Summary of e- cloud activity in straight sections during the scrubbing run 2012

C. Octavio Domínguez

Thanks to the machine Coordinators, Cryogenics, Damper, EN/STI, Injection, Operation, Vacuum

teams, ABP, RF and BI colleagues contributing to measurements

11 January 2013 - e- cloud meeting

Nb (Beam 1)

Nb (

10∙14

p+ )

Overview

Time (hours)11 January 2013 - e- cloud meeting

P (

10∙-8

m

bar)

VGI.454.4R7.BVGI.99.4L3.B

Nb (Beam 1)

Nb (

10∙14

p+ )

Overview

Time (hours)11 January 2013 - e- cloud meeting

VGI.454.4R7.BVGI.99.4L3.B

Nor

m. P

(10∙

-22 m

bar/

p+ )

Fill 3396

Fill 3397Fill 3398

Fill 3405

Fill 3

406

Fill 3407

Overview

11 January 2013 - e- cloud meeting

• No dedicated fills for straight sections benchmarking• Instable beams Losses No stable pressure Some needed considerations:

P = 11.83n_t - 5.8486R² = 0.9978

0

20

40

60

80

100

120

140

160

180

0 2 4 6 8 10 12 14 16

Pres

sure

[nTo

rr]

# of "double trains" in the machine

VGI.141.6L4.B

10 April 2011

P = 7.6131n_t - 17.485R² = 0.9911

0

10

20

30

40

50

60

70

80

0 2 4 6 8 10 12 14

Pres

sure

[nTo

rr]

# of "triple trains" in the machine

VGI.141.6L4.B

19 May 2011

Overview

11 January 2013 - e- cloud meeting

• No dedicated fills for straight sections benchmarking• Instable beams Losses No stable pressure Some needed considerations:

DP1

DP2

DP3DP4

DPav

DPav

DPav

dmax evolution

11 January 2013 - e- cloud meeting

Fill 3396 ≈ Fill 3397

…

925 ns

250 ns

925 ns 925 ns

Coarse grid!

dmax evolution

11 January 2013 - e- cloud meeting

Coarse grid!

Further analysis

11 January 2013 - e- cloud meeting

Fill 3406 ≈ Fill 3407

…

925 ns

250 ns

925 ns 925 ns

Small DP

No DP!

• Scrubbing effect can be noticed from fill to fill

Further analysis

11 January 2013 - e- cloud meeting

Fill 3407

…

925 ns

250 ns

925 ns 925 ns

No DP!

• We can check into simulations to find a pair of values [dmax, R] which fulfills:

not to saturate for a batch of 144 bunches (at the measured pressure) to saturate for a batch of 288 bunches (at the measured pressure)

• We find dmax < 1.24 for any R, and dmax ≈ 1.22 if we consider R=0.2 In agreement with previous analysis

Further analysis

11 January 2013 - e- cloud meeting

… …

Fill 3406Fill 3405

N

i measured

simulation

rr

NQ

1

2

11Quality factor

vs.

• Qmin d max = 1.23 and R=0.2

• Not very accurate in this case because: N = 1 too small d max might have varied during fill 3405 difficult comparison

• But still in agreement with previous estimations

Threshold

11 January 2013 - e- cloud meeting

• A revision of the threshold has become necessary (previous value given for injection energy was d max = 1.25)

• I used 3 trains of 4 batches each

• For R=0.2 the threshold at 450 GeV would be d max ≈ 1.16

Summary

11 January 2013 - e- cloud meeting

• The scrubbing effect is clearly visible through the reduction of the D P along the different fills

• Several fills at injection energy have been used to infer beam chamber properties in straight sections (where pressure gauges are located)

• Analysis is still on going but a clear reduction of can be observed (from ~1.3 to ~1.23)

• Different methods point out to a similar solution at the end of the fills at injection energy (d max ≈ 1.23 and R ≈ 0.2 )

• The threshold at injection energy for these locations has been calculated:

d max ≈ 1.16 with R ≈ 0.2