electrons/positrons · 2005-08-11 · synchrotron oscillations and tune. electrons: synchrotron...
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�� � �� �� �� �� �� � � � � � � � ��
Protons:
• Transverse beam dynamics.
� Simple model of the proton.
� Spin dynamics.
� Depolarizing resonances.
� Siberian snakes.
� The real machines: RHIC and injectors.
Electrons/Positrons:
• Longitudinal beam dynamics.• Synchrotron oscillations and tune.• Electrons: Synchrotron radiation
� Radiative polarization.
� Quantum fluctuations ⇒ Spin Diffusion
� Polarization in some real e± machines.
� Measurements with polarized e± beams.
1 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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+ - ++ + +
+ ++++ - -
- - -
-- -
-
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Linac: ~F = q ~E(t). Ring with rf cavity
• Must maintain synchronism of bunch with rf phase.
• Particles oscillate in energy about the stable synchronous phase.
2 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Dipole magnets bend the beamaround the ring.
B
p
proton
q=+1
F
Bend magnet (dipole)
Field out of screen
Charged particles are deflected bymagnetic fields. Lorentz Force:
~F =q
γm~p× ~B
Quadrupole magnets focus thebeam for stability.
MagneticField
Protons moving into screen
S
N
N
S
Magnetic Lens (quadrupole)
Force
Vertically focusing
Horizontallydefocusing
3 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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H(X,PX , Y, PY , Z, PZ ; t) =
√
(~P − q ~A)2 +m2c4 + qφ
After a bunch of canonical transformations and φ = 0, ~A = (0, 0, As):
H(x, x′, y, y′, z, δp/p0; s) ' − q
p0
As −(
1 +x
ρ
)(
1 +δp
p0
− 1
2(x′2 + y′2) + · · ·
)
s= ρθρ
xz
y
Z
X
Y
Design trajectory coordinate systemLocal traveling
Fixed lab coordinatesystem
θ
ρ =p
qB⊥
x′ =dx
ds
y′ =dy
ds
Paraxial approx.: |x′|, |y′| � 1
4 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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x′′ + kx(s)x =δ
ρ(s),
y′′ + ky(s)y = 0,
with δ =δp
p0
.
For quadrupoles:
kx =q
p
∂By
∂x
ky = −qp
∂By
∂x
Harmonic oscillator with periodic spring constant.
Periodic conditions: kj(s+ L) = kj(s), ρ(s+ L) = ρ(s)
where L is length of periodic cell.
• Horizontal motion has inhomogeneous dispersion term.◦ Ignore it for now.
5 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Use Floquet’s (Block’s) Theorem ⇒Quasi-periodic solutions of form:
x(s) =√
Wβ(s) cos(ψ(s)), with
ψ′(s) =1
β(s).
Periodicity of β-function: β(s+ L) = β(s).
Note: In general ψ(s+ L) 6= ψ(s) + n2π. Resonances are bad!
x′(s) = −√
Wβ
(α cosψ + sinψ) ,
with α = − 12β′.
6 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Alternate focusing and defocusing lenses for stability.
Horizontal Betatron Oscillationwith tune: Qh = 6.3,
i.e., 6.3 oscillations per turn.
Vertical Betatron Oscillationwith tune: Qv = 7.5,
i.e., 7.5 oscillations per turn.
7 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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For a particular trajectory with initial conditions:
• Solve for sinψ and cosψ from equations for x and x′.
• Use sin2 ψ + cos2 ψ = 1 to get an invariant:
W =1
β
[
y2 + (αy + βy′)2]
(1)
• Functions of s: y(s), y′(s), β(s), α(s). (β and α are periodic.)
• Eq. (1) is the equation for an ellipse.• Area of ellipse = πW.
• Beam envelope: ±√
β(s)ε• πε is the rms emittance
8 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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• Most beams have a low enough density, so that we ignore hard collisionsbetween particles.• Thus we can use a 6d phase space rather than a 6N-d phase space.
• In the phase space of coordinates and their corresponding canonical mo-menta, the phase flow of the particle trajectories evolves so that the volumesof differential volume elements are preserved.• In other words, the Jacobian determinant is 1.
• Emittance is the area of the projection of the beam’s phase-space volumeonto a particular (xi, Pi) plane.
9 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Horizontal Betatron Oscillationwith tune: Qx = 3.28,tracked through 10 turnswith 8 periodic cells.
x
x’
Poincare plot of proton on suc-cessive turns for one location inthe ring.
10 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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.Energy =−
B
µ B
µ B
r
µx=dF Bdq v
µ= πr2
dFi
x
dj=dq v
Torque =
� Semiclassical model:• The spin ~S has a constant magnitude in the rest frame.• The magnetic moment ~µ ∝ ~S.
• ~µ has a constant magnitude in the rest frame.(Sort of like a loop of infinite inductance.)
11 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Bar magnet+ "proton"=
+ =+
+ Charge
N
SS
N
Gyroscope
MagneticDipoleSpin
Moment
++ +
Polarization: Average spin of the ensemble of protons.
~P =1
N
N∑
j=1
~S
|S|
12 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Energy-momentum tensor (a la Weinberg)
Tαβ(x) = T βα(x) =∑
n
pαnp
βn
Enδ3(x− xn(t))
For isolated system∂
∂xαTαβ = 0.
Define 4d analogue of ~r × ~p:
Mαβγ = xαT βγ − xβTαγ
Jαβ =
∫
M0αβd3x =
∫
xαT β0 − xβTα0d3x
Spin (intrinsic angular momentum):
Sα = 12cεαβγδJ
βγuδ, proper velocity: uδ = dxδ
dτ .
13 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
For a particle at rest with CM at rest at the origin:
J�µν :
0 0 0 00 0 S�
z −S�y
0 −S�z 0 S�
x
0 S�y −S�
x 0
, ( ~J� = ~S�)
Boost along z:
Jµν :
0 γβS�y −γβS�
x 0−γβS�
y 0 S�z −γS�
y
γβS�x −S�
z 0 γS�x
0 γS�y −γS�
x 0
, ⇒ ~J =
γS�x
γS�y
S�z
Sµ :
γβS�z
S�x
S�y
γS�z
, ⇒ ~S =
S�x
S�y
γS�z
, S0 = ~β · ~S
~J − ~S =
(γ − 1)S�x
(γ − 1)S�y
(1 − γ)S�z
14 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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~rCM × ~pCM = ( ~J − ~S)⊥
γβmc(−xCM y + yCM x) = (γ − 1)~S�⊥
γβmc(~xCM + ~yCM) = (γ − 1) z × ~S�⊥
~r⊥CM =γ
γ + 1
~β × ~S
mc
CM shifts to right.v=aω
CM at rest.S
FasterSlower
SBoost into screen
Center of charge wobbles: classical “Zitterbewegung”
15 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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1. Boost observer to left.2. Boost observer downward.3. Boost back to rest.
• Net rotation of rest frame.
Rest Sytem: SSytem: S'
Sytem: S'' Rest Sytem: S'''
Boost alonghorizontal (-y)
γ=2
Boo
st a
long
ver
tical
(-x
)
γ=2
63.43°
γ=4
Boo
st b
ack
36.87°
16 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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In the local rest frame of the proton, the spin precession of the proton obeysthe Thomas-Frenkel equation:
d~S�
dt=
q
γm~S� ×
[
(1 +Gγ) ~B⊥ + (1 +G) ~B‖ +
(
Gγ +γ
γ + 1
) ~E × ~v
c2
]
.
This is a mixed description: t, ~B, and ~E in the lab frame, but spin ~S� in localrest frame of the particle:
Proton: G =g − 2
2= 1.792847, 523.34 MeV/unit Gγ
Electron: a = G =g − 2
2= 0.001159652, 440.65 MeV/unit aγ
γ =Energy
mc2.
17 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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In the local rest frame of the proton, the spin precession of the proton obeysthe Thomas-Frenkel equation:
Torque :d~S�
dt=
q
γm~S� ×
[
(1 +Gγ) ~B⊥ + (1 +G) ~B‖]
TF
Force :d~p
dt=
q
γm~p × ~B⊥ Lorentz
(This is a mixed description: t, and ~B in the lab frame, but spin ~S� in local restframe of the proton.)
G =g − 2
2= 1.7928, γ =
Energy
mc2.
18 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Example with 6 precessions of spin in oneturn:
Gγ + 1 = 6.
Spin tune: number of precessions per turnrelative to beam’s direction.
So we subtract one:
νspin = Gγ ∝ energy,
i.e., 5 in this example.
19 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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misalignedquad
• A misaligned quadrupole creates a steering error which propagates throughthe lattice.
• For an accelerator ring, this shifts the closed orbit away from the designtrajectory.
• If the misalignment is vertical, then the design trajectory will have a periodicset of small vertical bends interspersed with the normal horizontal bends ofthe bending magnets.
• This leads to an integer resonance condition for the spin tune.
20 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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� � � � �� � �� � � � � �
x
y
zRz(90°) Rx(−90°)
1
2
3x
y
z
1
2
3
Rx(−90°) Rz(90°)
21 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Simple Resonance Condition:
νspin = N + NvQv,
(imperfection) (intrinsic)
where N and Nv are integers.
MagneticField
Protons moving into screen
S
N S
Magnetic Lens (quadrupole)Vertically focusing
NForce
22 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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0 + Qy
24 - Qy
12 + Qy
36 - Qy
24 + Qy 48 - Qy
36 + Qy
0 5 10 15 20 25 30 35 40 45 50
Gγ
0
0.01
0.02
0.03
Res
onan
ce S
tren
gth
AGS Intrinsic Resonances
23 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Adding a partial snake opens up stopbands around the integer imperfectionresonances.
At the snake the stable spin directionpoints along the snake’s rotation axiswhen Gγ = integer.
Partial snake strength: µπ
cosπνs = cos(Gγπ) cos µ2
46 47 4846
47
48 SnakeStrength
0%25%50%100%
Gγ
ν s
24 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Froissart—Stora Formula:
Pf
Pi
= 2 exp
(
−π|ε|2
2α
)
− 1.
Ramp rate: α = dGγdθ , (θ : 2π/turn.)
Resonance strength: ε =Fourier amplitude.
25 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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7.5 7.7 7.9 8.1 8.3 8.5 8.7 8.9 9.1 9.3 9.5Gγ
−1
−0.8
−0.6
−0.4
−0.2
0
0.2
0.4
0.6
0.8
1
Sy
0+ν, (Qx,Qy)=(8.7,8.8), (εx,εy)=(20,10)πwesting house
δ=0.0
Coupling res.νs=Qx
Intrinsic res.νs=Qy
Imperfection resonancesνs=N
7.5 7.7 7.9 8.1 8.3 8.5 8.7 8.9 9.1 9.3 9.5Gγ
−1
−0.8
−0.6
−0.4
−0.2
0
0.2
0.4
0.6
0.8
1
Sy
0+ν, (Qx,Qy)=(8.7,8.8), (εx,εy)=(20,10)πwesting house, w. 10mm coherence amplitude(Qm=0.215, ∆BL=18Gm)
δ=0.0, no coupling
AC dipole used to increase strengthof νs = Qy resonance.
(Simulations by Mei Bai)
26 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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12+Qy 36-Qy 24+Qy 48-Qy 36+Qy Extract
20 25 30 Gγ 35 40 45150 170 190 210 230 250 270 290 310 330 350 370 390 410 430 450
Scaled gauss clock counts
-0.015
-0.01
-0.005
0
0.005
0.01
AG
S R
aw A
sym
met
ry
AGS has 12 superperiods.Vertical betatron tune: 8.7Snake strength: 5%
(From Jeff Woods)
AC dipole pulses at resonances:• 0 +Qy
• 12 +Qy
• 36 −Qy
• 36 +Qy
27 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
28 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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0 100 200 300 400 500Gγ
0
0.2
0.4
0.6
0.8
1
1.2
intr
insi
c re
sona
nce
stre
ngth
pp rhicb.2001.twiss(10mβ*)
Qx = 28.236
Qy = 29.219
πεy = 10π µm
Will depolarize beamduring acceleration.
Solution: Snakes
29 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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• 2 snakes: spin is up in one half of the ring,and down in the other half.
• Spin tune: νspin = 12
(It’s energy independent.)
• “The unwanted precession which happensto the spin in one half of the ring is un-wound in the other half.” Unwinds
Winds
30 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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(Here I drop the “�” superscript on ~S.)
d~S
dt= ~W × ~S
H(~q, ~P , ~S; s) = Horb + Hspin
= Horb + ~W · ~S +O(h2)
Group symmetries:
• Orbital motion without spin: Sp(6,r).
• Spin by itself: SU(2, c) ∼= SO(3, r) (homomorphic).
• Full blown symmetry: Sp(6, r) ⊕ SU(2, c).• Spin dependence on orbit (Thomas-Frenkel).• Orbit dependence on spin (Stern-Gerlach Force)—Usually ignored.
31 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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SU(2) with usual spinor notation:
Pauli matrices: σx =
(
0 11 0
)
, σy =
(
0 −ii 0
)
, σz =
(
1 00 −1
)
.
Rn(θ) = ei n·~σ θ/2 =
(
cos θ2
+ inz sin θ2
(ny + inx) sin θ2
(−ny + inx) sin θ2
cos θ2− inz sin θ
2
)
.
SO(3) :Rn(θ) =I cos θ +
0 nz −ny
−nz 0 nx
ny −nx 0
sin θ
+
n2x nxny nxnz
nxny n2y nynz
nxnz nynz n2z
(1 − cos θ).
32 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Turn: j Turn: j+1
Closed orbit
Unclosed trajectory
• For the closed orbit: ~n0(s) = ~n0(s+ L),
with ~q0(s) = ~q0(s+ L) and ~P0(s) = ~P0(s+ L).
• For other locations in phase space: ~n(~q, ~P , s) = ~n(~q, ~P , s+ L),even though in general q(s+ L) 6= q(s) and P (s+ L) 6= P (s).
33 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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� �� � �� � �� �� � �
a: HERA-p / 8 snakes / 4 pi mm mrad / 800 GeV
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 -1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.8
1
00.10.20.30.40.50.60.70.80.9
1
n-vector at 1σ and 800 GeV
b: HERA-p / 8 snakes / 4 pi mm mrad / 802 GeV
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 -1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.8
1
00.10.20.30.40.50.60.70.80.9
1
n-vector at 1σ and 802 GeV
• Simulation with only vertical betatron motion.
• 802 GeV is closer to a resonance spin resonance than 800 GeV.
Des Barber et al.
34 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
�
� �� � �� � �� �� � �
a: HERA-p / 8 snakes / 64 pi mm mrad / 800 GeV
-1-0.5
00.5
1 -1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.8
1
-0.8-0.6-0.4-0.2
00.20.40.60.8
1
n-vector at 4σ and 800 GeV
b: HERA-p / 8 snakes / 64 pi mm mrad / 802 GeV
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 -1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.8
1
-1
-0.5
0
0.5
1
n-vector at 4σ and 802 GeV
• Larger amplitude oscillations have a larger tune shift due to nonlinear ele-ments.
• 802 GeV is closer to a resonance spin resonance than 800 GeV.
Des Barber et al.
35 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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Particles with largeramplitude betatronoscillations may expe-rience more precessionaway from the stablespin direction of thecenter of the beam
(Alfredo Luccio)
36 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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RHIC
AGSLINAC
BOOSTERSOURCE
LINAC: Linear AcceleratorAGS: Alternating Gradient SynchrotronRHIC: Relativistic Heavy Ion Collider
37 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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STARPHENIX
PHOBOS BRAHMS
PolarimetersHjet CNI
SnakesRotators
AC Dipole
RHIC
AGSLINAC
BOOSTERSOURCE
Solenoid Snake
Helical SnakeACDipole
Polarimeters
38 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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KEK OPPIS∗
upgraded at TRIUMF
70 → 80% Polarization
15 × 1011 protons/pulse
at source
6 × 1011 protons/pulse
at end of LINAC
∗Optically Pumped Polarized Ion Source
39 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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a) TRIUMF OPPIS b) ECR PROTON SOURCE
Fig. 1. 1) ECR Proton Source, 2) Superconducting Solenoid, 3) Optically-Pumped Rb Cell, 4) Deflection Plates, 5) SonaTransition Region, 6) Ionizer Cell, 7) Ionizer Solenoid, 8) Quartz Tube, 9) ECR Cavity, 10) Three Grid Extraction System, 11) Boron-Nitride End Cups, 12) Indium Seals.
Capture polarized
electron from
alkali atomoptically pumped
Transfer ofelectron-spinpolarization tonuclear-spinpolarization
(Sona transition)
Ionization
H - (p )(p )H 0H 0 (e )H +
protonsGenerate
40 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� ��
� � � �� �� � � � � � �
0 5 10Longitudinal position (m)
−5
−3
−1
1
3
5
B fi
eld
(T)
Fields through first Snake100 GeV proton
BxByBz
0 5 10Longitudinal Position (m)
−0.005
0
0.005
0.01
Tra
nsve
rse
Dis
plac
emen
t (m
)
Orbit Trajectories through Snake100 GeV proton
XY
0 5 10Longitudinal position (m)
−1
−0.5
0
0.5
1
Spi
n P
olar
izat
ion
Spin motion through one Snake100 GeV proton
SxSySz
02
46
s [m] 810
12-4
-2
0
2
4
-10
-5
0
5
10
41 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
y
x
sφsnake axis
µ
(beam)The rotation axis ofthe snake is φ, and µ isthe rotation angle.
Note that the φ con-tours shift slightlyfrom injection (red)at 25 GeV to storage(pink) at 250 GeV.
Rotation Angles for a Helical Snake-5
-4
-3
-2
-1
00 1 2 3 4 5
Bout [T]
Bin [T]
10
20
30
40 50 60 70 80 90100110120130140
150
160
170
190
180
-10
-20
-30
-40
-50
-60
-70
0 10 20 30 40 50 60 70 80
φ µ
42 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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43 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� � � �� �� � �ν yjM ,j 0 P ij
M ,j 1 P fjM ,j 2
eint = 0.5, εimp = 0.05, 2 Snakes, spin tune = 0.5
29.15 29.16 29.17 29.18 29.19 29.2 29.21 29.22 29.23 29.24 29.251
0.5
0
0.5
1
3/16
3/14
Pf
1/41/6
Vertical Betatron Tune
44 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� � � �� �� � � � � �
-5
-4
-3
-2
-1
0
1
2
3
4
5
0 2 4 6 8 10
B [
T]
s [m]
BxByBz
Magnetic Field24.3 GeV proton
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
0.02
0.025
0 2 4 6 8 10T
raje
ctor
y [m
]s [m]
xy
Beam Trajectory24.3 GeV proton
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 2 4 6 8 10
Spin
s [m]
SxSySz
Spin Components24.3 GeV proton
02
46
810
12 -10
-5
0
5
10
-4
-2
0
2
4
45 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� � � � � �� � �� � � �
-1-0.5
00.5
1
Sz
-1 -0.5 0 0.5 1
Sx
-1
-0.5
0
0.5
1Sy
E = 25 GeV
1.8 2.2 2.6 3.0 3.4 3.8B1 [T]
2.2
2.6
3.0
3.4
3.8
B2
[T]
γ
SPIN ROTATOR
25
75
3040
50
275
300
100 125
150
175
200
225
250
OH Fmap
-1-0.5
00.5
1
Sz
-1 -0.5 0 0.5 1
Sx
-1
-0.5
0
0.5
1Sy
E = 250 GeV
DX
Rotator D0
DX
D0 Rotator
46 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
µ
θRotat
or ax
is
y
s
x
Beam
The rotation axis ofthe spin rotator is inthe x-y plane at an an-gle θ from the vertical.The spin is rotated bythe angle µ around therotation axis. 0 0.5 1 1.5 2 2.5 3 3.5 4
B1 [T]
0
0.5
1
1.5
2
2.5
3
3.5
4
B2
[T]
µθ
−10°
−30°
−60°
−90°
−120°
−150° −180°
0°
−10°
−20°
−30°
−40°
30°
25
100
200
250
Rotation Angles for a Helical Spin Rotator
Note: Purple contour for rotation into horizontal plane.Black dots show settings for RHIC energies inincrements of 25 GeV from 25 to 250 GeV.
47 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� � � � �� � � � � � ��
x
y
z
Rotator’s spin vector at injection energy
x
y
z
Rotator’s spin vector at 250 GeV
48 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� � � � � �� � � � �� �� � � �
x
φ Spin −
Spin +
"Left−Right" Asymmetry(Tilted at 45 )
x
x
Schematic layout of PHENIX polarimetersYellow from left. Blue from right.
The PHENIX Local Polarimeter measures an asymmetry in small anglescattered neutrons which is proportional to transverse polarization.
ALR =
√L+R− −
√L−R+
√L+R− +
√L−R+
∝ Py
49 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
�� �� � � ��
Vertical polarizationwith rotators off.
Spin is down.
Rotators on
Spin is radially inwards!
OOPS!
Reverse all rotatorpower supplies and tryagain.
YES!
50 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� � � � � � � Gγ = 0 +Qy
Top: AC dipole pulse amplitude(current)
Bottom: Beam current.(Just scrapes the beam pipe.)
Top: Beam coherence
Bottom: Tune spectrum
51 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� � � � � �� � � � � � � �� � � � � � ��
• Radiated power:
Pγ =2
3remc
3 γ4β4
ρ2, re =
e2
4πε0mc2.
Radiation in forward direction with opening angle ∝ γ−1
• Energy loss per turn:
Uγ =
∮
Pγ
cds
• Critical energy: half the power is radiated by photons less than the criti-cal energy, and the other half, above.
uc = hωc =3hc
2ργ3
52 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
• Number of photons per second:
Nγ =
∫ Umax
0
nγ(uγ) duγ =5
2√
3
αc
ργ
here: α = 1/137)
• Number of photons per radian:
Nr =5α
2√
3γ
• Average photon energy and 2nd moment:
〈uγ〉 =1
Nγ
∫ Umax
0
unγ(u) du =8
15√
3uc ' 0.32uc
〈u2γ〉 =
1
Nγ
∫ Umax
0
u2nγ(u) du =11
27√
3u2
c ' 0.41u2c
53 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
• Energy spread: σu =√
Cq
Jsργ2mc2
with Cq = 3.8 × 10−8 m and Js ∼ 2 + D.
Ring Energy σu
[GeV] [MeV]CESR 5.5 3HERAe 27.5 3LEP 45 30LEP 60 53LEP 100 150
Remember: Integer resonances separated by only 440 MeV.
The polarization in LEP dropped down to nothing just above 60 GeV.
54 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
�� � � �� �� � � � � � �� � � �� � � � �� �
ωrf = hωrev
W = −U − Us
ωrf
dW
dt=
qV
2πh(sinφs − sinφ)
dϕ
dt' ω2
rfηph
β2UsW
dωrev
ωrev
=dβ
β− dL
L= ηph
dp
p
ϕs ϕs+2π
τ+|dτ|τ
τ−|dτ|
Vrf
ϕ=ωrft
ηph < 0 above transition energy.
Add in synchrotron oscillations to resonance condition:
νspin = N +NvQv +NhQh +NsyQsy
55 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
�� � � �� �� �� � �
Canonical cordinate: ϕ and conjugate momentum: W
a) ηtr > 0W
φπ−π φs
b) ηtr < 0W
φ2πφs
56 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
�� � � � �� � � � �� � �
In a homogenious magnetic field the transition rates are
W↑↓ =5√
3
16
e2γ5h
4πε0mec2|ρ|3(
1 +8
5√
3
)
W↑↓ =5√
3
16
e2γ5h
4πε0mec2|ρ|3(
1 − 8
5√
3
)
.
Evaluating the equilibrium polarization have (Sokolov Ternov)
PST =W↑↓ −W↓↑W↑↓ +W↓↑
=8
5√
3= 0.9238.
An unpolarized beam polarizes:
P (t) = PST [1 − exp(−t/τST)] ,
where the polarization rate is given by
τ−1ST
=5√
3
8
e2γ5h
4πε0m2ec
2
1
L
∮
ds
|ρ|3 .
57 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� � �� � � � � � � � � � � � �
Ring Particle Energy Nγ ∆U τST
W↑↓
frevNγ
[GeV] [/turn] [loss/turn]
CESR e± 5.5 700 −1 MeV 167 min 1 × 10−13
HERAe e± 27.5 3600 −83 MeV 23 min 1 × 10−12
LEP e± 45 5800 −120 MeV 300 min 2 × 10−13
LEP e± 60 7800 −380 MeV 81 min 8 × 10−13
RHIC p 100 7 −3 meV 3 × 1014 yr 6 × 10−29
RHIC p 250 18 −0.13 eV 3 × 1012 yr 2 × 10−27
HERAp p 920 65 −8.5 eV 1 × 1011 yr 3 × 10−26
Tevatron p 1000 70 −8.5 eV 2 × 1011 yr 2 × 10−26
SSC p 20000 1400 −0.12 MeV 7 × 107 yr 3 × 10−23
58 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� �� � � � � � � � �� �
uγ
θx pu
W
ϕ
In phase space quantum fluctuations cause instantaneous hops of momentumfrom one ellipse to another. (Hops in the Action.)
59 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
�� � �� � �� �� � �
Turn: j Turn: j+1
Closed orbit
Unclosed trajectory
• For the closed orbit: ~n0(s) = ~n0(s+ L),
with ~q0(s) = ~q0(s+ L) and ~P0(s) = ~P0(s+ L).
• For other locations in phase space: ~n(~q, ~P , s) = ~n(~q, ~P , s+ L),even though in general q(s+ L) 6= q(s) and P (s+ L) 6= P (s).
60 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� �� � � � � � �� � � �
Derbenev–Kondratenko formula for equilibrium polarization:
PDK =8
5√
3
∮
⟨
1|ρ|3 b ·
(
n− ∂n∂δ
)
⟩
sds
∮
⟨
1|ρ|3
[
1 − 29(n · s)2 + 11
18
(
∂n∂δ
)2]⟩
sds
1
τDK
=5√
3
8
reγ5h
me
1
L
∮
⟨
1|ρ|3
[
1 − 29(n · s) + 11
18
(
∂n∂δ
)2]⟩
sds
averaged over phase space at azimuth s.
δ = ∆p/p is the fractional momentum deviation from design.n is the invariant spin field.
b = s× ˙s| ˙s| is the direction of magnetic field if ~E = 0.
ρ is the cyclotron radius of the trajectory.L is circumference of synchrotron.
61 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
�� � �� �� � � � �
62 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
�� �� �� � � �� �
1τdep
' 5√
38
reγ5hme
1L
∮
⟨
1|ρ|3
(
∂n∂δ
)2⟩
sds
1
τpol
' 1
τST
+1
τdep
63 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� � �� � �� �� � �� � � � �
As an example from CESR (CUSB): MΥ = 9459.97 ± 0.11 ± 0.07 MeV
[Phys Rev D29, 2483 (1984)].
64 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� �� � � �
From Angelika Drees’ Thesis
65 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� �� � � �� � � �� � � � �� �
(Des Barber in “eRHIC Zeroth-Order Design Report)
66 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
�� �� �� � � �� �� � �
67 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
� � � � � � � � � �� � �� � � �
1. M. Conte and W. W. MacKay, An Introduction to the Physics of Particle
Accelerators, World Sci., (1991).
2. L. H. Thomas, Phil. Mag. S. 7, 3, 1 (1927).
3. M. H. L. Pryce, Proc. Royal Soc. of London, A195, 62 (1949).
4. S. Weinberg, Gravitation and Cosmology: Principles and Applications of
the General Theory of Relativity, John Wiley & Sons, (1972).
5. Misner, Thorne, and Wheeler, Gravitation, Freeman, San Francisco,(1973).
6. R. Gilmore, Lie Groups, Lie Algebras, and Some of Their Applications,John Wiley & Sons, (1974).
7. Ya. S. Derbenev and A. M. Kondratenko, JETP 37, 968 (1973).
8. Brian W. Montague, Phys. Rep., 113 (1984).
9. S. Y. Lee, Spin Dynamics and Snakes in Synchrotrons, World Sci., (1997).
10. K. Yokoya, DESY 86-057 (1986), and KEK Report 92-6 (1992).
11. D. P. Barber et al., DESY 98-096 (1998).
68 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
12. D. P. Barber, “Electrons are not protons”, EICA Workshop, BNL, UptonNY, BNL-52663 (Feb. 2002).
13. Y. Mori, “Present Status and Future Prospects of Optically Pumped Po-larized Ion Source”, AIP Conf. Proc. 293, 151 (1994).
14. A. N. Zelenski et al., Proc. of the 1995 Part. Accel. Conf. and Int. Conf.
on High-Energy Accel., Dallas, 864 (1996).
15. A.A. Sokolov and I.M. Ternov, Synchrotron Radiation, Pergamon Press(1968).
16. V.B. Berestetskii, E.M. Landau and L.P. Lifshitz, Quantum Electrodynam-
ics, Pergamon Press (1982). (Landau & Lifshitz Course on Theor. Phys.,Vol. 4)
17. W. W. MacKay et al., Phys. Rev. D29, 2483 (1984).
18. J. Johnson, “SPEAR Polarization” in Polarized Electron Acceleration and
Storage Workshop, DESY-M-82/09 (1982); S. R. Mane, Phys. Rev. A36,120 (1987).
19. W. W. MacKay et al., Phys. Rev. D29, 2483 (1984).
20. K. A. Drees, Thesis, WUB-DIS 97-5, Wuppertal (1997).
21. http://www.rhichome.bnl.gov/RHIC/Spin/
69 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
22. Eds. Farkhondeh and Ptitsyn, “eRHIC Zeroth-Order Design Report”, C-A/AP142 (2004).
70 �
QCDSP: Spin Dynamics in AcceleratorsWaldo MacKay 7 June, 2004
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