Transcript EXPERIMENTAL FACILITIES OVERVIEW

ANKA Seminar
CLIC
Ultra-low emittance for the
CLIC damping rings using
super-conducting wigglers
Yannis PAPAPHILIPPOU
October 8th, 2007
Outline
CLIC
 Overview of the CLIC Project
 CLIC damping rings design








M. Korostelev
(PhD thesis, EPFL 2006)
Design goals and challenges
Energy
Lattice choice and optics optimisation
Circumference
Wiggler design and parameter scan
Final emittances including Intra-beam scattering
Chromaticity correction and dynamic aperture
Low emittance tuning in the presence of coupling
 Summary and open issues
08/10/2007
ANKA Seminar, Y. Papaphilippou
2
CLIC



Compact Linear Collider : multi-TeV
electron-positron collider for high energy
physics beyond today's particle accelerators
Center-of-mass energy from 0.5 to 3 TeV
RF gradient and frequencies are very high


100 MV/m in room temperature accelerating
structures at 12 GHz
Two-beam-acceleration concept


The CLIC Project
High current “drive” beam, decelerated in
special power extraction structures (PETS) ,
generates RF power for main beam.
Challenges:






Efficient generation of drive beam
PETS generating the required power
12 GHz RF structures for the required gradient
Generation/preservation of small emittance
beam
Focusing to nanometer beam size
Precise alignment of the different components
08/10/2007
ANKA Seminar, Y. Papaphilippou
3
Injector complex
CLIC
 30 m
e- Main Linac
12 GHz, 100 MV/m, 21 km
12 GHz, 100 MV/m, 21 km
e+ BC2
9 GeV
Booster Linac
6.6 GeV
12 GHz
2.3 GV
 10 m
e+ DR
2.424 GeV
DC gun
Unpolarized e-
Primary beam
Linac for e2 GeV
1.5 GHz
 150 m
e+ BC1
3 GHz
 360 m
12 GHz
2.3 GV
Base line
configuration
 10 m
3 GHz
162 MV
e- PDR
e+ PDR
Pre-injector
Linac for e+
200 MeV
1.5 GHz
 15 m
BC2
3 TeV
3 GHz
162 MV
e-/e+
Target
e-
48 km maximum
e- BC1
Injector Linac
2.2 GeV
2.424 GeV
360 m
 30 m
e+ Main Linac
e- DR
2.424 GeV
360 m
2.424 GeV
L. Rinolfi
1.5 GHz
 150 m
Pre-injector Laser
Linac for e200 MeV
1.5 GHz
 15 m
DC gun
Polarized e-
4
Damping ring design goals
CLIC

Ultra-low emittance and high beam
polarisation impossible to be
produced by conventional particle
source:


Intra-beam scattering due to high
bunch current blows-up the beam



Ring to damp the beam size to desired
values through synchrotron radiation
Equilibrium “IBS dominated” emittance
should be reached fast to match collider
high repetition rate
Other collective effects (e.g. e-cloud) may increase beam losses
Starting parameter dictated by design
criteria of the collider (e.g.
luminosity), injected beam
characteristics or compatibility with
the downstream system parameters
(e.g. bunch compressors)
PARAMETER
NLC
CLIC
bunch population (109)
7.5
4.1
bunch spacing [ns]
1.4
0.5
number of bunches/train
192
316
3
1
120
50
Extracted hor. normalized emittance [nm]
2370
<680
Extracted ver. normalized emittance [nm]
<30
< 20
10890
<5000
Injected hor. normalized emittance [μm]
150
63
Injected ver. normalized emittance [μm]
150
1.5
13.18
1240
number of trains
Repetition rate [Hz]
Extracted long. normalized emittance [eV m]
Injected long. normalized emittance [keV m]
Ring energy



Advantages of higher energy

E = E0 (n + 1/2)/
6
For same equilibrium emittance
i.e. smaller circumference and
radiated power (cost), high
momentum compaction
(longitudinal stability).

7
For fixed damping fraction due
to wigglers and wiggler peak
field,
5
Energy [GeV]

CLIC
Choice dictated by spin tune
(half integer) for maintaining
high-spin polarisation
Frozen on early design stage
Advantage of lower energies:
4
ILC DR
3
CLIC DR
2
NLC DR
1
0
0
i.e. easier magnetic design
(lower main field) and smaller
total wiggler length
08/10/2007
ANKA Seminar, Y. Papaphilippou
5
10
15
n
6
Lattice choice
CLIC
 Usually racetrack configuration
with Theoretical Minimum
Emittance (TME) arcs and
damping wigglers in the straights
 NLC DR was based on lattice with
32 TME arc cells and wigglers of
62m total length (A. Wolski et al. 2003)
 ILC has a large ring of more than
6km for accepting large number
of bunches with reduced e-cloud
effect
 TME and FODO lattice
considered (A. Wolski et al. 2007)
08/10/2007
7
CLIC damping ring layout
CLIC
08/10/2007
ANKA Seminar, Y. Papaphilippou
8
CLIC





TME arc cell
TME cell chosen for
compactness and efficient
emittance minimisation
over Multiple Bend
Structures (or achromats)
used in light sources
Large phase advance
necessary to achieve
optimum equilibrium
emittance
Very low dispersion
Strong sextupoles needed
to correct chromaticity
Impact in dynamic
aperture
Phase advance choice




CLIC
Optimum horizontal phase
advance of cells for
minimising zero current
emittance is fixed (284o for
TME cells)
Vertical phase advance is
almost a free parameter
First iteration based on
lattice considerations, i.e.
comfortable beta functions
and relaxed quadrupole
strengths and chromaticity
Low horizontal phase
advance gives increased
momentum compaction
factor (high dispersion) but
also chromaticity
08/10/2007
ANKA Seminar, Y. Papaphilippou
10
CLIC
Phase advance with IBS




08/10/2007
Horizontal phase advance for minimum
horizontal emittance with IBS, is found in an
area of small horizontal beta and moderate
dispersion functions (between 1.2-1.3π, for
CLIC damping rings)
Optimal vertical phase advance quite low (0.2π)
The lowest longitudinal emittance is achieved for
high horizontal and low vertical phase advances
The optimal point has to be compromised due
to chromaticity considerations and dynamic
aperture optimisation
ANKA Seminar, Y. Papaphilippou
11
Circumference
CLIC




Usually chosen big enough to
accommodate number of bunches
Drift space increase essential for
establishing realistic lattice, reserving
enough space for instrumentation and
other equipment
For constant number of dipoles (TME
cells), zero equilibrium emittance is
independent of circumference
Normalised emittance with IBS increases
with circumference (no wigglers)
When dipole lengths increase with drifts,
emittance grows due to increase of damping
time (inversely proportional to radiation
integral I2 which decreases with length)
 When only drifts increase, smaller emittance
growth due to increase of optics functions
 Impact on chromaticity + dynamic aperture
Drifts + dipoles
Only Drifts


Drifts + dipoles
Only Drifts
Compensation may be achieved due to
increase of bunch length with
circumference (momentum compaction)
08/10/2007
ANKA Seminar, Y. Papaphilippou
12
Damping wigglers
CLIC




Damping wigglers are used to increase radiation
damping and reduce the effect of IBS in order to
reach target emittances
The total length of wigglers is chosen by its
dependence with the peak wiggler field and
relative damping factor
Damping factor increases for higher fields and
longer wiggler occupied straight section
Relative momentum spread is independent of
total length but increases with wiggler field
08/10/2007
ANKA Seminar, Y. Papaphilippou
13
Wigglers effect in emittance
CLIC




For fixed value of wiggler period, equilibrium emittance minimum for
particular value of wiggler field
By reducing total length, optimal values necessitate higher fields and
lower wiggler periods
Optimum values change when IBS included, necessitating higher
fields
Damping rings cannot reach 450nm with normal conducting wigglers
08/10/2007
ANKA Seminar, Y. Papaphilippou
14
Wigglers’ effect with IBS
CLIC

BINP PM
wiggler

BINP SC
wiggler
ANKA SC
wiggler

The choice of the wiggler parameters
is finally dictated by their
technological feasibility.


Normal conducting wiggler of 1.7T can
be extrapolated by existing designs
Super-conducting options have to
designed, built and tested
For higher wiggler field and
smaller period the transverse
emittance computed with IBS
gets smaller
The longitudinal emittance has a
different optimum but it can be
controlled with the RF voltage
The choice of the wiggler
parameters is finally dictated by
their technological feasibility
Wiggler prototypes

CLIC
Two wiggler prototypes






Parameters
2.5Τ, 5cm period, built by BINP
2.7Τ, 2.1cm period, built by ANKA
Aperture reduced for the more
challenging design
Current density can be increased
by using different conductor type
Short version to be installed and
tested at ANKA (energy of
2.5GeV)
Lifetime of 8-10h for lower gap,
enough for the beam tests
08/10/2007
BINP ANKA
Bpeak [T]
2.5
2.7
λW [mm]
50
21
Beam aperture full height
[mm]
12
5
NbTi
NbSn3
4.2
4.2
Conductor type
Operating temperature [K]
ANKA Seminar, Y. Papaphilippou
16
RF voltage and frequency
CLIC


The smallest transverse emittance is achieved for the lowest RF frequency and
higher voltage, while keeping the longitudinal emittance below 5000 eV.m
Reversely the longitudinal emittance is increased for small RF frequency
08/10/2007
ANKA Seminar, Y. Papaphilippou
17
Wiggler FODO cell
CLIC

Average horizontal β function should be
small enough for the wiggler period not to
exceed the value producing efficient
damping

FODO cell structure chosen with phase
advances close to 90o giving average β’s of
around 4m and reasonable chromaticity
Quad strength adjusted to cancel wiggler
induced tune-shift

18
Non-linear dynamics
CLIC

Two sextupole schemes considered



Two families / 9 families of sextupoles
Dynamic aperture is 9σx in the
horizontal and 14σy in the vertical
plane (comfortable for injection)
Wiggler effect should be included
and optimised during the design
phase
Coupling correction





CLIC
Coupling effect of wigglers should be
included in simulations
Correction with dispersion free steering
(orbit and dispersion correction)
Skew quadrupole correctors for correcting
dispersion in the arc and emittance
minimisation
Iteration of dynamic aperture evaluation
and optimisation after correction
In CLIC damping rings, the effect of
vertical dispersion is dominant (0.1% of
coupling and 0.25μm of dispersion
invariant)
20
5
500
4
400
3
Vertical
approx.
Horizontal
approx.
300
2
200
1
100
0
0
0
2
4
6
8
Horizontal emittance [nm]
600
Longitudinal emittance [keV.m]
CLIC
6
Vertical emittance [nm]
Bunch charge
5.5
5
4.5
4
3.5
3
3
Bunch charge [109]
3.5
4
Vertical emittance [nm]
 Approximate scaling laws can be derived for a given damping ring design
 For example, for the CLIC damping rings, the horizontal
normalized emittance scales approximately as
 The above relationship is even more exact when the longitudinal emittance is kept constant
(around 5000 eV.m, in the case of the CLIC damping rings)
 Vertical and longitudinal emittance are weakly dependent on bunch charge, and almost linear with
each other
08/10/2007
ANKA Seminar, Y. Papaphilippou
21
Damping rings’ parameters
CLIC
 2005: original
ring
 2006a: superconducting
wiggler
considered
 2006b: vertical
dispersion
included
 2007a: 12GHz
structure
 2007b: reduced
bunch
population
 2007c:
CLIC_G
structure
08/10/2007
ANKA
CLICSeminar,
PWG Y. Y.
Papaphilippou
Papaphilippou
22
Concluding remarks
CLIC

Robust design of the CLIC damping rings,
delivering target emittance with the help of superconducting wigglers
 Prototype

to be built and tested in ANKA
Areas needing further optimisation
 Pre-damping
ring optics design
 Collective effects including electron cloud
 Realistic cell length and magnet design
 Sextupole optimisation and non-linear dynamics
including wiggler field errors
08/10/2007
ANKA Seminar, Y. Papaphilippou
23