Thomas Jefferson National Accelerator Facility. Page 1. Concepts for ELIC- a High Luminosity. CEBAF based Electron-Light Ion Collider. Ya. Derbenev, B. Yunn ...
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
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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
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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 …
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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
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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
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ERL-based ELIC Design I on L i na c
and
pre-
boos ter
Electron Cooling
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
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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.
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A New Concept for ELIC Electron Cooling Snake
IR
30-150 GeV light ions
IR Snake
3-7 GeV electrons
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Polarized Electron Injection & Stacking J
Injector 3000 pulses 5μs
4ms*
1 mA
t J
Storage ring
t *4 ms is the radiation damping time at 7 GeV Thomas Jefferson National Accelerator Facility
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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
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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) …..
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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
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dipole
Achieving the Luminosity of ELIC Ni Ne L= f *2 b 4πσ 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 (ξi ~ 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 (σ
z
~ 5 mm)
• Very strong focus (β* ~ 5 mm) • Crab crossing Thomas Jefferson National Accelerator Facility
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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
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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
ERL
GeV GHz 1010 A MeV A 10-4 mm mm μm μm
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
-2
-1
cm s h
.015 7.7 4 24
Ring-Ring 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
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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
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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