triangle universities nuclear laboratory july 26, 2001-tunl reu the making and using of...

July 26, 2001-TUNL REU

Triangle Universities Nuclear Laboratory

The Making and Using of

Spin-Polarized H and D Beams



Talk Outline

• What does it mean to polarize a beam?

• How do we polarize beams at TUNL?

• What are polarized beams used for?



What Does it Mean to Polarize a Beam?

Underlying Basic Physics• Electrons and nucleons all have spin magnetic

moments.– For electrons: eeħ/2me

– For protons: peħ/2mp

• Note that since me << mp, then e >> p.



Underlying Basic Physics• Like for simple magnets, electrons and proton

magnetic moments have orientations in magnetic fields which determine their energy.

• Energy = - . B = -Bcos

NS

B-field




Physics Processes Used

• Make H or D atom

• Polarize electron

• Polarize atomic nucleus via hyperfine coupling with its atomic electron

• Ionize atomE

ner

gy

e p

Magnetic Field

Ener

gy

e d





Polarize Atomic Electron

• Select atoms with electron spins aligned in one direction in an external B-field.

e d

Magnetic FieldMagnetic Field

En

ergy

e p




P o la r i z e A t o m ic N u c le u s -f o r h y d r o g e n

• I m p le m e n t t r a n s i t i o n s t o p o p u la t e a to m ic s t a t e s w i th d e s i r e d n u c l e a r s p in d i r e c t i o n .

p

P o la r i z a t io n S p e c t r u m P z = ( N - N ) / ( N + N )

Inte

nsit

y

B z ( m T e s l a )

+ 1 /2

- 1 /2

P z = + 0 .6 0 2



Bz (mTesla)

Inte

nsit

y

Polarize Atomic Nucleus -for hydrogen

• Implement transitions to populate atomic states with desired nuclear spin direction.

p

Polarization Spectrum Pz = (N - N ) / (N + N )

+1/2

-1/2Pz =-0.689






• For deuterium one has both

Polarize Atomic Nucleus -for deuterium

+1 0

-1

d

Pz = 0.518

Pzz = -0.034

Vector Polarization Pz = (N - N ) / (N + N + N )

Tensor Polarization Pzz = (3N -1) / (N + N + N )

+1 0

-1




Polarize Atomic Nucleus -for deuterium


d

-10

+1

Pz = -0.554

Pzz = 0.155

Pz = 0.073

Pzz = -1.352

0

-1+1



Physics Processes Used

• Make H or D atom

• Polarize electron

• Polarize atomic nucleus via hyperfine coupling with its atomic electron

• Ionize atomE

ner

gy

e p

Magnetic Field

Ener

gy

e d




TUNL Atomic Beam Polarized Ion Source

Atomic Beam SystemsIonizer Systems

Acceleration & Spin Precession Systems




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.




Polarize atomic electrons by sextupole focusing

• Resulting beam is polarized in electron spin. • Multiple sextupoles efficiently focus a beam

with wide energy spread along the source axis.

Electron spin-up atoms focused

Electron spin-down atoms defocused




Ene

rgy

B-Field

Polarize atomic nuclei using RF transitions

• Populations of coupled states 2 and 4 are inverted.

• Carefully designed RF electric and magnetic fields cause precessing spins to invert their direction.

How Do We Polarize Beams at TUNL?



Ionize atoms by collisions with fast electrons

• Polarized atoms are ionized by the process H + e --> H+ + 2e


Microwave discharge produces and accelerates electrons

Polarized Hatoms enter H+ out

Electron Cyclotron Resonance (ECR) Ionizer

20 - 80 W of 3 GHz -wave Power

Solenoidal coils produce axial B-field



Produce H-/D- by Cesium Charge Exchange

• 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+

Heated Cesium Reservoir (260-300 deg.)

H+ in H- out



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.


triangle universities nuclear laboratory july 26, 2001-tunl reu the making and using of...

Documents

resulting beam

tunl reu energy bfield

tunl reu talk outline

atomic electrons

spinpolarized h

d atoms

atoms focused electron

polarized beams