The Large Hadron ColliderContents:

1. The machineII. The beam

III. The interaction regionsIV. First LHC beam

[R. Alemany][CERN AB/OP]

[Engineer In Charge of LHC]Lectures at NIKHEF (11.12.2008)

II. The beam

II. Injection mechanismI. Injection from pre-acceleratorsII. Injection into LHCIII. How the injection affects the beam

parametersIV. Injection commissioning

III. The RF systemI. Functionality and beam parameters used to

design itII. RF componentsIII. RF synchronization: injection process and

experimentsIV. The vacuum chamber and the beam size V. Acceleration

Contents:I. Beam parameters

II.I Beam parameters (nominal)

Injection CollisionProton energy GeV 450 7000Particles/bunch 1.15 x 1011

Num. bunches 2808Longitudinal emittance (4) eVs 1.0 2.5Transverse normalized emittance µm rad 3.5 3.75Beam current A 0.582Stored energy/beam MJ 23.3 362

Peak luminosity related dataRMS bunch length cm 11.24 7.55RMS beam size @IP1 & IP5 x,y = µm 375.2 16.7RMS beam size @IP2 & IP8 x,y = µm 279.6 70.9Geometric luminosity reduction factor (F) 0.836Instantaneous lumi @IP1 & IP5 (IP2Pb-Pb, IP8)

cm-2s-1 1034(1027 , 1032)

Instantaneous lumi/bunch crossing @IP1 & IP5

cm-2s-1 3.56 x 1030

= 0.55 m = 0.5 nm rad

= 10 m = 0.5 nm rad

II. The beam

II. Injection mechanismI. Injection from pre-acceleratorsII. Injection into LHCIII. How the injection affects the beam

parametersIV. Injection commissioning

III. The RF systemI. RF componentsII. RF synchronization

IV. The vacuum chamber and the beam sizeV. Acceleration

Contents:I. Beam parameters

II. II. Injection mechanism: injection from pre-accelerators

1

2

3

4

5

7

8

6

SPS

LINAC

2

CPSPSB

Top energy(GeV) Circumference(m) LINAC2 0.12 30PSB1.4 157CPS 26

628 = 4 PSBSPS 450

6911 = 11 x PSLHC 7000

26657 = 27/7xSPS

B2 Dump

B1 Dump

II. II. Injection mechanism: injection from pre-

accelerators BOOSTER (1.4 GeV) PS (26 GeV) SPS (450 GeV) LHC

BOOSTER (4 rings)

PS

h=1 h=7 (6 buckets filled + 1 empty)

Two injections fromBOOSTER to PS

1st batch 2nd batch

II. II. Injection mechanism: injection from pre-accelerators

BOOSTER

PS

Triple splittingQ

uadruple splitting

h=7

h=21

h=84

6 bunches7 buckets

18 bunches21 buckets

72 bunches84 buckets

1.4 GeV

1.4 GeV

26 GeV

Two injections fromBOOSTER to PS

SPS Up to four injections from PS of 72 bunches

h=1

12x25 ns GAP to cover the rise time of the PS ejection kicker

II. II. Injection mechanism: injection into LHC25 ns Filling Scheme (2808 bunches/ring)

Ref: LHC-OP-ES-0003

II. II. Injection mechanism: injection into LHC75 ns Filling Scheme (936 bunches/ring)

Ref: LHC-OP-ES-0003

II. II. Injection mechanism: injection into LHC

TI8

~ 3 km

~ 70 m

ALIC

E

FBCT

~ 12 mm

II. II. Injection mechanism: injection into LHC

Proton machines: single turn injection

II. II. Injection mechanism: How the injection affects the beam

parameters

(αx,βx,αy,βy,D,D’)ext (αx,βx,αy,βy, D,D’)inj

(αx(s),βx(s),αy(s),βy(s), D(s),D’(s))trans

Twis parameters at start and end of the transfer line are fixed

β(m)

II. II. Injection mechanism: How the injection affects the beam

parameters

Transferlines & Injection: Errors & Tolerances* quadrupole strengths --> "beta beat" Δβ / β * alignment of magnets --> orbit distortion in transferline & storage ring * septum & kicker pulses --> orbit distortion & emittance dilution in storage ring

Kicker "plateau" at the end of the PS - SPS transferline measured via injection - oscillations

Example: Error in position Δa:

Δa =0.5 σ

)2

1(*2

0a

new

0*125.1 new

II. II. Injection mechanism: How the injection affects the beam

parameters

Transverse phase space

x

x’

Injection errors (position or angle) dilute the beam emittance

Non-linear effects (e.g. magnetic fieldmultipoles ) introduce distort the harmonic oscillation and lead to amplitude dependent effects into particle motion.

Over many turns, a phase-spaceoscillation is transformed into an emittanceincrease.

Filamentation

II. II. Injection mechanism: How the injection affects the beam

parameters

II.II. Injection mechanism:Injection commissioning

II.II. Injection mechanism: Injection commissioning

II. The beam

II. Injection mechanismI. Injection from pre-acceleratorsII. Injection into LHCIII. How the injection affects the beam

parametersIV. Injection commissioning

III. The RF systemI. Functionality and beam parameters used to

design itII. RF componentsIII. RF synchronization: injection process and

experimentsIV. The vacuum chamber and the beam sizeV. Acceleration

Contents:I. Beam parameters

II.III. The RF system: functionality and beam parameters

Main beam and RF parameters directly relevant to the design of the RF:

Functionality:• Proton machine:

1. Injection synchronization2. Capture bunches3. Accelerate/decelerate4. Beam measurements

• Lepton machine:1. Accelerate2. Compensate for

synchrotron radiation losses

Unit Injection

Collision

Bunch area (2) eVs 1.0 2.5Bunch length (4) ns 1.71 1.06Energy spread (2) 10-3 0.88 0.22Protons/bunch 1011 1.15Num. bunches 2808Transverse normalized emittance (H/V)

µm rad

3.5 3.75

Ibeam A 0.582Synchrotron radiat. loss/turn keV 7Longitudinal damping time h 13Intra beam scattering growth time H

h 38 80

Intra beam scattering growth time V

h 30 61

RF frequency MHz 400.789 400.790Harmonic number 35640RF voltage/beam MV 8 16Energy gain/turn (20 min ramp)

keV 485

RF power supply during accel./beam

kW ~275

Synchrotron frequency Hz 63.7 23.0Bucket area eVs 1.43 7.91RF(400MHz) component of Ibeam

A 0.87 1.05

II.III. The RF system: components• Main 400 MHz Accelerating System (ACS)• Transverse damping and feed-back system

(ADT)• Functionality:

• Dumps transverse injection oscillations• Prevents transverse coupled bunch

instabilities (dipole modes)• Can excite transverse oscillations for beam

measurements• Low-level RF (part of the 400 MHz

Accelerating Sys.)Low level RF components:Cavity controller (RF feedback and tuning)

Beam control & RF synchronization

Fast timing distribution to kickers, dump and experiments

Longitudinal damper

II.III. The RF system: IR4S34 S45

B2

B1194 mm420 mm

ADT Q5 Q6 Q7ACSACS

ACSACS

Tunnel

Second beam

Power Coupler

Wave guide

4xFour-cavity cryo module 400 MHz, 16 MV/beamNb on Cu cavities @4.5 K (=LEP2)Beam pipe diam.=300mm

D3 D4

Beam separation - recombination dipoles

Matching Section Quadrupoles

II.III. The RF system: synchronization at injection (RF low level)

• The synchronization of the injection kicker timing system with the injected and circulating beam is performed with the RF system via the generation and distribution of the fast injection pre-pulse. This is done via a dedicated fibre optics links that connect IR4 RF with the IR2 injection kicker (inj of B1) and IR8 injection kicker (inj of B2).

• The pre-pulse is locked to the SPS/LHC common frequency.Proton machines: single turn injection

II.III. The RF system: synchronization with experiments (RF low level)

CCC

1

2

3

4

5

7

8

6

SPSPCR(CCC)

Revolutio

n frequency

B1,B2

(40 MHz)

Orbit frequency

(11 kH

z

= fRF/h

)

GPS timeMachine modeBeam typeBeam energyNum. Injected bunchesetc

BST msg from LHC Timing System

B.G. Taylor, “Timing distribution at the LHC”, 8th workshop on Electronics for LHC experiments, Comar 2002

II. The beam

II. Injection mechanismI. Injection from pre-acceleratorsII. Injection into LHCIII. How the injection affects the beam

parametersIV. Injection commissioning

III. The RF systemI. Functionality and beam parameters used to

design itII. RF componentsIII. RF synchronization: injection process and

experimentsIV. The vacuum chamber and the beam sizeV. Acceleration

Contents:I. Beam parameters

II.IV. Vacuum chamber & beam size• The beam vacuum requirements are very stringent, driven

by the requested beam lifetime (100 hours) and background to the experiments• 1015 H2/m3 • 1013 H2/m3 in the interaction regions

• Heat sources:• Synchrotron light radiated by the beam (0.2 Wm-2 per

beam)• Energy loss by nuclear scattering (30 mWm-1 per beam)• Image currents (0.2 Wm-1 per beam)• Electron clouds

beam

Beam pipe

Image current

By O. Brüning (AB/ABP CERN)

Synchrotron radiation from proton bunches in the LHC creates photoelectrons at the beam screen wall. These photoelectrons are pulled toward the positively charged proton bunch. When they hit the opposite wall, they generate secondary electrons which can in turn be accelerated by the next bunch. Depending on several assumptions about surface reflectivity, photoelectron and secondary electron yield, this mechanism can lead to the fast build-up of an electron cloud (the animation shows simulation results by O. Brüning for 10 subsequent bunch passages, during which the pictures become red) with potential implications for beam stability and heat load on the beam screen.

II.IV. Vacuum chamber & beam size

In order to reduce the heat input to the cryogenic system the following design choices were made:• Beam screen

determines the mechanical aperture• Cu layer• Gas density restriction

Cooling tubes (5-20 K)

Cold bore

Dimensions: height ~ 2x17 mmwidth ~ 2x22 mm

The mechanical aperture, i.e. the beam screen:• Combined with a peak function in the arc of

180 m implies a maximum acceptable transverse beam emittance of n=3.75 µm.

• Combined with the limit on the linear beam-beam tune shift limits the maximum bunch intensity to 1.15 x 1011 protons per bunch.

II. The beam

II. Injection mechanismI. Injection from pre-acceleratorsII. Injection into LHCIII. How the injection affects the beam

parametersIV. Injection commissioning

III. The RF systemI. Functionality and beam parameters used to

design itII. RF componentsIII. RF synchronization: injection process and

experimentsIV. The vacuum chamber and the beam sizeV. Acceleration

Contents:I. Beam parameters

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8000

10000

12000

-3000 -2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000

Time [s]

MB

cur

rent

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B [T

]

Preinjection plateau

Ramp down

Start ramp

Injection

Beam dump

Physics PreparePhysics

SqueezeLumi optimiz

II.V. Acceleration

Ramp down 18 Mins Pre-I njection Plateau 15 Mins

I njection 15 Mins Ramp 28 Mins

Squeeze 20 Mins Prepare Physics 10 Mins

Physics 0 - 20 Hrs

Snap

-bac

kPersistent current

decay effects!!!

Correct for them at the beginning of the ramp

Snap-back (topic for an advance school):• phenomena typical of SC magnets• happens during the first couple of seconds after

acceleration starts• one needs to correct for it!!!

Acceleration ~20 min