electron cloud diagnostics in the sps machine

SPS Working Group, 09 October 2001prepared by J.M. Jimenez, CERN Division LHC - Vacuum GroupG

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Electron Cloud Diagnostics in the SPS Machine

Electron Cloud DiagnosticsElectron Cloud Diagnosticsin the SPS Machinein the SPS Machine

G. Arduini1, V. Baglin3, P. Collier1, B. Dehning2,

G. Ferioli2, B. Henrist3, N. Hilleret3,

B. Jenninger3, L. Jensen2, J.M. Jimenez3,

J.M. Laurent3, K. Weiss3, F. Zimmermann4

1SL/OP, 2SL/BI, 3LHC/VAC, 4SL/AP CERNCERN, Geneva, Switzerland


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Beam effects: bunch intensity, threshold

• Intensity threshold : August 1999: 4.3x1010 p/b April 2000: 6.4x1010 p/b

Pressures do not vary appreciably up to a threshold bunch intensity and then, increase with the bunch intensity.

Amplitude of the signals measured on the pick-up also increase with the bunch intensity.

• Influence of a magnetic field Threshold in magnetic field free regions: 6.0 to 7.0x1010 p/b

Threshold in dipole magnetic fields: 3.0 to 4.0x1010 p/b

Cannot be attributed to systematic errors since the gauges do not resent the magnetic field. One explanation could come from the simulations which showed that the electrons of the e- cloud are confined in the vertical plane in a dipole magnetic field (F. Zimmerman).

Remind

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Beam effects: bunch intensity- No magnetic field -

0

2

4

6

8

10

0.0E+00 2.0E+10 4.0E+10 6.0E+10 8.0E+10 1.0E+11Protons bunch intensity

P/P

Duty cycle ~ 45 %after 17h integratedtime of LHC beam

threshold

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Beam effects: bunch intensity

- Dipole magnetic field -

0

2

4

6

8

10

12

14

0.E+00 1.E+10 2.E+10 3.E+10 4.E+10 5.E+10 6.E+10 7.E+10 8.E+10 9.E+10 1.E+11

Proton bunch intensity

P/P

Duty cycle ~ 45 %after 17h integratedtime of LHC beam

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Beam effects: bunch intensity- No magnetic field -

6.9x1010 p/b21 bunches visible

LHC-type beam characteristics: 1 batch of 72 bunches

8.3x1010 p/b41 bunches visible

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Magnetic field free region

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Dipole magnetic field region

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Scrubbing effect

• Scrubbing effect observed in the SPS Pressure rises decrease with time 30 times after about 2.5 integrated

days of LHC-type beam e- cloud activity no longer affect pressures Threshold bunch intensity increased from 4.0x1010 in August 1999 up to

6.6x1010 in June 2000 Clear indication of a modification of the characteristics of the surface

• N2 glow discharge against e- cloud First cycle of experiments showed no difference between the non-

treated and treated chambers After air exposure, treated chamber showed a memory of the scrubbing

Scrubbing effect is effective up to the bunch intensity used for the commissioning. Pressure will rise for higher bunch intensities

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Scrubbing effect

P/P = 27xe-1.2t

1

10

100

0:00 12:00 24:00 36:00 48:00 60:00LHC beam time (hh:mm)

P

/P

VG51540

VG51833

VG52940

Dipole magnetic field (MBB/MBB)Duty cycle: 45%

Remind

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Scrubbing effect

P/P = 33xe-1.5t

1

10

100

0:00 12:00 24:00 36:00 48:00 60:00LHC beam time (hh:mm)

P

/P

VG51890VG51880

No magnetic fieldDuty cycle: 45%

Remind

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“Strip” detector

300

Beam

Vacuum chamber

Strip detector

Holes


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holes

- Holes distribution -

Transparency of 7.5 % to avoid the extinction of the multipacting


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Strips

Connecting

wires


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Triangle detector- Holes distribution -

Transparency of 42 % to avoid the extinction of the multipacting


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Triangle detector

Vacuum chamberBeam

Filtering grid

Detecting plates

Holes


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Triangle detector

Vacuum chamber

Beam

Filtering gridDetecting plates

Holes


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Reference plate

“Triangle detector”

Beam

axis

Measuring plate

Grid to avoid an extinction of the e- cloud


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Strip detector calibration

-16.5 -14.0 -11.5 -9.0 -6.5 -4.0 -1.5 1.0 3.5 6.0 8.5 11.0 13.5 16.0 18.5 21.0S1

S14

S27

S40

S53S66

0

25

50

75

100

125

150

175

200

Inte

nsity

(arb

. uni

ts)

Lateral position (mm)

175-200

150-175

125-150

100-125

75-100

50-75

25-50

0-25

Signal expected without holes

-16.5 -14.0 -11.5 -9.0 -6.5 -4.0 -1.5 1.0 3.5 6.0 8.5 11.0 13.5 16.0 18.5 21.0S1

S10

S19

S28

S37

S46

S55S64

0

25

50

75

100

125

150

175

Inte

nsity

(arb

. uni

ts)


150-175

125-150

100-125

75-100

50-75

25-50

0-25

Signal expected without holes

Varying the bump amplitude to see the effect

of the holes on the vacuum chamber


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Beam effects: Bunch intensity, threshold

Threshold before (April 2000) and after venting (July 2001)

Field free region

0

2

4

6

8

10

0.0E+00 1.0E+10 2.0E+10 3.0E+10 4.0E+10 5.0E+10 6.0E+10 7.0E+10 8.0E+10 9.0E+10 1.0E+11

Protons bunch intensity

P/P

25/07/200117/04/2000


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Threshold before (April 2000) and after venting (July 2001)

Dipole field region

0

2

4

6

8

10

12

14

16

18

20

0.E+00 1.E+10 2.E+10 3.E+10 4.E+10 5.E+10 6.E+10 7.E+10 8.E+10 9.E+10 1.E+11

Proton bunch intensity

P/P

25/07/2001

17/04/2000


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Threshold of the e- cloud in a dipole field

Limit of detection: 4.2x10-7 A/m2

Magnetic field: 2000 Gauss

0.0E+00

1.0E-05

2.0E-05

3.0E-05

4.0E-05

5.0E-05

6.0E-05

7.0E-05

8.0E-05

0.0E+00 1.0E+10 2.0E+10 3.0E+10 4.0E+10 5.0E+10 6.0E+10 7.0E+10

Protons/bunch

Inte

nsi

ty (

A/m

2 )

After 7 h of LHC beam

(above the threshold: 2.0x10-10 p/b)

First measurementswith LHC beams

Measurements made with 48 bunches in the batch


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Beam effects: Bunch intensity, thresholdMeasurements made with 48 bunches in the batch

Strip width as a function of the bunch intensity


Magnetic field: 2000 Gauss

0

5

10

15

20

25

0.0E+00 1.0E+10 2.0E+10 3.0E+10 4.0E+10 5.0E+10 6.0E+10 7.0E+10

Protons/bunch

Str

ip w

idth

(m

m @

2

)

After 7 h of LHC beam

(above the threshold: 2.0x10-10 p/b)

First measurementswith LHC beams

file MD_25-07-2001-std-LHC-beam-threshold


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Appearance of two strips for high intensity beam (>6.0 1010 p/b)

-17 -14 -12 -9 -7 -4 -2 1 4 6 9 11 14 16 19 21S1

S4

S7

S10

S13

S16

S19

S22

S25

S28

S31

S34S37

S40S43

S46

1.E-06

3.E-06

5.E-06

7.E-06

9.E-06

1.E-05

Inte

nsi

ty (

A/m

2 )

Transverse position (mm)

Tim

e (ms)

t = 10 m

s

9.00E-06-1.10E-057.00E-06-9.00E-065.00E-06-7.00E-063.00E-06-5.00E-061.00E-06-3.00E-06


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0

1

2

3

4

5

6

7

8

9

10

11

12

0.0E+00 2.0E+10 4.0E+10 6.0E+10 8.0E+10 1.0E+11

Bunch intensity (p/b)

Dis

tan

ce b

ea

m a

xis/

strip

(m

m)

y = 2.10-10x - 7

R2 = 0.959

Pumping holes in the LHC beam screen

Two strips at high intensities


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Energy distribution of the electrons in the cloud

1.0E-07

1.0E-06

1.0E-05

1.0E-04

600 1100 1600 2100 2600 3100

Time (ms)

e- clo

ud

in

ten

sity

(A

/m)

0

50

100

150

200

250

300

Fil

teri

ng

po

ten

tial

(V

)

Strip channel 5Strip channel 7e- cloud signal measuredFiltering grid potential


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Beam effects: Bunch intensity, thresholdEnergy distribution of the electrons in the cloud

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 50 100 150 200 250 300 350

Electron energy (eV)

Pe

rce

nta

ge

(%

)

75 eV


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Beam effects: Bunch intensity, thresholdEffect of the magnetic field on the energy

distribution of the electrons in the cloud

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 50 100 150 200 250 300

Electron energy (eV)

Per

cen

tag

e (%

)

30 A

15 A

5 A

2.5 A


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Beam effects: Bunch lengthEffect of the bunch length on the electrons in the cloud

-19

-14 -9 -4 1 6

11 16

S1

S6

S11

S16

S21

S26

S31

S36

S41

S46

S51

S56

S61

S66

S71

S76

S81

S86

S91S96S101

0255075

100125150175200

Intensity


175-200

150-175

125-150

100-125

75-100

50-75

25-50

0-25

-19

-14 -9 -4 1 6

11 16

S1

S6

S11

S16

S21

S26

S31

S36

S41

S46

S51

S56

S61

S66

S71

S76

S81

S86

S91S96S101

0255075

100125150175

Intensity


150-175

125-150

100-125

75-100

50-75

25-50

0-25

150 Gauss2100 GaussB

unch

leng

th: 5

ns -

> 2

ns

Bun

ch le

ngth

: 5ns

->

2ns


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Beam effects: Filling pattern

1

5

9

13

S1

S8

S15

S22

S29

S36

S43

S50

S57

S64

S71

S78

S85

S92

S99

S106

S113

S120

050

100150200250300350400450500550600650

600-650

550-600

500-550

450-500

400-450

350-400

300-350

250-300

200-250

150-200

100-150

50-100

0-50

Effect of the injection of three batches in the SPS


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y = 10-7x

R2 = 0.9888

0.0E+00

1.0E-07

2.0E-07

3.0E-07

4.0E-07

5.0E-07

6.0E-07

7.0E-07

8.0E-07

9.0E-07

-20 -15 -10 -5 0 5 10 15 20


Inte

ns

ity

(A

/m)

0.0E+00

5.0E-07

1.0E-06

1.5E-06

2.0E-06

2.5E-06

3.0E-06

3.5E-06

4.0E-06

4.5E-06

Tota

l in

ten

sit

y (

A/m

)

1 batch

2 batches

3 batches

I e- cloud = f( nbre ofbatches)Linear (I e- cloud = f(nbre of batches))

Effect of the injection of three batches in the SPS


. Ard

uini

, V. B

aglin

, P. C

ollie

r, B

. Deh

ning

, G. F

erio

li, B

. Hen

rist

, N. H

iller

et B

. Jen

ning

er, L

. Jen

sen,

J.M

. Jim

enez

, J.M

. Lau

rent

, K. W

eiss

, F. Z

imm

erm

ann



0.0E+00

2.0E-07

4.0E-07

6.0E-07

8.0E-07

1.0E-06

1.2E-06

1.4E-06

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Time (ms)

Inte

nsi

ty (

A/m

)

Ch 01 : 8 bucket spacing




Effect of an increase of the batch spacing


. Ard

uini

, V. B

aglin

, P. C

ollie

r, B

. Deh

ning

, G. F

erio

li, B

. Hen

rist

, N. H

iller

et B

. Jen

ning

er, L

. Jen

sen,

J.M

. Jim

enez

, J.M

. Lau

rent

, K. W

eiss

, F. Z

imm

erm

ann


Dipole field effect: Bunch intensity, threshold

-19

-4

11

S1

S11

S21

S31

S41

S51

S61

S71

S81

S91

S101

S111

S121

S131S141

S151S161

S171S181

1.0E-042.0E-043.0E-044.0E-045.0E-046.0E-047.0E-048.0E-049.0E-041.0E-03

Inte

ns

ity

(A

/m2 )

Transverse position

(mm)

9.0E-04-1.0E-03

8.0E-04-9.0E-04

7.0E-04-8.0E-04

6.0E-04-7.0E-04

5.0E-04-6.0E-04

4.0E-04-5.0E-04

3.0E-04-4.0E-04

2.0E-04-3.0E-04

1.0E-04-2.0E-04

No e- cloud

detected

-200 G

+200 G

Magnetic field passing through 0 Gauss


. Ard

uini

, V. B

aglin

, P. C

ollie

r, B

. Deh

ning

, G. F

erio

li, B

. Hen

rist

, N. H

iller

et B

. Jen

ning

er, L

. Jen

sen,

J.M

. Jim

enez

, J.M

. Lau

rent

, K. W

eiss

, F. Z

imm

erm

ann



Magnetic field passing through 0 Gauss


0.0E+00

1.0E-04

2.0E-04

3.0E-04

4.0E-04

5.0E-04

6.0E-04

-160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 140 160

Field strength (Gauss)

Inte

ns

ity

(A

/m2)


. Ard

uini

, V. B

aglin

, P. C

ollie

r, B

. Deh

ning

, G. F

erio

li, B

. Hen

rist

, N. H

iller

et B

. Jen

ning

er, L

. Jen

sen,

J.M

. Jim

enez

, J.M

. Lau

rent

, K. W

eiss

, F. Z

imm

erm

ann



e- cloud intensity as a function of the dipole magnetic field


0.0E+00

1.0E-04

2.0E-04

3.0E-04

4.0E-04

5.0E-04

6.0E-04

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200

Magnetic field (Gauss)

Inte

ns

ity

(A

/m2 )

782653

782648

782547

782519

782504

Starting from 1200 GStarting from 2200 G

Starting from 200 G


. Ard

uini

, V. B

aglin

, P. C

ollie

r, B

. Deh

ning

, G. F

erio

li, B

. Hen

rist

, N. H

iller

et B

. Jen

ning

er, L

. Jen

sen,

J.M

. Jim

enez

, J.M

. Lau

rent

, K. W

eiss

, F. Z

imm

erm

ann




0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

3.00E-04

3.50E-04

4.00E-04

4.50E-04

5.00E-04

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Time (ms)

Str

ip in

ten

sit

y (

A/m

2 )

0

300

600

900

1200

1500

1800

2100

2400

Ma

gn

eti

c f

ield

(G

au

ss

)

782491

782496

782504

Mag. Field

e- cloud intensity as a function of the dipole magnetic field


. Ard

uini

, V. B

aglin

, P. C

ollie

r, B

. Deh

ning

, G. F

erio

li, B

. Hen

rist

, N. H

iller

et B

. Jen

ning

er, L

. Jen

sen,

J.M

. Jim

enez

, J.M

. Lau

rent

, K. W

eiss

, F. Z

imm

erm

ann



Strip width as a function of the dipole magnetic field

-19 -16 -14 -11 -9 -6 -4 -1 1 4 6 9 11 14 16 19

S1

S4

S7

S10

S13

S16

S19

S22

S25

S28

S31

S34

S37

S40

S43

S46

S49

0255075

100125150175200225250

Intensity


225-250

200-225

175-200

150-175

125-150

100-125

75-100

50-75

25-50

0-25

-19 -16 -14 -11 -9 -6 -4 -1 1 4 6 9 11 14 16 19

S1

S4

S7

S10

S13

S16

S19

S22

S25

S28

S31

S34

S37

S40

S43

S46

S49

0255075

100125

150

175

200

225

Intensity


200-225

175-200

150-175

125-150

100-125

75-100

50-75

25-50

0-25

-19 -16 -14 -11 -9 -6 -4 -1 1 4 6 9 11 14 16 19

S1

S4

S7

S10

S13

S16

S19

S22

S25

S28

S31

S34

S37

S40

S43

S46

S49

0255075

100125

150

175

200

225

Intensity


200-225

175-200

150-175

125-150

100-125

75-100

50-75

25-50

0-25

-19 -16 -14 -11 -9 -6 -4 -1 1 4 6 9 11 14 16 19

S1

S4

S7

S10

S13

S16

S19

S22

S25

S28

S31

S34

S37

S40

S43

S46S49

0

25

50

75

100

125

Intensity


100-125

75-100

50-75

25-50

0-25

2100 Gauss 1100 Gauss

550 Gauss 200 Gauss


. Ard

uini

, V. B

aglin

, P. C

ollie

r, B

. Deh

ning

, G. F

erio

li, B

. Hen

rist

, N. H

iller

et B

. Jen

ning

er, L

. Jen

sen,

J.M

. Jim

enez

, J.M

. Lau

rent

, K. W

eiss

, F. Z

imm

erm

ann



Strip width as a function of the dipole magnetic field


0

5

10

15

20

25

30

35

40

45

0 500 1000 1500 2000 2500

Magnetic field (Gauss)

Wid

th (

mm

@ 2

)

782653

782648

782606

782590

782574

782519

782504

782496

782491


. Ard

uini

, V. B

aglin

, P. C

ollie

r, B

. Deh

ning

, G. F

erio

li, B

. Hen

rist

, N. H

iller

et B

. Jen

ning

er, L

. Jen

sen,

J.M

. Jim

enez

, J.M

. Lau

rent

, K. W

eiss

, F. Z

imm

erm

ann


Conclusions• Beam effects: bunch intensity, threshold, bunch length

– Dipole field regions: threshold measured at 2.0x1010 p/b– 3.0x1010 p/b in 2000

– Field free regions: threshold measured at 5.0x1010 p/b– 6.0x1010 p/b in 2000

– lower threshold measured could be explained by the venting of the whole SPS to air during the long shutdown.

Below the threshold of the field free region, when the dipole magnetic field is switched off, the e- cloud signal immediately disappeared.

The bunch length affects strongly the e- cloud, decreasing the bunch length from 5ns to 2ns increase the intensity by 50%.

• Current density– Above the threshold, the current increases linearly, up to

5.5x1010 p/b, no saturation effect was observed


. Ard

uini

, V. B

aglin

, P. C

ollie

r, B

. Deh

ning

, G. F

erio

li, B

. Hen

rist

, N. H

iller

et B

. Jen

ning

er, L

. Jen

sen,

J.M

. Jim

enez

, J.M

. Lau

rent

, K. W

eiss

, F. Z

imm

erm

ann


Conclusions• Width of the e- cloud

– The width of the e- cloud strip increases with the beam intensity. At 6.0x1010 p/b, the width is already bigger than 20mm and therefore, the first line of holes (7.5 mm from the axis) in the beam screen sees the e- cloud. With the present design of the beam screen, the e- cloud will see the second line (11.5mm from the axis) at an intensity of 7.0x1010 p/b.

• Effect of the magnetic field strength on the e- cloud– A strong effect of the dipole field strength on the e- could

behavior was shown, mainly for field below 200 G.– Below 20 Gauss, the electron cloud disappears and a

maximum was found around 50 gauss. This effect does not affect the LHC since the field at

injection is about 5500 Gauss


. Ard

uini

, V. B

aglin

, P. C

ollie

r, B

. Deh

ning

, G. F

erio

li, B

. Hen

rist

, N. H

iller

et B

. Jen

ning

er, L

. Jen

sen,

J.M

. Jim

enez

, J.M

. Lau

rent

, K. W

eiss

, F. Z

imm

erm

ann


Conclusions

• Beam scrubbing– After 7h of LHC-type beam (integrated time above the

threshold of 2.0x1010 p/b in the dipole field region), no cleaning effect is visible.

This result is consistent with the measurements of last year presented in EPAC.

Only low intensities <5.0x1010 p/b with small duty cycle (~ 5-10%) were used. This limitation was imposed by the fixed-target beam blow up induced by the e- cloud pressure rises

electron cloud diagnostics in the sps machine

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