ilc beam dynamic

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Freddy Poirier, 12/06/06, DESY student seminar.

ILC Beam Dynamic Freddy PoirierFLC / EUROTEV group

It is a project designed to smash together electrons and positrons at the center of mass energy of 0.5 TeV initially and 1 TeV later.

The ILC Global Design Effort team, established in 2005, has been making its accelerator design. Recently, it worked out the baseline configuration for the 30-km-long 500 GeV collider.

ILC= International Linear Collider

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Why a straight machine?• Synchrotron RadiationBending a particle = loosing some energy

E ~ (E4 /m4 R)

• From a cost point of view:

Rm,E

cost

Energy

CircularCollider

Linear Collider

At high energy,linear collider ismore cost effective

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Physics at the ILC (1)• Explore new Physics through high precision at

high energy• Study the properties of new particles (Cross-sections, BR’s,

Quantum numbers) ILC=microscope• Study known SM processes to look for tiny deviations

through virtual effects (needs precision of measurements and theoretical predictions)

– Precision measurements will allow:• Distinction of different physics scenarios• Extrapolation to higher energies

ILC=telescope

ILC will provide a detailed map of new physics

Exemple with e+/e- LEP experiment: Indirect determination ofthe top quark mass.Proves high energy reachthrough virtual processes

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Physics at ILC (2)• Comprehensive and

high precision coverage of energy range from Mz to ~ 1TeV

Physics Topics:Higgs MechanismSupersymmetryStrong Electroweak

Symmetry BreakingPrecision Measurements

at lower energies

cross sections few fb to few pb e.g. O(10,000) HZ/yr

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Luminosity• Parameters for the ILC from physics point of view:

– Ecms adjustable (90500GeV)– Luminosity int Ldt=500 fb-1 in 4 years– Ability to scan – Energy stability and precision below 0.1%– Polarisation of electrons (at least 80%)

To achieve high luminosity small sizes at the interaction point have to be achieved

What is needed to reach high luminosity?

Before going to the world of beam dynamic, let’s have a look at the ILC

Dyx

repb HfNn

L4

:Luminosity2

factort enhancemen beam-Beam

beam)(gaussian size Transverse

rate Repetition bunchper Particles

nbunch/trai ofNumber where

,

D

yx

rep

b

H

fNn

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Layout of the ILC

500 GeV

Upgraded energy (~1TeV)

Long straight sections (e-/e+)

Nominal:nm 5 ,500, yx

10 km~31 km

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Scheme of the ILC

Squeeze the beam as small as possible for High luminosity

5 nano m

Electron source

　 To produce electrons, light from a titanium-sapphire laser hit a target and knock out electrons. The laser emits 2-ns "flashes," each creating billions of electrons. An electric field "sucks" each bunch of particles into a 250-meter-long linear accelerator that speeds up the particles to 5 GeV.

Damping Ring for electron beam

In the 6-kilometer-long damping ring, the electron bunches traverse a wiggler leading to a more uniform, compact spatial distribution of particles.

Each bunch spends roughly 0.2 sec in the ring, making about 10,000 turns before being kicked out. Exiting the damping ring, the bunches are about 6 mm long and thinner than a human hair.

Main Linac

2 main linear accelerators, one for electrons and one for positrons, accelerate bunches of particles up to 250 GeV with 8000 superconducting cavities nestled within cryomodules. The modules use liquid helium to cool the cavities to - 2°K. Two ~10-km-long tunnel segments, house the two accelerators. An adjacent tunnel provides space for support instrumentation, allowing for the maintenance of equipment while the accelerator is running.

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Beam Dynamic

• Beam dynamic is the study of the evolution of the beam through the various sections:– Here we’ll look at the beam dynamic in the linear

accelerator section.• i.e. after the Bunch compressor and before the Beam

Delivery System (BDS)

– The accelerator section is part of the LET (Low Emittance Transport):

• The goal of game here is to accelerate the beam from 15 GeV up to 250 GeV (for center of mass energy of 500 GeV)

• Keep the emittance growth as low as possible

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Lattice• The lattice is a series of components (periodic arrangement) in the

beam line– It is constituted mainly of

• Magnets (quadrupoles, dipoles,…)• Accelerating cavities - SuperConducting Radio Frequency (SCRF)• Diagnostic Systems

– The most basic repetitive sequence of components is called a FODO cell (focusing and defocusing quadrupole interspaced with drift space)

1 FODO cell

Trajectory of an individual electron in the FODO lattice.•The magnetic lattice is periodic (2d)

•The pseudo-sinusoidal motion is referred to as the Betatron oscillation.

•The phase advance per FODO cell period is here µ=π.

x

QF QD

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Betatron Oscillation• Property of the focusing arrangement

phase advance variation

• The betatron oscillation are e.g. dependent on the strength of the quadrupole, (independently) for x and y:

y

x

Nominal focus. Quad. strength |k0|= 0.0524 m-2

Changed to |k1|= 0.0624 m-2

k0

k1

QD QF

)(/1)(' ss

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Motion• From the equation of motion (Hill’s equa.):

Where K(S) is the quadrupole strength and is periodic i.e. K(S)=K(S+2d) One can get the solution in the form (Floquet’s theorem):

0)('' xsKx

))(cos()( 0 ssx xx

Emittance: (initial condition)

Beta amplitude: periodic(dependant on focusing strength)

Initial phase

Phase advance (dependant on focusing strength)

And get the differentiate along the beam axis:

))(sin()( 0

ssds

dxxx

x

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Emittance• To talk to an accelerator physicist, talk in

phase-space diagram (x’ vs x):– 1 particle travelling along the linac will

describe in x’,x plane an ellipse (approx.)

– Now we are not dealing with 1 particle but with a bunch of them.

– At 1 location, x’,x plane:– All particles travelling will form an elliptical

surface on the plane.– The ellipse envelope is a characteristic of

the quality of the beam (it encompasses 95% particles). It is called the emittance .

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Beam Size• The Beam size is computed with

Luminosity is then defined (gaussian beam) by:

yxyxyx ,,,

D

yyxx

repb HfNn

L****

2

4

Defined by focussing arrangement at IP

Quality of the beam at IP and dependent of emittance prior to IP

The challenge with the (normalised) emittance is that along a transport line it can only get worse.

Dispersion not included

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Degradation of emittance

• In a linac the emittance will inevitably degrade due to:– Synchrotron Radiation– Collective effects

• Wakefields– Residual gas scattering– Accelerator errors:

• Beam mismatch (field errors)• Dispersion, x-y coupling

– Magnet alignment errors

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Wakefields• Passage of charged particle beams induce

electromagnetic field in RF cavities and other structures in accelerator.

• These wakefields act back on the beams and may cause instabilities– Long range Wakes: acts on following beam– Short range W: head of bunch acts on its tail

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Wakefields

• Bunch ‘current’ generates wake that decelerates trailing bunches.

• Bunch current generates transverse deflecting modes when bunches are not on cavity axis

• Fields build up resonantly: latter bunches are kicked transversely

tb

bunch

0 km 5 km 10 km

head

head

headtailtail

tail

accelerator axis

cavities

y

tail performsoscillation

Long range:

Short range:When bunch is offset wrt cavity axis, transverse (dipole) wake is excited.

Wt α a-3.5

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Effect of misalignment

Multibunch emittance growth for cavities with 500m RMS misalignment

The misalignements contribute largerly into the emittance growth along the linac.

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A challengeRMS random misalignments to produce 5%

vertical emittance growthBPM offsets 11 mRF cavity offsets 300 mRF cavity tilts 240 rad

• Impossible to achieve with conventional mechanical alignment and survey techniques

• Typical ‘installation’ tolerance: 300 m RMS– On BPM this would imply an emittance growth of

3800%• At Beginning of linac y=20 nm.rad• At IP y=~40 nm.rad

Beam Based Alignment is crucial

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Beam Based Alignment• Alignment performed on the beam using

the beam itself.• It involves steerers and BPM (measure beam centroid position)

• BACK to BASIC:

YjYi

Ki

gij 1. A particle arriving non centered on a quad will get a kick.

2. Betatron oscillation surimposed

3. Emittance grows

1

j

j ij i i ji

y g K Y Y

yj

Standard notation used: i.e. focusing for x, but defocusing of y

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A BBA solution? 1-to-1 steering

• To limitate the kick one could think of a solution:

simply apply one to one steering to orbit: i.e. at each BPM zeroing the orbit with a steerer such that the bunch centroid is in the central axis of the quad.

steererquad mover

dipole corrector

Assuming:

-A BPM adjacent to each quad,

-A ‘steerer at each quad

BPM

1-2-1 corrected orbit But BPM are offset wrt quad.

Dispersion are increased(Particle with different energy will undergo a different angle in electromagnetic field)

Emittance grows

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BBA - DFS

• Dispersion Free Steering (DFS)– Measure beam orbit (BPM) for a beam at E0– Measure beam orbit for beam(s) at other

energies– Find a set of steerer settings which minimise

the orbit difference. (for the case of curved linac: minimize wrt to the designed orbit difference)

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BBA (2)• An exemple of results for the BBA:

Good result for DFS technique.

- Benchmarking of the various DFS algorithm are being done

- Dynamic effect of ground motion not included

DFS lower emittance growth

Nor

mal

ized

em

ittan

ce (m

.rad)

DFS along linacWith 2 beams

No position jitter

Energy (GeV)

Transverse Quadrupole 300 µm Wrt to CM axis

Rotation Quadrupole 300 µrad

Transverse BPM Alignment error 200 µm CM

Transverse RF Structure 300 µm CM

Rotation RF Structure 300 µrad CM

Cryomodule Offset 200 µm Accel. Ref

BPM Resolution 5 µm (10 µm in TDR)

With jitter

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BBA(3)

• BBA when?– In general following a startup, or at regular

intervals (DFS for SLC: monthly basis)

– this process takes time; during which the machine is not integrating luminosity (TT)

– typically takes ~ 100 pulses per focusing magnet; with ~5 different energies.

– 300 magnets: ~ 2 hours per linac

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Measuring the Emittance

• Conventional (wire scanners) diagnostic: damaged

• Need for a non-invasive system

How to measure the emittance:

At Several (≥3) locations measure beam size emittance

It is foreseen to use laser-wires (finally focused laser) diagnotics system to perform emittance measurements.

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Laser-Wire Principle•Collision between electron and laser beam

•Detection of scattered photons

•Waist of laser < e- beam size

•Number of scattered photons depend on:

*Compton cross section

*Number of electrons / bunch

*Laser power and wavelength

*1/ interaction area

*relative position of laser and el. beam

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Laser-Wire at PETRA• Positron Electron Tandem Ring

Accelerator• Long free straight section• Easy installation of hardware due to

existing access pipe and hut outside tunnel area

• 1 IP

4.5 to 124.5 to 12~100~1003 to 203 to 201000 to 1001000 to 100100 to 10100 to 10

E/GeVE/GeVzz/ps/ps

nCnCxx//mm

yy//mm

EnergyEnergyBunch LengthBunch LengthCharge/bunchCharge/bunchHor. beam sizeHor. beam sizeVer. beam sizeVer. beam size

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Laser-Wire (2)

A new high power laser is being installed at PETRA will be used in 2006

2nd vertical plane at IP is in place for horizontal measurements

First vertical beam size measurements: 2003

2005: New vacuum chamber faster scan

m = (68 ± 3 ± 14) m

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2005 2006 2007 2008 2009 2010

Global　Design　Effort Project

Baseline configuration

Reference Design

ILC R&D Program

Technical Design

Expression of Interest to Host

International Linear Collider Timeline

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ILC Design

• Linear collider design is complex due to the interrelationships among the various parameters and the soft constraints on their values.

Bob　Palmer1990

Here was presented a snapshot of studies related to the ILC Beam Dynamic.

More is done at DESY on:

Damping Ring, Bunch Compressor, Failure mode, Vibrations,…

Check Beam Dynamic activities website at DESY.

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References

Picked up of lot of the plots, drawings, … from: • recent ILC school:

– http://www.linearcollider.org/school/

• Accelerator school:– USPAS 2003

• and other reference papers or conference:– Baseline Configuration Design (BCD) website:

http://www.linearcollider.org/wiki/doku.php?id=bcd:bcd_home

– Talks at Snowmass 2005

http://www.linearcollider.org/school/



http://www.linearcollider.org/wiki/doku.php?id=bcd:bcd_home

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More slides / bk-up

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Both frequency spectrum and spatial correlation important for LC performance

Ground motion spectra

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Bunch Compression• bunch length from ring ~ few mm• required at IP 100-300 mm

RF

z

E /E

z

E /E

z

E /E

z

E /E

z

E /E

dispersive section

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Wake Amplitude

NLC RDDS1 bunch spacing

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Test of Unification

Extrapolation of SUSY parameters from weak to GUT scale (e.g. within mSUGRA)

Gauge couplings unify at high energies,

Gaugino masses unify at same scale

Precision provided by ILC for sleptons, charginos and neutralinos will allow to test if masses unify at same scale as forces

Gluino　(LHC)

SUSY　partners　of　electroweak　bosons　and　Higgs

MSSM:　105　parameters:　some　from　LHC,　some　from　ILC

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Extra dimensions

measurement of cross sections at different energies allows to determine number and scale of extra dimensions

(500 fb-1 at 500 GeV,

1000 fb-1 at 800 GeV)

cross section for anomalous single photon production

Energy

　=　#　of　extra　dimensionse+e-　->　G

Emission of gravitons

into extra dimensions

Experimental signature:

single photons

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Precision Electroweak Tests

together with

ΔMW = 7 MeV(threshold scan)

and

ΔMtop = 100 MeV

high luminosity running at the Z-poleGiga Z (109 Z/year) ≈ 1000 x “LEP” in 3 months with e- and e+ polarisation

ΔsinΘW = 0.000013

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ilc beam dynamic

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