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Triangle Universities Nuclear Laboratory
The Making and Using of
Spin-Polarized H and D Beams
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
Talk Outline
• What does it mean to polarize a beam?
• How do we polarize beams at TUNL?
• What are polarized beams used for?
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
Underlying Basic Physics
• Electrons and nucleons all have spin magnetic
moments.
– For electrons: me = eħ/2me
– For protons: mp = eħ/2mp
• Note that since me << mp, then me >> mp.
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
Underlying Basic Physics
• Like for simple magnets, electrons and proton
magnetic moments have orientations
in magnetic fields which
B-field
determine their

energy.
S
• Energy = - m . B
= -mBcos
July 26, 2001-TUNL REU
m
N
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
• Make H or D atom
• Polarize electron
• Polarize atomic nucleus
via hyperfine coupling
with its atomic electron
e d
Energy
• Ionize atom
Magnetic Field
July 26, 2001-TUNL REU
e p
Energy
Physics Processes Used
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
Polarize Atomic Electron
• Select atoms with electron spins aligned in
one direction in an external B-field.
e d
Energy
e p
Magnetic Field
July 26, 2001-TUNL REU
Magnetic Field
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
Polarize Atomic Nucleus for hydrogen
• Implement transitions to populate atomic
states with desired nuclear spin direction.
Intensity
p
+1/2
Pz = +0.602
-1/2
Bz (mTesla)
Polarization Spectrum Pz = (N - N ) / (N + N )
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
Polarize Atomic Nucleus for hydrogen
• Implement transitions to populate atomic
states with desired nuclear spin direction.
Intensity
p
Pz =-0.689
-1/2
+1/2
Bz (mTesla)
Polarization Spectrum Pz = (N - N ) / (N + N )
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
Polarize Atomic Nucleus for deuterium
• Implement transitions to populate atomic states
with desired nuclear spin direction.
d
+1 +1
00
Pz = 0.518
-1
Pzz = -0.034
• For deuterium one has both
Vector Polarization Pz = (N - N ) / (N + N + N )
Tensor Polarization Pzz = (3N -1) / (N + N
July 26, 2001-TUNL REU
+N)
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
Polarize Atomic Nucleus for deuterium
• Implement transitions to populate atomic states
with desired nuclear spin direction.
d
-1
0
+1
Pzz = 0.155
0
Pz = 0.073
-1
+1
July 26, 2001-TUNL REU
Pz = -0.554
Pzz = -1.352
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
• Make H or D atom
• Polarize electron
• Polarize atomic nucleus
via hyperfine coupling
with its atomic electron
e d
Energy
• Ionize atom
Magnetic Field
July 26, 2001-TUNL REU
e p
Energy
Physics Processes Used
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
TUNL Atomic Beam Polarized Ion Source
Acceleration &
Spin Precession Systems
Atomic Beam Systems
Ionizer Systems
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
TUNL Atomic Beam Polarized Ion Source
Acceleration &
Spin Precession Systems
Atomic Beam Systems
Ionizer Systems
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
Dissociate H2 or D2 to make H or D atoms
• Dissociate molecules to produce emerging jet of H (or D)
atoms traveling at ~1 km/sec along the source axis.
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
What Does it Mean to Polarize a Beam?
Polarize atomic electrons by sextupole
focusing
Electron spin-down
atoms defocused
Electron spin-up
atoms focused
• Resulting beam is polarized in electron spin.
• Multiple sextupoles efficiently focus a beam
with wide energy spread along the source axis.
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
How Do We Polarize Beams at TUNL?
Energy
Polarize atomic nuclei using RF transitions
B-Field
• Populations of coupled states 2 and 4 are inverted.
• Carefully designed RF electric and magnetic fields cause
precessing spins to invert their direction.
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
How Do We Polarize Beams at TUNL?
Ionize atoms by collisions with fast electrons
Electron Cyclotron Resonance (ECR) Ionizer
Solenoidal coils produce axial B-field
Polarized H
atoms enter
Microwave discharge produces
and accelerates electrons
H+ out
20 - 80 W of
3 GHz m-wave Power
• Polarized atoms are ionized by the process H + e --> H+ + 2e
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
How Do We Polarize Beams at TUNL?
Produce H-/D- by Cesium Charge Exchange
H+ in
H- out
Heated Cesium Reservoir
(260-300 deg.)
• When needed to make H- or D- ions, the H+ or D+
beam passes through a curtain of cesium vapor.
• Processes Used:
H+ + Cs  Ho(2S) + Cs+
Ho(2S) + Cs  H- + Cs+
July 26, 2001-TUNL REU
Triangle Universities Nuclear Laboratory
How Do We Polarize Beams at TUNL?
Accelerate Beam and Precess Spins
Accelerate and transport beams to
experimental target stations for
use in experiments.
• Deflect beam to target with bending magnets.
• Nuclear spins precess when beam is deflected.
• Pre-orient spins at the polarized ion source to
orient spin in desired direction at target after
deflection.
July 26, 2001-TUNL REU