JAERI-Conf 95-021

PA46
Correcting Slanted Beam Profiles in Superconducting Storage Rings.
Koji YAMADA, Masayuki NAKAJIMA, and Teruo HOSOKAW A
LSI Laboratories, Nippon Telegraph and Telephone Corporation (NTT)
3-1 Morinosato-W akamiya, Atsugi, 243-01 Japan
Abstract
In the Super-ALIS superconducting storage ring forsynchrotron radiation, the electron beams have been
suffering from slanted profiles. These profiles degrade theuniformity of exposure in X-ray lithography. The mostpossible reason for this slanting problem is x-y coupling
originating from the combination of the sextupolecomponents and the vertical closed orbit distortion (COD)in the superconducting bending magnets. In this work,
we present the results of correcting profiles in the SuperALIS by reducing COD and canceling out the sextupolecomponents.
1. Introduction
Compact storage rings for synchrotron radiation (SR)have recently been developed[l,2]. The magnetic fields insuperconducting bending magnets for these machines
generally have a large amount of sextupole components.
In these sextupole fields, vertical closed orbit distortion(COD) creates skew-quadrupole components whosestrength is where is the strength of the sextupole kick andis the vertical COD. Such localized skew-quadrupole
components make the principal plane of the betatronoscillations slanted to the ordinary (x,y) axes[3]. Thismeans that the beam profiles become slanted. Especiallyin the condition close to the difference resonance, thisproblem becomes serious.

Superconducting
bending magnet(BM2)
RF cavity Vertical steering

Such slanted beam profiles are undesirable forexperiments using SR. In X-ray lithography beamlinesthat generally adopt toroidal mirrors, the asymmetry of
the beam profiles are much emphasized on the exposure
plane and the uniformity of exposure is therefore
seriously degraded. In beamlines using monochromators,
the intensity is decreased because the slit of themonochromator must be narrow for fine resolution.
Especially in the Super-ALIS superconducting storage
ring[ 4], the slanting of beam profiles is serious because
the operation point of the. machine must be set close to
the difference resonance to increase the beam lifetime. In
this work, we present the methods and results ofcorrecting these distorted profiles in Super-ALIS.
2. Sextupole components of Super-ALIS
Super-ALIS is a compact storage ring for SR as shownin Fig. 1. The machine parameters are shown in Table 1.
This machine has two superconducting 180-degree
bending magnets; BM 1 and BM2. The magnets have amaximum magnetic field of 3 tesla. The uniformity of
the field is not much better than that of normal
conducting magnets. Therefore, these magnets havecancellation coils for multipole components.
The measured magnetic field at the center of BM 1 excited
to 3 tesla is shown in Fig. 2(a). The solid line is the field
produced without employing cancellation coils. The solidline in Fig. 3 shows the sextupole components along theorbit in BMI. The sextupole component in the magnet
is about -1.8 T/m except for the edges. At the edges, theSRPort
BL1

Vertical steering
Superconducting
bending magnet(BM1)

Fig. 1. The superconducting storage ring Super-ALIS.

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Table 1. Super-ALIS machine parameters.
Max. energy
Max. bending Field
RF frequency
Peak RF voltage
Betatron tune, horizontal
verticalSynchrotron tune
Natural emittance
Circumference

600MeV
3.0 T
124.855 MHz
45.0 kV-1.59-0.59-0.003
9.35x10-7 1t m rad
16.8 mJAERI-Conf 95-021

3.0485BM1 center: ( 1.585, 0.583 )Tune
Emittance : 4 x 10 -6 1t m rad
Sextupole : uncorrected: uncorrected
COD

3.0480~t9!

3.0475~3.0470

~c:

~
::;:

---~- --- -ts:--

f:&----- ____ A ____

ZI.

After correction
ks = -0.13 T/m 2

3.0465.~3.04603.0455-40-30100-10-20

203040

Radial displacement from the designed orbit [ mm 1'-(a)L,_j

1 mm

Horizontal)I1.6150
BM1 edge~t9!

Before correction
ks = 1.38 T/m 2

1.6050I!

"" \_"C~~c:Fig. 4. Simulated beam profile at the 135-degree positionin BMl. The betatron tunes are (1.585,0.583) and theCODs are assumed to be -1 mm in BM1 and +1 mm inBM2. The initial horizontal emittance is 4xl0-67t m rad.

., .
.
..,.A{.

.A

1.6100/1.6000• .1:1'~::;:

After correction
ks =2.80 T/m 2•
1.59501.5900-40-20-30

0-1010204030

Radial displacement from the designed orbit [ mm I(b)Fig. 2. Radial distribution of the magnetic field on themedian plane in BMl. (a) at the center and (b) at theentrance edge.

field distribution is quite different as shown in Fig. 2(b).
The effect of these sextupole components on the beamprofiles is very serious. As shown in Fig. 4, beam
tracking simulations including the sextupole components
with the corresponding COD show that even 1-mm
vertical COD is critical.
By using cancellation coils, the sextupole components
can be reduced to one tenth (except for the edges) as
shown by dotted lines in Figs. 2 and 3. At the edges,
however, the sextupole components become large
even if the cancellation coils are used.

3.0'''' '''''''"'E'

Before profile correction the sextupole components werepresent and the vertical COD was large as represented by
the solid line in Fig. 5. The beam profiles in thiscondition are slanted as shown in Fig. 6. The profile wasobserved from BL9 SR port in BM2. The SR light
extracted from the port was telescoped and monitored by aCCDcamera.

j:::

:§,c:

!I! 0.0u;"'c.

0::Jx"'

Cll-3.0045

go135

3. Correction of the beam profiles

180

Bending angle in BM1 [degrees]Fig. 3. Sextupole components of BM1 along thedesigned central orbit.

To cure the slanted profiles, two methods can beproposed; reducing vertical COD and canceling the
sextupole components by cancellation coils. In practical
reducing COD seems to be easier than cancelingsextupole components. However, we must take into
account the high sensitivity of COD to profile slanting- 157-

JAERI-Conf 95-021

as described in Section 2. If the sextupole components are
not reduced, COD must be reduced with 0.1-mm
precision. However, such a high sensitivity is notpreferable for stable operation of storage rings. Moreover,such precise COD reduction might be technically difficult
especially in superconducting bending magnets. This ismainly because the median plane of the magnetic field,
which is mainly determined by the shape and position of
the coils as well as the yoke geometry, may be slightly
displaced from the geometrical median of the iron yoke.
The restricted number of steerings also makes precisely
reducing COD difficult.

EE00(.)'(g't:Jr------t::!!/-4.0 L __ _ _,L__ _ __L__ _ _,_L__ _ ___,0U

U

1U

1M

Orbit length [ m ]Fig. 5. Vertical CODs in the experiments for profile
correction.

To correct the beam profiles, therefore, we first reduced
the vertical COD as small as possible and then canceled
the sextupole components. The vertical COD was reduced
as shown by the dotted line in Fig. 5. The resulting beamprofiles are shown in Fig. 7. The slant angle of the beamprofiles was completely corrected and the intensity
distribution on the exposure plane of the X-ray
lithography beamline was greatly improved.
4. Summary
We can draw the following conclusions about slanting
beam profiles in superconducting SR rings.
1) The vertical COD in the large sextupole component of
a superconducting bending magnet generates large x-ycoupling. This coupling seriously distorts beam profiles.
2) Theoretically, this problem can becorrected by either reducing vertical COD or the sextupolecomponents.
3) In a real machine, however, using both methods makes
it easier to correct the profiles and to ensure stable
operation of the machines.

Fig. 6. Beam profiles before correction.

References[1] T. Takayama and SHI Accelerator Research Group,
Rev. Sci. Instrum. vol. 60 (1989) p.1786.
[2] A. R. Jordan, R. J. Anderson, R. C. Lobel, A. S.
Bhutta and D. E. Andrews, Proc. of 1989 Intern. Symp.
on MicroProcess Conference (1989) p.104.
[3] S. Peggs, IEEE Trans. Nucl. Sci., vol. NS-30 (1983)
p.2460.
[4] T. Hosokawa, T. Kitayama, T. Hayasaka, S. Ido, Y.
Uno, A. Shibayama, J. Nakata, K. Nishimura and M.
Nakajima, Rev. Sci. Instrum., vol. 60 (1989) p.1783.
Fig. 7. Beam profiles with canceled sextupole
components and reduced COD.

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