Transcript Document 7320894

SuperB Accelerator
& ILC
M. E. Biagini, LNF-INFN
for the SuperB Team
ILC GDE visit, LNF, Jan. 22th 2008
D. Alesini, M. E. Biagini, R. Boni, M. Boscolo, A. Drago, S. Guiducci, G. Mazzitelli, M.
Preger, P. Raimondi, S. Tomassini, C. Vaccarezza, M. Zobov (INFN/LNF, Italy)
K. Bertsche, Y. Cai, A. Fisher, S. Heifets, A. Novokhatski, M.T. Pivi, J. Seeman, M.
Sullivan, U. Wienands, W. Wittmer (SLAC, US)
T. Agoh, K. Ohmi, Y. Ohnishi (KEK, Japan)
I. Koop, S. Nikitin, E. Levichev, P. Piminov, D. Shatilov (BINP, Russia)
G. Bassi, A. Wolski (Cockcroft, UK)
M. Venturini (LBNL, US)
S. Bettoni (CERN, Switzerland)
Variola (LAL, France)
E. Paoloni, G. Marchiori (Pisa Univ., Italy)
SuperB: a 1036 cm-2 s-1 accelerator
SuperB is an international enterprise aiming at the
construction of a very high luminosity (1036 cm-2 s-1)
asymmetric e+e- Flavor Factory, with location at the
campus of the University of Rome Tor Vergata, near the
INFN Frascati National Laboratory
Aims:
 Very high luminosity
• Desire 1036: experimenters say 1035 will not get to the physics soon
enough.
 High reliability
• The goal is integrated luminosity!
 Polarized e- at IP
• This is a relatively new addition by the users.
 Ability to collide at Y4S and lower energy (~J/Psi)
• For maximum number of experimenters.
A Conceptual Design Report, signed by 85 Institutions was
published in March 2007 (arXiv:0709.0451 [hep-ex])
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Accelerator basic concepts (1)
B-Factories (PEP-II and KEKB) have reached high
luminosity (>1034 cm-2 s-1) but, to increase L of ~ 2 orders
of magnitude, bordeline parameters are needed such as:
 Very high currents
HOM in beam pipe
• overheating, instabilities, power costs
• detector backgrounds increase
 Very short bunches
RF voltage increases
• costs, instabilities
 Smaller damping times
Wiggler magnets
• costs, instabilities
 Crab cavities for head-on collision
• KEKB experience
Difficult and costly operation
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Accelerator
basic concepts
Basic concepts
(2) (2)
SuperB exploits an alternative approach,
with a new IP scheme:
 Small beams (ILC-DR like)
•
very low emittances, ILC-DR R&D
 Large Piwinsky angle and “crab waist” with a
pair of sextupoles/ring (F = tg(q)sz/sx)
•
interaction region geometry
 Currents comparable to present Factories
•
lower backgrounds, less HOM and instabilities
x
Requires a lot of fine machine tuning
Y
e+
q
2sz*q
Small collision area: sx/q
e-
2sx/q
z
2sz
4
2sx
A new idea for collisions
Thigher focus on beams at IP and a “large” crossing
angle (large Piwinski angle) + use a couple of
sextupoles/ring to “twist” the beam waist at the IP
Ultra-low emittance
Small collision area
Very small * at IP
Lower * is possible
Large crossing angle
NO parasitic crossings
“Crab Waist”
NO x-y-betatron
transformation
resonances
Already
proved at DAFNE
1. P.Raimondi, 2° SuperB Workshop, March 2006
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2. P.Raimondi, D.Shatilov, M.Zobov, physics/0702033
and...
Relatively easier to make small sx with respect to
short sz
Problem of parasitic collisions automatically
solved due to higher crossing angle and smaller
horizontal beam size
There is no need to increase excessively beam
current and to decrease the bunch length:
 Beam instabilities are less severe
 Manageable HOM heating
 No coherent synchrotron radiation of short bunches
 No excessive power consumption
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How it works
Crab sextupoles OFF: Waist line is orthogonal to the axis of other beam
All particles in both beams collide in the minimum y region,
with a net luminosity gain
Crab sextupoles ON: Waist moves parallel to the axis of other beam:
maximum particle density in the overlap between bunches
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Plots by E. Paoloni
Example of x-y resonance suppression
D.Shatilov’s (BINP), ICFA08 Workshop
Much higher luminosity!
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1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
0
0
0.2
0.4
0.6
0.8
Typical case (KEKB, DAFNE):
1
0
0.2
0.4
0.6
0.8
1
Crab Waist On:
1. low Piwinski angle F < 1
1. large Piwinski angle F >> 1
2. y comparable with sz
2. y comparable with sx/q
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Comparison of SuperB to Super-KEKB
IP beam distributions for KEKB
Parameter
Units
SuperB
Super-KEKB
Energy
GeV
4x7
3.5x8
1036/
cm2/s
1.0 to 2.0
0.5 to 0.8
A
1.9x1.9
9.4x4.1
y*
mm
0.22
3.
x*
cm
3.5x2.0
20.
Crossing
angle (full)
mrad
48.
30. to 0.
RF power
(AC line)
MW
20 to 25
80 to 90
Tune shifts
(x/y)
0.0004/0.2
0.27/0.3
Luminosity
Beam
currents
IP beam distributions for SuperB
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SuperB main features
Goal: maximize luminosity while keeping wall power low
2 rings (4x7 GeV) design: flexible but challenging
Ultra low emittance optics: 7x4 pm vertical emittance
Beam currents: comparable to present Factories
Crossing angle and “crab waist” used to maximize
luminosity and minimize beam size blow-up
Presently under test at DAFNE
No “emittance” wigglers used in Phase 1 (save in power)
Design based on recycling PEP-II hardware
(corresponds to a lot of money)
Longitudinal polarization for e- in the HER is included
(unique feature)
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Lattice overview (1)
The lattice for SuperB rings needs to comply with several
issues:





small emittances
asymmetric energies
insertion of a Final Focus (similar to ILC), with very small *
large dynamic aperture & long lifetimes
spin rotator section in HER
The new large crossing angle & small collision
parameters scheme with “crab waist” has relaxed the
requests on the bunch lengths and beam currents
Main objective is to design a lattice that can deliver
1x1036 luminosity while keeping wall power requirements
as low as possible
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Lattice overview (2)
First design was derived by ILC-DR OCS lattice
with TME cells and ILC-like Final Focus, but
shorter rings
Then a solution using the PEP-II hardware and
smaller intrinsic emittance (higher x-phase
advance in a cell) was designed
The present layout has small emittances (1.6
nm/4 pm (HER x/y) and 2.8 nm/7 pm (LER x/y))
and 20 msec longitudinal damping times without
insertion of wiggler magnets
However space is provided for wiggler
installations whenever needed (ex. luminosity
upgrade option)
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Ring optical functions

LER
No spin
rotator
here

HER
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SuperB design challenges
Beam beam
 high tune shift
 strong-strong simulations for large crossing angle
 effect of tolerances and component errors
Low emittance




tolerances
achieving vertical emittance
tuning and preserving
vibrations
IR design
 50 nm IP vertical beam size
 QD0 design
 luminosity backgrounds
Polarization




All topics are being
addressed
in the TDR
impact on lattice
depolarization time
impact on beam-beam
continous injection
Lattice
 dynamic aperture with crab sextupoles and spin rotator
 choice of good working point
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Low emittance tuning
VERY important in SuperB, since design ey is 7 and 4 pm
Contributions to ey come mainly from:







tilts in quadrupoles
misaligned sextupoles
vertical dispersion
beam coupling
IBS
trickle injection
beam instabilities
Computer modeling as well as diagnostics will help in
achieving and maintaining ey
This work has just started, luckily we can profit of work
performed for, and experience at, ATF, SLS, CESR-TA and
ILC-DR
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Low emittance tuning
Comparison of achieved beam emittances
Comparison of rings with similar beam energy
and ATF, SLS (* achieved)
E (GeV)
C (m)
Gamma
ex (nm)
gex (mm)
ey (pm)
gey(nm)
Spring-8
8
1430
15656
6
94
5
78
ILC-DR
5
6400
9785
1
10
2
20
Diamond*
3
561
5871
2.7
16
2
29
ATF*
1.28
138
2524
1
3
4
10
SLS*
2.4
288
4700
6
28
3.2
15
SuperB LER
4
1800
7828
2.8
22
7
55
SuperB HER
7
1800
13699
1.6
22
4
55
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Polarization
Polarization of one beam is included in SuperB
 Either energy beam could be the polarized one
 The LER would be less expensive, the HER easier
 HER was chosen
Longitudinal polarization times and short beam lifetimes indicate a
need to inject vertically polarized electrons.
 The plan is to use a polarized e- source similar to the SLAC SLC
source.
There are several possible IP spin rotators:
 Solenoids look better at present (vertical bends give unwanted vertical
emittance growth)
Expected longitudinal polarization at
IP ~ 87%(inj) x 97%(ring) =
85%(effective)
Polarization section implementation in
lattice is in progress
Half IR with spin rotator (Wienands, Wittmer)
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IP
Lattice layout: PEP-II magnets reuse
Total length 1800 m
Lmag (m)
0.45
5.4
PEP HER
-
194
PEP LER
194
-
Available
SBF HER
-
130
Needed
SBF LER
224
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SBF Total
224
148
Needed
30
0
Dipoles
Quads
280
m
Lmag (m)
0.25
0.5
PEP HER/LER
188
-
SBF Total
372
4
Needed
184
4
Sexts
Lmag (m)
0.56
0.73
0.43
0.7
0.4
PEP HER
202
82
-
-
-
PEP LER
-
-
353
-
-
SBF HER
165
108
-
2
2
SBF LER
88
108
165
2
2
SBF Total
253
216
165
4
4
Needed
51*
134
0
4
4
All PEP-II magnets can be used, dimensions and fields are in range
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RF requirements are met by the present PEP-II RF system
IR layout, siam twins QD0 (R&D)
M.Sullivan (SLAC)
QD0 is common to HER and LER, with
axis displaced toward incoming beams to
reduce synchrotron radiation fan on SVT
Dipolar component due to off-axis QD0
induces, as in all crossing angle
geometries, an over-bending of low
energy out coming particles eventually
hitting the pipe or detector
New QD0 design based on SC “helicaltype” windings
S. Bettoni (CERN), E. Paoloni (Pisa)
A pm QD0 design also in progress (SLAC)
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SuperB footprint on Tor Vergata site
SuperB rings
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Synergy with the ILC (1)
ILC-DR and SuperB will face similar demands on beam
quality and stability: SuperB for direct production of
luminosity, and ILC-DR for reliable tuning and operation of
the downstream systems, for luminosity production from
the extracted beams
There are significant similarities between SuperB storage
and ILC-DR parameters (see Table)
Beam energies and bunch lenghts are similar
ILC-DR have a circumference 3 times larger and smaller
nominal bunch charge. Nevertheless, one may expect the
beam dynamics to be in comparable regimes
Emittances are also similar (lower in ILC-DR), with similar
problems for tuning
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Comparison of parameters
for SuperB and ILC-DR
SuperB LER
SuperB HER
ILC-DR
Beam energy
4 GeV
7 GeV
5 GeV
Circumference
1800 m
1800 m
6695 m
Particles per bunch
5.51010
5.51010
21010
Number of bunches
1250
1250
2767
Average current
1.85 A
1.85 A
0.40 A
Horizontal emittance
2.7 nm
1.6 nm
0.8 nm
Vertical emittance
7 pm
4 pm
2 pm
Bunch length
5 mm
5 mm
6 mm
Energy spread
0.08%
0.058%
0.13%
3.210-4
3.810-4
210-4
Transverse damping time
40 ms
40 ms
25 ms
RF voltage
5 MV
8 MV
24 MV
476 MHz
476 MHz
650 MHz
Momentum compaction factor
RF frequency
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Synergy with the ILC (2)
Significant issues common to both SuperB and ILC
include:
 Alignment of magnets, and orbit and coupling correction
with the precision needed to produce vertical emittances of
just a few pico-meters on a routine basis
 Optimization of lattice design and tuning to ensure sufficient
dynamic aperture for good injection efficiency (for both) and
lifetime (particularly for SuperB LER), as well as control of
emittances
 Feedbacks (IP and rings)
 Control of beam instabilities, including electron cloud, ion
effects and CSR
 Reduction of magnet vibration to a minimum, to ensure
beam orbit stability at the level of a few microns
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An example: proposed new 3 Km DR layout
• Using the DCO lattice straights a shorter layout (half) has been designed
• SuperB-like arc cells used (large x-phase advance/cell) instead of FODO
• Lower emittance, same damping time, has been achieved
• Emittance tunable with x-phase advance/cell#1 Momentum compaction also
easily tunable from 1.4x10-4 to 2.7x10-4
ILC Damping Ring
0
-100
-200
-300
-400
-500
-600
-400
-200
0
200
400
600
800
LCWS08 Workshop, Fermilab, Dec. 2008
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Synergy with the ILC (3)
All these issues are presently active areas of
research and development for the ILC
Advantage could be taken whether the facilities
are constructed and commissioned sequentially,
or in parallel.
In general, the similarity of the proposed
operating regimes for the ILC-DR and SuperB
presents an opportunity for a well-coordinated
program of activities that could yield much
greater benefits than would be achieved by
separate, independent research and
development programs
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Conclusions
A Conceptual Design Report has been published in May
2007 and positively reviewed by an International Review
Committee, chaired by J. Dainton (UK)
A Machine Advisory Committee, chaired by J. Dorfan
(SLAC), has scrutinized the machine design in July 2008
endorsing the design approach
The next step will be to complete the Technical Design
Report by 2010 (SuperB Workshop in Paris, Feb. 15-18,
will be the starting time)
Synergy with the ILC accelerator R&D are many.
Collaboration started already on personal basis, it would
be good to strenghten it with official commitments from
both communities
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