Transcript Slide 1

Freddy Poirier, 12/06/06, DESY student seminar.
ILC Beam Dynamic
Freddy Poirier
FLC / EUROTEV group
ILC= International
Linear Collider
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.
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Freddy Poirier, 12/06/06, DESY student seminar.
Why a straight machine?
• Synchrotron Radiation
Bending a particle = loosing some energy
DE ~ (E4 /m4 R)
m,E
R
cost
• From a cost point of view:
Circular
Collider
Linear Collider
Energy
At high energy,
linear collider is
more cost effective
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Freddy Poirier, 12/06/06, DESY student seminar.
Physics at the ILC (1)
• Explore new Physics through high precision at
high energy
Exemple with e+/e- LEP
• Study the properties of new particles
(Cross-sections,
BR’s,
experiment:
Indirect
determination of
Quantum numbers) ILC=microscope
the top quark mass.
• Study known SM processes to look
for tiny
Proves
highdeviations
energy reach
through virtual effects (needs precision
measurements
throughofvirtual
processes 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
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Freddy Poirier, 12/06/06, DESY student seminar.
Physics at ILC (2)
• Comprehensive and
high precision
coverage of energy
range from Mz to ~
1TeV
Physics Topics:
Higgs Mechanism
Supersymmetry
Strong Electroweak
Symmetry Breaking
Precision Measurements
at lower energies
cross sections few fb to few pb
 e.g. O(10,000) HZ/yr
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Freddy Poirier, 12/06/06, DESY student seminar.
Luminosity
•
Parameters for the ILC from physics point of view:
–
–
–
–
–
Ecms adjustable (90500GeV)
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
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Luminosity: L 
nb N f rep
4 x y
HD
where
nb  Number of bunch/t rain
N  P art iclesper bunch
f rep  Repet it ionrat e
 x , y  T ransversesize (gaussian beam)
H D  Beam - beam enhancement fact or
What is needed to reach high luminosity?
Before going to the world of beam dynamic, let’s have a look at the ILC
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Freddy Poirier, 12/06/06, DESY student seminar.
Layout of the ILC
Long straight
sections (e-/e+)
500 GeV
10 km
~31 km
Upgraded
energy
(~1TeV)
Nominal:
 x, y  500, 5 nm
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Freddy Poirier, 12/06/06, DESY student seminar.
Scheme Electron
of the
sourceILC
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
Damping Ring for electron beam
electrons. An electric field "sucks" each
In
the 6-kilometer-long
ring, the
bunch
of particles into adamping
250-meter-long
electron
bunches traverse
a wiggler
leading
linear accelerator
that speeds
up the
toparticles
a more uniform,
to 5 GeV.compact spatial
distribution of particles.
Each bunch spends roughly 0.2 sec in the
ring, making about 10,000 turns before being
Main Linac
kicked out. Exiting the damping ring, the
2 main linear accelerators, one for
electrons
one6for
positrons,
bunches
areand
about
mm
long and thinner
accelerate bunches of particles up than
to 250
GeV
with
8000
5 nano m
a human hair.
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
the beamallowing
as small
asmaintenance
possibleof
space forSqueeze
support instrumentation,
for the
7
equipment while the accelerator
is running.
for High
luminosity
Freddy Poirier, 12/06/06, DESY student seminar.
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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Freddy Poirier, 12/06/06, DESY student seminar.
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)
x
QF
QD
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
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µ=π.
1 FODO cell
Freddy Poirier, 12/06/06, DESY student seminar.
Betatron Oscillation
• Property of the focusing arrangement
 ' (s)  1 /  (s) phase advance variation
• The betatron oscillation are e.g. dependent on the strength
of the quadrupole, (independently) for x and y:
Nominal focus. Quad.
strength |k0|= 0.0524 m-2
Changed to |k1|= 0.0624 m-2
x
y
k0
k1
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QD
QF
Freddy Poirier, 12/06/06, DESY student seminar.
Motion
• From the equation of motion (Hill’s equa.):
x' ' K ( s) x  0
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):
Initial phase
x   x  x (s) cos( (s)  0 )
Phase advance (dependant on
focusing strength)
Emittance: 
Beta amplitude: , periodic
(initial condition)
(dependant on focusing strength)
And get the differentiate along the beam axis:
x 
x
dx

sin( ( s)  0 )
ds
 x ( s)
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Freddy Poirier, 12/06/06, DESY student seminar.
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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Freddy Poirier, 12/06/06, DESY student seminar.
Beam Size
• The Beam size is computed with
 x, y   x, y  x, y
Dispersion not included
Luminosity is then defined (gaussian beam) by:
L
nb N 2 f rep
4  x*  x*  *y  y*
Quality of the beam at IP
and dependent of emittance
prior to IP
HD
Defined by focussing
arrangement at IP
The challenge with the (normalised) emittance is that along
a transport line it can only get worse.
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Freddy Poirier, 12/06/06, DESY student seminar.
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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Freddy Poirier, 12/06/06, DESY student seminar.
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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Freddy Poirier, 12/06/06, DESY student seminar.
Wakefields
Dtb
Long range:
• 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
cavities
tail performs
oscillation
bunch
Short range:
When bunch is offset wrt
cavity axis, transverse
(dipole) wake is excited.
Wt α a-3.5
accelerator axis
tail
head
Dy
tail
head
head
tail
0 km
5 km
10 km
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Freddy Poirier, 12/06/06, DESY student seminar.
Effect of misalignment
Multibunch
emittance growth for
cavities with 500mm
RMS misalignment
The misalignements contribute largerly into the emittance
growth along the linac.
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Freddy Poirier, 12/06/06, DESY student seminar.
A challenge
RMS random misalignments to produce 5%
vertical emittance growth
BPM offsets
RF cavity offsets
RF cavity tilts
11 mm
300 mm
240 mrad
• Impossible to achieve with conventional
mechanical alignment and survey techniques
• Typical ‘installation’ tolerance: 300 mm RMS
– On BPM this would imply an emittance growth of
3800%
• At Beginning of linac gy=20 nm.rad
• At IP gy=~40 nm.rad
Beam Based Alignment is crucial
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Freddy Poirier, 12/06/06, DESY student seminar.
Beam Based Alignment
• Alignment performed on the beam using
the beam itself.
• It involves steerers and BPM
• BACK to BASIC:
(measure beam centroid position)
gij
Yi
1. A particle arriving
non centered on a
quad will get a kick.
2. Betatron oscillation
surimposed
Yj
yj
Ki
 j

y j    gij KiYi   Y j
 i 1

3. Emittance grows
Standard notation used: i.e. focusing for
x, but defocusing of y
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Freddy Poirier, 12/06/06, DESY student seminar.
A BBA solution? 1-to-1 steering
Assuming:
-A BPM adjacent to each quad,
-A ‘steerer at each quad
quad mover
steerer
dipole corrector
• 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.
But BPM are offset wrt quad.
1-2-1 corrected orbit
BPM
Dispersion are increased
(Particle with different energy will
undergo a different angle in
electromagnetic field)
 Emittance grows
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Freddy Poirier, 12/06/06, DESY student seminar.
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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Freddy Poirier, 12/06/06, DESY student seminar.
BBA (2)
• An exemple of results for the BBA:
DFS  lower emittance growth
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)
DFS along linac
Good result for DFS technique.
- Benchmarking of the various
DFS algorithm are being done
- Dynamic effect of ground
motion not included
Normalized emittance (m.rad)
With 2 beams
With jitter
No position jitter
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Energy (GeV)
Freddy Poirier, 12/06/06, DESY student seminar.
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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Freddy Poirier, 12/06/06, DESY student seminar.
Measuring the Emittance
How to measure the emittance:
At Several (≥3) locations measure
beam size  emittance
• Conventional (wire scanners)
diagnostic: damaged
• Need for a non-invasive system
It is foreseen to use laserwires (finally focused laser)
diagnotics system to
perform emittance
measurements.
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Freddy Poirier, 12/06/06, DESY student seminar.
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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Freddy Poirier, 12/06/06, DESY student seminar.
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
Energy
Bunch Length
Charge/bunch
Hor. beam size
Ver. beam size
E/GeV
z/ps
nC
x/mm
y/mm
4.5 to 12
~100
3 to 20
1000 to 100
100 to 10
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Freddy Poirier, 12/06/06, DESY student seminar.
Laser-Wire (2)
First vertical beam size
measurements: 2003
2005: New vacuum
chamber faster scan
m = (68 ± 3 ± 14) m m
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
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Freddy Poirier, 12/06/06, DESY student seminar.
International Linear Collider Timeline
2005
2006
2007
2008
2009
2010
Global Design Effort
Project
Baseline configuration
Reference Design
Technical Design
ILC R&D Program
Expression of Interest to Host
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Freddy Poirier, 12/06/06, DESY student seminar.
ILC Design
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.
• Linear collider design
is complex due to the
interrelationships
among the various
parameters and the
soft constraints on
their values.
Bob Palmer
1990 29
Freddy Poirier, 12/06/06, DESY student seminar.
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
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Freddy Poirier, 12/06/06, DESY student seminar.
More slides / bk-up
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Freddy Poirier, 12/06/06, DESY student seminar.
Ground motion spectra
Both frequency
spectrum and
spatial
correlation
important for
LC performance
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Freddy Poirier, 12/06/06, DESY student seminar.
Bunch Compression
• bunch length from ring ~ few mm
• required at IP 100-300 mm
DE/E
DE/E
z
RF
DE/E
z
DE/E
z
DE/E
z
z
dispersive section
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Freddy Poirier, 12/06/06, DESY student seminar.
Wake Amplitude
NLC RDDS1
bunch spacing
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Freddy Poirier, 12/06/06, DESY student seminar.
Test of Unification
MSSM:
105 parameters: some from LHC,
some from ILC
Gluino (LHC)
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
SUSY partners of
electroweak bosons and Higgs
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Freddy Poirier, 12/06/06, DESY student seminar.
Extra dimensions
cross section for anomalous single
photon production
d = # of extra dimensions
e+e- -> gG
Emission of
gravitons
into extra
dimensions
Experimental
signature:
single
photons
measurement of cross
sections at different energies
allows to determine number
and scale of extra dimensions
(500 fb-1 at 500 GeV,
Energy
1000 fb-1 at 800 GeV)
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Freddy Poirier, 12/06/06, DESY student seminar.
Precision Electroweak Tests
 high luminosity running at the Z-pole
Giga Z (109 Z/year) ≈ 1000 x “LEP” in 3 months
with e- and e+ polarisation
ΔsinΘW = 0.000013
together with
ΔMW = 7 MeV
(threshold scan)
and
ΔMtop = 100 MeV
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Freddy Poirier, 12/06/06, DESY student seminar.
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