Transcript [Enter Presentation Name Here]

Concepts for ELIC- a High Luminosity
CEBAF based Electron-Light Ion Collider
Ya. Derbenev, B. Yunn, A. Bogacz, G. A. Krafft, L. Merminga, Y. Zhang
Center for Advanced Studies of Accelerators
XX-th Russian Accelerator Conference
BINP, Novosibirsk
September 10-14 , 2006
Thomas Jefferson National Accelerator Facility
Page 1
Outline
 Nuclear Physics Motivation / Requirements
 ELIC: An Electron-Light Ion Collider at CEBAF
 Achieving the Luminosity of ELIC
 Achieving Polarization in ELIC
 ELIC Parameters
 Advantages/Features of the ELIC Design
 R&D Required
 Summary
Thomas Jefferson National Accelerator Facility
Page 2
Nuclear Physics Motivation
 A high luminosity polarized electron – light ion collider
has been proposed as a powerful new microscope to
probe the partonic structure of matter.
 Over the past two decades we have learned a great
amount about the hadronic structure.
 Some crucial questions remain open …
Thomas Jefferson National Accelerator Facility
Page 3
CEBAF II/ELIC Upgrade - Science
Science addressed by the
second Upgrade:
• How do quarks and gluons
provide the binding and
spin of the nucleons?
• How do quarks and gluons
evolve into hadrons?
• How does nuclear binding
originate from quarks and
gluons?
From A. W. Thomas at NSAC
LRP implementation review
(2005)
Thomas Jefferson National Accelerator Facility
Page 4
Nuclear Physics Requirements
 The features of the facility necessary to address these questions:
• Center-of-mass energy between 20 GeV and 65 GeV
with energy asymmetry of ~10, which yields
Ee ~ 3 GeV on Ei ~ 30 GeV up to Ee ~ 7 GeV on Ei ~ 150 GeV
• CW Luminosity from 1033 to 1035 cm-2 sec-1
• Longitudinal polarization of both beams in the interaction
region  50% –80% required for the study of generalized parton
distributions and transversity
• Transverse polarization of ions extremely desirable
• Spin-flip of both beams extremely desirable
Thomas Jefferson National Accelerator Facility
Page 5
ERL-based ELIC Design
IR
IR Solenoid
IR
3-7
3 -7 GeV electrons
Snake
30--150
30
150 GeV light ions
Electron Injector
CEBAF with Energy Recovery
Beam Dump
Thomas Jefferson National Accelerator Facility
Page 6
Challenges of ERL-based ELIC
 Polarized electron current of 10’s of mA is required for ERL-based
ELIC with circulator ring. Present state of art ~0.3 mA.
 A fast kicker with sub-nanosecond rise/fall time is required to fill the
circulator ring. Present state of art is ~10 nsecs.
 Substantial upgrades of CEBAF and the CHL (beyond the 12 GeV
Upgrade) are required. Integration with the 12 GeV CEBAF accelerator
is challenging.
 Exclusion of physics experiments with positron beam.
 Electron cooling of the high energy ion beam is required.
Thomas Jefferson National Accelerator Facility
Page 7
A New Concept for ELIC
Electron Cooling
Snake
IR
30-150 GeV light ions
IR
Snake
3-7 GeV electrons
Thomas Jefferson National Accelerator Facility
Page 8
Polarized Electron Injection & Stacking
J
Injector
3000 pulses
5s
4ms*
1 mA
t
J
Storage ring
t
*4 ms is the radiation damping time at 7 GeV
Thomas Jefferson National Accelerator Facility
Page 9
Ion Complex
“Figure-8” boosters and storage rings
• Zero spin tune avoids spin resonances.
• No spin rotators required around the IR.
• Ensure longitudinal polarization for deuterons at 2 IP’s
simultaneously, at all energies.
Ion Collider Ring
Collider Ring
spin
Source
Source
200 MeV
CCL
DTL
RFQLinac
120 keV 3 MeV 50 MeV 200 MeV Pre-Booster
Pre-Booster
3 GeV/c
3 GeV/cm
C~75-100
C~75-100 m
Ion
Large
Booster 20 GeV
Large
Booster
(Electron
(CR)Storage Ring)
20 GeV
Thomas Jefferson National Accelerator Facility
Page 10
Positrons!
Generation of positrons:
(based on CESR experience)
 Electron beam at 200 MeV yields unpolarized positron
accumulation of ~100mA/min
 ½ hr to accumulate 3 A of positron current
Possible applications:
 e+i colliding beams (longitudinally polarized)
 e+e- colliding beams (longitudinally polarized up to 7x7 GeV)
 …..
Thomas Jefferson National Accelerator Facility
Page 11
Positron Production at CEBAF injector
Transverse
emittance
filter
10 MeV
5 MeV e+
Longitudinal
emittance filter
converter
epolarized
source
e-
15 MeV
dipole
e-
e-
e+
e+
115 MeV
ee+
dipole
eunpolarized
source
15 MeV
During positron production:
- polarized source is off
- dipoles are turned on
Thomas Jefferson National Accelerator Facility
Page 12
dipole
Achieving the Luminosity of ELIC
Ni N e
L
f
*2 b
4
For 150 GeV protons on 7 GeV electrons, L~ 7.7 x 1034 cm-2 sec-1
compatible with realistic Interaction Region design.
Beam Physics Issues
 Beam – beam interaction between electron and ion beams
(i ~ 0.01 per IP; 0.025 is presently utilized in Tevatron)
 High energy electron cooling
 Interaction Region
• High bunch collision frequency (f = 1.5 GHz)
• Short ion bunches (
z
~ 5 mm)
• Very strong focus (* ~ 5 mm)
• Crab crossing
Thomas Jefferson National Accelerator Facility
Page 13
3 THE ELIC LUMINOSITY CONCEPT
The concept of ELIC luminosity has been established based on
considerations of the beam-beam, space charge, IBS and EC
1. EC in cooperation with bunching SRF resonators provides very short
ion bunches (5 mm or less ), thus design a correspondently short betastar
2. Reduction of transverse emittance by EC allows one to increase
extension beam in the final focusing magnet, hence, reach a lower
beta-star
3. Short bunches make it possible implementation of the crab-crossing
colliding beams that allows one to eliminate parasitic beam-beam
interactions
4. Reduction of charge/bunch increases beam stability against
microwave interaction (electron cloud, in particular)
5. Large synchrotron tune ( exceeding beam-beam tune shift) eliminates
the synchro-betatron non-linear resonances in beam-beam interaction
6. Flat beams (at fixed beam area) reduce IBS rate against EC
7. Equidistant fraction phase advance between four IPs of ELIC
normalizes the critical beam-beam tune shift to one IP
Thomas Jefferson National Accelerator Facility
Page 14
ELIC Parameters
Parameter
Beam energy
Bunch collision rate
Number of particles/bunch
Beam current
Cooling beam energy
Cooling beam current
Energy spread, rms
Bunch length, rms
Beta-star
Horizontal emittance, norm
Vertical emittance, norm
Beam-beam tune shift
(vertical) per IP
Laslett tune shift (p-beam)
Luminosity per IP, 1034
Number of interaction points
Core & luminosity IBS lifetime
Unit
GeV
GHz
1010
A
MeV
A
10-4
mm
mm
m
m
-2
-1
cm s
h
Ring-Ring
ERL
150/7
1.5
.4/1.0
1/2.4
75
2
3/3
5/5
5/5
1/86
.04/3.4
.01/.086
.015
7.7
4
24
150/7
100/5
30/3
.4/1.0
1/2.4
75
2
.4/1.1
1/2.7
50
2
.12/1.7
.3/4.1
15
.6
1/86
.04/3.4
.01/.086
.7/70
.06/6
.01/.073
.2/43
.2/43
.01/.007
.015
7.7
.03
5.6
.06
.8
24
24
 24
Thomas Jefferson National Accelerator Facility
Page 15
Stacking polarized proton beam over space charge
limit in pre-booster
To minimize the space charge impact on transverse emittance, the circular painting
technique can be used at stacking. Such technique was originally proposed for
stacking proton beam in SNS [7]. In this concept, optics of booster ring is designed
strong coupled in order to realize circular (rotating) betatron eigen modes of two
opposite helicities. During injection, only one of two circular modes is filled with the
injected beam. This mode grows in size (emittance) while the other mode is not
changed. The beam sizes after stacking, hence, tune shifts for both modes are
then determined by the radius of the filled mode. Thus, reduction of tune shift by a
factor of k (at a given accumulated current) will be paid by increase of the 4D
emittance by the same factor, but not k2.
Circular painting principle: transverse
velocity of injected beam is in correlation
with vortex of a circular mode at stripping
foil
Stacking proton beam in pre-booster
over space charge limit:
1 – painting resonators
2, 3 – beam raster resonators
4 – focusing triplet
5 – stripping foil
Thomas Jefferson National Accelerator Facility
Page 16
Overcoming space charge at stacking
Stacking parameters
Unit
Value
Beam energy
MeV
200
H- current
mA
2
Transverse emittance in linac
μm
.3
Beta-function at foil
cm
4
Focal parameter
m
1
Beam size at foil before/after stacking
mm
.1/.7
Beam radius in focusing magnet after stacking
cm
2.5
Beam raster radius at foil
cm
1
Increase of foil temperature
oK
<100
Proton beam in pre-booster after stacking
2 x1012
Accumulated number of protons
Increase of transverse temperature by scattering
%
10
Small/large circular emittance value
μm
.3/15
Regular beam size around the ring
cm
1
Space charge tune shift of a coasting beam
.02
This reduction of the 4D emittance growth at stacking 1-3 Amps of
light ions is critical for effective use of electron cooling in collider ring.
Thomas Jefferson National Accelerator Facility
Page 17
Electron Cooling
 Beam cooling required to suppress IBS and reduce
emittances
 Bunch length shortening particularly important
 EC for RHIC
• 55 MeV ERL at 100 mA electron beam
• Use of an SRF gun
• R&D in progress
 EC for ELIC
• 75 MeV at 2A electron beam
• Use circulator ring with 100 revolutions
• Staged cooling
Thomas Jefferson National Accelerator Facility
Page 18
ELIC Interaction Region Concept
Crab
cavity
m
44m
Crab
cavity
spin
i
2m
focusing
triplet
spin tune
solenoid
e
cross
bend
focusing
doublet
detector
α
80 MV
cross
bend
focusing
triplet
focusing
doublet
Crab
cavity
0.1 rad
0.1
rad
Crab
spin tune cavity
solenoid
Focal Points
Thomas Jefferson National Accelerator Facility
Page 19
i
Crab Crossing
Short bunches make Crab Crossing feasible.
SRF deflectors at 1.5 GHz can be used to create a proper bunch tilt.
SRF dipole
F
Final lens
F
Parasitic collisions are avoided without loss of luminosity.
Thomas Jefferson National Accelerator Facility
Page 20
Polarization of Ions
Protons and 3He
Deuterons
collision
collision
pointpoint
collision
collision
pointpoint
Snake
collision
collision
pointpoint
collision
collision
pointpoint
P, He3d
Protons and 3He:Two IP’s (along straight section) with simultaneous
longitudinal polarization with no snakes.
Two ease snakes in arcs are required to ensure longitudinal polarization
at 4 IP’s simultaneously.
Deuterons: Two IP’s with simultaneous longitudinal polarization with no
snakes (can be switched between two cross-straights).
Solenoid (or ease snake for p and He) to stabilize spin near longitudinal
direction for all species.
Thomas Jefferson National Accelerator Facility
Page 21
Polarization of Electrons
spin
rotator
spin rotator
with 90º
solenoid snake
collision
point
collision
point
collision
point
collision
point
spin
rotator
spin
rotator
spin rotator
with 90º
solenoid snake
spin
rotator
Spin injected vertical in arcs (using Wien filter).
Self-polarization in arcs to maintain injected polarization.
Spin rotators matched with the cross bends of IPs.
Thomas Jefferson National Accelerator Facility
Page 22
Electron Spin Matching at the IR
spin
spin rotator
spin rotator
spin tune
solenoid
Spin tune
solenoid
e
e
collision point
collision point
i
i
90º
90º
spin tune
solenoid
spin tune
solenoid
snake solenoid
Rotation of spin from vertical in arcs to longitudinal at IP:
- Beam crossing bend causing energy-dependent spin
rotation, together with
- Energy-independent orbit spin rotators [two SC solenoids
with bend in the middle] in the arc and after the arc.
Thomas Jefferson National Accelerator Facility
Page 23
e- Polarization Parameters
Parameter
Energy
Beam cross bend at IP
Radiation damping time
Accumulation time
Self-polarization time*
Equilibrium polarization, max**
Beam run time
Unit
GeV
mrad
ms
s
h
%
h
3
70
50
15
20
92
5
7
12
3.6
10
91.5
Lifetime
4
1
2
90
*One e-folding. Time can be shortened using high field wigglers.
**Ideal max equilibrium polarization is 92.4%. Degradation is due
to radiation in spin rotators.
Thomas Jefferson National Accelerator Facility
Page 24
Features of RR ELIC
 JLab DC polarized electron gun already meets beam current
requirements for filling the storage ring.
 A conventional kicker already in use in many storage rings would be
sufficient.
 The 12 GeV CEBAF accelerator can serve as an injector to the ring. RF
power upgrade might be required later depending on the performance
of ring.
 Physics experiments with polarized positron beam are possible.
 Possibilities for e+e-, e-e-, e+e+ colliding beams.
 No spin sensitivity to energy and optics.
 No orbit change with energy despite spin rotation.
 Collider operation appears compatible with simultaneous 12 GeV
CEBAF operation for fixed target program.
Thomas Jefferson National Accelerator Facility
Page 25
R&D Required for Ring-Ring ELIC
 High energy electron cooling of protons/ions
(collective stability…)
 Beam dynamics issues with crab crossing
 Ion space charge at stacking in pre-booster
 Beam-beam interactions (large synchrotron tune;
4 IPs)
Thomas Jefferson National Accelerator Facility
Page 26
Summary
 A compelling scientific case is developing for a high luminosity,
polarized electron-light ion collider, to address fundamental
questions in hadron Physics.
 JLab design studies have led to an approach that promises
luminosities up to nearly 1035 cm-2 sec-1, for electron-light ion
collisions at a center-of-mass energy between 20 and 65 GeV.
 A fundamentally new approach has led to a design that can be
realized on the JLab site using CEBAF as a full energy injector into
an electron storage ring and can be integrated with the 12 GeV
fixed target program for physics.
 This ring-ring design requires significantly less technological
development compared to the ERL-based design, for the same
luminosity level.
 Planned R&D will address open readiness issues.
Thomas Jefferson National Accelerator Facility
Page 27