pressure observations in the lss of the lhc octavio domínguez

Pressure observations in the LSS of the LHC

Octavio Domínguez

e-cloud meeting, 22 November 2013

Acknowledgements

H. Bartosik, G. Iadarola and G. Rumolo

O. Domínguez – e-cloud meeting – 22 November 2013

Outline

I. Bunch intensity thresholds for 50 ns

II. Conditioning over time

III. Behavior during pre-ramp and energy ramp

IV. Conclusions


• Maximum activity for Nb=1.3-1.4• Thresholds around dmax ≈ 1.45 – 1.55

450 GeV


Nb thresholds

50 ns

4 TeV


• Maximum activity for Nb=1.3-1.4• Thresholds around dmax ≈ 1.45 – 1.55

Nb thresholds

50 ns

Nb ( 10∙ 11 ppb)

dmax,thres (450 GeV) dmax,thres (4 TeV)

1.0 1.50 1.50

1.15 1.50 1.45

1.3 1.45 1.45

1.4 1.45 1.45

1.5 1.50 1.45

1.6 1.50 1.50

emax=230 eV

sz,450 GeV= 10 cm

sz,4 TeV= 9.5 cm

ex= 2.4 mm

ey= 2.9 mm

Ø = 80 mm

• The maximum e-cloud activity occurs at Nb = 1.3-1.4 10∙ 11 ppb.

• Thresholds are quite similar for all bunch populations.

• Despite a stronger activity at 4 TeV (photoelectrons), threshold values are very similar at both energies


Nb thresholds

50 ns


Outline




IV. Conclusions



Conditioning over time

• Pressure rises were the first ECE observed in the LHC with 150 and 75 ns

• I focused on pressure gauges located in warm-warm transitions (VGI type):

They are more accurate than other types of gauge in the machine They are all located in the same type of module (with simple geometry)

Ø 80 mm StSt – Cu coated



• Pressure rises were the first ECE observed in the LHC with 150 and 75 ns

• I focused on pressure gauges located in warm-warm transitions (VGI type):

They are more accurate than other types of gauge in the machine

They are all located in the same type of module (with simple geometry)

These modules are located between two 7 m NEG-coated beam pipes

> 7 m NEG coating> 7 m NEG coating

There are 173 gauges of this type around the ring (easier comparison and extrapolation)

There are few exceptions where one side is shorter

For the conditioning I’ll focus on beam 1 (68 gauges), although conclusions are equivalent for both beams.


Conditioning over time• I base my observations on 50 ns on following fills:

2124: 19 September 2011 (before MDs with 25 ns)2240: 22 October 2011 (between 14 October MD and 24 October MD)2261: 27 October 2011 (after 25 ns MDs)

Nb≈1.37e11 ppb for all three2736: 16 June 2012 (Nb≈1.47e11 ppb)3000: 24 August 2012 (Nb≈1.52e11 ppb)3135: 6 October 2012 (Nb≈1.63e11 ppb)3185: 15 October 2012 (Nb≈1.58e11 ppb)3236: 28 October 2012 (Nb≈1.65e11 ppb)3286: 14 November 2012 (Nb≈1.65e11 ppb)

6 random long physics fills during 2012 operation• I’ll show observations of 25 ns for the 24-25/10/11 MD



2011 20121-2Fill 2124 (19 Sep.)

sz



We observe different behaviors Different conditioning states?

2011 20121-2Fill 2124 (19 Sep.)

sz



DP after 5th injection No DP for the rest

of the gauges

There is a visible conditioning effect after the MD on 14 October with 25 ns

2011 20121-2Fill 2240 (22 Oct.)

sz



With 25 ns we observe DP in all the gauges

2011 20121-2MD 25 ns (24-25 Oct.)



No e-cloud related DP observed in any of the gauges Clear improvement after conditioning

2011 20121-2Fill 2261 (27 Oct.)

sz



DP after 5th injection

Nb≈1.47 10∙ 11 ppb, but it seems that some deconditioning took place in gauge VGI.137.7R1.B

2011 20121-2Fill 2736 (16 Jun., Nb≈1.47 10∙ 11 ppb)

sz



DP after 4th injection

DP after last injection

Nb≈1.52 10∙ 11 ppb, DPFill3000> DPFill2736 some deconditioning without 25 ns beams?

2011 20121-2Fill 3000 (24 Aug., Nb≈1.52 10∙ 11 ppb)

sz



Nb≈1.65 10∙ 11 ppb. It has a higher threshold. All gauges must be below this threshold

2011 20121-2Fill 3286 (14 Nov., Nb≈1.65 10∙ 11 ppb)

sz



Similar behavior as in sector 1-2

2011 2012

2-3 Fill 2124 (19 Sep.)



Similar behavior as in sector 1-2 (some conditioning observed after MD with 25 ns)

2011 2012

2-3 Fill 2240 (22 Oct.)



Again, with 25 ns we observe DP in all the gauges

2011 2012

2-3 MD 25 ns (24-25 Oct.)

Again, conditioning observed after MDs with 25 ns.



• Still some DP after 25 ns MDs• 20 gauges along the machine

2011 2012

2-3 Fill 2261 (27 Oct.)



After the 25ns MDs, there are two gauges still showing large DP

2011 2012

3-4 Fill 2261 (27 Oct.)



Nb ≈ 1.65 10∙ 11 ppb. It has a higher threshold, but still some gauges show DP

2011 2012

3-4 Fill 3286 (14 Nov., Nb≈1.65 10∙ 11 ppb)



All gauges show DP before the 25 ns MDs

2011 2012

6-7 Fill 2124 (19 Sep.)



No visible DP after the 25 ns MDsEnhanced conditioning in sector 6-7?

2011 2012

Fill 2261 (27 Oct.)6-7



Summary of results

Scrubbing campaigns

MDs

No measurements possible

This values correspond to gauge VGI.141.6L4.B, which shows the worst state of conditioning over time.



2011 2012

LSS5Fill 3557 (12 Feb., Nb≈1.2 10∙ 11 ppb)

2013

After 2012 scrubbing run with 25 ns, no e-cloud related DP can be observed in the entire machine with 50 ns…

Systematic behaviour for this gauge



2011 2012

LSS4Fill 3557 (12 Feb., Nb≈1.2 10∙ 11 ppb)

2013

After 2012 scrubbing run with 25 ns, no e-cloud related DP can be observed in the entire machine with 50 ns… Excepting 5 gauges in LSS4 (was it opened during the WS?)


Outline




IV. Conclusions



Pre-ramp and ramp

In this example, none of the gauges exhibit DP during injection and all detect some DP during the ramp (at about 2.4 TeV)

2011 20122-1Fill 2261 (27 Oct.)


• Not all gauges show a response to the ramp (especially the most active at injection)

No clear response to the ramp

• “Funny” DP behavior before the ramp Uncaptured beam?

Pre-ramp and ramp

2011 2012

2-3 Fill 2124 (19 Sep.)


Pre-ramp and rampVGI.804.4R6.B

Good example of the DP likely caused by uncaptured beam

2011 2012

Fill 2261 (27 Oct.)


Pre-ramp and ramp

Yet “another” pre-ramp behavior P follows sz (usual behavior

for many guages)

sz

2011 2012

Fill 2124 (19 Sep.)VGI.141.6L4.B


Pre-ramp and ramp

No effect during the energy ramp (likely due to higher pressures)

2011 2012

Fill 2124 (19 Sep.)6-7


Pre-ramp and ramp

Symmetric gauges (both in inner ring)

Systematic behaviour for this gauge

Some symmetric DP can be observed in IPs 1 and 5

2011 2012

LSS5Fill 2736 (16 Jun., Nb≈1.47 10∙ 11 ppb)


Outline




IV. Conclusions



Conclusions• Nb thresholds are between 1.45 and 1.5 for Nb=1.0-1.6 10∙ 11 ppb

• Thresholds at 450 GeV and 4 TeV are very similar

• Different gauges in the warm-warm straight sections show different behaviors

• Conditioning effects seem to be stronger for some gauges

• The DP diminishes for increasing Nb, as predicted by simulations

• No DP during 2013 pp fills with 50 ns can be appreciated, excepting 5 gauges in LSS4

• There are some behaviors during pre-ramp and ramp that are not fully understood yet (uncaptured beam, sz, photoelectrons)

• Some symmetries can be observed between gauges around IPs 1 and 5

THANKS FOR YOUR ATTENTION

pressure observations in the lss of the lhc octavio domínguez

Documents

mmthe maximum ecloud

ns mdsnb1

bunch intensity thresholds

energy ramp iv

type of module

pressure gauges

warmwarm transitions

nb thresholds50 nsnb