Design and Performance of the 40 MeV
Linac and neam Transport System for the 1 GcVSynchrotron Radiation Source at SOHTEC
M. Shiota, A. Hiraki
Communication Equipment Works, Mitsubishi Electric Corporation,
Tr.uk:J.guchi Honmachi 8-1-1. Amagasaki, Hyogo 661. Japan
M. Mi zo La . T. I i da
Accelerator Projects. Nuclear Fusion Development Dept, Mitsubishi Electric Corporation,Marunouchi 2-2-3, Chiyoda, Tokyo 100, Japan

M. Haraguchi, K. Kuno
Kobe Works, Mitsubishi Electric Corporation, Wadasaki I-I-2. Hyogo-ku. Kobe 652. Japan
S. Nakamura, M. Ohno
SORTEC Corporation. Wad a i 16-1, Tsukuba 300-42, JapanT. Tomimasu
Electrotechnical Laboratory, Umezono 1-I-4, Tsukuba 305, Japan(UABSTRACTA I GcV synchrotron radiation source (SOR) system has
been installed and is now being adjusted at SORTEC corporation. This paper reports the configuration and thebeam test results of the 40 MeV electron linac (preinjector) and the beam transport line to the electron
synchrotron used in this system.
The output beam from the linac musl be low emittance,
small energy spread, and stable in energy. The beamtransport line must also efficiently lead the beam fromthe linac to the electron synchrotron. This linac
produced the beam current of 130 mA, with an energy
spread of 1. 3% (FWHM) , and an emittance of 0. 7 7! mm · mrad.
The beam characteristics were verified by various beam
monitors on the beam transport line.

INTHODUCTION
The essential function of linac that serves as a preinjector of the SOR system is to provide high quality
beam. The value of both emittance and energy spreadrequired for this linac are an order of magnitude
severer than those for the conventional industrial or
medical electron linac. This report includes measurestaken in designing to meet these severe conditions andtest results of beam quality. About the beam transport
line, discussions center on design of the device
configuration and beam trajectory.

LINAC DESIGNIn designing the electron linac, the following
measures were taken to minimize the output beam emittanceand energy spread, and to st.abi 1ize the energy.

PB,

Generation of low emittance electron beam
To acquire low emittance output beam, it is important for the electron gun to emit beam withlow emittance. A low-perviance electron gun isused to obtain electron beam with small
divergence angles. The emitted electron beam isthen forced to pass through a circular slit andthereby outer beam is cut out. The central
electron beam of low emittance only is used.
(2) Enhanced electron beam trapping efficiency
For efficient use of electron beam, we employeda double-prebuncher system that has two single-gap
prebunchcrs arranged in the direction of the beam
acceleration axis.
The above two measures are major· means tominimize the emittance.
(3) Use of a buncher accelerator tube with excellentbunching characteristics
Heducing the energy spread of incident electron
beam into a small angle is more effective in
minimizing the output beam energy spread. This
prompted us to use a 7! /2 mode s landing wave
buncher as the buncher accelerator tube in placeof the conventional traveling wave type. For themain accelerator tube, a 27! /3 mode traveling wave
type is employed.
(4) Stabi 1ization of dominant parameters for output
beam energy
The parameters are stabilized with respective
minor loops. The klystron output is stabilized byusing a shunt regulator type pulse modulator.
This modulator stabilizes the output pulse voltage
below ±0.1% by directly controlling the P.F.N
charging voltage.
These two measures are major means to minimize
the energy spread and stabilize the energy.

Figun: 1 Con! iguralion of I inac bco.m I ine-10-LINAC CONFIGURATION
Figure 1 shows the configuration of 1inac beam 1ine
designed as described above.
It is designed to produce the current of 200 mA or
more through the 2 <b s I it at the anode vo llage 90 kV
using a triode type electron gun.
The double-prebuncher in which RF voltages 5 KVP and!5KVP are applied to the first and second prebunchers,
respectively, bunches 75% {corresponding to 270' )of
the electron beam into so· in phase angle.
The buncher accelerator tube is a side coupled
standing wave type which has nine cavities. The calculation of beam dynamics shows that the output energy
Table .I

5.3 MeV, energy spread 4%. and beam current !50 mA are
obtained at the input power of 2 MW. It is also provedthat the incident beam with the bunch width of so· isbunched in to s· .
The main accelerator section consists of two quasiconstant gradient traveling wave accelerator lubes(27!/3 mode), can accelerate the beam current 150 mA up to40 MeV at the input power of 8 MW. Each accelerator tube
has 63 cavities.
A single S-hand pulse klystron (PV-3035A)is used as
the RF source. Although the rated peak power of PV-3035A
is 35 MW, the RF source is designed to produce about
20 MW. The klystron output is distributed to fivesystems, where a phase shifter and an attenuator areinstalled as required.

Results of output beam performance.. !!

Measured value

Design value

210 mA

200 mA

Energy (buncher)

6.5 MeV(2.4MW)

5.3 MeV (2MW)

Emittance(buncher)

2. 47r:mm·mrad

Energy (output)

40 MeV

40 MeV

Beam current(total)

130 mA

150 mA

Beam trapping effi.

62%

75%

Beam current(usefu ll
Pulse width

60~80!.7.us!.5J,.£S.t:.E/E (FWIIM)
Beam si:z.e
Beam divergence±0.67%±!. 5 mm
±0. 6mrad ·±!. 5%± 2mm· ± 3 mrad·

Emittance {output)

0. 7 7! mm · mrad3. 87!mm·mrad

I t e mGun emission~( •1.33"mA!-ci; ~--40 MeV'e..... i 0. 77!mm·mrad

. 1!

mm 22

Beam· intensity 10% --~.....:.:j_•. !

I ..... 1'.:._Ji----1---:--k· -! -~l--~~~~-:. . _;30 mAFigure 4 Emittance of linac output··;t:''( FWHM)

0.2A

10,.

20(A)

Analizing magnet current
Figure 2 Energy spectrum

Beam energy

1%Figure 3 Fineslruclure of beam energy-11-6.5 MeV
2. 4.7! mm·mrad

LINAC

BEAM PERFORMANCE TESTTab lc I lists the results of output beam performance
tests that agree well with the design values.
The measured energy spread proves lhal AE/E is±0.67?6. within 1/2 of the design value.
figure 2 illustrates an example of measurement charts.
Figure 3 shows the finestructurc of beam energy,
The beam emittance obtained from the area of the phasechart in Fig.4 is about 0. 7 n:mm·mrad.
The beam emittance at bunchcr· outlet ohlained from areaof lhc phase chart in Figur·e 5 is about 2. 4 n: rnm·mrad.
ln addition to above results, lhe fact that theobtained beam current has attained double or more value
shows that these comprehensive beam characteristcs fully
meet the requirements of the pre-injector to an electron
synchrotron.

rrom LJNAC'Voo;,t''-00l~l1r.

I ON PUMP. ,G MONITORO"SY.?

'6M1

GF6~"

,. ·'~~·.

_/Ft.R>.OAY CUPSLIT~igure b

The layout of low energy beam transport line!mml

70. 00
BEMl SIZEo X

60. 00• y

50.00

LOW ENERGY BEAM TRANSPORTLINE (LBT)The layout of the LBT is shown in Figure 6. Two dipolemagnets, nine quadrupole magnets and correction coils
are involved to consti lute a favorable beam optics. Thisline can be divided into three sections from thestandpoint of the optics.
(I) The straight section from the l inac.
(II) The bending section of !01" .
( ][) The straight section to the synchrotron.
The straight section ( l) consists of four quadrupoles
to have a flexibility to optimize Lhe beam dynamics into
the bending section, whenever the incoming beam shapefrom the 1inac is distorted.
At the bending seetion (!I ),a non-dispersive deflection system (which means telescopic as well as achromaticsystem) are constructed with two focusing quadrupoles
and two 50.5" bend dipoles each of which has edges of
13.87" . The beam should be so focused at the center ofthis system with the maximum momentum dispersion that wecould, if necessary, make energy-distribution analysisof the beam as well as energy selection, using a slit.
The straight section (D[) is similar to the section(I) in respect of the beam matching and consists of fivequadrupoles, which enables us to adjust not only
betatron functions but dispersion function with thereduction of the focusing strength of the downstream
quadrupole of section (JI ). It provides, therefore nondispersive transport as well as dispersive one .
Figure 7 shows the beam size of the LBT calculated withan estimation of the emittance of 0. 7n:mm·mrad andmomentum spread being not greater than ± l. 5%.
The large beam size at the downstream is mainly
attributed to the large dispersion function.
Distortions of the beam orbit should be adjusted withfive correction coils followed by wire-grid monitors.
The parameters of these magnets are summarized atTable 2.
According to the above classification in optics,
three kinds of apertures are adopted to the beam chamber.
Their dimensions are 56. 5mm in inner diameter, 40mmX80mm
cross section, and 97. 6mm in inner diameter, downstrearn
along the. line. The main pumping is achieved by twosputtering ion pumps with the pumping speed of 140P /seach, associated with a turbo-molecular pump(!OOP /s)and a rotary pump (100 P /min) for rough pumping. Thebeam-on operating pressure of I X 10-• torr, or less isrealized by the system.

40.00

Table 2:30. 00..= . /.

20. 00

NumberLengthDipole

244.07 em

etc
0.27 T 13. 87" edges

Quad. (1)6Quad.

'rG1(2)5
1 - - - - - - - ·t - - ·'o'G3

Correc.

1----'-+H+-t-f--+t-'-++--+0-+--++-88 8 I 88 ~~001 QF2003 QF4 IJ,ll QF5 QF6 !J,12

Plgure 7l~e

007 008 QF9 0010 QF11Field strength (max.)

LT y p e'··········•..

10. 00The parameters of the LBT magnets

510.0 em

4.0 T/m

10.0 em

3. 0 T/m

5. 0 em

0. 055 T·-Y-SMl

REFERENCE

beam size
(1)

-12-

S. Nakamura et al.
Proc. of the 13th Linear
Accelerator Meeting in Japan (Sept, 1989)