowsver，thefirst and secaid 22.5° -bending magnets are satisried{iioto-cathode RF gun will be used the f u l l 10 " s pulse

achromatic coiditioi，and parallel beam is transported

lengthbetweei thanf u l l 10jus pulse laigth of the Klvstroa

As a result of achranatic transport，thefocused electron beam passes throu^i the undulator.
2.2

The

beam passing throi#i the undulator is focused and sent toThe hi^i power RF syston

a beam dump using a 4o -bmding nagnet.

The RF systan caisists of a 20 勝 nigh po\\Br klvstrcxi
drivai by a 10 kW klystroi，1H2436.

This PV3020 klystronwas developed for a 10- fi s pulse operatiai from thePV3030A3 klystrm

2. 5The undulator

A modulator for the PV3020 klystronThe undulator is of the Halbach type with NdFdBassists of 2 parallel networks of 24 capacitors and 24

permanait magnets of 28 periods of 8 cm The dimensions ofvariable reactors, and it has a line-switch of the F-241

a caiponBit permanent magnet is 10 X20 X170 mrf.

thyratroa

magnetic field and the correspmding K-value cover theThe flatness of our klystrai modulator for

ranges of 1300-3100 G and 1-2.3， respectively, according

PV3020 is 0.3% at 10/is pjlse operation*

to the gap range of 38-60 n m
2. 3 Linac section
An EIL type 2 m laig accelerator section is used foracceleraticrL

This accelerator section with a length of

2 m is of linearly narrowed iris type to prevait beam olow
up (fflJ) effects at hi^i peak current acceleration,rig.

2 sk)ws the electrai beam macropulses before and after theaccelerator sectioi
The measured mergy spread is 0.6% at FWHM

The bunchwidth after acceleiation, m s measured with a streak
camera with 2 ps time resoluticrLof about 3-5 ps.

The peakIt gave an FWHM value

While, the range of the gap

distance can be set to cover 30-150 mn.

Fig. 3 shows the3. !^)ontaneous emiss^mThe Ge-Ga detector cooled by liquid helium is used forassanbly plan of the undulator.

detecting the spmtaneous anissioa The detector spectral
2.6

respaise is provided by 52 micrai cut-oi filter installed

The optical cavity

at the coie entrance aperture.

The optical cavity is a Fabry-^erot cavity which

are shown below.

The measured parameters

The signal at preamplifier output at

axisists of two mirror vacuum diambers. The cavity mirrors

1000 Hz of this detector is 0.6 V.

are s{terical and gold coated m copper substrate.

falling cn detector of 0.455 /iW.

AnThe diopped power

The noise referaice toaperture of 3 nm dianeter in the upstream mirror provides

the detector is 1.82mV人T Hz.

oatcoupling of a fractiai of the optical radiatiai.

The cmstant background power is 2.17E-06 W.

After

The S/N ratio is 3.3CE+05.

extractiai fran the upstream mirror, the laser beam passes

NEP is 1。3部 -12.

throu^i a vacuum pipe and sait to the diagnostic room.

current respmsibility is 1.32 E+02 A/W.

optical window

Thelow and hi出 vacuum is used diamond,

while tte output window is used polyethylaie.

rig. 4Same way as the other F H J facility was used to alignThe optical axis of two mirrors isadjusted to coincide with the electrai beam position.

TheFig. 5 shows both the electrai pulses (lower 3 parts)and the spontaneous emission (upper part).

The electronpulses 1-3 are of before and after the accelerator sectiai

shows a bird’s eye view of the FELI facility 5.
the cavity [2].

The measured

The quantum efficiaicy is 1.05E-02.

Theand before the undulator, respectively.

The experiment at

the beam currmt of 200 nA is not measured because of theRF breaking in the gun cavity.

After this breaking, theeiectroi beam position is detected using three profile

beam current of 200 nA is not obtained fran the accelerator.

nmitor in the undulator and images of profile at the plate

Therefore, it will need more RF aging for the linac toare observed by CO) cameras.

achieve the more beam curreit operatioa

The referoxe He-Ne laser

was used to nmitor the position of the tv'D mirrors by
Spontaneous esnissioi

observing the shift of the laser spot reflected fran thetwo mirrors.

First, the reference laser beam is reflected
before the undulator

to the optical axis by a beam splitter, ana is reflectedby the dovMistream mirror.

Then, images of the laser
after the accelerator

profile is observed to reflect by a beam splitter with theupstream stopper of a beam splitter.

sectimSecaidly, the laser

beam throu^i a beam splitter is reflected by the upstream

before the accelerator

mirror without the upstream stopper of a beam splitter, issection
Fig. 5 (a)reflected by the downstream mirror, and then images of thelaser profile is observed to reflect by a beam splitter.

Spaitaneous onission

The secondly observed laser spot is adjusted to coincidewith the firstly observed laser spot by the tilt of the

before the undulator
after the accelerator
sectiai
before the accelerator
sectionFig. 5(b)Fg. 5Spontaneous emission measuned with a Ge<3adetector at 80//m

Refaiences[1]T. Tomiinasu, et al, Nucl. Instr. and ]\feth, A375 (1996)
626-631.
[2] K. Sadki, et al, Nucl. Instr. and ^feth, A375 (1996)
Fig. 4 Bird's eye view of the FEU facility 510-12.