Collimators and Beam Absorbers for Collimators and Beam Absorbers for Cleaning and Machine ProtectionCleaning and Machine Protection

Ralph AssmannRalph Assmann

Workshop Chamonix XIVWorkshop Chamonix XIV

17-21.01.200517-21.01.2005

Acknowledgements to the members of the Collimation Acknowledgements to the members of the Collimation

Project, the Collimation WG and the Machine Protection WG!Project, the Collimation WG and the Machine Protection WG!

Collimators and Protection DevicesCollimators and Protection Devices

• CollimatorsCollimators:: 20 + 15 per beam ( 20 + 15 per beam (TCP,TCP, TCSGTCSG + + TCSMTCSM) )

– Interact with primary, secondary or tertiary beam halo.Interact with primary, secondary or tertiary beam halo.

– Scattering devices for spoiling and inducing inelastic interactions for protons Scattering devices for spoiling and inducing inelastic interactions for protons lost from the beam!lost from the beam!

– Precise devices with two jaws, used for efficient beam cleaning. Small gaps Precise devices with two jaws, used for efficient beam cleaning. Small gaps and stringent tolerances.and stringent tolerances.

– Absorb little energy. Very robust.Absorb little energy. Very robust.

• Movable absorbersMovable absorbers:: 20 per beam ( 20 per beam (TCTTCT, , TCLATCLA, , TCLPTCLP))

– Interact with shower products from p-p and p-collimator interactions.Interact with shower products from p-p and p-collimator interactions.

– Devices for absorbing the lost energy.Devices for absorbing the lost energy.

– High-Z jaws. Larger gaps and more relaxed tolerances.High-Z jaws. Larger gaps and more relaxed tolerances.

• DilutersDiluters:: 4 + 7 per beam (TDI, 4 + 7 per beam (TDI, TCLITCLI, TCDQ + TCDI), TCDQ + TCDI)

– Interact with mis-kicked beam or irregular beam tails (injection and dump Interact with mis-kicked beam or irregular beam tails (injection and dump protection).protection).

– Strong dilution (emittance blow-up) and partial absorption of energyStrong dilution (emittance blow-up) and partial absorption of energy

• ScrapersScrapers:: 3 per beam ( 3 per beam (TCHSTCHS))

– Thin one-sided objects. Used for beam shaping and diagnostics.Thin one-sided objects. Used for beam shaping and diagnostics.

CLEANINGCLEANING(continuous)(continuous)

PROTECTIONPROTECTION(accidents)(accidents)

SPECIALSPECIAL(exceptional)(exceptional)

Detailed TableDetailed TableAcronym Material Length Number Locations INJ TOP Purpose

[m]

Scrapers

TCSP tbd tbd 6 IR3, IR7 Beam scraping

Collimators

TCP C-C 0.2 8 IR3, IR7 Y Y Primary collimatorsTCSG C-C 1.0 30 IR3, IR7 Y Y Secondary collimatorsTCSM tbd 1.0 30 IR3, IR7 Hybrid secondary collimatorsTCSG C-C 1.0 2 IR6 Y Y Help for TCDQ set-up

DilutersTDI Sandwich 4.2 2 IR2, IR8 Y Injection protectionTCLI C 1.0 4 IR2, IR8 Y Injection protectionTCDI C 1.2 14 TI2, TI8 Y Injection collimation

TCDQ C-C 6.0 2 IR6 Y Y Dump protection

Movable AbsorbersTCT Cu/W 1.0 16 IR1, IR2,

IR5, IR8 Y Tertiary collimators

TCLP Cu 1.0 8 IR1, IR5 Y Secondaries from IP

TCLA Cu 1.0 16 IR3, IR7 Y Y Showers from collimators

In total 138 collimator locations138 collimator locations in LHC and transfer lines!Installed active length of ~ 145 m~ 145 m plus ~70 m overhead (215 m total)Injection: up to 39 collimators per beamTop energy: up to 41 collimators per beam

Sophisticated Cleaning Design in IR3 and IR7Sophisticated Cleaning Design in IR3 and IR7

Line input file for FLUKA generated from collimation halo tracking program.

Automatic generation of FLUKA geometry with dynamic placement of collimators.

Powerful tool Powerful tool Automatic generation of full LHC FLUKA geometry on the horizon? Automatic generation of full LHC FLUKA geometry on the horizon?

V. Vlachoudis et al

Cleaning optics in collaboration with TRIUMF!

Not more than 1 out of 10000 impacting protons may escape the cleaning system at 7 TeV:

Cleaning S. Redaelli

Phase Space Coverage InjectionPhase Space Coverage Injection

-15

-10

-5

0

5

10

15

-15 -10 -5 0 5 10 15

X' [

sig

ma]

X [sigma]

Beam 3 Beam 3 envelopenvelopee

Decent coverage of coverage of phase spacephase space:

Beam will likely first be first be intercepted at a intercepted at a collimator or absorber collimator or absorber or diluteror diluter (also for asymptotic orbit change)!

BLM’s at collimator protect against beam loss!

Not very comfortable margin though (profit from tighter settings)!

Cold aperture

Limitations from Collimation & Protection in Limitations from Collimation & Protection in

Commissioning Towards Nominal PerformanceCommissioning Towards Nominal Performance

Beam-induced damage to the machine (collimators): Robust collimators!

Quenches or beam loss related aborts: Efficient cleaning!

Experimental background: Efficient cleaning!

Instabilities: Impedance from collimators!

Limitation in operational efficiency!

Limitation in intensity/luminosity!

Efficiency is Already Optimized in Design PhaseEfficiency is Already Optimized in Design Phase- Robust collimators -- Robust collimators -

Robustness maximized with C-C jaws Robustness maximized with C-C jaws

and powerful water cooling!and powerful water cooling!

Design Verification with Beam TestDesign Verification with Beam Test

• Two prototype collimatorsTwo prototype collimators installed. installed.

• SPS ringSPS ring::

– Functional testFunctional test

– Beam-based alignment with small gapsBeam-based alignment with small gaps

– Measurement of impedance, HOM, vacuum, e-cloud, ...Measurement of impedance, HOM, vacuum, e-cloud, ...

• TT40TT40::

– Robustness test with 2.4 MJ/mmRobustness test with 2.4 MJ/mm22

All VERY successful!All VERY successful!

S. RedaelliS. Redaelli

Robustness TestRobustness Test

C-C jaw

C jaw

TED Dump

450 GeV450 GeV3 103 101313 p p

2 MJ2 MJ0.7 x 1.2 mm0.7 x 1.2 mm22

• Jaw impact could be measured during all expected hits: no change in jaw dimensionsno change in jaw dimensions (nothing fell off)

• Closure of two jaws to 1mm gap after test1mm gap after test (no large debris).

• Take out collimator in January and inspectTake out collimator in January and inspect.

• Analyzing measurements of temperature, vibration and sound.

~ Tevatron beam

~ ½ kg TNT

Microphone

Jaws after Shock ImpactJaws after Shock Impact

Damage Limits in Present designDamage Limits in Present design

• Danger to Danger to regular machine equipmentregular machine equipment andand metallic absorbersmetallic absorbers: :

– Above 1e12 p at injection: Above 1e12 p at injection: 4e-3 of beam4e-3 of beam

– Above 5e9 p at 7 TeV: Above 5e9 p at 7 TeV: 2e-5 of beam2e-5 of beam

• Danger to Danger to C-C collimators/absorbersC-C collimators/absorbers::

– Above 3e13 p at injection:Above 3e13 p at injection: 10% of beam10% of beam

– Above 8e11 p at 7 TeV:Above 8e11 p at 7 TeV: 3e-3 of beam3e-3 of beam

• Maximum Maximum allowed loss rates at collimatorsallowed loss rates at collimators (goal): (goal):

– 100 kW continuously.100 kW continuously.

– 500 kW for 10 s (1% of beam lost in 10s).500 kW for 10 s (1% of beam lost in 10s).

– 1 MW1 MW for 1 s. for 1 s.

• Commissioning must Commissioning must respect these limitsrespect these limits: we cannot relax more!: we cannot relax more!

Impedance Limit for Movable DevicesImpedance Limit for Movable Devices

• Collimators and absorbers are close to beam: A Collimators and absorbers are close to beam: A resistive wall impedanceresistive wall impedance is is

induced (gap size depends on induced (gap size depends on *)!*)!

• C-C materialC-C material has reduced electrical conductivity (price to pay for a robust has reduced electrical conductivity (price to pay for a robust

system). Fix with phase 2 advanced collimators.system). Fix with phase 2 advanced collimators.

• Increase from collimators (nominal settings) for the imaginary part of the Increase from collimators (nominal settings) for the imaginary part of the

effective vertical impedanceeffective vertical impedance::

– 8 kHz:8 kHz: factor 3factor 3 for injectionfor injection

factor 69factor 69 for 7 TeVfor 7 TeV

– 20 kHz:20 kHz: factor 3factor 3 for injectionfor injection

factor 145factor 145 for 7 TeVfor 7 TeV

• Large increase in impedance must be actively counteracted by transverse Large increase in impedance must be actively counteracted by transverse

feedback and octupoles!feedback and octupoles!

F. Zimmermann et al

Collimator-Induced Tune Change Collimator-Induced Tune Change (Changing Collimator Gap)(Changing Collimator Gap)

Gap: 2.1 51 mm

So-called BBQ device(M. Gasior & R. Jones)

SPS tune depends on SPS tune depends on collimator gap!collimator gap!

M. Gasior, R. Jones et al

0.001 0.0008 0.0006 0.0004 0.0002

0.00001

0.00002

0.00003

0.00004

0.00005

25 ns

50

75

150 300

900

Single bunch

Stability diagram (maximum octupoles) and collective tune shift for the most

unstable coupled-bunch mode and head-tail mode 0 (1.15e11 p/b at 7 TeV)

Effect of the bunch spacing…

QRe

Q Im

Vertical plane

STABLE

Even single bunch unstable for nominal *!

Setting Strategy for Collimation and Protection Setting Strategy for Collimation and Protection Elements at Injection PlateauElements at Injection Plateau

• Clear requirements for settings:Clear requirements for settings:

LHC ring apertureLHC ring aperture sets scale sets scale aaringring

tight LHC aperture tight LHC aperture

Protection devicesProtection devices must protect ring aperture must protect ring aperture aaprotprot < a < aringring protect against injected beam; take into account accuracies protect against injected beam; take into account accuracies

Secondary collimatorsSecondary collimators tighter than protection tighter than protection aasecsec < a < aprotprot avoid too much secondary halo hitting protection devices avoid too much secondary halo hitting protection devices

Primary collimatorsPrimary collimators tighter than secondary tighter than secondary aaprimprim < a < asecsec

primary collimators define the aperture bottleneck in primary collimators define the aperture bottleneck in

the LHC for cleaning of circulating beam! the LHC for cleaning of circulating beam!

• These conditions should always be fulfilled: These conditions should always be fulfilled:

Avoid using protection devices as a single-stage cleaning system!Avoid using protection devices as a single-stage cleaning system!

Settings during injection (in Settings during injection (in ))

aabs = ~ 10.0 Active absorbers in IR3 and IR7

asec3 = 9.3 Secondary collimators IR3 (H)

aprim3 = 8.0 Primary collimators IR3 (H)

aring = 7.5 7.5 Ring cold aperture

aprot = 6.8 6.8 TDI, TCLI (V)protection elements

aprot ≥ 7.0 7.0 TCDQ (H) protection element

asec = 6.7 6.7 Secondary collimators IR7

aprim = 5.7 5.7 Primary collimators IR7

aTL = 4.5 4.5 Transfer line collimators

(ring protection at 6.9 6.9 )

Tight settings below “canonical” 6/7 collimation settings!Tighter for larger beta beat (smaller cold aperture)!Tighter for larger beta beat (smaller cold aperture)!

Settings at 7 TeV (in Settings at 7 TeV (in nominalnominal))

aabs = ~ 20.0 Active absorbers in IR3

asec3 = 18.0 Secondary collimators IR3 (H)

aprim3 = 15.0 Primary collimators IR3 (H)

aabs = ~ 10.0 Active absorbers in and IR7

aring = 8.4 8.4 Triplet cold aperture

aprot = 8.3 8.3 TCT protection and cleaning at triplet

aprot ≥ 7.5 7.5 TCDQ (H) protection element

asec = 7.0 7.0 Secondary collimators IR7

aprim = 6.0 6.0 Primary collimators IR7

“Canonical” 6/7 collimation settings are achievable!

Setting versus energySetting versus energy

Collimator Set-up and Extrapolation to High IntensityCollimator Set-up and Extrapolation to High Intensity

• Several procedures are used: Several procedures are used: Collimator touching beam and observation with BLM’s, scraping of intensity, Collimator touching beam and observation with BLM’s, scraping of intensity, transmission measurement, … transmission measurement, … See also talks by S. Redaelli and V. Kain!See also talks by S. Redaelli and V. Kain!

• All these methods set up the collimators in a All these methods set up the collimators in a single stage processsingle stage process!!

• Intensities must be limitedIntensities must be limited because of reduced cleaning efficiency with single stage because of reduced cleaning efficiency with single stage cleaning process.cleaning process.

• Reference collimator and beam positionsReference collimator and beam positions will be recorded at low intensity and will be recorded at low intensity and must be re-established at high intensity!must be re-established at high intensity!

• Cleaning set-up relies on Cleaning set-up relies on excellent stability and reproducibility of machineexcellent stability and reproducibility of machine, even , even while current is changed significantly!while current is changed significantly!

• Limited empirical optimization at top energy is possible!Limited empirical optimization at top energy is possible!

• Can we conceive a Can we conceive a high current set-uphigh current set-up for collimation? for collimation? (also request from (also request from external review)external review)

Commissioning of Cleaning SystemCommissioning of Cleaning System

43

Pilot

No collimationNo collimation

Single-stage cleaningSingle-stage cleaning

Two-stage cleaning (phase 1)Two-stage cleaning (phase 1)

Two-stage cleaning (phase 2)Two-stage cleaning (phase 2)

Commissioning a Single-Stage Cleaning/Protection Commissioning a Single-Stage Cleaning/Protection System with Circulating BeamSystem with Circulating Beam

1.1. Put Put 3 betatron primary collimators3 betatron primary collimators to coarse 6 to coarse 6 setting (single-stage cleaning always in cleaning setting (single-stage cleaning always in cleaning insertions). Put insertions). Put 1 momentum primary collimators1 momentum primary collimators to 8.5 to 8.5 ..

2.2. Put Put 8 TCLA absorbers8 TCLA absorbers in cleaning insertions to coarse 9 in cleaning insertions to coarse 9 position (shadow SC arc aperture and position (shadow SC arc aperture and capture shower debris).capture shower debris).

3.3. Set up Set up 1 TDI and 1 TCLI1 TDI and 1 TCLI for injection protection (collimators can be out during set-up). for injection protection (collimators can be out during set-up).

4.4. Set up Set up 1 TCDQ1 TCDQ for dump protection. for dump protection.

5.5. Accumulate and ramp.Accumulate and ramp.

6.6. Set up up to Set up up to 8 TCT’s8 TCT’s at top energy to protect triplets. at top energy to protect triplets.

This system involves 22 movable elements per beam22 movable elements per beam with increased margin for set-up errors and increased margin for set-up errors and

transient beam changestransient beam changes (orbit, beta-beat):

Injection: 3.0 mm margin instead of 1.0 mm margin7 TeV: 0.6 mm margin instead of 0.2 mm margin

Fully functional 1 stage cleaning with injection and dump protection, as well as full Fully functional 1 stage cleaning with injection and dump protection, as well as full

protection of triplets!protection of triplets! It’s surely worth it!

Required time for set-up: ~1 day per beam~1 day per beam based on SPS experience!

Extend towards two-stage system by moving in secondary collimators! Reduce margin!

How to Overcome Beam Loss Limitations?How to Overcome Beam Loss Limitations?

1.1. Increase available apertureIncrease available aperture for the beam (work on orbit and beta beat). for the beam (work on orbit and beta beat).

2.2. Improve stabilityImprove stability of the machine (lower loss rates). of the machine (lower loss rates).

3.3. Improve cleaning efficiencyImprove cleaning efficiency (close collimators (close collimators reduce tolerances, increase reduce tolerances, increase impedance, increase complexity).impedance, increase complexity).

4.4. Decrease intensityDecrease intensity..

Sorted in order of priority for collimation/machine protection!

Solution 4 reduces the performance and is only the last resort! It is the easy way!

For above ~ 5-10% of nominal intensity we need to work hard on all topics 1-3!For above ~ 5-10% of nominal intensity we need to work hard on all topics 1-3!

Don’t cut too many corners in the early commissioning!

For detailed scenarios: Need estimate on beta beat and orbit during different Need estimate on beta beat and orbit during different

phases of commissioning!phases of commissioning!

The Human Side of Machine ProtectionThe Human Side of Machine Protection

• People can have People can have deep insight and deep insight and

great ideasgreat ideas: :

We are the only chance to make the We are the only chance to make the

accelerator work!accelerator work!

• People can have People can have very bad ideas and very bad ideas and

do stupid actionsdo stupid actions: :

We are the greatest risk to the We are the greatest risk to the

accelerator! We can destroy the accelerator! We can destroy the

accelerator in a second!accelerator in a second!

The machine protection enforcement

The “boss”

We can try to avoid unnecessary

problems:

ONE central applicationONE central application for all

movable elements in LHC and TL’s!

Close integrationClose integration into online knowledge of orbit, optics, … Interlocking.

Clear and formal definition of responsibilitydefinition of responsibility for functions, optimization, operation, …

Redundant checkingRedundant checking of machine status, e.g. positions of collimators/absorbers/diluters!

(“Trust is good but control is better”)

Using Sensors to Monitor Jaw PositionsUsing Sensors to Monitor Jaw Positions

Side view at one end

Motor Motor

Temperature sensor

Gap opening (LVDT)Gap opening (LVDT)

Gap position (LVDT)Gap position (LVDT)ResolverResolver

Reference Reference

Microphonic sensor

Vacuum tank

Baseline Control ArchitectureBaseline Control Architecture

Motor Drive Control

Position Readout and Survey

Environmental Survey System

Collimator Supervisory System

Central Control Application

Function of motor setting, warning levels, dump levels versus time. Motor parameters (speed, …). Beam-loss driven functions.

BLM’sBPM readings

Timing

From MP channel:Intensity, energy, *

Warning & error levels. Info and post mortem.

Temperature sensors (jaw, cooling water, …) Vibration measurements & water flow ratesVacuum pressure & radiation measurementsMotor status & switches

Abort

Functions (motor, warning, dump level). Info and post mortem.

All position sensors.

STOP

Function motor. Motor parameters.

Measurements. Post mortem. Warnings.

Motor and switches.

AbortPreliminary by R. Assmann, M. Jonker, M. Lamont

Detailed design by R. Losito et al

Motivation for this Controls ApproachMotivation for this Controls Approach• Experience shows that Experience shows that advanced and automatic collimator control algorithms must be advanced and automatic collimator control algorithms must be

usedused (TEVATRON, RHIC): (TEVATRON, RHIC):

– BLM-based setting: “Move until BLM #i reads value X.”BLM-based setting: “Move until BLM #i reads value X.”

– Automatic movements for beam-based alignment requires functions.Automatic movements for beam-based alignment requires functions.

– Functions also allow fastest possible and most tolerant squeeze (move collimators during Functions also allow fastest possible and most tolerant squeeze (move collimators during squeeze) squeeze) useful once we are in routine operation? useful once we are in routine operation?

– Full integration into machine control and machine protection required, while preserving maximum Full integration into machine control and machine protection required, while preserving maximum flexibility for optimization of cleaning.flexibility for optimization of cleaning.

• Break complicated system into manageable packagesBreak complicated system into manageable packages::

– Central Control ApplicationCentral Control Application to generate simple or complicated functions and to provide dump and to generate simple or complicated functions and to provide dump and warning levels.warning levels.

– Collimator Drive ControlCollimator Drive Control: Simple system which provides minimum required control (motor : Simple system which provides minimum required control (motor movement). Without MP functionality. Can be specified quickly and bought from external movement). Without MP functionality. Can be specified quickly and bought from external company. company. MUST be ready in early 2007MUST be ready in early 2007..

– Position Readout & SurveyPosition Readout & Survey and and Environmental Survey SystemEnvironmental Survey System: Independent checks with various : Independent checks with various sensors. Provides position verification and protection functionality. Developed at CERN and sensors. Provides position verification and protection functionality. Developed at CERN and expected to mature with beam experience.expected to mature with beam experience.

– Collimator Supervisory SystemCollimator Supervisory System: System for many collimators (1-2 per IR) with interface to other : System for many collimators (1-2 per IR) with interface to other systems (e.g. BLM’s). Provides advanced features. Expected to develop with needs of LHC systems (e.g. BLM’s). Provides advanced features. Expected to develop with needs of LHC operation.operation.

Summary: Preparing Commissioning of Summary: Preparing Commissioning of Absorbers, Collimators and DilutersAbsorbers, Collimators and Diluters

• Collimation (phase 1) and protection design with movable devices essentially finalized! Collimation (phase 1) and protection design with movable devices essentially finalized! Coherent settings have been worked out.Coherent settings have been worked out.

• Detailed commissioning models require Detailed commissioning models require scenarios for evolution of beta beat and orbit scenarios for evolution of beta beat and orbit during the commissioningduring the commissioning (we need to know what we have to protect)! (we need to know what we have to protect)!

• Now Now define control algorithms up to middle of 2005define control algorithms up to middle of 2005 for most movable collimators, for most movable collimators, absorbers and diluters in the LHC and the transfer lines! Additional manpower after absorbers and diluters in the LHC and the transfer lines! Additional manpower after “warning message” in Chamonix 2004 will arrive and will be essential for our success!“warning message” in Chamonix 2004 will arrive and will be essential for our success!

– Goal: Simple low level scheme with advanced medium and top level!Goal: Simple low level scheme with advanced medium and top level!

– Functions can be used!Functions can be used!

• Proposals:Proposals:

– Separate set of BLM’s for collimator tuning!Separate set of BLM’s for collimator tuning! Don’t mix machine protection and cleaning problems! Don’t mix machine protection and cleaning problems!

– Further tests with SPS beamFurther tests with SPS beam in 2006 (final motors, sensors, control, …) are proposed. in 2006 (final motors, sensors, control, …) are proposed.

– Include proposed Include proposed one-stage cleaning and protection into early commissioningone-stage cleaning and protection into early commissioning plan! plan!

– Include Include MD time for phase 1 limitations and phase 2 testsMD time for phase 1 limitations and phase 2 tests into 2008 schedule! Decision 2008! into 2008 schedule! Decision 2008!

– Only Only ONE central control for collimators/absorbers/dilutersONE central control for collimators/absorbers/diluters! No special commissioning tools!! No special commissioning tools!

– Very Very limited tools for control of experimental backgroundlimited tools for control of experimental background: Input required from experiments!: Input required from experiments!