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Running in 2012 @ 4 TeV/beamPreambleIs it worth from the Physics point of view?What do we gain in terms of luminosity?What is the overhead in terms of machine/beam commissioning?

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Many thanks to: L. Bottura, E. Todesco, J. Wenninger, M. Zerlauth, E. Nebot, 2xB. Holzer, J. Steckert, A. Siemko, M. Brugger, M. Lamont, P. Baudrenghien, E. Shaposhnikova, T. Baer, L. Pape, P. Sphicas, J. Varela, V. Kain, R. Assmann, R. Schmidt, M. Koratzinos

Preamble• Why LHC did not run @ 4 TeV in 2011? Let’s recall Chamonix 2011:

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Main argument against running @ 4 TeV Status at the end of 2011

(Un)known number of expected quenches in 2011 (20 in 2010)

HW = 0 quenches Beam = 1 single-magnet spurious quench with beam*

Ref: A. Verweij, Probability of burn-through of defective 13 kA joints at increased energy levels,

Chamonix 2011

* Firing of Quench heater probably due to SEU, but not proven

There is the (≈)same risk associated with

running at 4 TeV and 3.5 TeV down time of 8-12 months

given the present consolidation status

• QPS consolidation work all over the year• Snubber capacitors installed in all dipole circuits• Efficient BLM protection

Is it worth from the Physics point of view?

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Ref: P. Sphicas, View on CMS and ATLAS results, APPS 2011, Nov 30 – Dec 02, 2011

gg H (Hϒϒ,ZZ,WW)

Factor ~ 1.2

qq, gg

Factor ~ 1.5

qq, gg, qg

Factor ~ 4

Mx (GeV)

qq

Factor ~ 3.5

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What do we gain in terms of luminosity?

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FNfNN

L brev2

21

4

FLL ooTeV

TeV

TeVoTeV LL 5.3

5.3

44

*5.3

4

5.3*4 TeV

TeV

TeVTeV

oTeV

TeV

TeVoTeV LL 5.3

2

5.3

44

F: Xangle factor =f(ϵ,β*)!!

1. Due to ϵ↓: 2. Because ϵ↓ more aperture margin at the IT & TCT we get↓β*:

mTeV 875.0*4

~14% L ↑ for free from ε shrink due to 12.5% E ↑

3E+33

3.5E+33

4E+33

4.5E+33

5E+33

5.5E+33

6E+33

6.5E+33

7E+33

7.5E+33

8E+33

2 2.5 3

L(cm

-2s-1

)

εn (μm rad)

Lumi increase @ IP1/5 Lumi: Xangle factor @ 3.5 TeV

Lumi: Xangle factor+emittance srink @ 4 TeVLumi: Xangle factor+emittance + beta* srink @ 4 TeVLumi: Xangle factor+emittance @4TeV+ beta* = 0.7 m

+23% L increase if β* = 0.7 m0.88

0.89

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

2 2.5 3

Xang

le fa

ctor

εn (μm rad)

30% L ↑ from ε & β* shrink

+23% L ↑ if β*=0.7m

L (c

m-2

s-1)

F

ϵn

10

15

20

25

30

35

40

2 2.5 3

Pile

-up

εn (µm rad)

Pile

-up

ϵn

303540

25201510

Nb=1380N1=N2=1.5 1011 p+/bunch

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Overhead in terms of HW Commissioning• Main circuits• Extra powering tests today the powering test stops @6000

A; two extra steps @7000 A would be needed:• One cycle• One energy extraction from QPS• Time estimate: ~ 5 hours/circuit (circuit = RB, RQD, RQF)

• Inductance coefficients recalculation (at least 2 ramps one per QPS board) • RB.A78 - ElQA tested up to 1.6 kV instead of 1.9 kV due to bad insulation on

magnet B30.R7 (NC 1060444) --> limited to 4 TeV, veto to be lifted for higher energies

• Things that are not needed • Reconfiguration of energy extraction – not for 4 TeV (certainly needed for 5

TeV) See next slide• Change of nQPS thresholds to adapt to reduced quench margin (not for 4

TeV)• No quench issue expected till ~5 TeV (RB.A78 had a training quench below!)

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Energy Extraction System

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** nQPS SymQ Thresholds will have to be recalculated for 6800 A ?

OK

to g

o

Ref: J. Steckert, Implication of increased beam energy on QPS, EE, Time Constants, Chamonix 2011

τ (time constant)

Limit=150

Limit=|15.5|

**

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Overhead in terms of HW Commissioning

• Inner Triplets:• All commissioned up to 5 TeV except:• IT.R1 weak electrical insulation of QH YT1121 to coil

and/or ground (NC 1017174) --> limited to 3.5 TeV without QH reconfiguration (high capacitance PS)• Dedicate Quench Heater Power Supply under

construction to be installed and ready for start up with beam

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7/18

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Overhead in terms of HW Commissioning• IPQ/IPD• The current powering test commissions them

up to 3.5 TeV. What has to be done is, simply, to extend the last powering test to I_PNO corresponding to 4 TeV.

• Others• 600 A 5 TeV• 120 A 5 TeV• 60 A 7 TeV

Total Estimated Overhead 3 days

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UFOs: Energy Extrapolation

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17 dumps by UFOs in 2011: 11 MKI UFOs 4 UFOs @Experiments 2 Arc UFOs

Ref: T. Baer, UFOs at LHC, Evian Workshop 2011

3 dumps at 4 TeV

by Arc UFOs

Losses of all arc UFOs in 2011 are scaled up = f(energy Eduardo’s IPAC’11 paper) and compare to the BLM thresholds at the corresponding energy

(MKI UFOs scale similarly with energy)

• Signal/threshold for UFOs is about 55% higher at 4TeV than at 3.5 TeV. Hence, we would have had 3 dumps if we were running at 4TeV this year, compared to 2 dumps which we actually had.

• For >1000 bunches the UFO rate ~ kte energy dependence takes over > 5 TeV

• Not included (margin between BLM thresholds and actual quench limit, 25ns bunch spacing, intensity increase, beam size, scrubbing)

Data 14.04. and 31.10.2011

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SEU Evolution 2011

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Ref: G. Spiezia, M. Brugger, M. Calviani, J. Mekki for R2E, Overview of R2E related events during 2011, CERN-R2E Review 12.11.11

Ref: G. Spiezia, R2E – experience and outlook for 2012, Evian 2011

• 50% of the events are located in the Dispersion Suppression elements and are dominated by QPS

• The most critical areas are UJ14/UJ16 where 50% of the events provoked a beam dump

By Equipment• QPS SEU: Reiner’s talk on

Monday mitigation measures during Xmass’11 shut down to keep the SEU kte regardless the luminosity

• Cryo SEU: Serge’s talk on Monday mitigation measures during Xmass’11

22% of STABLE BEAMS fills were dumped by SEU Markus’ talk on Monday

480b768b

912b1092b

1236b1380b

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SEU: Summary & Forecast

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Ref: G. Spiezia, M. Brugger, M. Calviani, J. Mekki for R2E, Overview of R2E related events during

2011, CERN-R2E Review 12.11.11

LHC

Ref: J. Christiansen, SEE’s In the LHC experiments, CERN-R2E Review 12.11.11

EXPERIMENTS

2012 predictionNo mitigation With mitigation

150 SEU 45 SEU

Ref: G. Spiezia, R2E – experience and outlook for 2012, Evian 2011

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BLM

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X axis = dump threshold for 40 μs RSY axis = maximum noise observed in each monitor during a period of NO BEAM

• Ideally everything should stay below 10% we have some margin and we are confident that we would not dump on noise spikes.

• A few monitor go above 10% of the threshold and it will be studied whether or not need new thresholds.

• Data from 34 hours starting on 2011-11-07 07:00:00 (last technical stop)

NOISE at 100% of dump thresh.NOISE at 10% of dump thresh.

• 450 GeV• 3.5 TeV• 4 TeV

Dump Threshold 40 μs RS (Gy/s) (from simulations)

Noi

se (G

y/s)

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LBDS

• XPOC BLM limits extrapolated to 4.0 TeV from 2011 measurements at energies up to 3.5 TeV • (Likely) to be fine tuned during operation when data

with high intensity dumps at 4.0 TeV are available.• Abort gap cleaning validation at 4.0 TeV needed• but probably this will be requested any way if 3.5 TeV

after the winter TS• The energy of the LBDS is presently clamped at 5.0 TeV

(in the Beam Energy Interlock) no changes to be made at 4.0 TeV• TCDQ functions to be extended to 4.0 TeV (like all the

other collimators)

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BTVDD B1 1380 bunches @ 3.5 TeV

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Machine Protection Validation

• Standard MP tests to be done irrespective of the energy• The exact details also depend on changes that are

made in the stop (that may be unrelated to the energy itself !). • Tests at 4 TeV take a bit longer since the ramp

will be longer (84 s!)• Settings @4 TeV will be different (BLMs, etc) to

be checked more carefully (since the values change), but most of this will be transparent

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RF: Longitudinal stability

15/18

Broadband stability criteria

Narrow-band stability criteria

Without blow-up the threshold quickly decreases during the acceleration ramp

With a blow-up that keeps bunch length constant, the threshold increases linearly with the RF voltage

Thanks to the longitudinal blow-up, the stability is actually improved during the acceleration ramp as the voltage rises

At constant bunch length and voltage, it is independent of energy

Ref: E. Shaposhnikova, Longitudinal Beam Parameters during acceleration in the LHC, LHC Project Note 242, Dec 2000

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Courtesy of P. Baudrenghien & E. Shaposhnikova

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Chromaticity Control @ 4 TeV

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16/18Ref: N. Aquilina, E. Todesco, Decay of chromaticity at injection and operation at 4 TeV,

LMC 07.12.2011

N. Mounet, Impedance effects on beam stability, Evian S7

We learnt the importance of keeping the chromaticity under

control next year if tight collimator settings.

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Re-commissioning in 2012

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Ref: M. Lamont, Operational Overhead of Moving to Higher Energies, Chamonix 2011

2012

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Conclusion

• No show-stoppers from equipment point of view• Total commissioning overhead half a week• ~ Same Probability of burn-through of defective 13 kA

joints as for 3.5 TeV• Risk @ 3.5 TeV ≈ Risk @ 4 TeV down-time 8-12 months

• Important Gain in cross-section & luminosity ( L ~ 30%)

Running @ 4 TeV in 2012 is WORTH DOING!

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Dipole B30R7

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19

QUALIFICATION VOLTAGE1600 V = 600 V (EE+PC) + 1000 V

(Voltage inside the coil)

Simulated MIITS by A. Verweij

Main arc dipole Voltage developed in the coil

1000 V

6771 A ~ 4 TeV

Only a change in the energy extraction resistors = decay time constant during a FPA, could release the veto on the 4 TeV, however at Chamonix 2011 this

solution was not considered safe

RB.A78 - ElQA tested up to 1.6 kV instead of 1.9 kV due to bad insulation on magnet B30.R7 (NC 1060444). Fault inside the cold mass, no possible to repair in situ the Emax for which the use of this magnet is still safe is 4 TeV, above this energy the magnet should be replaced.

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Preamble• What has radically reduced the number of spurious quenches in 2011:• QPS consolidation work all over the year• Snubber capacitors installed in all dipole circuits• Efficient BLM protection

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20Ref: F. Bordry, LHC Energy in 2012 3.5 TeV or 4 TeV, LMC 30th Nov 2011

Preamble• Possibility asynchronous dump with multiple quenches (S56&S67)

Possibility of bus bar quenches + blindness of the nQPS SymQ if > 15 magnets quench

• 1 in 2010***, 0 in 2011 (N.B. S56-65 good sectors in terms of Rspl,max)

14/12/2011R. Alemany, Evian 2011, Session 8: 201221

Limit=150

Limit=|15.5|

**

** nQPS SymQ Thresholds will have to be recalculated for 6800 A

OK

to g

o

Ref: J. Steckert, Implication of increased beam energy on QPS, EE, Time Constants, Chamonix 2011

***2010: faulty power MOSFET in one of the trigger fan-out units qith ion pilot beam; no losses.

τ (time constant)

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FLUKA Studies of the asynchronous beam dump effects on LHC point 6

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22

quenches have to be expected

quenches are possible

quenches are unlikely to happen

12

3

4 5

MQY.4R61, MQY.5R62, MB.A8R63, MB.B8R64, MQML.8R65

5 magnets will quench for sure+ 3 possible = 8 magnets

Energy deposition in bus bars ~ tenth mJ cm-3; but for bus bars in cell C8.R6 peaks a factor 10 higher are expected

Systematic uncertainties = factor 5 to 10!

Ref: R. Versaci et al, FLUKA Studies of the Asynchronous Beam Dump Effects on LHC Point 6, CERN-ATS-2011-236

Eb = 4.5 TeV 150 MJ50 ns bunch spacing, 42 bunches are swept from ideal trajectory = ~5 1012 p+

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Preamble• On top of this: the analysis of pyramid tests and ~375 ramps to 3.5 TeV

allowed to consolidate the Maximum Splice Resistance (Rspl,max) knowledge in a Bus Segment over LHC and so far, no degradation with time has been observed

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23

Splice Type Magnet Rspl,max (nΩ)

Comments

Bus segment RB,RQD/F 0.3±0.8 Few ~ 3 nΩ

Intramagnet*

RB 3.3±0.9 8 dipoles

Intramagnet*

QRD/F 1.2±0.8 3+2 quad

* Intramagnet splices are less dangerous than bus segment splices, since the former are protected by the diodes. Additionally, all intramagnet splices have already been exposed to quenches.

Ref: Z. Charifoulline, Current Status & Long Time Evolution of Main Splice Resistances at 1.9K, 2nd LHC Splice Review, 29.11.2011

However, the knowledge of th

e

copper stabilize

rs status in the

machine has not changed

Preamble

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s12 s23 s34 s45 s56 s67 s78 s81100

120

140

160

180

200

220

240

260

280

300RRR of busbar

RBRQ

The error bars are the RMS spreads of the distributions

Mean RRR of the copper busbar of the machine: 250±50

All sectors measured

Ref: F. Bordry, LHC Energy in 2012 3.5 TeV or 4 TeV, LMC 30th Nov 2011