a rb spin filter - thomas jefferson national accelerator ... · a rubidium spin filter - prototype...
TRANSCRIPT
A Rubidium Spin Filter -
Prototype and Prospects for a Turnkey Source of Polarized Electrons
Perpetrators
UNL
Levi NeukirchAdam GreenBrooks HittMark RosenberryHerman BatelaanTJG
LANL
Dale Tupa
He direct extraction source
McCusker, Hatfield and Walters, PRA 5, 177 (1972)
Rolla Source Results
The Good News: 50μA of current (@ 3% polarization)
The Bad News: Stringent requirement for high percentage of discharge in excited states; ΔE ~ 6 eV
Improvements: LMA laser; side-
pi pumping
Answer: use ground state atoms
e-
+ Rb
→ e-
+ Rb
Fabrikant
and Thumm, JPB 40, 1245 (1999)
Require (at 5 eV) that σex
nRb
ℓ
~ 1 →
nRb
~ 1014
cm-3
Other (Electron) Spin Filters
Ann.Phys. 2, 465 (1993)
See also work on neutron spin filters by Gentile, Chupp, Cates etc…
An early spin-exchange source
Krisciokaitis-Krist
and Tsai, NIM 83, 45 (1970)
Chanin
et alii, PR 80, 67 (1962)
N2 pressure (Torr)1.0e-4 1.0e-3 1.0e-2 1.0e-1
0.01
0.10
1.00
B-field (T)0.000 0.005 0.010 0.015 0.020 0.025
0.0
0.0
0.2
0.3
0.4
0.5
0.6Tr
ansm
issi
onPo
lariz
atio
nTr
ansm
issi
onPo
lariz
atio
n
Some model calculations for nRB
= 3 x 1014
cm-3
Rb
optical pumping
σ+
5P1/2
= 795nm
F = 1
λ
5S1/2
F = 2
+σ
F = 1
F = 2
λ = 78
0nm
5P3/2
F = 0
F = 2F = 1
F = 3
pumpprobe
Rb optical pumping and radiation trapping
rogue photons
collisional
quenching
One solution: Gausses
1012
Tupa
et al., PRA 33, 1045 (1986); 36, 2142 (1987)
rogue photons
collisional
quenching
vibrational
quenching
Another Solution: Add Buffer Gas
Rb optical pumping with N2
First attempt
1 mm APERTURE
ELECTRON OPTICS
CATHODE
+σ
ANODE
N2 INLET
Rb
POLARIMETERNe OPTICAL
B
LC
e-
spin filter(OPESF)
Ar
+
laserDye laser
DiodeLaser
Optical Polarimeter
Reference cell
Pump beam
Photodetector
Photodetector
Magnetic coillenses
λ /4-plate
mirror
beamsplitter
Probe beam
Analyzer
polarizerPolarizer +
Probe data
Bln
BRb μλ
δφπ2
2)(8ΓΔ
=
23)(56λδφπ
ΓΔ
=ln
PRb
Rb
• ΔΦ
= optical rotation of probe
• δ
= probe beam detuning
• l = path length
• λ
= D2 wavelength
• Γ
= D2 natural width
Results
Batelaan
et alii, PRL 82, 4216 (1999)
Figure of Merit = P2I = 0.28 μA
¡Nitrogen - the wonder buffer!
•
provides the electrons•
narrows their energy spread
•
thermalization
increases σex
•
increases path length, l•
vibrational
quenching
•
diffusion barrier•
broadens absorption profile
v.2
Problem
Pump beam is most efficient at entrancepoint, where the electrons that will ultimatelybe polarized aren’t.
High magnetic field side-pumping scheme
Martin, Walker, Anderson, and Swenson, NIM A 335, 233 (1993)
Rb absorption vs. B-field
Side-pumping geometry
Possibilities for the future
T. Walker et al.