Status of Solenoid System to Suppress the Electron Cloud
Effects at the KERB
H. Fukuma, J. Flanagan, K. Hosoyama, T. leiri, T. Kawamoto, T. Kubo
M. Suetake, S. Uno, S. S. Win and M. Yoshioka
High Energy Accelerator Research Organization (KEK)
Abstract. A large number of solenoids have been installed in the KEKB LER to remove the electron cloud. This paper
describes recent solenoid winding work and the effect of it on electron cloud effects.
INTRODUCTION
TAB LEI. Parameters of solenoids.
Length Diameter Turns
Type
A blow-up of the vertical beam size in single beam
and multi-bunch operation has been observed in the
KEKB LER [1]. Observations [1,2] have shown that
the main characteristics of the blow-up are consistent
with the model of the head-tail instability caused by
the electron cloud which was proposed by F.
Zimmermann and K. Ohm [3].
(mm)
Bz (center)
(mm)
@5A
(Gauss)
To remove the electron cloud a large number of
solenoid magnets were installed in the KEKB LER
several times since September 2000 [2]. The number of
the solenoids installed so far amount to about 8600. As
the result the measurement by an interferometer in
February 2002 showed no beam size blow-up up to
1300 mA in regular operation condition for the physics
experiment.
Bobbin
150 - 650
148
250(typ.)
45
Bobbinless
Bobbinless
Bobbinless
40
220
40
40
250
300
190, 200
200
200
48
43
37
TABLE2. Parameters of power supply for
the solenoids.
KEKB corrector TRISTAN corrector
P.S.
P.S.
Current(A)
5
3
This paper describes solenoid winding work in
September 2001 and January 2002 and consequence of
it on the electron cloud effects.
TABLE3. Installation history of the solenoids.
Second and third columns show the number of
the installed solenoids.
Location
Date Bobbinless Bobbin
SOLENOID SYSTEMS
2000. 9.
to
2001. 8.
Parameters of solenoid system are shown in Tables
1 and 2. There are two kind of solenoids, one is a
bobbin-type solenoid and the other a bobbinless-type
solenoid. The length of the bobbin-type solenoid is
from 150 to 650 mm depending on the length of
available free space for winding. The bobbinless-type
solenoid has the length of 40 mm and is located
mainly on bellows and both sides of NEG pumps and
ion pumps to cover regions where the bobbin-type
solenoids can not be wound. The longitudinal
magnetic field at the center of a solenoid is about 45
Gauss. A picture of the solenoids is shown in Fig. 1.
2204
2793
Arc section
(Cu chamber, Bellows,
NEG)
Straight section
(Cu chamber, Bellows)
2001.9.
3411
43
Arc section
(NEG, IP, Bellows)
Straight section
(Cu chamber, Bellows)
2002. 1.
119
0
Arc section
(Between quad and
sextupole magnet)
5734
Total
Units
2836
616
40
CP642, High Intensity and High Brightness Hadron Beams: 20th ICFA Advanced Beam Dynamics Workshop on
High Intensity and High Brightness Hadron Beams, edited by W. Chou, Y. Mori, D. Neuffer, and J.-F. Ostiguy
© 2002 American Institute of Physics 0-7354-0097-0/02/$ 19.00
357
As
As expected
expected by
by the
the measurement
measurement of
of the
the beam
beam size
size
the
the luminosity
luminosity was
was improved
improved after
after the
the installation
installation of
of
the
the solenoids.
solenoids. Fig.
Fig. 33 shows
shows the
the luminosity
luminosity per
per bunch
bunch
as
as aa function
function of
ofthe
the bunch
bunch current
current product
product of
ofHER
HERand
and
LER.
LER.An
An envelope
envelopecurve
curveof
ofthe
the luminosity
luminositytaken
taken for
for aa
Luminosity/bunch (1030 cm-2 sec-1)
6
FIGURE
FIGURE 1.1. Solenoids
Solenoids in
in an
an ion
ion pump
pump (IP)
(IP) section.
section. Long
Long
solenoids
solenoids are
are the
the bobbin-type
bobbin-type solenoids
solenoids and
and short
short solenoids
solenoids
arethe
arethebobbinless-type
bobbinless-typesolenoids.
solenoids.
Vertical beam size at IP (micron)
J
0
2001 July
2001 Dec.
2002 Feb.
0O
200
200
400
400
0.1
0.1
0.2
0.2
0.3
0.3
0.4
0.4
0.5
0.5
0.6
O.6
0.7
O.7
0.8
O.8
According
According to
to aa model
model of
ofthe
the single
single bunch
bunch instability
instability
due
due to
to the
the electron
electron cloud
cloud the
the threshold
threshold bunch
bunch intensity
intensity
of
of the
the blow-up
blow-up IIb,b, thth isis proportional
proportional to
to aa bunch
bunch
separation
separation LLbb for
for the
the regular
regular and
and the
the strong
strong head-tail
head-tail
instability
instability and
and isis proportional
proportional to
to the
the square
square root
root of
of LLbb
for
for the
the beam
beam break-up
break-up instability
instability [4].
[4]. The
The average
average
beam
beam size
size atat several
several bunch
bunch separations
separations was
was measured
measured
by
bythe
the interferometer
interferometer as
as aa function
function of
of the
the beam
beam current
current
as
as shown
shown inin Fig.
Fig.4.4.In
Inthe
themeasurements
measurementsthe
thenumber
number of
of
bunches
bunches times
times the
the bunch
bunch separation
separation was
was set
set to
to be
be
equal.
equal. Comparing
Comparing the
the blow-up
blow-up for
for two
two fill
fill patterns,
patterns, ifif
the
the blow-up
blow-up starts
starts atat same
same beam
beam current
current the
the scaling
scaling of
of
IIb,
holds. Fig.
Fig.44shows
showsthat
thatthe
thescaling
scalingIb,Ib?thth∝^LLb
b, thth∝^LLb
b holds.
b
was
was observed
observed and
and not
not changed
changed after
after the
the installation
installation of
of
the
the solenoids
solenoids in
in September
September 2001.
2001.
1 tl
1
1
week
week isis plotted
plotted for
for each
each data
data set
set because
because the
the
luminosity
luminosity isis affected
affected by
by the
the beam
beam tuning.
tuning. As
As seen
seen inin
Fig.
Fig. 33 the
the luminosity
luminosity was
was enhanced
enhanced after
after the
the
installation
installation of
of the
the solenoids
solenoids in
in September
September 2001.
2001. The
The
luminosity
luminosity may
may be
be slightly
slightly improved
improved above
above 0.5
0.5 mA
mA22
after
after the
the installation
installation in
in January
January 2002
2002 though
though the
the
improvement
improvementmight
mightbe
becaused
causedby
bythe
thebeam
beamtuning.
tuning.
1 train,
rain,1153
1153bunches,
bunches,
44rf
rfbucket
bucketspacing
spacing
2
2
FIGURE
FIGURE3.3. The
Theluminosity
luminosityper
perbunch
bunchatatseveral
severalinstallation
installation
stages
stagesof
ofthe
thesolenoids.
solenoids.
Fig.
Fig. 22 shows
shows the
the vertical
vertical beam
beam size
size in
in aa long
long train
train
for
for physics
physics experiment
experiment at
at several
several installation
installation stages
stages of
of
the
the solenoids.
solenoids. The
The threshold
threshold current
current of
of the
the blow-up
blow-up
3
July 1-10 2001
3
22
LER
))
LER.bunch
bunchcurrent
current••HER
HERbunch
bunchcurrent
current(mA
(mA.
Beam
Beam blow-up
blow-up
4
Dec. 8-17 2001
4
0
"0O
Power
Power supplies
supplies of
of the
the solenoids
solenoids are
are those
those for
for
correctors
correctors of
of the
the KEKB
KEKB rings
rings and
and the
the TRISTAN
TRISTAN
collider.
collider. The
The solenoids
solenoids were
were installed
installed in
in LER
LER five
five
times.
times. Before
Before September
September 2001
2001 about
about 1280
1280 m
m were
were
covered
covered by
by the
the solenoids.
solenoids. In
In September
September 2001
2001 the
the
bobbinless
bobbinless solenoids
solenoids were
were mainly
mainly installed
installed in
in NEG
NEG
and
and ion
ion pump
pump sections
sections and
and in
in January
January 2002
2002 the
the
bobbinless
bobbinless solenoids
solenoids were
were installed
installed between
between
quadrupole
quadrupoleand
and sextupole
sextupole magnets.
magnets. The
The length
length covered
covered
by
by the
the solenoid
solenoid field
field larger
larger than
than 20
20 Gauss
Gauss isis about
about 870
870
m
m in
in the
the installation
installation in
in September
September 2001
2001 and
and 28
28 m
m in
in
the
the installation
installation in
in January
January 2002.
2002. Now
Now the
the solenoid
solenoid
field
field covers
covers about
about 75%
75% of
of the
the circumference.
circumference. Table
Table 33
shows
shows installation
installation history
historyof
ofthe
the solenoids.
solenoids.
5
Feb. 8-14 2002
5
600
600 800
800 1000
1OOO1200
12OO1400
14OO1600
16OO
LER
LER beam
beam current
current(mA)
(mA)
FIGURE
FIGURE2.2. Effect
Effect of
ofsolenoids
solenoidson
onthe
thevertical
verticalbeam
beamsize
sizefor
for
aalong
longtrain
trainmeasured
measuredby
bythe
the interferometer
interferometer [2].
[2].
increased
increased in
in each
each installation
installation of
of the
the solenoids
solenoids and
and
finally
finally the
the blow-up
blow-up disappeared
disappeared in
in the
the measurement
measurement in
in
February
February 2002.
2002.
358
Vertical beam size at IP (micr
Low alpha lattice
r o 1 1rain, 1153
-— -|^ • 1 1rain, 1537
^JMF
^jjr
400
SUMMARY
j
'
6C>0
800
1000
1^ER beam current (mA)
1200
Dec.
To it rain, 1153
: ~"\» I t rain, 1318
The solenoids for suppressing the electron cloud
were added in LER at September 2001 and January
2002 in the KEKB LER. After the addition of the
solenoids the electron cloud effects were measured to
see the effect of it. Results are summarized as
\
jJ»
i^H*
»0
Vertical beam size at IP (micron)
blurches, 4 bucket spacing
b
bunches, 4 bucket spacing
bunches, 3-4 bucket spacing
;
14C
2001
1) The blow-up of the beam size was disappeared up
to 1300 mA with the fill pattern of 4 rf bucket spacing
after the installation of the solenoids in January 2002.
I
J
;
I
~_j*---i
2) The luminosity was improved after the installation
of the solenoids in September 2001 and seems to be
slightly improved after that in January 2002.
f ----$;---*-----® i =t
6OO
8OO
i
1OOO
LER beam current (mA)
3) Tune shift along the train was decreased at least
40% after the installation in September 2001.
FIGURE 4. Vertical beam size in several rf bucket spacing
measured by the interferometer. "3-4 bucket spacing means
that the bunch spacing in the unit of rf bucket is 3,4,3,4,...
4) Growth rate of the coupled bunch instability
decreased by 70 % after the installation in September
2001, while the mode spectrum was not changed
much.
Tune shift and coupled bunch instability
The betatron tune of the bunch increases along the
bunch train due to the electric force of the electron
cloud [5]. Fig. 5 shows the tune shift before and after
the installation of the solenoids in September 2001.
The tune shift along the train decreased when the
solenoids were added.
5) Threshold bunch current of the blow-up is
proportional to the bunch separation.
ACKNOWLEDGMENTS
The authors would like to thank the members of
KEKB group for their help for installing the solenoids
and measuring the beam parameters. They also thank
K. Oide for his support to winding the solenoids.
0.005
IO.OO4
i O.OOS
........... ..^1.01
i
mA/bunch f
---<=> ~~f --o-j-Q-- ;
0.002
_
O.OO1
:
o
o
r.........|..........f
O
-0.001
O
boOOO
c)
2O
4O
p^l Dec.
01
O.31mA/bunch
6O
8O
Bucket
1OO
O.OO3
O.OO2
0.001
O
-O.OO1
REFERENCES
14O
1. K. Akai et al., "COMMISSIONING OF THE KEKB BFACTORY", PAC'99, New York, Particle Accelerator
Vol. 1,288-292(1999).
All solenoid on
O.OO6
O.OOS
0.004
12O
Apr.
Cn
O.26m A/bunch
H'o b o o
5-6^--°-|---L........I-0000
!
^
•^
j-^
°
!
i
:
!°
'-
!
;
°f
^
f0o°--?----...........L.......LO.31mA/bunch
. . . i . . .
. . .
|
. . .
2. H. Fukuma, "ELECTRON CLOUD EFFECTS AT
KEKB", ECLOUD02, CERN, April 2002, to be
appeared in CERN-2002-001.
"
:
i . . . E
6O
SO
Bucket
3. K. Ohmi and F. Zimmermann, "Head-Tail Instability
Caused by Electron Clouds in Positron Storage Rings",
Phys.Rev.Lett.85: 3821- 3824(2000).
FIGURE 5. The effect of the solenoids on the horizontal
and vertical tune shift along the train. Bunch current was
0.31 A.
4.
The electron cloud can cause the transverse
coupled bunch instability. In fact the mode spectrum
of the coupled bunch instability observed in LER was
changed with and without solenoid field [6]. The
growth rate of the coupled bunch instability decreased
by 74% and 66% in horizontal and vertical planes
respectively after the installation of the solenoids in
September 2001. The mode spectrum was not changed
much, which can be expected because the addition of
the solenoids would not change the transverse
distribution of the electron cloud.
F. Zimmermann, "THE ELECTRON CLOUD
INSTABILITY: SUMMARY OF MEASUREMENTS
AND UNDERSTANDING", 666, PAC2001, Chicago,
June 2001.
5. K. Ohmi et al., "STUDY OF COHERENT TUNE SHIFT
CAUSED BY ELECTRON CLOUD", APAC01,
Beijing, September 2001.
6. S. S. Win et al., "Effect of Electron Cloud on the Bunch
Oscillations in KEKB LER ", ECLOUD02, CERN, April
2002, to be appeared in CERN-2002-001.
359