1. News from the LHC J. Wenninger CERN Beams Department Operation Group
LHC news - CMS - J. Wenninger
Evian – 19th October 2009
16th Nov. 2009

2. Outline Recap of joint story and operating energy
Status of the LHC: HWC and beam tests
2009/10 LHC run
Outlook
LHC news - CMS - J. Wenninger
16th Nov. 2009

3. Joint recap & maximum energy
LHC news - CMS - J. Wenninger
16th Nov. 2009

4. High current busbar joints
He heat exchanger
Quadrupole
Busbars (M1,M2)
LHC news - CMS - J. Wenninger
Vac. chamber
Dipole busbar (M3)
16th Nov. 2009

5. Busbar soldering problems
Careful inspection of all joints was performed when sector 34 was repaired, including systematic X-rays of interconnections.
The repair team found to quality issues (systematic !):
Overheating leading to SnAg solder flowing out of the busbar and leaving empty spaces.
Un-melted SnAg solder.
B25R3-M3 (dipole) before disconnection
LHC news - CMS - J. Wenninger
16th Nov. 2009
Courtesy C. Scheuerlein

6. Joint problem summary
Case A: Small – 10’s of nW level - anomalous resistance within the joint when the magnets are at 1.9 K: may trigger S34 type accidents (bad soldering of the 2 busbar cables).
Detectable at 1.9 K with an upgrade of the quench detection and protection system.
Case B: Poor joint quality (voids…) - excess resistance of 10’s of mW at room T - that do not pose an immediate threat, but can trigger a S34 incident in the event a quench (busbar or magnet).
Detectable at room temperature with a DC resistance measurement.
LHC news - CMS - J. Wenninger B B
16th Nov. 2009 A

7. Dipole magnets in arc cryostat
154 dipole magnets are connected as one circuit to the power converter.
Time for the energy/field ramp is about min (energy from the grid)
Time for regular discharge (ramp down) is about the same (energy to the grid)
Power Converter
Energy Extraction: switch closed
Magnet 3
Magnet 2
Magnet 152
Magnet 154
Magnet 4
DFB
Magnet 1
Magnet 153
Magnet 5

8. Quench protection
Quench detected: energy stored in magnet dissipated inside the magnet (time constant of 200 ms).
Parallel diode becomes conducting: current of other magnets through diode.
Resistances are switched into the circuit: up to 1 GJ of energy is dissipated in the resistances (nominal decay time constant: 100 s).
DFB
DFB
Magnet 2
Magnet 4
Magnet 152
Magnet 154
Magnet 1
Magnet 3
Magnet 5
Magnet 153
Energy Extraction: switch open
Energy Extraction: switch open
Bus-bar must carry the current during the discharge through interconnections
Power Converter

9. ‘Safe’ energy for 2009/10 run
The energy at which the LHC can be operated safely is determined by a number of factors:
Maximum additional room T joint resistance (wrt nominal value).
- recommendation: 90 mW (measurement uncertainties).
Copper resistance (RRR value, resistance ratio 300K/4.2K).
- recommendation : RRR = 120
Quench propagation (time) from magnet to busbar.
- ten’s of seconds
Discharge time of the circuits.
- dipole : reduced from 103 s to 50 s
- quads : reduced from 15 s to 10 s
>> sets an absolute max of 5 TeV (induced voltage during discharge)
Direct busbar quenches by the beam.
- not a problem (geometry and loss monitor protection)
LHC news - CMS - J. Wenninger
16th Nov. 2009

10. Simulations for dipoles
LHC news - CMS - J. Wenninger
3.5 TeV
16th Nov. 2009
Courtesy A. Verweij

11. 3.5 TeV and…. The decision on the energy in August 2009:
Initial operation at 3.5 TeV.
Increase energy to 4-5 TeV once sufficient experience has been gained at 3.5 TeV.
It is not evident what facts can be used to decide on an energy increase, since the risk will still be present (hidden in the joints, can only be measured at room temperature).
Simulations clearly indicate considerable risk.
LHC news - CMS - J. Wenninger
16th Nov. 2009

12. LHC status
LHC news - CMS - J. Wenninger
16th Nov. 2009

13. Cryogenics
All sectors are ready for powering or in the last phase of cool-down (< 4K).
This year cryogenic conditions are more stable – much better than 2008. 67 34 45 81 23
01.09
01.10
01.11

14. Quench protection system upgrades
nQPS: joint protection system covering all busbar joints of the dipole and quadrupole circuits.
Up to 2 kA/1.1 TeV the system is used for monitoring & measurements of the busbar resistances (not needed for protection).
For 3.5 TeV operation the system must be fully commissioned and connected to the magnet protection (energy discharge) system.
SymQ: protection system against symmetry quenches of the 2 magnet apertures (beam 1 and beam 2 of the same magnet).
Required for operation > 5 TeV.
Design, installation and commissioning of those systems (mostly nQPS) have largely dictated the pace of LHC re-commissioning.
LHC news - CMS - J. Wenninger
16th Nov. 2009

15. Hardware Commissioning (HWC)
HWC of all sectors in progress.
HWC now split into 2 phases (personnel safety – Helium release):
Phase 1: max current 1 kA, access authorized.
Phase 2: current above 1 kA, 3 sectors closed for access.
The commissioning progress of the nQPS was not fast enough to commission all sector to 6 kA/3.5 TeV for this week.
Some time ago it was decided to fall back to 2kA – 1.1 TeV – to be able to stick to the schedule.
Commissioning to 3.5 TeV (~3 weeks) will be done after the Christmas break. Planning to be defined…
LHC news - CMS - J. Wenninger
16th Nov. 2009

16. Largest excess resistance (nΩ)
nQPS commissioning (1)
Commissioning of the new quench protection system was THE major activity of the HWC for the main dipoles and quadrupoles.
Measurement results are very good:
First measurements up to 2 kA for indicate no anomalous R above few nW in the busbars (limited by noise).
Sector
circuit
Missing channels
Largest excess resistance (nΩ)
Sector 12 RB RQ
Sector 23
 2.5±0.3
Sector 34
  2.5±0.3
Sector 45  6
Sector 56
 2.0±0.4
Sector 67
Sector 78
Sector 81 1 2
LHC news - CMS - J. Wenninger
Status
16th Nov. 2009

17. nQPS results
LHC news - CMS - J. Wenninger
Measurement of the joint resistance at 1.9K with a current of 2 kA (dipoles) for sector 78.
Average R = 300 pW, all values < 1 nW
16th Nov. 2009
Courtesy K. Dahlerup Petersen

18. nQPS commissioning (2)
Commissioning progress of the new quench protection system was not as fast as expected.
The system is complex,
Thorough testing of all cables & connections is required since it is a protection system.
A problem with the connectors of the new QPS system was discovered during ELQA (Electrical Quality Assurance) tests.
Main circuits are tested at 1.9 kV for 1 minute.
Breakdowns were observed in certain sectors (most prominently 81) and they were traced to insulation problems of the nQPS cables (at the level of the connectors). 4 sectors were only tested to 1.2 kV.
>> ~3000 connectors must (most likely) be redone before going to 3.5 TeV (approx. 3 days/sector).
LHC news - CMS - J. Wenninger
16th Nov. 2009

19. nQPS cable damage G. J. Coelingh, LMC Nov 09
LHC news - CMS - J. Wenninger
16th Nov. 2009

20. HWC status 16th Nov 2009 98% of all circuits ready for 2 kA/1.2TeV.
All circuits, except the main dipoles (RB) and main quadrupoles (RQ), are commissioned directly to 3.5 TeV
LHC news - CMS - J. Wenninger
16th Nov. 2009

21. Main circuits
Sector 12 is the ‘test sector’ for going to 6 kA / 3.5 TeV.
Sectors 23, 56, 78 in the process of being handed over to OP group.
Status
Sector
circuit
Commissioned
to injection current
to 2 kA
to 4 kA
Sector 12 RB Y RQ -
Sector 23
Sector 34
Sector 45 
Sector 56
Sector 67
Sector 78
Sector 81
LHC news - CMS - J. Wenninger
16th Nov. 2009

22. Other issues…
An insulation vacuum leak appeared a few week ago in S34 during cool-down to 4.2 K.
Helium flowing from magnet enclosure into insulation vacuum
Situation stabilized using groups of turbo-pumps.
Cool-down & HWC to 1.9 K could proceed as foreseen.
So far so good…
LHC news - CMS - J. Wenninger
16th Nov. 2009

23. Injection tests The 2 injection tests were successful.
No major issues were un-covered, some follow up…
Vertical aperture bottleneck around injection point of beam 2 (IR8). Alignment being checked (looking for ~5 mm error !).
LHCb very sensitive to beam loss on injection dump (‘TDI’), while ALICE seems to be fine. Arghh !!
LHC news - CMS - J. Wenninger
16th Nov. 2009

24. Apertures Horizontal beam2 aperture scan Excellent !!
IR7
IR6
IR5
IR8
Horizontal beam2 aperture scan
x (m)
Excellent !!
LHC news - CMS - J. Wenninger
IR7
IR6
IR5
IR8
y (m)
Vertical beam2 aperture scan
16th Nov. 2009

25. Dump Beam was extracted into the dump channel.
The bucket number was varied to probe the beam dilution trace on the dump block.
Superposition of beam impacts on the dump block for different bucket numbers.
Follows nicely expected dilution shape.
LHC news - CMS - J. Wenninger
y (cm)
x (cm)
16th Nov. 2009

26. LHC Run 2009 (10)
LHC news - CMS - J. Wenninger
16th Nov. 2009

27. LHC run 2009
LHC news - CMS - J. Wenninger
Beam commissioning so far scheduled to start next Friday evening.
All CERN machines will stop on 17th December and be put on standby until the ~7th January: we have ~27 days before Xmas break.
16th Nov. 2009

28. The Grand Plan Beam ‘safety’ Essential 450 GeV commissioning
Energy
‘Safe’
Pretty Safe
450 GeV
1 e12
1 e11
1 TeV
2.5 e11
2.5 e10
3.5 TeV
3.0 e10
5 e9
Machine protection commissioning 1
Experiments’ magnets at 450 GeV
450 GeV collisions
Ramp commissioning to 1.2 TeV
LHC news - CMS - J. Wenninger
Machine protection commissioning 1.5
First collisions at 1.2 TeV
System/beam commissioning
Machine protection commissioning 2
3.5 TeV beam & first collisions
Full machine protection qualification
Pilot physics
16th Nov. 2009

29. End of 2009 beam commissioning
Very ambitious 4 week plan (in fact the plan requires ~30 days with 100% availability):
Commissioning at 450 GeV.
Collisions at 450 GeV (a few shifts).
Ramp to 1.2 TeV.
Collisions at 1.2 TeV with max. 2 bunches per beam, 2e10 p/bunch.
>> In theory feasible if everything works very well…
Predictions are difficult to make, but there is a good chance that we will be able to go as far as item 3.
Depends a lot on how we manage (or not) the ramp…
LHC news - CMS - J. Wenninger
16th Nov. 2009

30. In more details (1) Days 1-3: Days 4-10:
First turn, closed orbit, RF capture for both beams.
Days 4-10:
Optics measurement and correction.
Basic beam instrumentation.
RF commissioning.
Basic protection and collimation setup.
Aperture.
Beam dumping system.
Fundamental machine protection (beam loss monitors).
LHC news - CMS - J. Wenninger
16th Nov. 2009

31. In more details (2) Days 11-15: Days 15++:
2 beam operation.
Exp. magnets.
Exp. machine protection (IR aperture, IR loss monitors, BCMs).
Ramp attempts…
… leading to first collisions at 450 GeV
Days 15++:
Ramp to 1.2 TeV.
Beam dumping system & machine protection in the ramp.
Low intensity operation at 1.2 TeV.
Optics at 1.2 TeV.
Protection and collimation at 1.2 TeV.
… leading to collisions at 1.2 TeV.
LHC news - CMS - J. Wenninger
In practice many activities will be interleaved.
16th Nov. 2009

32. 450 GeV conditions
No squeeze (beta* = 10 m): large beam sizes (~0.27 mm).
Limited intensity (machine protection commissioning).
~ 2 weeks after first beam.
LHC news - CMS - J. Wenninger
Number of bunches / beam 2 4
Collision schedule
Particles per bunch
3x1010
4x1010
6x1010
Beam intensity*
1.6x1011
2.4x1011
beta* [m] 10
Luminosity [cm-2s-1]
1.1x1027
5.9x1027
1.3 x 1028
16th Nov. 2009

33. Beam operation at 3.5 TeV
Luminosity (head on case, no crossing angle) :
Nominal parameters
k = number of bunches = 2808
N = no. protons per bunch = 1.15×1011
f = revolution frequency = kHz
s*x,s*y = beam sizes at collision point (hor./vert.) = 16 mm
LHC news - CMS - J. Wenninger
The beam size s depends on the betatron function b* and on beam emittance en:
Everywhere in the ring the beam size scales with 1/g ~ 1/E.
Aperture margins are reduced wrt 7 TeV !
The quench levels at 3.5 TeV are a factor ~10 higher wrt 7 TeV and the stored beam energy is lower: advantage in the early days.
16th Nov. 2009

34. b* and triplets
Triplets
Triplets
ARC cells
CMS collision point
LHC news - CMS - J. Wenninger
At the IP the beams have a small size but a large DIVERGENCE (phase space conservation):
>> size grows rapidly between IR and triplets where it reaches a maximum.
>> aperture limit during collisions.
16th Nov. 2009

35. >> overall factor ~8
Luminosity at 3.5 TeV
A consequence of the small beam size at the IP (small b*) is a large beam size in the triplet magnets.
The physical aperture in the triplet quadrupoles defines the minimum of b*.
Limits b* to ~ 2 m at 3.5 TeV (instead of 0.55 m at 7 TeV)
LHC news - CMS - J. Wenninger
Beam size s* increase by:
Factor 2 (‘naturally’ larger size)
Factor ~2 (b* limit)
Luminosity loss wrt 7 TeV of:
Factor ~22 per plane (s*)
>> overall factor ~8
for same beam intensity
16th Nov. 2009

36. (Possible) luminosity evolution in 2010
Comment
energy
bunches
p/bunch
b* (m)
Peak L
(cm-2 s-1)
No crossing angle
3.5
43 x 43
3x1010 4
9x1029
5x1010
2.4x1030
156 x 156 2
1.7x1031
7x1010
3.4x1031
10x1010
6.9x1031
50 ns trains
144 x 144
3.1x1031
432 x 432
9.4x1031
9x1010
1.5x1032
LHC news - CMS - J. Wenninger
~1 event/crossing for b* = 2 m and intensity per bunch of 7x1010
Achievable integrated luminosity: ~300 pb-1.
16th Nov. 2009

37. Stored energy – a challenge !!!!
100 1k
10k
100k 1M
10M
100M 1T
Pilot b
3 kJ
Nominal b
65 kJ
Safe Beam Limit - 2x1010 p
12 kJ
Nominal beam
181 MJ
Stored
Energy
(J)
‘156 b’ physics
3.5-7 MJ
3.5 TeV
LHC news - CMS - J. Wenninger
TEVATRON : ~2 MJ
The stored energy in the LHC for the possible luminosity options will exceed what is done at TEVATRON by a factor ~10 for 50 ns operation!
16th Nov. 2009

38. Summary
More than one year after the beams are knocking on the LHC door again.
If all goes very well, by Xmas we have collisions at 450 GeV and ramps to 1.1 TeV.
If it goes incredibly well, we may even see collisions at 1.1 TeV.
Machine uptime will be a key factor – don’t ask for too many accesses !
The way to 3.5 TeV will lead us through another commissioning period of the main circuits of ~ 3 weeks in 2010.
LHC news - CMS - J. Wenninger
16th Nov. 2009