Recent Studies on Beam Pipes
and Electron Cloud Issues
The 14th KEKB Review on 9‐11 February 2009 at KEK
Kyo Shibata (for KEKB Vacuum Group)

Resent Study Items at LER
Various studies for SuperKEKB have been performed using an intense
beam of KEKB Low Energy Ring (LER).
Recent studies are focused on beam pipes and electron‐cloud eﬀects.
LER : Positron ring
Energy : 3.5 GeV, Current : ∼1600 mA, Bunch space : 2∼8 ns, Bunch charge : ∼1.0×10‐8 Ce+BelleDetectore‐

Recent study items at LER
Beam pipe with antechambersRFA in Q‐mag
Clearing electrode
Groove surface

Clearing electrode
Groove surface
TiN coaRng
GraphiRzaRon

TiN+ Antechamber
TiN, GraphiAzaAon
SEY measurement

RFA‐type electron detectors
SEY measurements

RFA in solenoid
The 14th KEKB Review on 9‐11 February 2009 at KEK2

Beam Pipes 1
Copper beam pipe with antechambers has been developed.

Beam pipe with antechambers

Beneﬁts of antechamber scheme are;
ReducRon of SR power density
at side wall.
ReducRon of photoelectrons inbeam channel (positron ring).
ReducRon of beam impedance.

NEG stripBeamSR

Beam channel

SR channel

Several beam pipes with antechambers have been installed into
KEKB LER, and tested with beam.
No serious problem has
been observed unRl now.

Straight pipe

Straight pipe is OK.
How about bent pipe?
We started manufacturing test.
The 14th KEKB Review on 9‐11 February 2009 at KEK

Q‐pipe with BPM ports3

Beam Pipes 2
Bending test was performed using a cold‐drawn pipe with a screen
for pumping channel.
EBW
SpeciﬁcaRons;
Cold drawn pipe.
Two antechambers.

screenScreen to hide pumps.
Curvature of 16 m for LER.

EBW

NEG strips(3 layer)

screenFabricaRon procedure;
Widen the aperture elasRcally in averRcal direcRon temporally, andinsert the screen in the pumpchannel.
Fix the screen posiRons by EBW
from outside.
Bend the beam pipe by three‐point
bending method.

grooveThe 14th KEKB Review on 9‐11 February 2009 at KEK4

Beam Pipes 3
We visually checked the test pipe aber the bending test.

FabricaRon accuracy :DeformaRon of the aperture was observedin the ﬁrst bending test without screen.
This problem was ﬁnally solved byinstalling a hard plasRc block into theantechamber during bending process.
ALer bending test
The screen (below) also helps prevent the deformaRon.
Screen :Some holes were made to check the gap between screens.
Molten copper leaked into the inside of the beam pipe.
It seems that the screens can be held in a stable posiRon
Weld beadeven without EBW.
Screen dose not have to be welded.
Weld bead
Screens
The 14th KEKB Review on 9‐11 February 2009 at KEK5

Beam Pipes 4
Manufacturing of two beam pipes (B‐chamber & Q‐chamber) isCopper‐alloy ﬂange
now proceeding.
Features of beam pipe :Copper‐alloy ﬂanges
We can omit transiRons between copper andstainless‐steel required in the case of stainless‐steelﬂange. (Simplify the manufacturing procedure andNEG strips
then reduce the cost.)(3 layers)
Cooling eﬃciency is also improved.
New pump system for antechamberThree layers of ST707 NEG strips was designed for thispipe. Pumping test has been performed.
These pipes will be completed by the end of March, and be installed into
KEKB LER this year for comprehensive test.

The 14th KEKB Review on 9‐11 February 2009 at KEK6

Beam Pipes 5
Tune shifts due to the quadrupole field (Eq)of resistive‐wall wakeof beam pipe with antechambers were also checked.

Estimation of Eq in beam channel with MAFIA electrostatic solver (2D)
In case of φ
φ50 beam channel ((for HER););||Eq| in beam channel
φ50 Circular

Elliptical beam channel is useful to spread the weak area of Eq.

In case of φ90 beam channel (for LER);(Ellipticity=1.0)

Eq in circular beam channel seems to be enough small.

Estimated tune shift at maximum beam currents of SuperKEKB;p;
Tune shift |∆ν| is within acceptable limit (0.1) even forcircular beam channel in both rings.

φ50 Elliptical

Elliptical beam channel can reduce the tune shift further.
0 04
0.04
0.03

0 04
0.04

HER (4.1 A)

0.03

φ50 ∆νx

0.02
0.01
0-0.01
-0.02

-0.04
0.6

0.7

0.8

0.9

ellipticity

1

φ90 ∆νx

0.01

φ90 CircularCi l0(Ellipticity=1.0)-0.01

φ90 ∆νy-0.02

φ50 ∆νy0 03-0.03

LER (9.4 A)

0.02
tune shhift

tune shhift(Ellipticity=0.86)

-0.03
0 03
1.1

-0.04
0.8

0.9

1

ellipticity
The 14th KEKB Review on 9‐11 February 2009 at KEK

1.1

0.0>1.07

TiN Coating 1
MiRgaRon of electron cloud in magnets is a key issue for SuperKEKB.
In magnets we can not use the solenoid coil which is apromising measure for drib space (discussed later).

K. Shibata, EPAC2008

ReducRon of SEY by coaRng has been studied.

Gas inlet

UncoatedSolenoid~4 mTiN coaRng system for long beam pipes was built at KEK.
CoaRng was done by DC magnetron spunering ofRtanium in Ar and N2.
Thickness : 200 nm
Maximum SEY of TiN ﬁlm on sample piece was 0.84
(electron dose : 0.001 C/mm2)
Several beam pipes have been coated with TiN, andinstalled in KEKB LER.

Pipe

TiN coatedPumpingsystem

The 14th KEKB Review on 9‐11 February 2009 at KEK

8

TiN Coating 2M
Measurementt off electronl tddensity
it iin KEKB LER ((no magnet)t)
Electron density in circular beam pipe (φ94 mm)
TiN (KEK) is as effective as TiN (BNL).
Mitigation of electron also comes from its surface structure?
KEK TiN 04Nov2008

4 10

φ 94 mm

K. Kanazawa-3Near Beam EN
Electron Clouud Density [mm ]11

D(D7)[4,200,3]Cu
D(D7)[4 200 3]TiN
D(D7)[4,200,3]TiN
D(D7)[1,1585,3.06]KEKTiN

CCopper

113 10TiN (KEK)

112 10TiN (KEK)
111 10TiN (BNL)

100 nmElectron Microscope Image

00

0.2

0.4

0.6

0.8

11.2

H. Hisamatsu and M. Nishiwaki

LER Bunch Current [mA]
The 14th KEKB Review on 9‐11 February 2009 at KEK

9TiN Coating 3
Measurement of electron density in KEKB LER (no magnet)
Electron density in beamPEM__Wigante_1kV_4_200_3pipe with antechambers
1x10-7

Electron Currrent [A]

VA_PEM:D05_W IG:CURRENTVA PEM:D05 W IG:CURRENT
VA_PEM:D05_W

8x10-86x10-84x10-8

φ 90 mm2006.05.17
2008 03 11
2008.03.11

W ithout TiN Coating

W ith TiN Coating
2x10-8Y. Suetsugu, ILCDR2008
00200

400600800

1000

LER Beam Current [mA]TiN can reduce electron cloud.
Combination of beam pipe with antechambers and TiN coating is a promisingmeasure ini magnets
t off SuperKEKB.
SKEKB
But more effective countermeasures are preferable to surely suppress theelectron cloud effect.
The 14th KEKB Review on 9‐11 February 2009 at KEK

10

Graphitization 1
Electron beam induced graphiRzaRon is also studied.

GraphiRzed surfaces have shown low SEY in laboratory experiments.
Maximum SEY decreased to 1.0‐1.1 (electron irradiated : 0.0016 C/mm2)
Setup for graphiRzaRon of copper beam pipe was newly developed.
500 eV electrons irradiate to pipe surface.
Emission Current Density : 170µA/cm2
1.35m

Copper Pipe
Electron GunFilament

SamplePiece

M. Nishiwaki and S. Kato, Vasscaa4 2008
The 14th KEKB Review on 9‐11 February 2009 at KEK

11Graphitization 2
Measurement of electron density in KEKB LER (no magnet)
GraphiRzaRon was eﬀecRve to reduce electron cloud density.
The eﬀect was less than TiN and NEG, however.
M. Nishiwaki and S.

Kato, Vasscaa4 2008

Graphite layer was too thin (FWHM ∼10 nm) ?
Thicker graphite coaRng on copper pipe is in preparaRon.
New test chamber will be installed this winter.
The 14th KEKB Review on 9‐11 February 2009 at KEK12

Clearing Electrode 1
Study on clearing electrode also started for miRgaRon of electron
cloud in magnets.

Very thin electrode (0.1 mm, Tungsten) and insulator (0.2 mm, Al2O3) weredeveloped. (Thermal Spray)
Clearing electrode and electron detector were installed in wiggler magnetof LER. (placed at the center of pole)
To demonstrate the eﬀect of electrode, the electron density wasmeasured by the electron detector with 7 strips.
7 strips can measure the horizontal spaRal distribuRon of the electron
Y. Suetsugu et al., NIM‐cloud.
PR‐A, 598 (2008) 372
Sustainability for high beam current was also tested.

Al2O3Feedthrough40 mm

Tungsten

Stainless steelThe 14th KEKB Review on 9‐11 February 2009 at KEK

13

Clearing Electrode 2Electron detector
Collector (7 strips, w5 mm)
Grid (~ 1 kV)
ShieldCross‐secRon
MonitorBlock

φ2 mm holes
BeamElectrode [W] (~ +1 kV)(w40, l440, t~0.1)
Electrode
Block

Vacuum seal bymetal O‐ring
Y. Suetsugu et al., NIM‐
PR‐A, 598 (2008) 372

Cooling channel

Clearing electrode

Insulator [Al2O3](t~0.2 mm)

Cooling Water
paths

Test chamber

Limited by magnet
aperture

Wiggler magnet

MagneRc ﬁled
: 0.77 T
EﬀecRve length : 346 mm
Aperture (height) : 110 mm
The 14th KEKB Review on 9‐11 February 2009 at KEK

14

Clearing Electrode 3
DrasRc decrease in electron density was demonstrated by applying
posiRve voltage.
Number of electrons was reduced to 1/10 ∼ 1/100 if applied voltage ofclearing electrode was more than 300 V for any bunch spacing.

Velec = 0Y. Suetsugu et al., NIM‐
PR‐A, 598 (2008) 372

Collector : #4

[6ns]

Ie [A]

1585 bunches(Bs ~ 6 ns)~1600 mA

Vr = -1.0 kV
B = 0.77 T[4ns][16ns]

Ie [A]

1 x 10-5
1 x 10-6
1 x 10-7
1 x 10-8
1 x 10-9[8ns]

Velec [V]

Collectors
The 14th KEKB Review on 9‐11 February 2009 at KEK

15

Clearing Electrode 5
Electrode was very eﬀecRve, but modiﬁcaRon of the feed‐throughconnecRon part is required for high beam current.
InsulaRon resisRvity decreased from 2 MΩ to several 10 kΩ during the trial
period due to discharge at feed‐through connecRon part.
Improved clearing electrode will be installed this winter.
insulator
electrodeY. Suetsugu

ConnecRon part
The 14th KEKB Review on 9‐11 February 2009 at KEK

16

Groove Surface 1Eﬀect of groove surface was also studied last autumn.

(collaboraRon with SLAC)
Flat surface [SUS + TiN]
Electrode was replaced by groove surface.
Same setup for clearing electrode was uRlized.
Groove structure was designed and manufactured in SLAC.
Flat surface with TiN coaRng was also tested for reference.
TiN~200 nm

Y. Suetsugu, ILCDR2008

TiN~200 nm

Magnetic field[Groove]

Beam[Monitor]
Groove surface [SUS + TiN]
The 14th KEKB Review on 9‐11 February 2009 at KEK

17

Groove Surface 2
Electrons for groove surface was reduced to 1/5 ∼1/10 the number
for ﬂat surface (3 buckets spacing).
Further R&D will be carried out toward the pracRcal use of groove surface.

Groove surface

Flat surface

1x10-6

Y. Suetsugu

1x10-6Preliminary result
The 14th KEKB Review on 9‐11 February 2009 at KEK18Mitigation Performance Comparison
Clearing electrode is much more effective than groove surface andTiN coating.-5
1x10r

Ele
ectron Currrent [A]b1/1585/3 06
1/1585/3.06~1x10
1 1012 e-/m/ 3
1x10

Vr = -1 kV

V = −1 kV, I = 1450 - 1550 mA(V-6elec= 0 V)

TiN~1x101１
1x10(1/1585/3 06)(1/1585/3.06)

W electrodel t dPreliminaryy result-7Groove+TiN~1x1010
1x10-8W electrode(V~1x109-9
1x1002x10

54x10

56x10

58x105elec> 300 V)

1x1061.2x10

6Beam Dose [mA Hours]

Ranking of estimated performance in magnet is ;Electrode >> TiN+Groove >> TiN(Flat) > Cu(Flat)×10×5∼10×2∼3

Electrode and groove surface are very promising, but more studies are
required to achieve the practical use of them.
The 14th KEKB Review on 9‐11 February 2009 at KEK

19

Near Beam Electron Cloud Density Measurement inMagnetic Field with RFA-type Electron Detector 1
New RFA‐type electron detector was installed into KEKB LER tomeasure electron density in a solenoid coil

Only high energy electrons produced near the bunch can enter the groove
and reach the detector behind it.
With a help of simulaRon, the detector current is converted into the density
StarRng points of electrons
near the beam.
K. Kanazawa and H. Fukuma
that can enter the detector
Groove+15Detector 1y[mm]Bunch size: σx = 0.434mm, σy = 0.061mm,
σz = 6mm, B = 50 G, NB = 7.5×1010

SR0Detector 2Beam

Only these electrons
reach the detector.

Detector
Monitor used without Monitor used withsolenoid ﬁeld
solenoid ﬁeld

‐15‐15The 14th KEKB Review on 9‐11 February 2009 at KEK

0x[mm]+1520

Near Beam Electron Cloud Density Measurement in
Magnetic Field with RFA-type Electron Detector 2Groove

Inside of the chamber
The 14th KEKB Review on 9‐11 February 2009 at KEK21

Near Beam Electron Cloud Density Measurement in
Magnetic Field with RFA-type Electron Detector 3
Electron cloud density with solenoid ﬁeld (B = 50 G) (0.005 T)

It was conﬁrmed that the electron cloud density decreased by more than
1/100 in solenoid ﬁeld.
Solenoid coil is a very promising measure for drib space of SuperKEKB.
Preliminary result

B=0
K. Kanazawa and H. Fukuma

The diﬀerence in two detectors
may be due to ;B=50 G, Detector 2

B=50 G, Detector 1

1. COD
2. Relative position to theprimary synchrotron radiation
3. Output offset of amplifier inmeasurement system

The measured current in a solenoid
ﬁeld might have included electrons
dribing along the wall.
The 14th KEKB Review on 9‐11 February 2009 at KEK

22

Near Beam Electron Cloud Density Measurement in
Magnetic Field with RFA-type Electron Detector 4
Electron density in a Q‐magnet was also measured.

Electrons accelerated by bunch with suﬃcient energy and with a direcRon
close to X‐axis can reach the detector.
With a help of simulaRon, the detector current is converted into the density
near the beam.
StarRng points of electrons
that can enter the detector+20

σx = 0.35 mm, σy = 0.094 mm,
σz = 6.0 mm, B’ = 3.32 T/m,
NB = 7.5×1010

X‐axis

Detector

Detector 2x [mm]SRDetector

Detector Bias = ‐1 keV0The big island is an expected source.

Detector 1‐20‐20Other small islands are unexpected.

K. Kanazawa and H. Fukuma

The 14th KEKB Review on 9‐11 February 2009 at KEK0y [mm]2023

Near Beam Electron Cloud Density Measurement in
Magnetic Field with RFA-type Electron Detector 5Detector

The 14th KEKB Review on 9‐11 February 2009 at KEK

24

Near Beam Electron Cloud Density Measurement in
Magnetic Field with RFA-type Electron Detector 6
Electron cloud density in quadrupole ﬁeld (B’ = 3.32 T/m)
The observed value in the Q‐Magnet was close to the esRmaRon bysimulaRon

Parameters ;Bunch current : 0.85 mA, 3 bucket spacing,
200 bunches in a train, Photoelectron yield :0.1, Reflectivity : 0.3, δ : 1.2, E at δmax : 250 eV,
Pipe radius : 46 mm, Q field : 3.32 T/m

The diﬀerence in two detectors
may be due to ;1. COD
2. Relative position to theprimary synchrotron radiation
3. Output offset of amplifier inmeasurement system

Preliminary result
K. Kanazawa and H. Fukuma

The 14th KEKB Review on 9‐11 February 2009 at KEK25Summary
Bending test of beam pipe with antechambers was performed, and an actual
B‐chamber is under fabricaRon based on the results of the test.
Various studies on the electron cloud miRgaRon have been done at KEKB
positron ring.
Clearing electrode, Groove surface, TiN coaRng, GraphiRzaRon,
Beam pipe with antechambers
The eﬀects of low SEY coaRng such as TiN and graphiRzaRon were conﬁrmed.
MiRgaRon eﬀect of clearing electrode and groove surface in magneRc ﬁeld werealso experimentally‐veriﬁed and found to be more eﬀecRve than other methods.

New RFA‐type electron detectors were developed and installed in KEKB LER tomeasure the electron cloud density in solenoid coil and quadrupole magnet.

It was conﬁrmed that the electron cloud density decreased by more than 1/100
in the solenoid ﬁeld.
The measured electron cloud density in Q‐Mag was consistent with the simulaRon.

For SuperKEKB :Drib space : antechamber + solenoid
In magnets : antechamber + TiN coaRng + groove surface?
+ groove surface?
More studies are required.
+ clearing electrode?
The 14th KEKB Review on 9‐11 February 2009 at KEK26