Transcript R&D Issues for Formation of MEIC Ion Beams

Issues for Formation of MEIC Ion Beam
Ya. Derbenev
MEIC Ion Complex Design Mini-Workshop
JLab, January 27-28, 2011
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
OutlIne
•
•
Concept of high luminosity
Required parameters, concepts and problems of :
- High energy EC for EIC
-Synchronization for EC-
- Beam emittance injected in collider ring (required)
- Luminosity lifetime (due to IBS and other)
- Crab Crossing
- Acceleration/rebunching in collider ring
- Synchronization for collisions- Emittance vs space charge at stacking
- Beam loss at re-bunching
- Microwave beam stability (wakes in SRF cavities and other)
- Electron cloud
- Gaps
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
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Luminosity in colliders with Electron Cooling
EC in cooperation with strong HF SC field allows one to obtain:
•Very short ion bunches (1cm or even shorter)
•Small transverse emittances
Decrease the bunch length  design low beta-star
Decrease transverse emittances  design low beta-star
Raise the beam-beam tune shift limit: large Qs (exceeding bb tune shift)
Raise repetition rate by arrangement for crab crossing to eliminate the
parasitic bb
-Crab crossing is effective at HF- matches short bunches !
Decrease charge/bunch- receive MW stability, reduce IBS
Diminish the IBS using flat beams (non-coupled optics)
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
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Forming the ion beam
Main issues:
•Initial cooling time
•Bunch charge & spacing
General recommendations:
•Prevent the emittance increase at beam transport (introducing a fast feedback)
•Use staged cooling
•Start cooling at possibly lowest energy
•Use the continuous cooling during acceleration in collider ring, if necessary
Beam bunching, cooling and ramp agenda:
•After stacking in collider ring, the beam under cooling can be re-bunched by high
frequency SC resonators, then re-injected for coalescence (if needed), more
cooling and final acceleration & cooling
•The final focus could be switched on during the energy ramp, keeping the Qvalues constant
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
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Lifetime due to Intrabeam Scattering

IBS heating mechanism: Energy exchange at intra-beam collisions leads to xemittance increase due to energy-orbit coupling, and y-emittance increase due
to x-y coupling

Electron cooling is introduced to suppress beam blow up due to IBS, and
maintain emittances near limits determined by beam-beam interaction.

Since L 1/ xy , reduction of transverse coupling while conserving beam area,
would result in decrease of impact of IBS on luminosity

Electron cooling then leads to a flat equilibrium with aspect ratio of 100:1.

Touschek effect: IBS at large momentum transfer (single scattering) drives
particles out of the core, limiting luminosity lifetime.

A phenomenological model which includes single scattering and cooling time of
the scattered particles has been used to estimate an optimum set of
parameters for maximum luminosity, at a given luminosity lifetime.
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
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High Energy Electron Cooling
ERL/CR based staged EC in collider ring
solenoid
Initial
cooling
ion bunch
electron
bunch
Electron
circulator
ring
Cooling section
Fast beam
kicker
Circulator ring by-pass
Fast beam
kicker
Momentum
Beam current
Particle/bunch
Bunch length
energy
recovery path
SRF
Linac
electron
injector
Path length
adjustment
dump
ERL based circulator electron cooler
Energy spread
Hori. Emit.
norm.
Vert. emtt. norm.
Laslett tune shift
Cooling length
Cooling time
IBS growth time
(longitudinal)
GeV/MeV 12/6.6
A
0.6/3
1010
0.7/3.8
200/20
mm
0
-4
10
5/1
Colliding
mode
60/33
0.6/3
0.7/3.8
60/33
0.6/3
0.7/3.8
10/30
5/15
5/1
3/1
mm
4
1
0.56
mm
4
0.002
15
92
1
0.006
15
162
0.11
0.1
15
0.2
m
s
s
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
After
bunching
0.9
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Feasibility of High Energy Electron Cooling
Advances on electron beam
SRF energy recovering linac (ERL)
•Removes the linac power show-stopper
•Allows for two stages cooling or even cooling while accelerating
•Allows for fast varying the e-beam parameters and optics when optimizing the
cooling in real time
•Delivers a low longitudinal emittance of e-beam
Electron circulator-cooling ring
•Eases drastically the high current and energy exposition issues of
electron source and ERL
Beam transport with discontinuous solenoid
•Solves the problem of combining the magnetized beam transport (necessary
for efficient EC) with effective acceleration
Beam adapters
•Allows one to flatten the e-beam area in order to reach the optimum cooling effect
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
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Beam-beam kicker for EC
Design parameters for beam-beam kicker
A schematic of beam-beam fast kicker
Kicker beam is not accelerated after the DC gun
Both beams are flat in the kick section
Flat beams can be obtained from magnetized
sources (grid operated).
•Kicker beam is maintained in solenoid. It can be
flatten by imposing constant quadrupole field
•Flat cooling beam is obtained applying round-toflat beam adapters
Circulating beam energy
MeV
33
Kicking beam energy
MeV
~0.3
Kicking frequency
MHz
5 – 15
Kicking angle
mrad
0.2
Kicking bunch length
cm
15 – 50
Kicking bunch width
Cm
0.5
Kicking bunch charge
nC
2
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
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Synchronization for EC
i
i
Cooling section
arc
arc
Fast kicker
Fast kicker
Injector 5 MeVx25
mA
ERL 75 MeV
Dumper 125
KWt
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
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Crab Crossing
R. Palmer 1988, general idea
Short bunches make feasible the Crab Crossing
SRF deflectors 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
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Page 10
Crab Crossing for EIC
• Short bunches also make feasible the Crab Crossing:
• SRF deflectors 1.5 GHz can be used to create a proper bunch tilt
E  100 GeV
 cr  2 f  2 t
eB l
t  t t
E
F

F 3 m
2
  20 cm
Bt  600 G
 cr  0.1
(1.5 GHz
 t  5  10 4
(  20 MV / m )
lt  4 m
 f  1 mm
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
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Preliminary IP layout for ion beam
CCB with inserted SRF for bunching and dispersive crabbing
•
• Dipoles bending the beam in addition to arcs
Inserted SRF resonators are sufficient for required
bunching and dispersive crabbing
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
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