Recent Electron-Cloud Mitigation Studies at KEK
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Transcript of Recent Electron-Cloud Mitigation Studies at KEK
Recent Electron-Cloud Mitigation Studies at KEK
E-cloud mitigation mini-workshop on 20-21 November at CERN
Kyo Shibata (for KEKB Group)
Introduction
E-cloud mitigation mini-workshop on 20-21 November at CERN
KEKB : double ring collider with one collision pointHigh Energy Ring (HER) : Electron ring Energy : 8 GeV, Current : 970 mA, bunch space : 36 ns, bunch charge : 0.910-8 C Low Energy Ring (LER) : Positron ringEnergy : 3.5 GeV, Current : 1600 mA, bunch space : 36 ns, bunch charge : 1.210-8 C
E-cloud study items at LER
TiN coating
Clearing electrode
Graphitization
RFA type electron detectors
e-
e+
clearing electrodeRFA in Q-mag
RFA in solenoid
TiN, Graphitization
TiN (antechamber)
Belle Detector
Wiggler
Wiggler
Beam duct with antechambers
and so on…
1
Circumference : 3016 m
Groove surfacegroove surface
Clearing Electrode 1
E-cloud mitigation mini-workshop on 20-21 November at CERN
Mitigation of E-cloud in Magnets Clearing electrode and electron detector was installed in Wiggler magnet. (placed at the center of pole)To ascertain the effect of electrode, the electron density was measured from just under electrode.
Electron detector
Clearing electrode
Test chamber
Y. Suetsugu, ILCDR2008
2
Wiggler magnet Magnetic filed : 0.77 T Effective length : 346 mm Aperture (height) : 110 mm
Tolerance for high beam current was also tested.
Clearing Electrode 2
E-cloud mitigation mini-workshop on 20-21 November at CERN
Cross-section Drawing
Electrode [W] (~ +1 kV)
Collector (7 strips, w5 mm)
Cooling channel
Insulator [Al2O3](t~0.2 mm)
Grid (~ 1 kV)
Vacuum seal by metal O-ring Cooling Water paths
ShieldMonitorBlock
ElectrodeBlock
2 mm holesR47
Limited by magnet aperture
(w40, l440, t~0.1)
Beam
7 strips measure the horizontal spatial distribution of the e-cloud.
Y. Suetsugu, ILCDR2008
Very thin electrode (0.1 mm, Tungsten) and insulator (0.2 mm, Al2O3) were developed.
3
Clearing Electrode 3
E-cloud mitigation mini-workshop on 20-21 November at CERN
Top view & side view
5
Electron Monitor Block
Electrode Block
Detachable Block
Feed-through
Magnet
Top view
Side view
Y. Suetsugu, ILCDR2008
4
Clearing Electrode 4
E-cloud mitigation mini-workshop on 20-21 November at CERN
Results Drastic decrease in electron density was demonstrated by applying positive voltage.
Y. Suetsugu, ILCDR20085
Vr = 1.0 kVB = 0.77 T[Logarithmic scale]
I e [
A]
Collectors
V elec
[V]
V elec
[V]
I e [
A]
Collectors
Vr = 0 VB = 0.77 T[Logarithmic scale]
1 x 10-5
1 x 10-6
1 x 10-7
1 x 10-8
1 x 10-9
1585 bunches(Bs ~ 6 ns)~1600 mA
Groove surface (preliminary)
E-cloud mitigation mini-workshop on 20-21 November at CERN
Effect of groove surface will be ascertained this autumn. (collaboration with SLAC)
Electrode will be replaced by groove surface.
6
Same setup for clearing electrode is utilized.Groove structure was designed and manufactured in SLAC.
TiN~50 nm
Flat surface with TiN coating is now tested for reference.
R47
Beam
[Groove]
[Monitor]
Mag
neti
c field
Y. Suetsugu, ILCDR2008
Groove surface [SUS + TiN]
Flat surface [SUS + TiN]
TiN~200 nm
TiN coating 1
E-cloud mitigation mini-workshop on 20-21 November at CERN
Reduction of SEY of beam duct by coating TiN coating system for long beam ducts was built at KEK.
Several beam ducts have been coated with TiN, and installed in KEKB LER.
~4 m
Gas inlet
Duct
Pumping system
Solenoid
Coating was done by DC magnetron sputtering of titanium in Ar and N2.
Thickness : 200 nm
Maximum SEY of TiN film on sample piece was 0.84 (electron dose : 0.001 C/mm2)
Uncoated TiN coated
K. Shibata, EPAC20087
TiN coating 2
E-cloud mitigation mini-workshop on 20-21 November at CERN
Measurement of electron density in KEKBElectron density in circular beam duct (94 mm)
0
1 1011
2 1011
3 1011
4 1011
0 0.2 0.4 0.6 0.8 1 1.2
KEK TiN 04Nov2008
D(D7)[4,200,3]CuD(D7)[4,200,3]TiND(D7)[1,1585,3.06]KEKTiN
Nea
r B
eam
Ele
ctro
n C
loud
Den
sity
[m
-3]
LER Bunch Current [mA]
Copper
TiN (KEK)
TiN (BNL)
TiN (KEK)
TiN (BNL)
Electron Microscope ImageK. Kanazawa
H. Hisamatsu and M. Nishiwaki
f 94 mm
8
TiN coating 3
E-cloud mitigation mini-workshop on 20-21 November at CERN
Measurement of electron density in KEKBElectron density in beam duct with antechambers
0
2x10-8
4x10-8
6x10-8
8x10-8
1x10-7
0 200 400 600 800 1000
PEM__Wigante_1kV_4_200_3
VA_PEM:D05_WIG:CURRENTVA_PEM:D05_WIG:CURRENT
Ele
ctro
n C
urre
nt [A
]
LER Beam Current [mA]
2008.03.112006.05.17
With TiN Coating
Without TiN Coating
Combination of beam duct with antechambers and TiN coating is a promising candidate for future high current machines.
f 90 mm
Y. Suetsugu, ILCDR2008
9
Graphitization 1
E-cloud mitigation mini-workshop on 20-21 November at CERN
Electron beam induced graphitization is also studied. Graphitized surfaces have shown low SEY in laboratory experiments.
Setup for graphitization of copper beam duct was newly developed.Maximum SEY decreased to 1.0-1.1 (electron irradiated : 0.0016 C/mm2)
500 eV electrons irradiate to duct surface.
Electron Gun
Filament
1.35m Copper Duct
SamplePiece
0
0.5
1
1.5
0 1000 2000 3000 4000 5000
NEG / SSCu (Oxygen Free Copper)TiN / SSSS
Primary Energy [eV]
Electron Irradiated ;
Normal Incidence
Cu
TiN
NEG
16 C cm -2
SS
M. Nishiwaki and S. Kato, Vasscaa4 2008
10
Emission Current Density : 170A/cm2
Graphitization 2
E-cloud mitigation mini-workshop on 20-21 November at CERN
Measurement of electron density in KEKB Graphitization is effective to reduce electron cloud density.Effect is less than TiN and NEG.
0
1 1011
2 1011
3 1011
4 1011
0 0.2 0.4 0.6 0.8 1 1.2LER Bunch Current [mA]
Cu
NEG Coated Cu
TiN Coated Cu
Graphitized Cu
Graphite layer was too thin (FWHM 10 nm).Thicker carbon coating on copper duct is in preparation.
M. Nishiwaki and S. Kato, Vasscaa4 2008
11
[4.200.3]
Monitor used without solenoid field
Monitor used with solenoid field
Groove
SR
Detector 1
Detector 2
Near Beam Electron Cloud Density Measurement in Magnetic Filed with RFA 1
E-cloud mitigation mini-workshop on 20-21 November at CERN
Measurement of electron density in solenoid coil Only high energy electrons produced near the bunch can enter the groove and reach the detector behind it.With the help of simulation detector current is converted into the density near the beam.
y[m
m]
x[mm]
+15
-15-15 +15
0
0
Starting points of electrons that enter the detector
Only these electrons reach the detector.
Beam
Detector
Bunch size: x = 0.434mm, y = 0.061mm, z = 6mm, B = 50 G, NB =
K. Kanazawa and H. Fukuma
12
E-cloud mitigation mini-workshop on 20-21 November at CERN
Groove
Inside of the chamber
13
Near Beam Electron Cloud Density Measurement in Magnetic Filed with RFA 2
109
1010
1011
1012
1013
0 0.2 0.4 0.6 0.8 1 1.2
Effect of a Solenoid Field
Nea
r B
eam
Ele
ctro
n C
loud
Den
sity
[m-3
]
LER Bunch Current [mA]
B = 0
B = 50 G, Detector 2
B = 50 G, Detector 1
Preliminary
13 November 2008 [4, 200, 3]At 7.2m from a Bend
Photon flux=3.9x1017I[A] photons/m
E-cloud mitigation mini-workshop on 20-21 November at CERN
Electron cloud density with solenoid field (B = 50 G)
1) CODThe difference in two detectors may be due to ;
The measured current in a solenoid field might have included electrons drifting along the wall.
K. Kanazawa and H. Fukuma
14
(0.005 T)
B=0
B=50 G, Detector 1
B=50 G, Detector 2
Near Beam Electron Cloud Density Measurement in Magnetic Filed with RFA 3
109
1010
1011
1012
1013
0 0.2 0.4 0.6 0.8 1 1.2
Effect of a Solenoid Field
Nea
r B
eam
Ele
ctro
n C
loud
Den
sity
[m-3
]
LER Bunch Current [mA]
B = 0
B = 50 G, Detector 2
B = 50 G, Detector 1
Preliminary
13 November 2008 [4, 200, 3]At 7.2m from a Bend
Photon flux=3.9x1017I[A] photons/m
Preliminary result
2) Relative position to the primary synchrotron radiation3) Output offset of amplifier in measurement system.
E-cloud mitigation mini-workshop on 20-21 November at CERN
Measurement of electron density in Q-magnet Electrons accelerated by a bunch along X-axis reach the detector.
With the help of simulation detector current is converted into the density near the beam.
Electrons accelerated with small angle to X-axis moves spirally around X-axis losing their energy along X-axis to the spiral motion.Electrons with sufficient energy and direction close to X-axis reach the detector.
X-axisDetector
Detector 2
Detector 1
SR
+20
0
-20
x [m
m]
-20 0 20
Detector
y [mm]
The big island is an expected source.
Other small islands are unexpected.
Detector Bias = -1 keV
x = 0.35 mm, y = 0.094 mm, z = 6.0 mm, B’ = 3.32 T/m, NB = 7.51010K. Kanazawa and H. Fukuma
15
Near Beam Electron Cloud Density Measurement in Magnetic Filed with RFA 4
Detector16E-cloud mitigation mini-workshop on 20-21 November at CERN
Near Beam Electron Cloud Density Measurement in Magnetic Filed with RFA 5
E-cloud mitigation mini-workshop on 20-21 November at CERN
Electron cloud density with quadrupole field (B’ = 3.32 T/m)
The difference in two detectors may be due to ;
The observed value in Q-Magnet is close to the estimation by simulation
0
1 1010
2 1010
3 1010
4 1010
5 1010
0 0.2 0.4 0.6 0.8 1 1.2
D(Q1)[1,1584,3.06]D(Q2)[1,1585,3.06]
Nea
r B
eam
Ele
ctro
n C
loud
Den
sity
[m-3
]
LER Bunch Current [mA]
8 November 2008, [1, 1585, 3.06]Normal Incident Energy >1 kV13.5m from a half bendB'=3.32[T/m]
Photon flux=3.17x1015I[A] photons/m
Simulation byCLOUDLAND
K. Kanazawa and H. Fukuma
17
Near Beam Electron Cloud Density Measurement in Magnetic Filed with RFA 6
Preliminary result
1) COD2) Relative position to the primary synchrotron radiation3) Output offset of amplifier in measurement system.
Summary
E-cloud mitigation mini-workshop on 20-21 November at CERN
Various studies on the electron cloud mitigation have been done at KEKB positron ring.
TiN coating
Clearing electrode
GraphitizationBeam duct with antechambers
Mitigation methods, such as clearing electrode and coating gave reasonable effect. New RFA type electron detectors was developed and installed in KEKB LER to measure the electron cloud density in solenoid coil and quadrupole magnet.
18
Groove surface
For SuperKEKB : Drift space : antechamber + solenoid + TiN coating Magnet space : antechamber + TiN coating + clearing electrode?
groove surface?