Ion Polarization In
MEIC
Pavel Chevtsov
Review 09/2010
Page 1
Outline
• Ion Polarization Requirements
• Figure-8-based design
• Proton polarization schemes
• Longitudinal polarization at IP’s
• Transverse polarization at IP’s
• Deuteron polarization schemes
• Longitudinal polarization at IP
• Transverse deuteron polarization at IP’s
• Summary
Review 09/2010
Page 2
Ion Polarization Requirements
• High polarization degree of stored high-current ion
beams
• Ion polarization preservation during acceleration and
storage
• Capability to provide both longitudinal and transverse
proton polarization in both straights
• Capability to provide both longitudinal and transverse
deuteron polarization
• Ability to accommodate highly polarized 3He++ and
6Li+++ ion beams
Review 09/2010
Page 3
MEIC Layout
Prebooster
0.2 GeV/c  3-5 GeV/c
protons
Big booster
3-5 GeV/c  up to 20 GeV/c
protons
3 Figure-8 rings
stacked vertically
Review 09/2010
Page 4
Figure-8 Shape by Prof. Y. Derbenev
• Greatly simplifies task of ion polarization preservation
during acceleration and storage
• Any spin direction periodic
• Spin tune energy independent and equal to zero
aˆ  (2n   )
aˆ  2n  
x
Review 09/2010

P
s
2n    (2n   )  0
Page 5
Longitudinal Proton Polarization at IP’s
• Two longitudinal-axis Siberian snakes in the arcs
make polarization longitudinal in both straights
• Third longitudinal-axis Siberian snake in straight
stabilizes spin motion by making spin tune energy
independent and equal to 1/2

PII

PI
Review 09/2010
Page 6
Transverse Proton Polarization at IP’s
• Two Siberian snakes with horizontal perpendicular
spin rotation axes in the arcs
• Vertical polarization direction periodic
• Spin motion stable with spin tune equal 1/2

PII
90

PI

Review 09/2010
Page 7
Proton Siberian Snakes
• RHIC-type helical Siberian snakes (V. Ptitsin and
Y. Shatunov)
• Automatic orbit restoration
• Both spin rotation angle and spin rotation axis
controlled by adjusting currents of helical magnets

• Same snakes for longitudinal and transverse proton
polarization schemes, only currents adjusted
Review 09/2010
Page 8
Siberian Snake Parameters
• Fields of helical magnets for different proton energies
• Longitudinal polarization scheme (longitudinal spin rotation axis)
E (GeV)
20
30
40
Bouter
(T)
-2.13
-2.15
-2.16
50
60
100
150
-2.166 -2.173 -2.177 -2.184
Binner (T) 2.83
2.85
2.86
2.87
2.88
2.89
2.894
• Transverse polarization scheme (snake axes at 45 with the beam)
E (GeV)
Bouter
(T)
Binner (T)
20
30
40
50
60
100
150
-1.225 -1.236 -1.241 -1.244 -1.247 -1.251 -1.253
3.943
3.977
3.994
4.005
4.012
4.026
4.033
• Maximum horizontal/vertical orbit excursion for 20 GeV/c
protons is 15/32 mm
Review 09/2010
Page 9
Combined Proton Polarization Scheme
• Two Siberian-snake-type devices with their parameters
satisfying certain requirements (Prof. A. Kondratenko)
• Longitudinal polarization in one straight and vertical
polarization in the other straight for all energies
• Spin tune can be made 1/2 for stabilizing spin motion
Review 09/2010
Page 10
Longitudinal Deuteron Polarization
• In figure-8 geometry, stable spin orientation can be controlled by
magnetic inserts providing small spin rotation around certain
axis and shifting spin tune sufficiently away from 0
• Polarization is stable as long as additional spin rotation exceeds
perturbations of spin motion
• Polarization direction controlled in one of two straights
• Longitudinal polarization in a straight by inserting solenoid(s) in
that straight

PII
Solenoid
Review 09/2010

PI
Page 11
Transverse Deuteron Polarization
• Magnetic insert(s) in straight(s) rotating spin by relatively
small angle around
 vertical axis (Prof. A. Kondratenko)
PII
Insert

PI
• Insert implementation
 x  spin rotation in dipole
 y  spin rotation in solenoid
Δν   x y / (2 )  spin tune shift
|Δzmax ||  x | ( Lx  2 Ly ) / (4ν)
 orbit excursion
Review 09/2010
Page 12
Summary
•
Ion polarization requirements
•
•
•
•
•
•
•
Figure-8 design simplifies spin preservation and control by making any
direction periodic and spin tune energy independent and equal to zero
Proton polarization schemes
•
•
•
•
•
High polarization degree
Acceleration and storage without depolarization
Longitudinally and transversely polarized protons
Longitudinally and transversely polarized deuterons
Accommodating polarized 3He++ and 6Li+++ ions
Three longitudinal-axis helical Siberian snakes provide longitudinal polarization
in both straights
Two Siberian snakes with perpendicular axes provide vertical polarization in both
straights
Same helical snakes used for both schemes with only currents adjusted
Other polarization arrangements also available
Deuteron polarization schemes
•
•
Solenoid in a straight provides longitudinal polarization in that straight
Insertion rotating polarization around vertical axis (Prof. A. Kondratenko)
provides vertical polarization in both straights
Review 09/2010
Page 13