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Technological Challenges for the LHC Upgrade Ingrid-Maria Gregor, DESY LISHEP 2011 Interna0onal School of HEP Rio de Janeiro, Brazil July 9, 2011 … a detector physicists view ….

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Page 1: Technological Challenges for the LHC Upgrade · lenges at High Lumi LHC LHC Collimation System Limited in LHC by collimation system to ~ 20% at 3.5TeV Under certain assumptions on

Technological Challenges for the LHC Upgrade

Ingrid-Maria Gregor, DESY

LISHEP2011Interna0onalSchoolofHEPRiodeJaneiro,BrazilJuly9,2011

… a detector physicists view ….

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Outline

Lately inside the LHC2 protons 0.000000000000000000001 sec before collision

Apologies for the many interesting topics I didn’t cover!

The LHC (current status)Future Plans OverviewBeam parameters and what they meanBeam IntensityHigher Field MagnetsLuminosity LevelingCrab Cavities

Conclusions

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The LHC (current status)

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The CERN accelerator complexLEP e+e-(1989-2000) 104 GeV/c per beam

LHC pp and ions7 TeV/c per beam26.8 km length8.3 Tesla superconducting magnets

SwitzerlandLake Geneva

France

LHC accelerator (100m below surface)

SPS accelerator

CMS

ALICE

LHCb

ATLASCERN

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LHC Accelerator Last magnet:April 26th 2007

27 km circumference8500 of 8.4T dipole magnets Cooled to 1.9K with 140 tons of liquid heliumEnergy of one beam = 362 MJ

Kinetic energy of a 747 at take off

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LHC challenges

The LHC surpasses existing accelerators/colliders in many aspects :The energy of the beam of 7 TeV that is achieved within the size constraints of the existing 26.7 km LEP tunnel.

LHC dipole field 8.3 T HERA/Tevatron ~ 4 T

The luminosity of the collider that will reach unprecedented values for a hadron machine:

LHC pp ~ 1034 cm-2 s-1

Tevatron pp 3x1032 cm-2 s-1

SppS pp 6x1030 cm-2 s-1

Very high field magnets and very high beam intensities:Operating the LHC is a great challenge.There is a significant risk to the equipment and experiments.

A factor 2 in fieldA factor 4 in size

A factor 30 in luminosity

6

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7based on graph from R.Assmann

Livingston type plot: Energy stored magnets and beam

Potential equipment damage in case of failures during operation.

Beam Power

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CERN Accelerator Complex

8

Year Top energy[GeV]

Length[m]

Linac

PSB

PS

SPS

LHC

1979 0.05 30

1972 1.4 157

1959 26.0 628

1976 450.0 6911

2008 7000.0 26657

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LHC Start Up

2008 Accelerator complete Ring cold and under vacuum 10.09: First beams around 19.09: Accident

2008 –2009 14 months of major repairs and consolidation NewQuench Protection System for online monitoring and protection of all inter-magnet joints But: uncertainties about the splice quality (copper stabilizer) Risk of thermal runaway scenarios => decision to limit beam energy to 3.5 TeV for first operation20.11. Restart LHC at 1.18TeV29.11: Both beams accelerated to 1.18 TeV simultaneously -> LHC Highest Energy Accelerator

9

O. Brüning et al.

2010 19.03 Ramp to 3.5 TeVCollisions at 3.5+3.5 TeVLHC Reaches target energy for 2010/2011

2011 22.04: LHC sets world record beam intensityrecord broken almost on daily basismore Tops recorded than Tevatron…..

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Current Status

10https://twiki.cern.ch/twiki/bin/view/AtlasPublic/LuminosityPublicResults#2011_pp_Collisions

LHC Design

July 2011

Momentum at collision [TeV/c]

7 3.5

Luminosity[cm-2s-1]

1.00E+34 1.26E+33

Number of bunches per beam 2808 1380

Bunch intensity 1.15E+11 1.25E+11

The performance of LHC is excellentWithin a few months the goal for the year 2011 was reached: 1fb-1 !Hopes are up to reach 5 fb-1 in 2011...

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Future Plans Overview

11

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Physics reason for an upgrade

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L. RossiOperation at even higher luminosity has three main purposes:

Perform more accurate measurement on the new particles discovered in the LHCObserve rare processes (predicted or newly discovered) with rates below the current sensitivityExtend the exploration of the energy frontier, extending the discovery reach by probing rare events.

Besides the with to increase the luminosity there are some more technical reason:Radiation damage limit of IR quadrupoles ~400/fb ->~2020 this limit will be reachedHardware and shielding has not really been optimized for very high radiationNecessity to increase the heat removal capacityRestoring cooling capacity in IR5 left and decouple RF from magnets

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How the luminosity might evolve

Int. Lumi by end of 2020: 220 fb-1

Or (positive assumption to reach L= 2·1034) 300 fb-1

13E. Todesco

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E. Todesco

How the luminosity might evolve

Err

or h

alvi

ng ti

me

(yea

rs)

Even with a terrific machine, at some point the time to accumulate enough statistics to reduce the error bands is getting very high -> an upgrade is needed!

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Future plans for LHC (“Chamonix 2011”)

Run until end of 2012constantly improvements of the beam parameters (i.e. bunch spacing)

Shut down for ~15 month to fully repair all ~10000 joints (non superconducting between SC magnets)

Resolder, install clamps ….Tie in LINAC4 (high intensity)

Shut down in 2018collimation upgrade (dispersion suppressors)preparation for crab cavities & RF cryosystemdetector upgrades

Shut down in ~2021Full luminosity: 5x1034 leveledNew inner triplets based on Nb3SnCrab cavities

15

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Understanding the Beam Parameters

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“So to achieve high luminosity, all one has to do is make high population bunches of low emittance to collide at high frequency at locations where the beam optics provides as low values of the amplitude functions as possible.” PDG 2010, chapter 25

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Beam Parameter Overview

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Parameter Unit nominal upgrade

Energy [TeV] 77Protons/Bunch [1011] 1.15 1.7Bunch Spacing [ns] 50…2550…25εn (x, y) [μm] 3.75 3.75σz (rms) [cm] 7.557.55Bunch Length (4 σ)  [ns] 1.01.0Longitudinal Emittance  [eVs] 2.52.5β* at IP1, IP5 [m] 0.55 0.25…0.14Betatron Tunes {64.31, 59.32}{64.31, 59.32}Piwinski parameter:  Piwinski parameter:   0.65 1.4…2.5BB Parameter, ξ , per IP 0.003 0.005…0.008Crossing‐angle: θc [μrad] 285 315…509Main RF [MHz] 400400Crab RF [MHz] 400

Peak luminosity w/o crab cavity 1034 cm‐2s‐1 1 3.3…3.8

Peak luminosity with crab cavity 1034 cm‐2s‐1 1.2 5.8…10.3

Pile up events per crossing 19 44…280

?

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! =!

"!#

!!

!

L = frevn1n2

4!"x"y n1n2 = nBNB2

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Understanding LHC Luminosity

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n1 n2

Interaction Regionarea A

with

is the beam envelope at the IP; determined by the magnet arrangement and poweringbeam emittance (the extent occupied by the particles of the beam in space and momentum phase space as it travels)

area A

for a bunched beamluminosity

“head on collision”

Beta function

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L =

!!frev

4"

"nbNb

#!

#!Nb

$NR"

"$

!c

!z !x

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Understanding LHC Luminosity

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Angle at IP to avoid that the bunches collide in other places that the IPCrossing angle reduces luminosity

“Piwinski parameter”

effective cross section Piwinski parameter describes the effect that the crossing angle is affecting the beam dynamicsThe shorter the bunches ( ) the smaller is the effect

B. Holzer

!z

Geometry factor 22

effective cross section

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Understanding Luminosity

20

L =

!!frev

4"

"nbNb

#!

#!Nb

$NR"

"$

Total beam current.

β*

Brightness

Geometry Factor

Number of bunches

Energy

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Collimation

21

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LHC Collimation

Provide passive protection against irregular fast losses and failures.Provide cleaning for slow losses in the super-conducting environment. Manage radiation impact of beam loss.Minimize background in the experiments.

22

LHC has almost 100 collimators and absorbers.

Alignment tolerances < 0.1 mm to ensure that over 99.99% of the protons are intercepted.

The presently installed LHC collimation system provides optimum robustness but its performance is limited to a beam intensity of 40% with respect to nominal.

beam

1.2

http://indico.cern.ch/conferenceDisplay.py?confId=139719

At higher energies collimation gets harder!

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Aperture and collimation

Primary6 σ

Secondary8.8 σ

Dump Protection10.5 σ

Tertiary 15 σ

Triplet 18 σ

With collisions the aperture limit of the LHC is in the strong focusing quadrupoles (triplets) that are installed just next to the experiments.

Hierarchy of collimators must be preserved in all phases to avoid quenching super-conducting magnets and for damage protection. β* is presently limited to 3.5 m by aperture and tolerances.

Collimation hierarchyExp.

23

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LHC Collimation System

Limited in LHC by collimation system to ~ 20% at 3.5TeVUnder certain assumptions on loss rates, imperfectionsInjectors can deliver nominal beams

With experience assume that LHC canMove to tight collimator settingsImprove loss ratesGet the imperfection factor down✦ Should allow to push to higher intensities (to ~40% nominal)

Then need to install something moreCollimators in the cold regions of the machine in 2012Using “missing magnet” space in the dispersion suppressorsRequires moving magnets in LSS3 and LSS7 (24 magnets each)Should allow us to get to nominal intensity at 7TeV

Phase II collimators installed in 2018

24

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H-LHC change in layout in the IR

Dispersion suppressor Matching section Separation dipoles Final focus

Today: 6x3 m x1.5 T; h=80 mmHL-LHC: 1x4 m x 7 T; Ø=150 mmToday: Two-in-One Ø =56 mm; 4.2K

HL-LHC: Two-in-One Ø70 mm; 1.9 K

Today: Q4 Two-inOne Ø=70 mm, 4.2 K; D2 ↑↑ 9 m x 3.5 T, 4.2 KHL-LHC: Q4 Two-in-One Ø=90 mm, 1.9 K; CRAB CAVITY; D2 ↑↑ 9 m x 5 T; 1.9 K

Today MQX: 4 x 6 m, Ø=70 mm;HL-LHC MQX: 4 x 8 m x; Ø=150 mm

25

CMS

L. Rossi

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Higher Field Magnets

26

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Critical technologies: Magnets

27

L. RossiSuper conducting magnets beyond 10 tesla of accelerator qualities.

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Motivation for Nb3Sn

Nb3Sn can be used to increase aperture/gradient and/or increase heat load margin, relative to NbTiNb3Sn allows higher current at higher B-fields

28

Technical challenges:Nb3Sn is difficult material

Requires high temperature coil reaction after winding Materials compatibility (coil parts, insulation) Thermal expansion differentials (more critical for long magnets) Need to prevent degradation under stressProgress in Nb3Sn current density rapidly translated in record field dipolesSince ~2003, the critical current density of Nb3Sn wires has been stable

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11 T LHC dipole

29

Here cryo-collimators could be accomodated

For HL-LHC the collimation needs to be improved, but no space is availablereplace 8T magnets (rather long) by 11 T magnets will gain space for collimation

11T magnets are under development within HL-LHC (in collaboration with Fermilab)

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Beta*

30

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The need for new quadrupoles

The minimum β* is limited by the aperture of the triplets at the IP and also by the chromatic aberations introduced by the very tight squeezeSmall β*⇒huge β at focusing quad

Need bigger quads to go to smaller β*

31

Existing quads• 70 mm aperture• 200 T/m gradient

Proposed for upgrade• At least 120 mm aperture• 200 T/m gradient• Field 70% higher at pole face

⇒ Also beyond the limit of NbTi -> Nb3Sn

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High Field Quadrupole (LARP)

32

US-LARP is engaged in the production of a model by 2013 (4...6 m length) for the decision on the technology to be used (Nb3Sn vs. Nb-Ti)120 mm aperture and 200 T/m gradientTesting first 1m long prototype

High Field Quadrupole HQ (120 mm aperture, 1 m long)

Achieved >155 T/m gradient in first test, at 4.5KAlready above NbTi intrinsic limit at 1.9K

First quench >150 T/m in second testSeveral coil failures due to insulation & conductor damageTraced to high compression during coil fabricationNew & more challenging design - requires optimization

The Nb3Sn development plan aims at demonstrating readiness for atechnology decision and construction initiation in 2014

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SQSM TQS

LR

LQS-4m

HQTQC

33L. Rossi

LARP (US LHC program) Magnets

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Luminosity Leveling

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Luminosity leveling

35see e.g. J.P.Koutchouk, Cham. 2010)

L ! 1

!!!

1 + !2c"2

z4#!$

Three possibilities in LHC, specific to crossing at an angle (no yet decided):➡ Leveling via dynamic beta* adjustments➡ no additional hardware necessary, but is probably complex to implement but is cheap.➡ Leveling via dynamic bunch length adjustments➡ no or minor side effect if the beam remains stable; needed: reduction of the voltage by 16 +

bunch shortening➡ Leveling via dynamic crossing angle adjustments➡ Leveling via the Xing angle appears to have the best potential (performance, complexity) but

requires unexplored solutions (Crab Crossing) or some interference with detectors (Early Separation).

Integrated Lumi is the same

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Crab Cavities

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Increase peak luminosity with increasing x-angle Increase intensities and smaller emittances beyond head-on beam-beam limit Level luminosity (reduce Pile-up, radiation damage)

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Crab Crossing Restores Bunch Overlap

RF crab cavity deflects head and tail in opposite direction so that collision is effectively “head on” for luminosity and tune shiftThe crab cavity creates two-loop magnetic field (blue) inside to kick bunches sideway.1st proposed in 1988, in operation at KEKB since 2007 → world record luminosity!*

http://www.kek.jp/intra-e/feature/2010/KEKBCrabCavity.html

Example of an crab cavity creating a two-loop magnetic field

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The challenge: a normal RF cavity requires a transverse dimension > 0.609 λ !For 400 MHz, this means > 460 mm.The LHC beams are separated 194 mm (0.26 λ)!Something very unconventional is needed!

38

Crab Cavities

E. Jenssen

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Parallel bar cavity (ODU) Half wave resonator (SLAC)

Four bar cavity (U Lancaster) Kota cavity (KEK)

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Ideas for Compact CC’s

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Back-up strategy: Elliptical Crab Cavities

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Retain a conventional cavity option in the unlikely event of major unforeseen ’show stopper’ with all compacts…Requires significant civil engineering costs due to needed dogleg sections in the IRs Still acceptable, in view of the importance gaining back luminosity from the crossing angle. A straightforward conventional cavity installation in IR 4 as a global scheme would serve as an alternate option in the worst case. Decision point 2015 – stop if Compact CC’s are validated!

Cryostat design exists (from LARP) compatible with P4 (800 MHz)

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Brightness

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!Nb

!N

"

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Brightness

42

LHC imposed brightness must be present from the lowest energy because brightness is (at best) conserved in a cascade of proton accelerators (Liouville’s theorem).Brightness (emittance and beam intensity) is defined in the accelerator chain before injection into the LHC.The emittance can be improved by increasing the injection energy

It was decided to build a new linear accelerator at the beginning of the chain

Increasing the beam intensity by a factor of 2Increase injection energy in the PS from 1.4 to 2 GeV, increasing the field in the PSB magnets and replacing its power supplyHigher energy out of the PS gives smaller transverse emittance and beam sizes => reducing the injections losses into the SPS

Building etc. already existing

https://indico.cern.ch/conferenceDisplay.py?confId=129870

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⇒ Increase injection energy in the PSB from 50 to 160 MeV, Linac4 (160 MeV H-) to replace Linac2 (50 MeV H+)

⇒ Increase injection energy in the PS from 1.4 to 2 GeV, increasing the field in the PSB magnets, replacing power supply and changing transfer equipment

⇒ Upgrade the PSB , PS and SPS to make them capable to accelerate and manipulate a higher brightness beam (feedbacks, cures against electron clouds, hardware modifications to reduce impedance…)

Brightness

To increase reliability and lifetime (until ~2030!) (tightly linked with consolidation) ⇒ Upgrade/replace ageing equipment (power supplies, magnets, RF…)

⇒ Procure spares

⇒ Improve radioprotection measures (shielding, ventilation…)

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Linac4 PS injector, PS and SPS Beam characteristics at LHC injection

2011 - 2012

Continuation of construction…

• Beam studies § simulations• Investigation of RCS option• Hardware prototyping• Design § construction of some

equipment• TDR

25 ns, 1.15 1011p/b, >2.9 mm.mrad50 ns, 1.7 1011p/b, >2.5 mm.mrad75 ns, 1.2 1011 p/b, ≤ 2 mm.mrad

2013 – 2014 (Long Shutdown 1)

• Linac4 beam commissioning

•Connection to PSB ?

• PSB modification (H- injection) ?• PSB beam commissioning ?• Modifications and installation of

prototypes in PS and SPS

2015 - 2017

• Progressive increase of Linac4 beam current

• If Linac4 connected: progressive increase of PSB brightness

• Some improvement of PS beam (Injection still at 1.4 GeV)

• Equipment design § construction for PS injector, PS and SPS

• Beam studies

• Little gain at LHC injection (pending PS and SPS hardware upgrades)

2018(Long Shutdown 2)

• Extensive installations in PS injector, PS and SPS

• Beam commissioning

2019 –2021After ~1 year of operation: beam characteristics for HL-LHC…

Preliminary Planning

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HL-LHC Luminosity

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L =

!!frev

4"

"nbNb

#!

#!Nb

$NR"

"$

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Recap

Total beam current. Limited by:• Uncontrolled beam loss!!• E-cloud and other instabilities• Action: Linac4

Reduce β*, limited by• magnet technology -> Nb3Ti• chromatic effects

Brightness, limited by • Injector chain• Max tune-shift

Geometric factor, related to crossing angle and bunch length

Maximize number of bunches

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Booster energy upgrade 1.4 → 2 GeV, ~2014

IR upgrades:detectors, low‐β quad’scrabcavi0es

etc.~2022

Linac4~2014

SPS enhancements2012-2022

F. Zimmermann

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What can HL-LHC reach ?

Leveled peak luminosity: L = 5 1034 cm-2 sec-1

Virtual peak luminosity: L = 10 1034 cm-2 sec-1

Integrated luminosity: 200 fb-1 to 300 fb-1 per yearTotal integrated luminosity: ca. 3000 fb-1

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Goal:

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Conclusions

The LHC is running extremely good, the goal for 2011 to collect 1 fb-1 was already reached -> nex goal is 5 fb-1

An even more potent machine is envisaged for 2020+ to access rare decaysR&D for this goal is in full swing, a good understanding of the current machine allows to plan for the future 5*1034 is a possible luminosity for HL-LHC

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2008 by Lars Ottesen Henriksen

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Acknowledgements and Further Reading

This talk represents the work of an almost countless number of people. I have incorporated significant material from:

The annual Chamonix meetingshttp://tinyurl.com/Chamonix2011

Frank Zimmermann’s many luminosity talks, Talks presented at LARP collaborations and DOE reviews

See http://www.uslarp.org/

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Accelerator Physics in general:Klaus Wille, “The Physics of Particle Accelerators”, Oxford University Press, 2000CERN Accelerator School:http://cdsweb.cern.ch/record/603056/files/CERN-2006-002.pdfFundamentals of Accelerator Physics and Technology: http://uspas.fnal.gov/materials/09UNM/UNMFund.html

HL-LHC Upgrade DetailsBreaching the Phase I Optics Limitations for the HL-LHC, S. Fartoukh

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F. Zimmermann

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LHC Layout

8 crossing interaction points (IP’s)Accelerator sectors labeled by which points they go between

ie, sector 3-4 goes from point 3 to point 452

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LHC Experiments

Compact Muon Solenoid (CMS) A Toroidal LHC ApparatuS (ATLAS)

A Large Ion Collider Experiment (ALICE) B physics at the LHC (LHCb) 53

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!"#$%#&$!!'()*++(,-./012( *3(41551678-( !"

Superconductivity and Particle Accelerators

Cryogenics is complicated and expensive,

so what is the interest of superconductivity?

•! High current density ! compact windings

! high magnetic fields and gradients

•! Larger ampere-turns in a small volume! no need for iron

(but iron is still useful for shielding)

•! Reduced power consumption ! lower power bills

(when cost of refrigeration power is offset) (

Superconductivity opens up new technical possibilities

•! Higher magnetic fields ! increased bending power

! greater energy for a given radius

•! Higher electric fields ! higher accelerating gradients

! greater increase of energy per unit length

•! Higher quadrupole gradients ! more focusing power

! higher luminosity

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Superconductivity and Accelerators

54

Cryogenics is complicated and expensive, so what is the interest of superconductivity?

High current density➡ compact windings➡ high magnetic fields and gradients Larger ampere-turns in a small volume -> no need for iron (but iron is still useful for shielding)Reduced power consumption ➡ lower power bills (when cost of refrigeration power is offset)

Superconductivity opens up new technical possibilities Higher magnetic fields -> increased bending power ➡ greater energy for a given radius Higher electric fields -> higher accelerating gradients ➡ greater increase of energy per unit lengthHigher quadrupole gradients ! more focusing power ➡ higher luminosity A. Ballarino

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Summary of LHC Intensity Limits (7 TeV)

Ideal scenario: no imperfections included!

R. AssmannR. Assman @ Chamonix 2010

Chamonix 2011

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eCloud Effect

Photoelectrons created in the vacuum pipe are accelerated by passing proton bunches.Slow or reflected secondary electrons survive until the next bunch arrivesDepending on the pipe surface conditions and bunch spacing this may lead to an electron cloud build-upEffects on stability, emittance growth etc. are the consequenceCurrently the LHC is running at 50ns bunch spacing to reduce this effect

56

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Crab Cavities

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Main Technical questionSpace constraints -> 800 MHz elliptical (simple) versus 400 MHz “exotic”

E. Jenssen

Simulations

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Jc(4.2 K, 6 T)!2300 A/mm2

Jc(1.9 K, 9 T)!2300 A/mm2

T(K)

B(T)

J(A/mm2)

49:(;(

;9<3&#=(

;9!3:(=(

#LHC Strands

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Operating temperature of superconductors (Niobium titanium)

R. Schmidt

The superconducting state only occurs in a limited domain of temperature, magnetic field and transport current density

Superconducting magnets produce high field with high current density

Lowering the temperature enables better usage of the superconductor, by broadening its working range

!"#$%#&$!!'()*++(,-./012( *3(41551678-( !"#

Jc(4.2 K, 6 T)!2300 A/mm2

Jc(1.9 K, 9 T)!2300 A/mm2

T(K)

B(T)

J(A/mm2)

49:(;(

;9<3&#=(

;9!3:(=(

#LHC Strands

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Hour Glass effect

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Hour glass effectRelevant when β* is decreased close to the bunch length σz.

Define r = β* / σz . Luminosity gets reduced. For round beams the factor is

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Beam Beam Effects

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Two crossing beams see the field of each otherSpace charge cancellation not present anymoreImportant limitation for high luminosityBeam beam effects: considered to be a major challenge to reach LHC luminosity

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Beam-beam interaction

32

- black witness bunches (zero collisions); - red bunches colliding in IP 1 5 and 2 (3 collisions); - blue bunches colliding in IP 1 5 and 8 (3 collisions); - green bunches colliding in IP 2 and 8 (2 collisions).

Effects of the beam-beam force are visible on the lifetime of the various bunches.

o Also sensitive to tune working point.o This will become even more complicated with trains of bunches.

Beams in collision Beams in collisionBeam1 Beam2Intensityloss (%)

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Total crossing angle of 300 µradBeam size at IP 16 µm, in arcs about 1 mBeams in the arcs in two vacuum chambers

Crossing angle for multibunch operation

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1232 dipole magnets.

B field 8.3 T (11.8 kA) @ 1.9 K (super-fluid Helium)

2 magnets-in-one design : two beam tubes with an opening of 56 mm.

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LHC dipole magnet

7

Operating challenges:o Dynamic field changes at injection.o Very low quench levels (~ mJ/cm3)

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1232 main dipoles +3700 multipole corrector magnets

392 main quadrupoles +2500 corrector magnets

Regular arc:Magnets

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Beam dump

Extraction kickers

Dilution kickers

Extraction septum magnets

Dump block

Complex beam dumping system commissioned.Beam swept over dump surface (power load)

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CERN Accelerators

[fromWikipedia]

“CERN operates a network of six accelerators and a decelerator. Each machine in the chain increases the energy of particle beams before delivering them to experiments or to the next more powerful accelerator… All these accelerators are used to prepare the beam needed by the Large Hadron Collider

Two linear accelerators generate low energy particles. Linac2 accelerates protons to 50MeV for injection in to the Proton Synchrotron Booster (PSB), and Linac3 provides heavy ions at 4.2MeVu fori injection into the Low Energy Ion Ring (LEIR). The Proton Synchrotron Booster increases the energy of particles generated by the proton linear accelerator before they are transferred to the other accelerators.The Low Energy Ion Ring (LEIR) accelerates the ions from the ion linear accelerator, before transferring them to the Proton Synchrotron (PS). This accelerator was commissioned in 2005, after having been reconfigured from the previous Low Energy Antiproton Ring (LEAR). The 28GeV Proton Synchrotron (PS), built in 1959 and still operating as a feeder to the more powerful SPS. The Super Proton Synchrotron (SPS), a circular accelerator with a diameter of 2 kilometres built in a tunnel, which started operation in 1976. It was designed to deliver an energy of 300GeV and was gradually upgraded to 450GeV. As well as having its own beamlines for fixed-target experiments (currently COMPASS and NA62),it has been operated as a proton–antiproton collider (the SppS collider), and for accelerating high energy electrons and positrons which were injected into the Large Electron Positron Collider (LEP). Since2008, it has been used to inject protons and heavy ions into the Large Hadron Collider LHC).

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