J. Wenninger LNF Spring School, May 2010 1 LHC : construction and operation Part 2: Machine...

J. Wenninger LNF Spring School, May 2010 1

LHC : construction and operationLHC : construction and operation

Part 2:•Machine protection•Incident and energy limits•Commissioning and operation

Jörg Wenninger

CERN Beams Department / Operations group

LNF Spring School 'Bruno Touschek' - May 2010

J. Wenninger LNF Spring School, May 2010

Machine protection

2


The price of high fields & high luminosity…

3

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 !


Stored Energy

4

Increase with respect to existing accelerators :

• A factor 2 in magnetic field

• A factor 7 in beam energy

• A factor 200 in stored energy


Comparison…

5

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!!

The energy stored in one LHC beam corresponds

approximately to…

• 90 kg of TNT

• 10-12 litres of gasoline

• 15 kg of chocolate

It’s how easily/quickly the energy is released that matters most !!


Machine protection: beam

6


To set the scale..

7

Few cm long groove of an SPS vacuum chamber after the impact of ~1% of a nominal LHC beam (2 MJ) during an ‘incident’:

Vacuum chamber ripped open.

3 day repair.

The same incident at the LHC implies a shutdown of > 3 months.

>> Protection of the LHC must be much stricter and much more reliable !


Beam impact in a target

8

Courtesy N. Tahir / GSI

20 bunches 180 bunches

100 bunches 380 bunches

The 7 TeV LHC beam can drill a hole through

~35 m of Copper

Simulation of a 7 TeV LHC beam impact into a 5 m long Copper target


From a real 450 GeV beam…

9

A B D C

Shot Intensity / p+

A 1.2×1012

B 2.4×1012

C 4.8×1012

D 7.2×1012

~0.1% nominal LHC beam

Cu plate ~20 cm inside the ‘target’.

30 cm

108 plates

6 cm

6 cm

Shoot a 450 GeV beam into a target…


‘Safe’ beams at the LHC…

10

L ~ 21028 cm-2s-1

LHC 2010

‘Safe beam’

‘Un-safe beam’

2011


Schematic layout of beam dump system in IR6

11

Q5R

Q4R

Q4L

Q5L

Beam 2

Beam 1

Beam dump block

Kicker magnets to paint (dilute)

the beam

700 m

500 m

15 fast ‘kicker’ magnets deflect the beam to the

outside

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 !

Septum magnets deflect the

extracted beam vertically

quadrupoles

The 3 ms gap in the beam gives the kicker time to reach

full field.

Ultra-high reliability system !!


The dump block

12

Approx. 8 m

concrete shielding

beam absorber (graphite)

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 !

Measurement

Simulation


Dump line in IR6

13


Dump line

14


Dump installation

15


‘Unscheduled’ beam loss due to failures

16

Beam loss over multiple turns

(~millisecond to many seconds) due to many types of failures.

Passive protection - Failure prevention (high reliability systems).- Intercept beam with collimators and absorber

blocks.

Active Protection- Failure detection (by beam and/or equipment monitoring)

with fast reaction time (< 1 ms).

- Fire beam dumping system.

Beam loss over a single turn

during injection, beam dump.

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):

Because of the very high risk, the LHC machine protection system is of unprecedented complexity and size.

A general design philosophy was to ensure that there should always be at least 2 different systems to protect against a given failure type.


Failure detection example : beam loss monitors

17

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 !


Beam loss monitoring


Machine protection

and quench prevention:

collimation

19


Operational margin of SC magnet

20

Temperature [K]

App

lied

field

[T]

Superconductingstate

Normal state

Bc

Tc

9 K

Applied Field [T] Bc critical field

1.9 K

quench with fast loss

of ~few 109 protons

quench with fast loss of ~106-7 protons

8.3 T / 7 TeV

0.54 T / 450 GeV

QUENCH

Tc critical

temperature

Temperature [K]

The LHC is ~1000 times more critical than

TEVATRON, HERA, RHIC


Quench levels

21

Example of the energy (mJ/cm3) required to quench an LHC dipole magnet with an instantaneous loss.

Steep energy dependence.

Models are confirmed at 0.45 TeV.

The phase transition from the super-conducting to a normal conducting state is called a quench.

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.– ..


Beam lifetime

22

Consider a beam with a lifetime :

Number of protons lost per second for different lifetimes (nominal intensity):

t = 100 hours 109 p/s

t = 25 hours 4x109 p/s

t = 1 hour 1011 p/s

While ‘normal’ lifetimes will be in the range of 10-100 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 high efficiency before they can quench a magnet : collimation!

/)()(

)( /0 tN

dt

tdNeNtN t

Quench level ~ 106-7 p


Collimation

23

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 protection by intercepting the beams.

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

Courtesy C. Bracco


Collimator settings at 7 TeV

24

1 mm

The collimator opening corresponds roughly to the size of Spain !

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 !

Opening ~3-5 mm

Carbon jaw

RF contact ‘fingers’


Collimation performance

IR8IR8 IR1IR1IR2IR2 IR5IR5

Momentum

Cleaning

Momentum

Cleaning

Dump Protection

Dump Protection

Measurements of the collimation efficiency from beam loss maps confirms the excellent performance : > 99.9% efficiency !

Collimation team

CleaningCleaning


Machine protection: magnets

26


Powering Sector

LHC powering in sectors

Sector 1

5

DC Power feed

3 DC Power

2

4 6

8

7LHC27 km Circumference

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 !


Powering from room temperature source…

28

Water cooled 13 kA Copper cables! Not superconducting !

6 kA power converter


…to the cryostat

29

Feedboxes (‘DFB’) : transition from Copper cable to super-conductor

Cooled Cu cables


Quench detection

30

When part of a magnet quenches, the conductor becomes resistive, which can lead to excessive local energy deposition (tT rise !!) due to Ohmic losses.

To protect the magnet:– The quench must be detected: this is done by monitoring the voltage that 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 is switched off within << 1 second.

18/04/10

Example of the voltage signals over 5 quenching dipole magnets (beam induced at injection).

Threshold of quench protection system (QPS)


Quench - discharge of the energy

31

Magnet 1 Magnet 2

Power Converter

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.

Discharge resistor


Dump resistors

32

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


Machine protection philosophy

33

Power permit

Power Converters

QPS

Cryo

→ Authorises power on→ Cuts power off in case of fault

→ Authorises beam operation→ Requests a beam dump in case of problems

Collimators

access

RF

Beam permit

Experiments

vacuum

BLMs

Warm Magnets

Software interlocks

Stored magnetic energy

Stored beam

energy

Power Permit Beam Permit


Beam interlock system

34

Beam Interlock System

Beam Dumping System

Injection BIS

PIC essential+ auxiliary

circuitsWIC

QPS(several 1000)

Power Converters

~1500

AUG

UPS

Power Converters

Magnets

FMCM

CryoOK

RFSystem

Movable Devices

Experiments

BCMBeam Loss

Experimental Magnets

CollimationSystem

CollimatorPositions

Environmentalparameters

Transverse Feedback

Beam Aperture Kickers

FBCMLifetime

BTV

BTV screens Mirrors

Access System

Doors EIS

VacuumSystem

Vacuumvalves

AccessSafetyBlocks

RF Stoppers

BLM BPM in

IR6

Monitorsaperture

limits(some 100)

Monitors in arcs

(several 1000)

Timing System (Post Mortem)

CCC Operator Buttons

SafeMach.Param.

SoftwareInterlocks

LHCDevices

SEQ

LHCDevices

LHCDevices

Tim

ing

SafeBeamFlag

Over 20’000 signals enter the interlock system of the LHC that will send the beam into the dump block if any input signals a fault !

Isn’t it a miracle that it works !


Incident of September 19th 2008

& Consequences

35


Event sequence on Sept. 19th

36

Introduction: on September 10th when the first beam made it around the LHC, not all 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 dipole circuit in sector 34 : ramp to 5.5 TeV.

At ~5.1 TeV 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).

Later traced to an anomalous resistance of 200 n (should be 0.3 n).

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.


Pressure wave

37

PTQVQV QV QVQV SVSV

Cold-massVacuum vesselLine ECold support postWarm JackCompensator/BellowsVacuum barrier

Q D D QD D D QD D D QD D D QD

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.


One of ~1700 bus-bar connections

Dipole busbar


Incident location

39

Dipole bus bar Dipole bus bar


Collateral damage : displacements

40

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).


Collateral damage : beam vacuum

41

Beam Screen (BS) : The red color is characteristic of a clean copper

surface

BS with some contamination by super-isolation (MLI multi layer

insulation)

BS with soot contamination. The grey color varies depending on the thickness of the soot, from grey to

dark.

Clean Copper surface.Contamination with multi-layer magnet insulation

debris.Contamination with sooth.

60% of the chambers 20% of the chambers

The beam vacuum was affected over entire 2.7 km length of the arc.


Quench - discharge of the energy

42

Magnet 1 Magnet 2

Power Converter

Magnet 154

Magnet i

Discharge resistor

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 !

The bus-bar must carry the current for some minutes, through interconnections


Bus-bar joint

43

24’000 bus-bar joints in the LHC main circuits.

10’000 joints are at the interconnection between magnets.

They are welded in the tunnel.

Nominal joint resistance:

•1.9 K 0.3 nΩ

•300K ~10 μΩ

For the LHC to operate safely at a certain energy, there is a limit to maximum value of the joint resistance.


Joint quality

44

The copper stabilizes the bus bar in the event of a cable quench (=bypass for the current while the energy is extracted from the circuit).

Protection system in place in 2008 not sufficiently sensitive.

A copper bus bar with reduced continuity coupled to a superconducting cable badly soldered to the stabilizer can lead to a serious incident.

During repair work in the damaged sector, inspection of the joints revealed systematic voids caused by the welding procedure.

X-ray of joint

bus U-profile bus

wedge

Solder No solder


superconducting cable with about 12 mm2 copper

copper bus bar 280 mm2copper bus bar 280 mm2

Magnet Magnet

Everything is at 1.9 Kelvin. Current passes through the superconducting cable.

For 7 TeV : I = 11’800 A

Normal interconnect, normal operation

Interconnection joint (soldered)

This illustration does not represent the real geometry

current

45

Helium bath



Magnet Magnet

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.

superconducting cable interconnection

Normal interconnect, quench

46



Magnet Magnet

Interruption of copper stabiliser of the bus-bar. Superconducting cable at 1.9 K Current passes through superconductor.

Non-conform interconnect, normal operation


47



Magnet Magnet

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.


Non-conform interconnect, quench.

48



Magnet Magnet

The superconducting cable heats up because of the combination of high current and resistive cable.



49



Magnet Magnet

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.



Depending on ‘type’ of non-conformity, problems appear : at different current levels. under different conditions (magnet or bus bar quench etc).

50



Magnet Magnet

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.

September 19th hypothesis

superconducting cable quench at the interconnection

51

>> A new protection system will be installed this year to anticipate such incidents in the future:

new Quench Protection System (‘nQPS’)


LHC repair and consolidation

52

14 quadrupole magnets replaced

39 dipole magnets replaced

204 electrical inter-connections repaired

Over 4km of vacuum beam tube cleaned

New longitudinal restraining system for 50 quadrupoles

Almost 900 new helium pressure release ports

6500 new detectors and 250km cables for new Quench Protection System to protect busbar joints: nQPSCollateral damage mitigation


Mechanical clamping (not present in Tevatron

and Hera …)

A glimpse in the future: the consolidated connection

In the next long (> 1 year) shutdown all the connections will be re-done.

Latest design:o Better electrical contacto Mechanical clamping

Courtesy F. Bertinelli


LHC energy target - way down

2002-20077 TeV

Summer 20085 TeV

Spring 2009

3.5 TeV

Nov. 2009

450 GeV

Detraining

nQPS2 kA

6 kA

9 kA

When Why

12 kA

Late 2008 Joints

1.18 TeV

DesignAll main magnets commissioned for 7TeV operation before installation

Detraining found when hardware commissioning sectors in 2008

o 5 TeV poses no problemo Difficult to exceed 6 TeV

Machine wide investigations following S34 incident showed problem with joints

Commissioning of new Quench Protection System (nQPS)

54


LHC energy target - way up

Train magnetso 6.5 TeV is within reacho 7 TeV will take time

Repair jointsComplete pressure relief system

Commission nQPS system

2014 ?

2010

Training

Joint repair

nQPS

When What

7 TeV

3.5 TeV

1.18 TeV

450 GeV

2011

2013

2009

6 TeV

55


Beam operation

56


Goals for 2010-2011

Repair of Sector 341.18TeV

nQPS6kA

3.5 TeVIsafe < I < 0.2 Inom

β* ~ 2 mIons

3.5 TeV~ 0.2 Inom

β* ~ 2 mIons

20092009 20102010 20112011

No Beam B Beam Beam

Ambitious goal for the run: collect 1 fm-1 of data/exp at 3.5 TeV/beam.

To achieve this goal the LHC must operate in 2011 with

L ~ 2×1032 Hz/cm2 ~ Tevatron Luminosity

which requires ~700 bunches of 1011 p/bunch(stored energy of ~ 30 MJ – 10% of nominal)

Implications:Strict and clean machine setup.Machine protection systems at near nominal performance.

β*inj β*

min

IP1 / IP5 11 m 2 m

IP2/IP8 10 m 2 m

IP5-TOTEM 11 m 90 m

Mininum β* in various IP’s

57


LHC schedule

58

Proton run until November.

Lead ion setup and run November and Decenber.


2010 commissioning milestones

27th Feb First injection

28th Feb Both beams circulating

5th March Canonical two beam operation

8th March Collimation setup at 450 GeV

12th March Ramp to 1.18 TeV

15th - 18th March Technical stop – dipoles magnets good for 3.5 TeV

19th March Ramp to 3.5 TeV

30th March First 3.5 TeV collisions in all experiments (media event)

4th - 5th April 19h-long physics fill with * 10/11 m - L ~ 1027 cm-2s-1

7th April *squeeze to 2 m in IP1 and IP5

24th April 30h-long physics fill with * of 2 m - L ~ 1.31028 cm-2s-1


LHC machine cycle

60

energy ramp

preparation and access

beam dump

injection phase

collisions

collisions

450 GeV

7 TeV

start of the ramp Squeeze

3.5 TeV


LHC cycle

61

Ramp-down/pre-cycle: 1 ½ - 2 hourso Depending on initial conditions, the magnets must either be ramped down (3.5 TeV

injection) or cycled (from access). Injection: > 15 minutes

o Probe beam: low intensity bunch (≤ 1010 p) that must be first injected when a ring is empty (safety !). Used to verify that beam parameters are OK for higher intensity.

o Nominal bunch sequence follows when beam parameters have been adjusted. Ramp: 40 minutes

o Machine energy is increase at constant optics (b-function) from 450 to 3.5 TeV. For the moment the ramp rate is limited to ~1 GeV/s.

o Ramp rate to nominal value ~5 GeV/s in June >> ramp will become a lot faster! Squeeze: ~30 minutes

o Injection * is larger (10 m in IR1/5, 11 m in IR2/8) because more aperture is needed to accommodate the larger beam emittance (triplet magnets).

o In the squeeze * is reduced to its nominal physics value (presently 2 m in all IRs). This implies gradient changes of most quadrupoles in the straight sections and first part of the arc.


Beam squeeze

62

10 m to 2 m10 m to 2 m

30 min 30 min

11 m to 2 m11 m to 2 m

Duration will soon be reduced to ~ 20 minutes

Duration will soon be reduced to ~ 20 minutes


How equal are the IPs?

63

The -function can be measured by exciting (shaking) the beams.

After correction of optics errors, the residual error is in a band of around +- 20% (specification).

>> * may vary from IP to IP by up to 20% !

Example of optics errors along the ring for * 2 m (beam1) Horizontal

Vertical


LHC cycle : physics

64

Stable beams: 10’s of hours and more…o Period with quiet running conditions for the experiments (with HV ON, etc).o Beam tuning activity reduced to the minimum (to keep good lifetimes…).o Collimators in fixed positions (they move during ramp and squeeze).o Note however that abrupt beam loss can occur in any phase due to powering

problems, cooling etc etc – even in stable beams. Experiments are protected by the collimators (shadowing), the LHC machine

protection system and by their own protection system (BCM : Beam Condition Monitors).

[1030 cm-2s-1]


Beam overlap

65

Because the beams circulate most of the time in different vacuum chambers, they also see slightly different magnetic fields.

>> no guarantee that they collide at the IP ! Small beam sizes !!

To optimize the beam overlap (hor. and vert. planes) the beams are scanned across one another until the peak luminosity if found (typical +- 2 sigma).

>> settings are quite reproducible – more experience needed.


Beam operation at 3.5 TeV

Luminosity (head on case, no crossing angle) :

**

2

4 yx

fkNL

The beam size s depends on * and on beam emittance n:

n** Everywhere in the ring the beam

size scales with 1/ ~ 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.


Peak luminosity at 3.5 TeV A consequence of the small beam size at the IP (small *) is a large beam

size in the triplet magnets. The physical aperture in the triplet quadrupoles defines the minimum of *.

o Limits * to ~2 m at 3.5 TeV (instead of 0.5 m at 7 TeV)

Beam size * increase by: Factor 2 (‘naturally’ larger size)

Factor ~2 (* limit)

Luminosity loss wrt 7 TeV of: Factor ~22 per plane (*)

>> overall factor ~8

for same beam intensity

Lower limit on * (with crossing angle)

Present operating conditions(no crossing angle) @ 2 m


Intensity increase plan

68

Stage N (protons) k Stored E (kJ) Peak L (Hz cm-2)

3 fat pilots 1.00E+10 3 17 1.34E+28

4 bunches 2.00E+10 4 44.8 7.63E+28

4 bunches 5.00E+10 4 112.0 4.77E+29

8 bunches 5.00E+10 8 224.0 9.54E+29

4x4 bunches 5.00E+10 16 448.0 1.91E+30

8x4 bunches 5.00E+10 32 896.0 3.81E+30

43x43 5.00E+10 43 1204.0 5.13E+30

8 trains of 6 b 8.00E+10 48 2150.4 1.33E+31

50 ns trains 8.00E+10 96 4300.8 2.67E+31

Assumption:

* = 2 m

nominal

To gain experience with the machine protection system, 2 weeks of running time (~10 fills, 40 h of physics) must be integrated before proceeding to the next step.

Some steps require additional (machine protection) commissioning.

Present phase

Next step (coming days)

Beams become rather dangerous


Performance estimate

69

charm, D’s, J/Psicharm, D’s, J/Psi

Weak bosons (W, Z)Weak bosons (W, Z)

30.3 - 19.4 * 10m 1.1e10 p/bch

30.3 - 19.4 * 10m 1.1e10 p/bch

23.4 - ... * 2m 1.1e10 p/bch

23.4 - ... * 2m 1.1e10 p/bch

November 7November 7

4 coll pairs2e10 p/bch4 coll pairs2e10 p/bch

Apr 23Apr 23

4 coll pairs5e10 p/bch4 coll pairs5e10 p/bch

If all goes well, we could reach

L 1032 cm-2s-1

by November!


Integrated luminosity projections

70

If maintain the high availability 100 pb-1 could be integrated

until November

Apr 23Apr 23

Apr 23Apr 23


LHC operation today

71

So far LHC operation is amazingly stable and efficient (we are still in commissioning !!).

But we are working with ‘tiny’ beams (on the nominal LHC scale).

In physics at the moment:

* = 2 m at IPs * 45 m

N 1.81010 p/bunch k = 2 bunches

1 colliding pair / IP L 1.31028 cm-2s-1

The next step in intensity is most likely:

N 41010 p/bunch k = 2 bunches

1 colliding pair / IP L 6.81028 cm-2s-1

We have been able to collide bunches with nominal population (N = 1011) at 450 GeV: this is a good omen for 3.5 TeV (cross fingers…)

o We may be able to push luminosity faster than anticipated (L N2)


To observe the LHC

72

http://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php?usr=LHC1


Outlook

73

The LHC beam commissioning has been progressing smoothly and rapidly so far – even we are sometimes surprised !!

o But the LHC remains a very complex machine, so far we operate under rather simple conditions.

The problem of the LHC: to reach ‚interesting‘ luminosities we must store very dangerous beams at a very early stage of the commissioning.

o We have little operational experience.

o We are still consolidating beam control software, debugging systems...

o We must be sure that they are no unexpected flaws in the machine protection system (or totally unexpected situations).

>> for this reason we increase the intensity/L in rather modest steps.

Assuming there are no surprises, and once we have passed the main hurdle of the initial machine protection commissioning (soon !), progress should be faster:

>> so far the target of 1031 – 1032 cm-2s-1 by November is within reach !


From darkness… …to light

74

Sept 2008

April 2010

J. Wenninger LNF Spring School, May 2010 1 LHC : construction and operation Part 2: Machine...

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