1. Hadron Collider Summer School - June 2009
The LHC Machine
Jörg Wenninger
CERN Beams Department
Operations group
Hadron Collider Summer School - June 2009
Part 2:
Machine Protection
Incident 19th September 2008
Commissioning and operation

2. Machine Protection

3. The price of high fields & high luminosity…
When the LHC is operated at 7 TeV with its design luminosity & intensity,
the LHC magnets store a huge amount of energy in their magnetic fields:
per dipole magnet Estored = 7 MJ
all magnets Estored = 10.4 GJ
the 2808 LHC bunches store a large amount of kinetic energy:
Ebunch = N x E = 1.15 x 1011 x 7 TeV = 129 kJ
Ebeam = k x Ebunch = 2808 x Ebunch = 362 MJ
To ensure safe operation (i.e. without damage) we must be able to dispose of all that energy safely !
This is the role of Machine Protection !

4. Stored Energy Increase with respect to existing accelerators :
A factor 2 in magnetic field
A factor 7 in beam energy
A factor 200 in stored energy

5. Comparison…
The energy of an A380 at 700 km/hour corresponds to the energy stored in the LHC magnet system :
Sufficient to heat up and melt 15 tons of Copper!!
90 kg of TNT
The energy stored in one LHC beam corresponds approximately to…
10-12 litres of gasoline
15 kg of chocolate
It’s how easily the energy is released that matters most !!

6. Machine protection: the beam

7. To set the scale..
Few cm long groove of an SPS vacuum chamber after the impact of ~1% of a nominal LHC beam during an ‘incident’:
vacuum chamber ripped open.
3 day repair.
The same incident at the LHC implies a shutdown of > 3 months.
>> The protection of the LHC must be much stricter and much more reliable !

8. LHC beam impact : energy deposition
7 TeV LHC beam into a 5 m long Copper target
20 bunches
180 bunches
380 bunches
100 bunches
N. Tahir / GSI

9. Beam impact in target : density
The 7 TeV LHC beam is able to drill a hole through ~35 m of Copper
20 bunches
180 bunches
100 bunches
380 bunches
N. Tahir / GSI

10. Cu plate ~20 cm inside a ‘target’.
From a real 450 GeV beam
Shot
Intensity / p+ A
1.2×1012 B
2.4×1012 C
4.8×1012 D
7.2×1012
Cu plate ~20 cm inside a ‘target’.
~0.1% nominal LHC beam
A B D C

11. Machine protection: how do we get rid of the beam?

12. Schematic layout of beam dump system in IR6
When it is time to get rid of the beams (also in case of emergency!) , the beams are ‘kicked’ out of the ring by a system of kicker magnets and send into a dump block !
Ultra-high reliability system !!
Septum magnets deflect the extracted beam vertically
Beam 1
Kicker magnets to paint (dilute) the beam
Q5L
Beam dump block
Q4L
15 fast ‘kicker’ magnets deflect the beam to the outside
about 700 m
Q4R
about 500 m
Q5R
The 3 ms gap in the beam gives the kicker time to reach full field.
quadrupoles
Beam 2

13. beam absorber (graphite)
The dump block
This is the ONLY element in the LHC that can withstand the impact of the full beam !
The block is made of graphite (low Z material) to spread out the showers over a large volume.
It is actually necessary to paint the beam over the surface to keep the peak energy densities at a tolerable level !
beam absorber (graphite)
Approx. 8 m
Beam dump at 450 GeV
concrete shielding
Sept. 2008

14. Dump line in IR6

15. Dump line

16. Dump installation
CERN visit McEwen 16

17. ‘Unscheduled’ beam loss due to failures
In the event a failure or unacceptable beam lifetime, the beam must be dumped immediately and safely into the beam dump block
Two main classes for failures (with more subtle sub-classes):
Passive protection
- Failure prevention (high reliability systems).
Intercept beam with collimators and absorber blocks.
Beam loss over a single turn
during injection, beam dump.
Active Protection
- Failure detection (by beam and/or equipment monitoring) with fast reaction time (< 1 ms).
- Fire beam dumping system
Beam loss over multiple turns
(~millisecond to many seconds) due to many types of failures.
Because of the very high risk, the LHC machine protection system against beam damage is of unprecedented complexity and size.
A general design philosophy was to ensure that there should always be 2 (or more than 2) different systems to protect against a given failure type.

18. Failure detection example : beam loss monitors
Ionization chambers to detect beam losses:
N2 gas filling at 100 mbar over-pressure, voltage 1.5 kV
Sensitive volume 1.5 l
Reaction time ~ ½ turn (40 ms)
Very large dynamic range (> 106)
There are ~3600 chambers distributed over the ring to detect abnormal beam losses and if necessary trigger a beam abort !

19. Beam interlock system
Over 10’000 signals enter the interlock system of the LHC that will send the beam into the dump block if any input signals a fault !
CCC
Operator Buttons
Safe
Mach.
Param.
Software
Interlocks
LHC
Devices
SEQ
Movable Devices
Experiments
BCM
Beam Loss
Experimental Magnets
Collimation
System
Collimator
Positions
Environmental
parameters
BTV
BTV screens
Mirrors
Timing
Transverse Feedback
Beam
Aperture
Kickers
FBCM
Lifetime
Beam
Dumping System
Beam Interlock System
Safe
Beam
Flag
PIC essential
+ auxiliary
circuits
WIC
QPS
(several 1000)
Power
Converters
~1500
AUG
UPS
Power Converters
Magnets
FMCM
Cryo OK RF
System
BLM
BPM in IR6
Monitors
aperture limits
(some 100)
Monitors in arcs
(several 1000)
Access
System
Doors
EIS
Vacuum
System
valves
Access
Safety
Blocks
RF Stoppers
Injection BIS
Timing System
(Post Mortem)

20. Machine protection and quench prevention: collimation

21. Operational margin of SC magnet
Applied Field [T]
The LHC is ~1000 times more critical than TEVATRON, HERA, RHIC
Bc critical field Bc
quench with fast loss of ~106-7 protons
8.3 T / 7 TeV
QUENCH
Tc critical
temperature
quench with fast loss
of ~4x109 protons Tc
0.54 T / 450 GeV
1.9 K
Temperature [K]
9 K

22. Beam lifetime Consider a beam with a lifetime t :
Number of protons lost per second for different lifetimes (nominal intensity):
t = 100 hours ~ p/s
t = 25 hours ~ 4x109 p/s
t = 1 hour ~ p/s
While ‘normal’ lifetimes will be in the range of hours (in collisions most of the protons are actually lost in the experiments !!), one has to anticipate short periods of low lifetimes, down to a few minutes !
 To survive periods of low lifetime we must intercept the protons that are lost with very very high efficiency before they can quench a magnet : collimation!
Quench level ~ p

23. Collimation
A 4-stage halo cleaning (collimation) system is installed to protect the LHC magnets from beam induced quenches.
A cascade of more than 100 collimators is required to prevent the protons and their debris to reach the superconducting magnet coils.
The collimators will also play an essential role for background reduction.
 the collimators must reduce the energy load into the magnets due to particle lost from the beam to a level that does not quench the magnets.
in front of the exp.
Exp.
Detectors

24. Collimator settings at 7 TeV
At the LHC collimators are essential for machine operation as soon as we have more than a few % of the nominal beam intensity at injection !
The collimator opening corresponds roughly to the size of Spain !
Carbon jaw
1 mm
Opening
~3-5 mm
RF contact ‘fingers’

25. Machine protection: magnets

26. LHC powering in sectors
To limit the stored energy within one electrical circuit, the LHC is powered by sectors.
The main dipole circuits are split into 8 sectors to bring down the stored energy to ~1 GJ/sector.
Each main sector (~2.9 km) includes 154 dipole magnets (powered by a single power converter) and 47 quadrupoles.
 This also facilitates the commissioning that can be done sector by sector ! 5 4 6
DC Power feed
LHC 3
DC Power 7
27 km Circumference
Powering Sector 2 8
Sector 1

27. Powering from room temperature source…
6 kA power converter
Water cooled 13 kA Copper cables
! Not superconducting !

28. Feedboxes (‘DFB’) : transition from Copper cable to super-conductor
…to the cryostat
Feedboxes (‘DFB’) : transition from Copper cable to super-conductor
Cooled Cu cables

29. Quench
A quench is the phase transition from the super-conducting to a normal conducting state.
Quenches are initiated by an energy in the order of few milliJoules
Movement of the superconductor by several m (friction and heat dissipation).
Beam losses.
Cooling failures.
...
When part of a magnet quenches, the conductor becomes resistive, which can lead to excessive local energy deposition (temperature rise !!) due to the appearance of Ohmic losses. To protect the magnet:
The quench must be detected: a voltage appears over the coil (R > 0).
The energy release is distributed over the entire magnet by force-quenching the coils using quench heaters (such that the entire magnet quenches !).
The magnet current has to be switched off within << 1 second.

30. Quench - discharge of the energy
Power Converter
Discharge resistor
Magnet 1
Magnet 2
Magnet 154
Magnet i
Protection of the magnet after a quench:
The quench is detected by measuring the voltage increase over coil.
The energy is distributed in the magnet by force-quenching using quench heaters.
The current in the quenched magnet decays in < 200 ms.
The current flows through the bypass diode (triggered by the voltage increase over the magnet).
The current of all other magnets is dischared into the dump resistors.

31. Dump resistors
Those large air-cooled resistors can absorb the 1 GJ stored in the dipole magnets (they heat up to few hundred degrees Celsius).

32. Incident of September 19th 2008

33. Event sequence on Sept. 19th
Introduction: on September 10th the LHC magnets had not been fully commissioned for 5 TeV.
A few magnets were missing their last commissioning steps.
The last steps were finished the week after Sept. 10th.
Last commissioning step of the main dipole circuit in sector 34 : ramp to 9.3kA (5.5 TeV).
At 8.7kA an electrical fault developed in the dipole bus bar (the bus bar is the cable carrying the current that connects all magnet of a circuit).
An electrical arc developed which punctured the helium enclosure.
Secondary arcs developed along the arc.
Around 400 MJ were dissipated in the cold-mass and in electrical arcs.
Large amounts of Helium were released into the insulating vacuum.
In total 6 tons of He were released.

34. LHC Status - Planck09 - Padova,IT
Inter-connection
Note the bellows that are needed to compensate for a 4.5 cm contraction per magnet between room temp. and 1.9 K.
Insulation blankets
Vac. chamber
Dipole busbar
LHC Status - Planck09 - Padova,IT

35. Pressure wave
Pressure wave propagates in both directions along the magnets inside the insulating vacuum enclosure.
Rapid pressure rise :
Self actuating relief valves could not handle the pressure.
designed for 2 kg He/s, incident ~ 20 kg/s.
Large forces exerted on the vacuum barriers (every 2 cells).
designed for a pressure of 1.5 bar, incident ~ 10 bar.
Several quadrupoles displaced by up to ~50 cm.
Connections to the cryogenic line damaged in some places.
Beam vacuum to atmospheric pressure.

36. LHC Status - Planck09 - Padova,IT
Incident location
Dipole bus bar
LHC Status - Planck09 - Padova,IT

37. Collateral damage : displacements
Quadrupole-dipole interconnection
Quadrupole support
Main damage area ~ 700 metres.
39 out of 154 dipoles,
14 out of 47 quadrupole short straight sections (SSS)
from the sector had to be moved to the surface for repair (16) or replacement (37).

38. Collateral damage : beam vacuum
The beam vacuum was affected over entire 2.7 km length of the arc.
Clean Copper surface.
Contamination with multi-layer magnet insulation debris.
Contamination with sooth.
 60% of the chambers
 20% of the chambers

39. What triggered the incident?

40. Dipole magnet protection - again
In case of a quench, the individual magnet is protected (quench protection and diode).
Resistances are switched into the circuit: the energy is dissipated in the resistances (current decay time constant of 100 s).
>> the bus-bar must carry the current until the energy is extracted !
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 for some minutes, through interconnections
Power Converter

41. One of ~1700 bus-bar connections

42. Bus-bar joint (1)
Superconducting cable embedded in Copper stabilizer.
Bus bar joint is soldered (not clamped).
Joint resistance ~0.35 nW 1.9 K).
Protection of the joint during quench relies on good joint quality.
~2 cm

43. Bus-bar joint (2)
A post-mortem analysis of the data from the sector with the incident revealed the presence of a 200 nW anomalous resistance in the cell of the primary electrical arc. This acted as a heat source that quenched the superconducting cable.
>> Unfortunately the evidence is destroyed…
An inspection of accessible joints revealed non- conformities like poor soldering and/or reduced electrical contact as in the example to the right.

44. Bad soldering surprise
Few cm long voids are created during soldering process – discovered during the repair of sector 34.
SnAg solder can flow out during soldering – present in MOST joints.
X-ray of joints in sector34

45. Normal interconnect, normal operation
Everything is at 1.9 Kelvin.
Current passes through the superconducting cable.
For 7 TeV : I = 11’800 A
Magnet
Magnet
Helium bath
copper bus bar 280 mm2
copper bus bar 280 mm2
superconducting cable with about 12 mm2 copper
current
Interconnection joint (soldered)
This illustration does not represent the real geometry

46. Normal interconnect, quench
Quench in adjacent magnet or in the bus-bar.
Temperature increase above ~ 9 K.
The superconductor becomes resistive.
During the energy discharge the current passes for few minutes through the copper bus-bar.
Magnet
Magnet
copper bus bar 280 mm2
copper bus bar 280 mm2
superconducting cable
interconnection

47. Non-conform interconnect, normal operation
Interruption of copper stabiliser of the bus-bar.
Superconducting cable at 1.9 K
Current passes through superconductor.
Magnet
Magnet
copper bus bar 280 mm2
copper bus bar 280 mm2
superconducting cable
interconnection

48. Non-conform interconnect, quench.
Interruption of copper stabiliser.
Superconducting cable temperature increase to above ~9 K and cable becomes resistive.
Current cannot pass through copper and is forced to pass through superconductor during discharge.
Magnet
Magnet
copper bus bar 280 mm2
copper bus bar 280 mm2
superconducting cable
interconnection

49. Non-conform interconnect, quench.
The superconducting cable heats up because of the combination of high current and resistive cable.
Magnet
Magnet
copper bus bar 280 mm2
copper bus bar 280 mm2
superconducting cable
interconnection

50. Non-conform interconnect, quench.
Superconducting cable melts and breaks if the length of the superconductor not in contact with the bus bar exceeds a critical value and the current is high.
Circuit is interrupted and an electrical arc is formed.
Magnet
Magnet
copper bus bar 280 mm2
copper bus bar 280 mm2
superconducting cable
interconnection
Depending on ‘type’ of non-conformity, problems appear :
at different current levels.
under different conditions (magnet or bus bar quench etc).

51. September 19th hypothesis
Anomalous resistance at the joint heats up and finally quenches the joint – but quench remains very local.
Current sidesteps into Copper that eventually melts because the electrical contact is not good enough.
Magnet
Magnet
copper bus bar 280 mm2
copper bus bar 280 mm2
superconducting cable
quench at the interconnection
>> A new protection system will be installed this year to anticipate such incidents in the future.

52. Joint issues
Anomalous resistance at 1.9 K that may lead to a quench (contact resistance between the SC cables).
Trigger for the incident in sector 34. Cannot be measured at room temperature (tens of nW).
>> New quench protection for the busbarjoints will be installed to minimize occurrence of a similar incident in the future and measure the resistance online (~few seconds).
>> Large (> 40 nW) resistances may be localized by temperature measurements.
Voids/absence of contact in the joint that may lead to an overheating if a quench occurs in the vicinity of the joint at high current.
Must be measured in normal-conducting state. Diagnostics through the joint resistance (good joint ~10-16 mW, excess should be ≤ ~ 20-ish mW).
>> Ongoing measurement campaign.

53. = The ‘silent killer’ Condition for a ‘silent killer’:
Interruption of the longitudinal Cu stabilizer coinciding with lack of thermal bounding of the cable over a few cm.
Condition for a bus burn-through/incident:
Silent killer, high current, and quenching busbar (due to beam losses, mechanical movement, warm helium etc).
wedge
bus
U-profile
bus =

54. Identification of bad joints @ 1.9 K: temperature…
Under controlled conditions, it is possible to localize anomalous heat sources down to ~ 40 nW from the temperatures.
>> Will now be done systematically during commissioning and operation.
DT (mk)
7 kA (~4 TeV) test on Sector 34
T keeps rising!
+40 mK
Current in kA
Relative temperature, increase from 1.9 K
Suspicious cell in sector 12.
See next slide…
9.3 kA (5.5 TeV) test on Sector 12
Powering test performed a few days before the incident on sector34. Early warning sign, but only discovered after the event.

55. Unsoldered joint INSIDE dipole
Sector 12 : the anomalous heat source was actually within a dipole, due to an unsoldered joint.
Note that this magnet was tested > 7 TeV !

56. Global R measurements at room T (1)
R (mW)
The two levels correspond
to different busbar lengths (30/50 m):
>> measurement of the joints + the busbar
Sector 56
Distance (m)

57. Global R measurements ‘at room T’ (2)
R (mW)
MBA.(B29-A30)R1
MBB.(B32-A33)R1
MBB.(C30-A30)L2
MBA.(C17-A17)L2
Sector 12
Outliers !!!!
Distance (m)

58. Joint measurements status
In 2008 about 60% of the ~20’000 joints were verified at 1.9 K.
No other large anomalous resistance was identified in the interconnection, but two dipoles with bad joints were localized and removed (see previous slide).
The joint resistances were measured on the 4 warm sectors.
~dozen suspicious cases have been identified (some already repaired).
Evaluation of joint measurements for the 4 cold sectors at 80K.
One sector (45) was measured and a large outlier (~100 mW) was found.
This sector will be warmed up to confirm measurement at room T.
Definition of a ‘safe’ excess resistance versus energy. Simulations in progress…
The situation is evolving rapidly these days!

59. Repair and consolidation
39 dipoles and 14 quadrupoles short straight sections (SSS) brought to surface for repair (16: 9D + 7SSS) or replacement (37: 30D + 7SSS).
All magnets are back in the tunnel. Interconnection work ongoing.
The vacuum chambers are cleaned in situ.
Major upgrade of the quench protection system.
- Protection of all main quadrupole and dipole joints.
- High statistics measurement accuracy to < 1 nW.
>> protection against sector34-type incidents in the future.
Reinforcement of the quadrupole supports.

60. Pressure relief consolidation
Improvement of the pressure relief system to eventually cope with a maximum He flow of 40 kg/s in the arcs (maximum conceivable flow, 2 x incident).
Warm sectors : 20 cm diameter relief valves mounted in SITU on every dipole cryostat.
Finished.
- Cold sectors : all ports equipped with spring relief system (not sufficient for 40 kg/s).
Temporary solution until next warm up.
- Straight sections : relief valves added on cryostats.

61. Commissioning & operation with reference to 2008…

62. First dipole lowered 7th March 2005
All magnets co(a)me down through a single shaft.
Transport in the tunnel with an
optically guided vehicle Approx magnets to be transported over up to 20 km at 3 km/hour

63. First beam around the LHC All sectors at nominal temperature
LHC cool-down
Cool-down time to 1.9 K ~ 4-6 weeks/sector
2009 cool-down has started
First beam around the LHC
All sectors at nominal temperature

64. LHC cool-down status
4 sectors were kept cold and floating < 80 K over the winter 2008/2009.
Click to get details

65. LHC cool-down status details
Sector 23 is cold.
Magnet tests start today.

66. LHC magnet commissioning
All magnets are tested step by step by increasing currents and stored energy.
LHC was/will be commissioned to 5.5 TeV (5 TeV for physics in 2009).
Why not to 7 TeV?
All magnets were trained to > 7 TeV on test stands. This typically requires a few quenches until the coils settle…
Once trained the magnets ramp to nominal field without quench (or else they are not usable for an accelerator !).
The magnets are then stored, moved to the tunnel and installed.
Assumption is that the magnets come back to their test stand performance with no or few quenches. Turned out to be wrong for one company!
Extrapolation from 2008 experience (~ 40 quenches) it is expected to be:
rather easy to reach 6 TeV (ten’s of quenches)
moderately easy to reach 6.5 TeV (~ hundred quenches)
difficult (lengthy) to reach 7 TeV (~ thousand quenches)
This effect is not understood !

67. First beam in the LHC after ~25 years of design and construction.
Injection tests
22nd – 24th of August
August – September 2008:
Injection tests of up to 4 adjacent sectors.
Essential checks for all accelerator systems and software.
>> Similar test will take place in Sept. 2009
8th – 10th of August
5th – 7th of September
Evening of August 8th 2008:
First beam in the LHC after ~25 years of design and construction.

68. First tests in 2009 Last weekend (June 6th-8th):
First beam ( bunches) down the 3 km transfer line to ring2.
Beam was stopped on a dump some 50 m from the tunnel.
LHCb exercised its DAQ system !
Tracks in the VELO detector
Courtesy LHCb/R. Jacobsson

69. Beam threading
Unique feature of LHC: threading the beam around the ring.
In 2008 after 3 days beam in ring 2 circulates with good lifetime, optics measured and most instrumentation operational – unexpectedly fast progress !
>> We hope to circulate beams again end September/early October 2009.
Beam 2

70. And then…
The first few days of excitement will be followed by some weeks/months of hard time to commission:
the optics,
the injection,
the ramp,
the protection systems,
the first collisions (starting probably at 450 GeV),
the backgrounds,
the polished and tuned machine cycle,
the same with more bunches, intensity, etc …
Time estimates to reach first stable collisions with reasonable luminosity range from weeks to few months - this is very difficult to anticipate !
Iterate,
iterate,
iterate…

71. preparation and access
The LHC machine cycle
collisions
beam dump
energy ramp
collisions
7 TeV
start of the ramp
Squeeze
injection phase
preparation and access
450 GeV

72. The injection phase should take ~20 minutes.
LHC cycle (1)
Magnet cycling before injection (reset magnetic history)
Injection… the ‘nominal’ sequence is expected to be:
Inject a single bunch into the empty machine:
Check parameters etc… and ensure that it circulates with reasonable lifetime.
Inject an intermediate beam of ~ 12 bunches:
Once the low intensity circulates, inject this higher intensity to fine tune parameters, adjust/check collimators and protection devices etc.
Once the machine is in good shape, switch to nominal injections:
Each ring requires 12 injections from the SPS, with a repetition rate of 1 every ~25 seconds. This last phase will last ~ 10 minutes.
The injection phase should take ~20 minutes.
Ramp to 7 TeV in 20 minutes. …

73. Time between 2 periods of data taking : ≥ 2 hours.
LHC cycle (2)
Preparation for collisions at 7 TeV:
The beams are ‘squeezed’: the optics in IR1 and IR5 is changed to bring down the b* (beam size at the collision point) from 11 m to the nominal b* of 0.5 m (or whatever value is desired).
The beams are brought into collision: the magnets that kept the beams separated at the collision points are switched off. First collisions…
The collimator settings are re-tuned, beam parameters are adjusted to optimize lifetime, reduce backgrounds etc (if needed).
all this is probably going to take ~ ½ hour++…
Collisions for hours.
- The duration results from an optimization of the overall machine efficiency…
- The faster the turn-around time, the shorter the runs (higher luminosity !).
Time between 2 periods of data taking : ≥ 2 hours.

74. … then a run over winter until November 2010.
Dates…
Tests of the transfer lines SPS-LHC:
June-August (3 weekends).
Injection tests into parts of the LHC:
~September.
First circulating beam:
~October.
First collisions at a few TeV: (Very low luminosity… )
~November.
… then a run over winter until November 2010.

75. Int. luminosity target of
Luminosity targets
The presently installed collimation system limits the total intensity to 10-20% of the nominal intensity.
Possible performance for the 2009/2010 run (5 TeV):
No. bunches/
beam
Protons/
bunch
% of nominal
intensity
Peak L
(cm-2 s-1) 43
51010
0.7
6.9x1030
156
2.4
5.0x1031
11011
4.8
2.0x1032
720 (50 ns)
11.1
1.2x1032
2808
1.151011
100
1.0x1034
Int. luminosity target of
pb-1
is achievable with
~40% availability.
One month Pb ion run foreseen end 2010.
Ion setup should be ‘straight forward’ as little difference wrt protons.

76. Final remarks (1)
Many knew since a long time that commissioning of the LHC would be a fantastic challenge, and that surprises had to be expected.
In 2008 we had:
A very good surprise with the beam at 450 GeV – incredibly fast and smooth start (but only for 3 days…).
A very bad surprise with the incident that revealed an unexpected problem with the bus-bar joints, related to the soldering process.
There is a large ongoing effort to repair sector 34 (on good track) and resolve/repair/detect problems related to the joints.
Many joints must still be verified. Bad surprises could have impact on:
the schedule
the maximum energy for 2009/2010

77. Let’s hope for first collisions in the fall of 2009…
Final remarks (2)
Given the stored energy, operation of the LHC will never be with ‘zero’ risk - but we (can) try to minimize risks and consequences.
Risk minimization implies a progressive commissioning with beam – we will increase performance in steps over a few years.
Let’s hope for first collisions in the fall of 2009…
Many thanks to all my colleagues for figures & info.