PULSED BEAM DEFLECTION AND TRANSPORT SYSTEMS OF THE ETL LINAC
S. Sugiyama, T. Noguchi, T. Yamazaki, T. Mikado, M. Chiwaki and T. Tomimasu
Electrotechnical Laboratory
Sakura, Niihari, Ibaraki, 305 Japan
ABSTRACT

current loss low and should have a high mechanicalstrength. Fig. 4 illustrates the arrangement of thepulsed coils and the ceramic beam duct. The ceramicvacuum duct used here have a length of 40 em, an overall
diameter of 7.6 em and wall thickness of 0.7 em and its
inside surface is coated with a low resistivity titanium
compound. Fig. 5 shows the wave form of RF power
measured at a water dummy of the 9 th accelerating tube.
The linac is operated in a pulse repetition rate of.50
pps. The patern of beam loading shows that a half of thepulses of electron beam are deflected. The deflection
system has no effect on the electron beam accelerated in
the succeeding accelerting tubes.

The pulsed beam deflection and transport systems
have been designed and constructed to deliver theelectron beam from the linac to the low energy
experimental room. Some characteristics of the systems
and some results on the performance are presented.
INTRODUCTION
For the multipurpose use of the electron beam,pulsed beam deflection and transport systems aredesigned at the three energy seitions, that is, low,
medium and high en2rgy sections • The pulsed beam
deflection systems are operated to split out the pulsed
electron beam alternatively and to have no effect of theresidual magnetic field on the electron beam in the
succeeding accelerating sections. The program of thestandadization of the electron absorbed dose in low
energy range is now planning and good focused electron
beams are required in this experiment. At low energy
section, the pulsed beam deflection system combined witha beam transport system provides the electron beam tothe low energy experimental room. The systems arecontrolled to have a point imaging on the entrance of awater bath for the calorimetric measurement of absorbed
dose.

AT-6
PC\0FC-1

7.5

ACCELERA10fl ROOMPULSED DEFLECTION SYSTEM
The plan view of the pulsed beam deflection andbeam transport systems is illustrated in Fig. 1. PC
refers to 7.5° pulsed deflection system, DL-I and DL-II
dipole magnets (bending angle 42° ), QE quadupole
singlet, Q-1"'3 quadrupole doublets, SL the energydefining slit system,TR-1'¥ 3 beam position monitors
using optical transition radiation 3 and FC-1 "" 3 Faradaycups. The pulsed deflection system is designed todeflect electron beam of momentum up to 80 MeV/c by anangle of 7.5°. This system is set at the loction between
4 th and 5 th accelerating tubes. The coil pair consistsof two saddle shaped coils with a length of 36 em and awidth of 12 em and is set with a ceramic beam duct of
7.6 em dia. compactly. The advantage of this shape is toobtain sufficiently strong magnetic field to deflect
electron beam in a very short distance and to reduce thebackward magnetic field in the fringe of the pulsed
coils. However, this structure slightly sacrifices theuniformity of the magnetic field in the off-axis part ofthe coils. The pulsed coils are excited by a silicon
controlled rectifier pulser which produces a current in a
half sinusoidal wave of 300 Hz at variable repetion
rates from 25 pps to 100 pps The exciting pulse current
circuit oscillates for little more than a half cycle andovershooting is prevented by a simple crowbar circuit asshown Fig. 2. Approximately 50 % of thePl.ll.lile .energy isreturned to a capacitor bank by the crowbar circuit.
Fig. 3 shows the wave of exciting current. The flattop
is maintained within 0.4 % for 50 psec. The stability ofpeak current is mainly limited by the thermal change ofthe charging capacitor bank and estmated to be 0,5 % for
one hour. The pulsed coils are wounded by copper braid
insulated with heat-treated glass fiber. To preventmechanical self-destruction and movement induced byexcitation, the coils are clamped by massive wooden
frames and bolts inserting insulation pads be~ween thecoil and the frames. The magnetic field strength needed
to deflect 60 MeV electrons by an angle of 7.~ is 725
gauss and. the corresponding pulse current is 179 ampere.
This mgnetic field is lower by 16 % than that estimatedfrom the experiment in the case of the de current
exciting. It is due to the eddy current loss in thecoils. Since the coil pair is excited by pulse current,
the beam duct installed between the saddle shaped coils
shoud have high electrical resistance to keep eddy-

LOW ENERGY EXPERIMENTAL
(Q-3)
ROOM

TR-3

169

Fig. 1

Plan view of the pulsed deflection and transportsystems.

Fig. 2

Schematic diagram of the exciting pulse current
circuit.

Fig. 3Fig. 5

The wave form of excitin pulse currnt. 1 V/div,0.5 msec/div

The wave form of Rf power measured at a water
dummy of 9 th accelerating tube.
Table 1Main parameters of magnetic elements

Dipole magnets ( DL )Radius ( m )Deflection angle ( degMaximum field ( T )Gap ( mm )Effective length ( mQuadrupole magnet ( QEBore radius ( em )Effective length ( mT/m
Maximum field gradientQuadrupole magnets ( Q1 3 )Bore radius ( em )Effectiv length ( m )Maximum field strength ( T/m )0.6087420.6360.446270.21
2.98
40.186
3.6

SYSTEM OPERATION

Fig. 4

To find out the optimum operation point of thepulse deflection and transport systems, beam positions
are monitored by observing optical transition radiationfrom Al plates • Electron beam profiles are alsomeasured by the use of the pattern of discolored spot of
polyvinyle chloride film caused by electron irradiation.
Fig. 6 shows the momentum spread of electron beam into a
Faraday cup at the exit of the analysing tube of the DLI. Optically considering,the pulsed beam deflection andtransport systems originate from the position of theShematic view of the arrangement of the pulsed
coils and the ceramic beam duct.
BEAM TRANSPORT SYSTEM

The purpose of the beam transport system istwofold;it delivers efficiently the .electron beam fromthe linac to the low energy experimental room and also
makes fine preselection of momentum of the electron
beam. Table 1 shows the main parameters of the magnetic

1.5

Ee = 51.1 MeV:~:::~~sf!~ !~6 ~=~~e:~~~~P~= :~=~~m;h!;oh~~=~pe sector
homogeneous magnetic field with a same entrance and exit
angle of 11.7° • The advantages of this design are thefollowing: the fabrication of the homogeneous-field
1.0
PC
magnets is of cause easy and this magntic structure isequivalent to a structure with a field index n = 0.5 atmagnetic field along radial direction and without edge
focusing. Two types of quadrupole magnet are used; the ~uTR-1
bore radii of 7 em for a singlet and 4 em for threedoublets. The quadrupole singlet QE is placed midpoint
0.5
between two bending dipole magnets DL-I and DL-II andalso provides a control for varying the beam dispersion
over wide range at the slit location. The symmetry
arrangement of DL-I - QE - DL-II is for the purpose of
making the beam achromatic in the beam transport system.
0Quadrupole doublets Q -1-3 limit the horizontal extent200150of the beam through dipole magnet DL-II and cotrol thePULSE MAGNET
beam size in both horizontal and vertcal planes at theFig. 6 The momentum spread of electron beam into aexit of the transport system. All m~net power supplies
Faraday cup.
have a long term stability of 1 x 10 •..

"'

170350pulsed coils where the accumulation of beam matrix
starts. For the calculation of the beam envelope of thesystems,we use the following accelerator beamspecifications; dimensions X = y = 3 mm, divergences 6 =~= 0.1 mrad and momentum spread~ 3 %. Fig. 7 shows thebeam half width fo both holizontal and vertical planes.
Fig. 8 shows a beam profile caused by electron
irradiation on polyvinyle chloride film which was set atthe exit window of the beam transport system. It showsthat the electron beam is well-focussed and the pulsed
beam deflection and transport systems have the uniquecapability in the beam control for the low energy
experimental facilities.

~0~ 30ENERGY58.5 MoV

K~

3.43/m'1.85/m 2
3.98 /m 2
5.48/ m2
5.20/

K-1-F
K-1-0
K-2-F
K-2-Dw

gw 20>

m'zw 1015( m)2010e • 0.5 m rod0o n oon

PMOL

QD-1

QE"DL, nnQD-2

Fig. 7

Beam half width of horizontal and vertialplanes.

Fig. 8A beam profile measured by th use of the patternof discolored spot of polyvinyle film at theexit window of the beam transpot system.
REFERENCES

1.
2.
3.

T. Tomimasu, IEEE Trans., NS-28, 3523, 1981
s. Sugiyama et al., Proc. the 4th Symposium on
Accelerator Science and Technology, RIKEN, 343,
1982
T. Noguchi et al., Ref. 3, 129, 1982
:ct,U'171