High-Field Moller

High Field
Møller Polarimetry
Status, Progress, and Plans
Jim Napolitano, Temple University
with Ted Berger, Ben LeRose, Paul Stoler, James Wilhelmi
and JJL Magnet Optics, LLC
PREX & CREX Collaboration Meeting
Jefferson Lab 11-12 April 2014
Outline for Today
Our goal is a <1% uncertainty in the beam
polarization using the existing (essentially)
“High Field” Møller Polarimeter apparatus.
There are several challenges. Right now, we
are focussing on two of them.
1) Foil orientation tolerance (better than 1°)
2) Average analyzing power uncertainty
2
Other Challenges to 1%
Save these for another time
•
Demagnetization due to target heating
•
Levchuk effect
•
Radiative corrections to the asymmetry
•
Statistical precision (including confirmation
of systematic uncertainties)
3
NUCLE
INSTRUME
Target Foil Apparatus
Nuclear
Instruments
and Methods in Physics Research A 400 (1997) 379-386
&METNo
IN PHVS
RESEA
Sectio
Why use a “High Field” Target Foil?
Nuclear
Instruments
and Methods in Physics Research A 400 (1997) 379-386
A target for precise Mdler polarimetry
L.V. de Bever”, J. Jourdan, M. Loppacher,
S. Robinson, I. Sick, J. Zhao
Dept. Jir Ph.vsik und Astronomie. Universitiit Basel, CH-4056 Basel, Switzerland
29 January
1997
Bottom
“Tilted,
low
field”
target
foils arepolarimetry
limited in
A Line:
target
forReceived
precise
Mdler
precision because of our knowledge of magnetization
alloy foils
external S.
fields,
and a I. Sic
L.V. indeferromagnetic
Bever”, J. Jourdan,
M.from
Loppacher,
Robinson,
fundamental limitation in knowing g′ for alloys used.
to achieve better accuracy on the measurement of electron beam polarization employing e’ - e’ scattering
Dept. Jir Ph.vsik und Astronomie. Universitiit Basel, CH-4056 Basel, Switzer
an improved polarized electron target. Using a pure iron foil saturated out-of-plane in a 4 T magnetic
the systematical errors to the promille level. Received
Measurement
the relative
4
29 of
January
1997target polarization using pola
B-field
’ (T&a)
Fig. 1. Magnetization
as function of applied field, for different
orientations of the foil plane. 0’ corresponds to in-plane, 90’ to
out-of-plane magnetization.
Solution: Fe Foils at 90°
L. V. de Bever et al. / Nucl. Instr. and Meth. in Phys. Res. A 400 (1997) 379-386
2
4. Kerr apparatus
,
383
’
As discussed in the previous section, we use the
magneto-optical
Kerr effect in order to continuously
measure the relative polarization of the foil. Various
types of Kerr effects are known. The one exploited
here is the polar Kerr effect: When reflecting linearly
polarized light from a surface of a material magnetized
in the direction perpendicular to the surface, the plane
of polarization of the light is rotated by a fraction
of a degree. The rotation angle is proportional to the
2
-4
-2
4
3.0
3.5
4.0
magnetization. 2.5
B-field
’ (T&a)
B-field
(Tesla)
The basic set-up of the Kerr apparatus developed is
Fig. 1. Magnetization
as function of applied field, for different
shown
Fig. as3. Fig.
The1, iron
target,close
placed
Fig. 2.inSame
for angles
to 90”.on a ladder
orientations of the foil plane. 0’ corresponds to in-plane, 90’ to
that carries several other targets and a view screen, is
out-of-plane magnetization.
placed in the center of the polarimeter vacuum chamber. The 4 T magnetic field is produced by a split-coil
ferromagnetic
particlessolenoid
in a non-magnetic
and
superconducting
which has itsmatrix,
own vacuum
,
similar
effects occur
in the case
thin electrons,
ferromagnetic
enclosure.
The scattered
and of
recoil
leaving
foils.the target foil under a very small angle, are detected
The
magnetization
curve for The
a thinlight
foilused
placed
at an
downstream
in coincidence.
for the
Kerr
anglemeasurements
8 relative to enters
the external
B-field
displayed chamin
and leaves
the isscattering
Fig. ber
1. For
a foil quartz
perpendicular
the driving
through
windows tocovered
with field,
a thin the
layer
5magnetization
is a nearly
linear
function
of gold to avoid
charging
of the
quartz of
by the
strayfield
elec-
1%
J
➜ We take the tolerance on the foil angle to be 1°
Note: These curves are from a ferromagnetic model
calculation by Stoner & Wohlfarth, Trans. Royal Society
of London, Series A, 240(1948)599
’
Asymmetry (Observed/Max)
Ultimate Demonstration
1.00
Foil at 90°
0.99
0.98
Foil slightly tilted
0.97
0.96
2.0
2.5
3.0
3.5
Applied Magnetic Field (T)
6
4.0
“High Field” Target: Results
Existing results (ca 2010?)
Foil saturation
observed (?)
at 3.5T
http://hallaweb.jlab.org/equipment/moller/talks.html
7
“High Field” Target: Results
Existing results (ca 2010?)
Note: Hall C results
are closer to model
calculation
Foil saturation
observed (?)
at 3.5T
http://hallaweb.jlab.org/equipment/moller/talks.html
7
Old “High Field” Target Chamber
8
Old “High Field” Target Chamber
Ambitious apparatus with
ability to orient target in all
six degrees of freedom.
8
New Target Motion Apparatus
Inspired by Hall C Møller Target
REVISIONS
MODEL REV DRAWING REV
DESCRIPTION
DATE(YEAR-MO-DA) APPROVED
Lightweight ladder with
room for four target foils.
Existing
target chamber
(Not to scale!)
Actuator for target ladder
insertion and rotation
(Two degrees of freedom)
9
Photos
Flange Assembly
Test Stand
10
Alignment Issues
Remember: We have 1° tolerances
•
Good News: Machining tolerances and actuator
and stepper motor should met easily for orienting
the target ladder assembly to the target chamber
•
How well is the magnetic field aligned to the axis of
the target chamber? Probably will need to remap
the magnet on the beam line because of probable
interference with quadrupole magnet iron.
•
How well is the electron beam aligned to the axis of
the target chamber/magnetic field?
11
Progress & Schedule
•
Vacuum parts have arrived. Actuator shipped.
Stepper motor options are under consideration.
•
Ladder parts in machine shop at RPI, done soon.
•
Stand for preliminary assembly almost completed.
•
Ladder, actuator, motor assembled and ready for
testing in three weeks. Move to Temple in Summer.
•
Preparations underway for target chamber move to
Temple this Summer. (Waiting on MOU from JLab.)
•
Ready to deliver to JLab by Spring 2015.
(Some uncertainty re availability of SERC@Temple)
12
Spectrometer Studies
Remember: Fourth Quad added for 11 GeV Beam
2×4 detector
array
Beam energy is 1.063 GeV. (Same for PREX & CREX?)
Magnets set to Dec 2000 note from Sasha and Eugene.
Investigate (This Week!) settings with JJL Magnet Optics.
13
All quads
focus
First two quads
must spread the
electrons apart
14
Default GEANT Settings
Generated
Detected (Coincidence)
What is determining the aperture?
15
Simple Check: Energy
This looks about right, but what’s causing the energy loss?
16
he longitudinal and transverse polarizations
azimuthal scattering angle, and B,T are the a
Analyzing
Power
rizations. The analyzing powers are
2
2
(7 + cos ✓) sin ✓
Along (✓) =
2
2
(3 + cos ✓)
and
h areDepends
maximized
at ✓ = angle,
90 with
Along (90 ) =
on CM Scattering
not energy.
However, acceptance is in lab angle, not cm angle.
e↵ect
of transverse
polarization
components
ar
Therefore,
the accepted
analyzing power
will depend
beam energy.
get on
foiltheplane
normal to the beam, with the p
T
➜
More
severe
systematic
uncertainty
at low energy.
verse target polarization Ptran should
be ver
ult to estimate its size, based on the understan
17
Increasing electron momentum
0.776
1%
0.744
0.712
18
Analyzing power
correlates with
hit position on
detector array.
Increasing electron momentum
0.776
1%
Analyzing power
correlates with
hit position on
detector array.
0.744
Probably want to
readjust “sweet spot”
0.712
18
Initial Systematic Checks
1%
1%
May need to cut
on detector pairs.
“Sweet Spot”
Blocks
Must be careful of
effects that change
shape of the tail!
19
First Thing Tried: Effect of Moving Detectors Up or Down
+1cm
1%
1%
⟨A⟩=0.7581
⟨A⟩=0.7745
-1cm
⟨A⟩=0.7581
1%
⟨A⟩=0.7732
20
1%
With 4T Holding Field
Big effect! We are just starting to look at how this
affects the acceptance function and analyzing power.
21
Such a big effect?
80
θ (mr)
60
Møller kinematics
40
20
0
0
∆φ/2π
0.1
2
10
12
“1 GeV”
Approximate
azimuthal kick at 4T
0.05
0
0
4
6
8
Beam Energy (GeV)
2
4
6
8
Beam Energy (GeV)
22
10
12
Conclusions
•
Biggest change (new target insertion) making good
progress, will be ready in Spring 2015
•
Alignment issues: Big question mark for now,
including likely need to remap target holding field
•
Spectrometer optics under study, will need to be
careful that we know analyzing power to 0.1%
•
Other effects (Levchuk, radiative corrections, target
heating) need work, but should be easy enough
23

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