KEKB

In-situ Measurement of Secondary ElectronYields at Positron Ring of the KEKB
Shigeki KATO

◆ Summary of Laboratory Results◆ Experimental Setup at LER◆ Sample Materials and Experimental Procedures◆ Experimental Result of SEYs
● Dependences on Materials and Primary Electron Energy● Comparison before and after Exposure to e-Cloud● Comparison w/ Solenoid Field and w/o Solenoid Field◆ Additional Experimental Result of SEYs at Lab● SEYs of CO Saturated NEG Surface● Incident Angle Dependence of SEYs
◆ SummaryShigeki KATO, KEKB Review, Mar., 20071286
285.5

XPS Spectrum of Carbon / Cu

285
284.5
284
3

1

2.5

20.8!max=2.1
0.6

1.5

1.3

1.3
0.4

1

1.0 1.0 1.0

0.5

0

0.2

Cu#20040122-2_Dose-dmax.data
Cu#20040122-2_Dose-dmax.plot

1017

As Received

1018

1019

Electron Beam
Irradiation

1020--2[e cm ]

1021

Ratio of Graphite Form toOther Carbon Forms)

1. Electron or ion dose effects of δmax at
different copper surfaces (mainly CERN
data) were reasonably explained with
Electron Beam Induced Surfacegraphitization.
2. More e- Dose : More Graphite : Lower SEY
3. Electron Beam Induced Surfacegraphitization was found at most metallic
surfaces.
4. Carbon source was found to becarbonatious contamination on as-received
metal surfaces.
5. This graphitization still occurs even for
sputtered clean copper owing to electron
beam irradiation or heating in UHV becauseof carbon diffusion from sub-surface andbulk.

Peak Energy [eV]

Summary of SEYs and Material Surfacesat KEK Laboratory

Secondary Electron Yield, ! max (KEKB

0Sputter
Cleaning

Shigeki KATO, KEKB Review, Mar., 20072KEKB

In-situ Measurement System of SEYs at LER◆ SEMS (Secondary Electron Measurement System) has been built
at Fuji straight of LER.
<Features>
UHV In-situ Measurements of SEYs at Surfaces Exposed to e-Cloud at LER● Primary Electron Beam : 50eV˜5KeV, Beam Scan Capability● Quick Sample Exchanging Capability with Loadlock Chamber● Electron Activity Monitoring Close to Sample @ Beam Chamber●It does not seem costeffective system!
What is the reason asample exposed to e-Cloudcannot be measured
existing SEMS of lab after
its transfer?

Shigeki KATO, KEKB Review, Mar., 20073Example (NEG) of Non In-situ SEY Measurement

KEKB
◆ SEY

SEY of NEG --> e-Cloud Exposure at LER -->Transfer via Air --> SEY of NEG
In-situ :δmax=0.98
δmax=1.96
δmax=1.87●

Meaningless measured value is given due to air exposure.

◆ Change of Surface State Observed Using XPS
3500

4500

CNEG

NEG

LT

e- Beam Irradiatedat Lab.

35at%

3500

44at%

2000

!max=0.98

CarbideCO, COH, etc

1500!

Graphitee+ Beam Exposure
1000 at KEKB D08 & Transfer via Air
290288286284

Binding Energy [eV]282max=1.96!max=1.87
280!"#$%&'()*$+,-$./0123

Intensity [a.u.]

2500

{

Intensity [a.u.]

3000

as-received

Ti

e- Beam Irradiatedat Lab.

4000 LT

3000
2500
2000
1500

8at%

as-received

TiCx

5at% TiO2

Ti2O3, TiO+e Beam Exposureat KEKB D08 & Tranfer via Air

1000
464

Ti 2p1/2
462

460

Ti 2p3/2
458

456

454

Binding Energy [eV]452

450!"#$%&'()*$+,-$&./0123● Surface is heavily contaminated due to air exposure.
● Surface history is almost reset.

★ In-situ Measurement in UHV is Always Mandatory!
Shigeki KATO, KEKB Review, Mar., 2007

4KEKB

In-situ SEMS at Fuji Straight Section at LER
Isolation
Valve
Electron
SourceY
Positron Beam
ChamberX
Three Sample Manipulators

Z

Base Pressure : ˜10-8 Pa
Shigeki KATO, KEKB Review, Mar., 2007

5

SEMS at LER (cntn'd)

KEKB
Electron
MonitorY

Samples

e+ Beam
Isolation
Valve

Y

Positron Beam
Chamber
Electron
SourceZX
Sample Storage

Hole (1.5mmφ) ofElectron Monitor
SampleFaraday Cups

ZSample Surface
Shigeki KATO, KEKB Review, Mar., 20076

Samples & Experimental Procedure

KEKB◆ Exposed Samples
Samples

Descriptions

TiNx

prepared by magnetron sputtering with a film thickness of0.1˜0.2μm on a type 304 stainless steel (P. He et al, BNL)

Cu

oxygen free copper (C10100) treated with a water solution of
H2O2 and H2SO4 (HITACHI-Cable)

NEG

Ti0.3Zr0.2V0.5 prepared by magnetron sputtering with a film
thickness of 1.5μm on a type 304 stainless steel(SAES Getters S.p.A.)

non gas-saturated◆ Experimental Procedure
1.
2.
3.
4.
5.

Sample Loading to SEMS and Baking at ˜180℃
Measurement of SEYs in UHV (Ambient Temperature, ⊥ IncidentAngle)
Sample Loading from SEMS to LER Beam Chamber
Exposure to Electron Cloud for Two Weeks during Physics Run
Sample Transfer Back to SEMS and Measurement of SEYs

◆ Conditions of SEY Measurement● Different Materials● Comparison before and after Exposure● Comparison w/ or w/o Solenoid Field

Shigeki KATO, KEKB Review, Mar., 2007

7

SEYs after Exposure to e-Cloud w/o Solenoid Field

KEKB

Primary Electron Energy Dependence of SEYs for Copper, TiN and NEG
2.5

2.5

Baked for 75 h at 430K

2.5+!max=1.90

22
Emax=250eV

TiN!max=1.76
Emax=375eV

1At LER
0.5
Before Exposure
SEY@KEKB D08 Str. Sec.
Normal Incidence
0TiN+Cu+NEG@D08BK_EpDep.plot

01000

2000

3000

4000

Secondary Electron Yield

Secondary Electron Yield

Cu

2!max=1.80
1.5(5keV, 1!1020e- cm-2)

Solenoid Field Off

Emax=250eV

At LER

Secondary Electron Yield

NEG

after e- Beam irradiation

Exposed to e Beam for 2 Weeks+(before Exposure to e Beam)

After Exposure

1.5

TiN !max=1.08 Emax=300eV
1

NEG !max=1.05Emax=275eV

Cu!max=0.96

0.55000

At LabAfter e- Irradiation

1.5TiN
1

Emax=300eV

NEG !max=0.98
Emax=375eV

Cu!max=0.98

0.5

Emax=275eV

Emax=300eV

Primary Energy [eV]!max=1.04

SEY@Lab.

SEY@KEKB D08 Str. Sec.
0

Normal Incidence
01000

2000

TiN+Cu+NEG@D082w_EpDep.plot

3000

4000

5000

Primary Energy [eV]Normal Incidence0

TiN+Cu+NEG@XHV2-EB_EpDep.plot

01000

2000

3000

4000

5000

Primary Energy [eV]● All as-received Samples : High δmax (NEG : Highest δmax)● After Exposure to e-Cloud : Drastic Decease ofδmax for All (Copper : Lowest δmax)● Results obtained at LER are almost consistent with those results obtained at Lab.
● Surface Analyses : e- beam induced graphitization was found for copper surface

exposed to e-Cloud as found in lab experiment. ( In lab, the same graphite formation atTiN surface + graphite and carbide formation at NEG surface were found.)Shigeki KATO, KEKB Review, Mar., 2007

8

KEKB SEYs after Exposure to e-Cloud w/ Solenoid Field
Primary Electron Energy Dependence of SEYs for Copper and NEG
2.52.5+Exposure to e+ Beam for 2 Weeks

Exposed to e Beam for 2 Weeks

Solenoid Field On

Solenoid Field Off
2w/ Solenoid Field
1.5

Secondary Electron Yield

Secondary Electron Yield

2NEG!max=1.20

Emax=250eV

Cu

1!max=1.03

Emax=325eV

w/o Solenoid Field
1.5

TiN !max=1.08 Emax=300eV
1

NEG !max=1.05!max=0.96

0.5

0.5

Emax=275eV

Cu
Emax=300eV

SEY@KEKB D08 Str. Sec.

SEY@KEKB D08 Str. Sec.
0

Normal Incidence
01000

2000

Cu+NEG@D082w-SolON_EpDep.plot

3000

Primary Energy [eV]

4000

5000

0Normal Incidence
01000

2000

TiN+Cu+NEG@D082w_EpDep.plot

3000

40005000

Primary Energy [eV]

● With Solenoid Field : Slightly Largerδmax for All--> Slow Aging of Surfaces with Less e-Cloud--> Less e- Beam Induced Graphite and/or Carbide Formation
Shigeki KATO, KEKB Review, Mar., 2007

9KEKB

SEYs of CO Saturated NEG Surface ( lab )◆ SEY of gas saturated NEG surface should increase because of pumpedcontamination. It is important to know it for designing.
◆ CO saturation was made until NEG pump speed deteriorates down to˜1/100.
22

NEGNEG Heating
After(200℃, 24h, Conditioning)

After e- Irradiation20e-/cm2)(5keV,101.5

NEG LTCO! m a x= 1 . 4 7
E m a x= 3 2 5 e V

CO Saturated NEG

1NEG LT! m a x= 1 . 0 40.5

Secondary Electron Yield

Secondary Electron Yield

1.5

NEG LTCO! m a x= 1 . 0 5 E m a x= 3 2 5 e V

1NEG LT! m a x= 0 . 9 8
E m a x= 3 7 5 e V

0.5

E m a x= 3 5 0 e V

Non Gas-saturated NEG
0NEG#20050902_EpDepend.data
NEGLT+LTCO-SEY-Act.plot01000

2000

3000

Primary Energy [eV]

4000

5000

0

NEG#20050902_EpDepend.data
NEGLT+LTCO-SEY-EB.plot

01000

2000

3000

40005000

Primary Energy [eV]

● After Heating : Large Increase of δmax --> More e-Cloud at Beginning of Beam Operation.
● After e- Beam Irradiation : Slight Increase of δmax due to Less Graphite and/or CarbideFormation.
● In This Case, CO Saturation is Small ( only 0.4 at%! ) : More Serious Issue when Repeat Use
Shigeki KATO, KEKB Review, Mar., 2007

10KEKB Dependence of SEYs on Incident e- Beam Angle ( lab )◆ Larger SEYs : Sallower Incident Angle of e- Beam.
◆ This dependence is important for both mag. field and field free spaces.
SEY Results for e- Beam Irradiated Surfaces : Close to Real Surface State
222Cu60
1.5

δmax : 30% Up

1! m a x( 0 ° ) = 1 . 0 0
E m a x( 0 ° ) = 2 5 0 e V
0.5

60! m a x( 6 0 ° ) = 1 . 1 3
E m a x( 6 0 ° ) = 4 2 5 e V

1δmax : 15% Up! m a x( 0 ° ) = 0 . 9 8E m a x( 0 ° ) = 3 7 5 e V

0.5

Cu#20040122-2_0625
Cu#20050112!"#$%&'()'*+,&$-&./0123

1000

2000601! m a x( 6 0 ° ) = 0 . 8 6
E m a x( 6 0 ° ) = 4 0 0 e Vδmax : 10% Up
0.5! m a x( 0 ° ) = 0 . 7 8
E m a x( 0 ° ) = 3 2 5 e V000

1.5

Secondary Electron Yield! m a x( 6 0 ° ) = 1 . 2 8
E m a x( 6 0 ° ) = 4 0 0 e V

Secondary Electron Yield

Secondary Electron Yield

1.50

Isotropic Graphite

NEG LT3000

Primary Energy [eV]400050000

NEG#20050902_EpDepend.data
NEGLT-SEY-0+60deg-AR+Act.plot

01000

2000

3000

Primary Energy [eV]

4000

5000

00

GraSEY-0+60deg-EB-2.plot

01000

2000

3000

4000

5000

Primary Energy [eV]

● Lower Z Materials : Less Enhancement of δmax with Sallower Incident Angle.
Shigeki KATO, KEKB Review, Mar., 2007

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KEKB

Dependence of SEYs on Incident Angle (cntn'd)◆ Sallower Incident Angle of e- Beam : Larger SEYs
SEYs Results for As-received Surface
33

as-received

TiN_5Ax 1.2

Ep=300eV

21.5x 2.1121.5x 1.1
1

Ep=250eV

Ep=2.9keV
0.5

0.5

0as-received

2.5

Secondary Electron Yield

Secondary Electron Yield

2.5

IsotropicGraphite!"#$%&#20030228'&()*+,-./0/0153045! [degrees]

60

75

900x 1.7

Ep=3keV!"#$%&&'&(%)*+,-.#&'&(%/01232!"#$%&&'&(%)*+,-.#&'&(%/0plot0153045607590! [degrees]● Metal Surfaces : High SEYs and Large Enhancement (x3) of SEYs withSallower Incident Angle at Initial Stage● Graphite Surfaces : Low SEYs and Small Enhancement (x2) of SEYs in a Wide
Range of Incident Angle● Proposal : Test Installation of Graphite Wall to Beam Chamber
12Shigeki KATO, KEKB Review, Mar., 2007

KEKBSummary

1. SEMS (Secondary Electron Measurement System) has been built at Fuji
straight of LER.
2. Results obtained at LER were almost consistent with those results obtainedat Lab.
3. e- beam induced surface-graphitization was found for copper surface
exposed to e-Cloud as found in lab experiment.
4. Slightly largerδmax of NEG and copper with solenoid field would be
explainable based on slow aging of surfaces without e-cloud due to less ebeam induced graphite and/or carbide formation.
5. After heating of NEG surface, large increase of δmax would cause more ecloud at beginning of beam operation.
6. 1st CO Saturation of only 0.4 at% of NEG showed remarkable increase of
δmax . Repeat use of NEG will cause further increase of δmax.
7. Larger SEYs with sallower incident angle of e- beam should be recognizedwell.
8. At metal surfaces, high SEYs and its large enhancement with sallower
incident angle at initial stage were shown.
9. At graphite surface, low SEYs and its small enhancement in a wide range ofincident angle were found.
10. Test installation of graphite wall to beam chamber was proposed.
Plan : Measurement of SEY Change after Long Term Exposure to e-Cloud andExposure to H2 or CO Gas during Beam Operation.
Shigeki KATO, KEKB Review, Mar., 2007

13

KEKB

FinThanks for Technical Assistance :Michiru NISHIWAKI
Michiru SHIRAI
and Tsuneyuki NOGUCHI

e-Cloude+ Bunch
Shigeki KATO, KEKB Review, Mar., 2007

14

KEKB

Shigeki KATO, KEKB Review, Mar., 2007

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KEKB

Typical Exposure to e-Cloud for Two Weeks
Without Solenoid Field

LER BeamCurrent :∫Idt = ˜500Ah

MonitoredElectronDose (┻) :3x10-4Ah--> 4x1020e-/cm2

Shigeki KATO, KEKB Review, Mar., 200716