Introduction to the LHC

Introduction to the LHC M. Giovannozzi

CERN – Beams Department

General layout The cell The IRs Aperture Filling Nominal vs. actual beam parameters

MP Review - Massimo Giovannozzi - CERN

ATLAS

CMS

LHC-BALICE

LAYOUT OF THE LHCLHC layout

ATLAS: High luminosity experiment. Search for the Higgs boson(s).

A Large Ion Collider Experiment (ALICE): Ions. New phase of matter expected (Quark-Gluon Plasma).

Compact Muon Solenoid (CMS): High luminosity experiment. Search for the Higgs boson(s). In this insertion is also located TOTEM for the measurement of the total proton-proton cross-section and study elastic scattering and diffractive physics.

LHCb: Beauty quark physics for precise measurements of CP violation and rare decays.

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Experimental magnets - I

Toroid -> no impact on beams ATLAS

Solenoid -> linear coupling ATLAS ALICE CMS

Spectrometer -> orbit bump closed by means of three dipoles (see later). ALICE (vertical bump) LHCb (horizontal bump)

MP Review - Massimo Giovannozzi - CERN 3

Experimental magnets - II

Solenoids (ATLAS, Alice, CMS) -> linear coupling


Courtesy H. Burkhardt - CERNCourtesy H. Burkhardt - CERN


Key nominal parameters

5


The LHC machine has an height-fold symmetry.

Eight arcs. Sixteen dispersion

suppressors to match the arc with the straight sections (geometry and optics).

Eight long straight sections.

Tunes: 64.28/59.31 injection 64.31/59.32 collision

LHC symmetry

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The arc cell

mid-cellsilver silver mid-cellsilver silver

beam waist

H

V

Six dipoles are located in each cell. Each dipole comprises spool pieces made of:

Sextupoles or

Sextupoles, octupoles, and decapoles Two quadrupoles are located in each cell.

Each quadrupole is e quipped with: Beam Position Monitor Dipole corrector (for closed orbit) Sextupoles (for chromaticity)

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7TeV• 8.33T• 11850A• 7MJ

Main dipoles - I

8


-5

-4

-3

-2

-1

0

1

2

3

4

5

0

Targets

Measured

Cold mass - systematic vs targets

a3 a4

b2 a

pert

ure

1

b2 a

pert

ure

2

b2 b

oth

aper

ture

s

b4 a

pert

ure

1

b4 a

pert

ure

2

b4 b

oth

aper

ture

s

a2 a5

AT-MAS-6

-4

-2

0

2

4

6

9

Targets

Measured

b3b5

b7

AT-MAS

Courtesy E. Todesco - CERNCourtesy E. Todesco - CERN

Main dipoles - II

Systematic field errors in dipolesSystematic field errors in dipolesSystematic field errors in dipolesSystematic field errors in dipoles

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Corrected by the spool pieces

Other arc correctors - I


Additional lattice correctors are installed in SSS to correct linear and non-linear effects: Trim quadrupoles: independent tuning of the two

rings and compensation of the b2 of main dipoles

Courtesy R. Tomás - CERNCourtesy R. Tomás - CERN

Measured phase shift with respect to nominal optics without (red) and with (blue) correction with MQTs

Other arc correctors - II

Skew quadrupoles (some correctors missing in sector 3-4): compensation of linear coupling

Skew sextupoles (central part of each sector): compensation of a3 effects

Octupoles: instabilities



LHC layout: IR1/5 - I

Interaction pointInteraction point

Low-beta quadrupolesLow-beta quadrupoles

Separation/ricombination dipole Separation/ricombination dipole ((NORMAL CONDUCTINGNORMAL CONDUCTING))

Separation/ricombination dipoleSeparation/ricombination dipole

Absorber (neutral particles)Absorber (neutral particles)

Towards dispersion Towards dispersion suppressor and arcsuppressor and arc

12A B A B AB AB

Q3 Q2b Q2a Q1

Lead 1 Lead 4 Lead 3 Lead 2

RQX

RTQX2RTQX1

Electrical Layout

Powering scheme of triplet quadrupoles


LHC layout: IR1/5 - II

High luminosity High luminosity insertions: insertions: injection optics. injection optics. Beta at Beta at interaction point interaction point equals equals 11 m11 m..

13


LHC layout: IR1/5 - III

High luminosity High luminosity insertions: insertions: collision optics. collision optics. Beta at Beta at interaction point interaction point equals equals 0.55 m0.55 m..

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LHC layout: IR2/8 - I

Separation/ricombination Separation/ricombination dipoledipole

Injection septumInjection septum

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Injection kickerInjection kicker

IPIP

SpectrometerSpectrometer and and compensatorscompensators

Separation/ricombination Separation/ricombination dipole (dipole (SUPERCONDUCTINGSUPERCONDUCTING))

LHC layout: IR2/8 - II Layout of IR8 is similar apart from a

displacement of the IP8 towards IP7 by about 11.25 m

Injection system and protection devices impose tight constrain on optics (phase advance between key elements)

Triplets needs to work at higher-than-nominal gradient (220 T/m instead of 205 T/m).

A stage of strength-reduction at constant beta* is needed before squeeze.


Crossing scheme - I To avoid parasitic collisions a crossing scheme

in implemented (parallel separation/crossing). IR1/5: the bumps are closed between Q6 (left/right) IR2/8: the bumps are closed between Q5 (left/right)

Crossing planes are alternating IR1/2: V-plane IR5/8: H-plane

Spectrometers and crossing scheme: IR2: V-plane, polarity change trivial (flip sign) IR8: H-plane, polarity change more difficult.


Beam 1 in IR1Beam 1 in IR1

Crossing scheme - II Spectrometers and crossing scheme:

The real crossing angle is the superposition of: Spectrometer crossing angle (so-called internal angle) External crossing angle (generated by the magnets in the

separated region))

Nominal parameters (IR1/5 for simplicity) Half separation: 2 mm (injection); 0.5 mm (7 TeV) Half crossing angle: 170 rad (injection); 142.5 rad

(7 TeV).


Nominal beta* and squeeze Nominal beta*:

IR2: 10 m (injection); 10 m (p collision, smaller value during initial commissioning – 0.5 m for Pb collisions)

IR8: 10 m (injection): 10 m (collision, smaller value during initial commissioning phases)

IR1/5: 11 m (injection); 0.55 m (collision) Squeeze challenges (only few listed):

Orbit control Optics control (e.g., quadrupoles hysteresis) Aperture Non-linear aberrations below 1 m beta*



Behaviour of optical parameters during Behaviour of optical parameters during squeeze of IR1 - Isqueeze of IR1 - I

-2.0E-03

-1.5E-03

-1.0E-03

-5.0E-04

0.0E+00

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0

Horizontal beta* (m)

Del

ta t

un

e

9.990E-03

1.009E-02

1.019E-02

1.029E-02

1.039E-02

1.049E-02

Tu

ne

split

DQ Hor. (Beam 1)

DQ Ver. (Beam 1)

Tune split


Behaviour of optical parameters during Behaviour of optical parameters during squeeze of IR1 - IIsqueeze of IR1 - II

2.0

2.1

2.2

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0

Horizontal beta* (m)

Ch

rom

atic

ity

Chrom. Hor. (Beam 1) Chrom. Ver. (Beam 1)


LHC layout: the other insertions

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IR3/7: Collimation system - I

The magnets in between Q6 (left and right) are normal conducting.

Difference in dogleg magnets.


IR3/7: Collimation system - II IR3 features a large normalised dispersion to

improve momentum collimation.


A so-called detuned optics (with nominal dispersion exists).

IR3/7: Collimation system - III IR7 features a small dispersion to improve betatron

collimation.


For the details of the collimation system see later talks

IR4: RF and instrumentation

RF equipment housed here (including damper) Instrumentation (wire scanner, beam current

transformers, synchrotron light monitor…) Some features:

Larger-than-nominal beam separation Superconducting magnets Missing quadrupoles


IR4 is used to tune the machine


IR6: Beam dumping system

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From the optical point of view: the missing quadrupoles imply large beta-function -> tight aperture (See later presentations for more details).

Aperture - I

Key quantity used to measure the available beam aperture in the design phase is “n1”.

It is not a simple conversion of the mechanical aperture in beam sigmas!

It is clearly LHC-oriented. The computation is implemented in MAD-X Its computation is based on

Knowledge of mechanical aperture tolerances on key parameters (alignment, orbit, optics) shape of the beam halo generated by interaction with a

primary collimator. MP Review - Massimo Giovannozzi - CERN 28

Aperture - II

Nominal parameters: Beta-beating: 20% Closed orbit tolerance: 4 mm

(injection); 3 mm (collision)


Aperture = n1 , the cold aperture is•1.22 n1 (H/V)1.22 n1 (H/V)•1.4 n1 radial1.4 n1 radial

Aperture - III

Design criterion: n1 ≥ 7 in superconducting magnets. Injection: arcs and dispersion suppressors are the aperture limits Collision: triplets are the aperture limits


Beam 1 Beam 1 in IR1in IR1

InjectionInjection CollisionCollision

LHC filling


Nominal vs. actual beam parameters

Beam commissioning needs to be split in stages (which were already outlined in the Design Report) with special beam parameters.

The unforeseen limitations (maximum energy) imposed to to prepare new series of beam parameters


A complete A complete discussion of the discussion of the beam parameters beam parameters for 2010/11 in the for 2010/11 in the next talk…next talk…

Backup material


Other nominal parameters - I

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Other nominal parameters - II

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Documents

Introduction to the LHC