Spin Filtering at COSY

Mitglied der Helmholtz-Gemeinschaft
Spin Filtering at COSY - First Results
Dieter Oellers
University of Ferrara,
INFN Ferrara
STORI11, Frascati
PAX-Collaboration
Goal:
Produce a beam of polarized antiprotons
Method:
Spin-filtering of a stored beam
Ongoing:
Commission and establish this technique with protons at COSY
Future:
Establish this method with antiprotons at AD
11.
2011
28.October
September
SPIN 2010
Folie 2
Outline
●
Spin Filtering
●
Experimental Setup
●
Online Results
●
11.
2011
28.October
September
Outlook
(see H. Stroeher on Friday)
SPIN 2010
Folie 3
Spin Filtering
Spin-dependent attenuation
Tested with protons (FILTEX)
Picture by H-O. Meyer
F. Rathmann. et al., PRL 71, 1379 (1993)
COSY-Experiment 199.2
08.08.2011 MD → end of August
August → 09.10.2011 data taking
11.
2011
28.October
September
SPIN 2010
Folie 4
Spin filtering cross section
→


σ to t = σ 0 + σ 1 ( S ⋅ Q) + σ 2 ( S ⋅ kˆ)(Q ⋅ kˆ)
→
Accessible region
with E-Cooling
T = 49.3 MeV
known Ay in pd elastic
11.
2011
28.October
September
SPIN 2010
FILTEX
@TSR
COSY
Folie 5
Outline
●
Spin Filtering
●
Experimental Setup
●
Online Results
●
11.
2011
28.October
September
Outlook
(see H. Stroeher on Friday)
SPIN 2010
Folie 6
Spin Flipper
RF Solenoid
Schematic overview
stored protons at T > 45 MeV
● polarized internal H-target
● electron cooler to reduce beam losses
● analyser reaction + detector to measure beam polarization
● spin flipper to reduce systematic effects
●
11.
2011
28.October
September
SPIN 2010
Folie 7
Beam lifetime: low-β-section
Target
position
Beam lifetime τ:
small β ⇨ residual gas &
target has small impact on
beam lifetime
Goal:
low pressure
high target
density
low pressure
Polarized H target
●
H flux:
3*1016 H1/s
storage cell:
Ø = 9.6 mm
L = 400 mm
dt = 5.5 * 1013H/cm2
●
●
P = 0.75
Holding field and storage cell
ABS Beam
To BRP
Beam through storage cell
Pictures of target cell in beam direction.
Left: Closed cell
Right: Opened cell
11.
2011
28.October
September
SPIN 2010
Holding field coils (dark brown)
compensation coils (light brown)
Folie 10
Vacuum system at PAX-IP
ABS-flux: 3*1016 H/s
⇨ requirements:
1. high pumping speed in target chamber
> 10.000l/s
Mounted at the
target chamber
11.
2011
28.October
September
SPIN 2010
Folie 11
Vacuum system at PAX-IP
ABS-flux: 3*1016 H/s
⇨ requirements:
1. high pumping speed in target chamber
2. low residual gas flow into adjacent sections
Flow limiter tubes:
Ø = 19 mm
L = 80 mm
11.
2011
28.October
September
SPIN 2010
Folie 12
Vacuum system at PAX-IP
ABS-flux: 3*1016 H/s
⇨ requirements:
1. high pumping speed in target chamber
2. low residual gas flow into adjacent sections
3. high pumping speed in adjacent sections
Flow limiter tubes:
Ø = 19 mm
L = 80 mm
2xTS
Fast Shutters
NEG 5000
l/s
NEG 5000
l/s
BPM
IG 100 l/s
BPM
IG 100 l/s
BPM
IG 100 l/s
IG 100 l/s
Target chamber
is installed in
this position
11.
2011
28.October
September
SPIN 2010
Folie 13
Detection system
2 times 3 layers
of double sided
silicon strip
detectors
p
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2011
28.October
September
SPIN 2010
D2
Folie 14
Outline
●
Spin Filtering
●
Experimental Setup
●
Online Results
●
11.
2011
28.October
September
Outlook
(see H. Stroeher on Friday)
SPIN 2010
Folie 15
Beam development
The machine has to be optimized for long
beam lifetimes and high intensities with low-β
section switched on at at experiment energy
and at injection energy:
1. flat orbit
2. optimal tunes
3. E-Cooler
4. Stacking injection
τ = 8000 s
11.
2011
28.October
September
SPIN 2010
Folie 16
Spin Filtering Cycle
11.
2011
28.October
September
SPIN 2010
Folie 17
Expected build-up rate
Input parameters:
target density: ~ 5.5 * 1013/cm2
target polarization: ~ 0.75
cross section: σ1 = -26.9 mb
(at T=49.3MeV, Θacc = 7mrad)
⇨ ΔPexpected ~ 0.002/h
Long filtering time necessary
⇨ high beam lifetime
⇨ highest possible target density
⇨ best possible vacuum
d stopped
in 3rd layer
(33.8 – 47.7)
p stopped in
3rd layer
(54.7 - 109.6)
FOM
d stopped
in 2nd layer
(19.3 – 37.9)
Polarimetry
Proton
beam
D2
Cluster
Target
d
p
11.
2011
28.October
September
d
p
SPIN 2010
Folie 19
Double ratio
luminosity cancels
geometrical acceptance & detector efficiency cancel
under the assumption, that they don't change between the P↑ and P↓ sample
controll ratio must be CONSTANT in time
spin flipper ⇨ both polarization states in one cycle
⇨
11.
2011
28.October
September
SPIN 2010
detector stability „only“ during each cycle
Folie 20
Cycle Structure
Pictures from data
Total trigger rate
2 Spin Flips
DAQ stopped
Target off
Beam intensity
Pressure at filter target
mbar
Pressure at deuterium target
16000s of spin-filtering
2500s of polarisation
measurement
Correlations in pd elastic (online)
Deuteron in left detector &
any track in right detector
Δφ-correlation
Deuteron in left detector &
any track in right detector
θ-correlation
clear recontructed pd elastic events
(background < 0.5% after cuts)
11.
2011
28.October
September
SPIN 2010
Folie 22
Polarization lifetime (online)
2 Periods of Measurement:
100s at beginning
300s at end
5000s gap (to prolongate cycle)
0 100
5100
5400
Result: τ = 200,000 s ± 50,000 s
⇨ ~ 5% polarization loss
11.
2011
28.October
September
SPIN 2010
Folie 23
Spin flip efficiency (online)
2 Periods of Measurement:
50s at beginning
60s at end
100s gap (with 99 Spin Flips)
Result: ε = 0.9872 s ± 0.0001
⇨ ~2% polarization loss
11.
2011
28.October
September
SPIN 2010
Folie 24
X / mm
Beam target overlap (online)
Runnumber
Beam target overlap and thus geometrical acceptance
is stable within 10 μm over all runs and
better than 5 μm with each spin flip
11.
2011
28.October
September
SPIN 2010
Folie 25
Next steps in Analysis
●
optimize energy calibration
●
analyse and handle dead time
●
check and correct any time dependence
●
calibrate analysis using data with unpolarized beam
●
run analysis on data with high polarized beam
●
blind analysis of spin filtering data
11.
2011
28.October
September
SPIN 2010
Folie 26
Summary
●
successfully set up COSY for spin filtering
●
successfully performed a spin filtering experiment
●
necessary subsystems work as expected or even better
(eg the vacuum system resulting in very long beam lifetimes)
●
sufficient data for statistical significant result
●
collected data to gain experience in high precission experiments
●
...
11.
2011
28.October
September
SPIN 2010
Folie 27
Summary
●
successfully set up COSY for spin filtering
●
successfully performed a spin filtering experiment
●
necessary subsystems work as expected or even better
(eg the vacuum system resulting in very long beam lifetimes)
●
sufficient data for statistical significant result
●
collected data to gain experience in high precission experiments
●
...
Thank you!
11.
2011
28.October
September
SPIN 2010
Folie 28
Title:PAXframesassembly.fig
Creator:fig2dev Version 3.2 Patchlevel 5
CreationDate:Fri May 6 08:21:50 2011
LanguageLevel:2
Lifetime /s
Determination of machine acceptance
using the frame system
4000
3000
2000
1000
-8.66
-4.33
0
4.33
8.66
x / mm
Measure beam lifetime at different positions of frame system.
Curvature at left and right edge due to beam emittance (out of fit)
Fit measurement with trapezodial shape.
Ax(π mm mrad)
Ay(π mm mrad)
Θx (mrad)
Θy (mrad)
Θacc (mrad)
20.4 ±1.2
13.2 ± 0.9
6.0 ± 0.2
5.7 ± 0.2
5.9 ± 0.2
11.
2011
28.October
September
SPIN 2010
Folie 29
Beam development procedure
1. Injection of unpolarized (polarized) protons and acceleration to T = 49.3MeV
2. Adjustment of E-Cooler
1 week
3. Beam on ANKE-Cluster-Target
4. Orbit Correction in x- and y-direction
5. Optimize E-Cooler (tilting angle, feedback etc.)
11. Switching to PAX-Optics
1 week
12. Orbit Correction in x- and y-direction
13. Vacuum break: Install moveable frame system (at PAX)
and detection system (at ANKE)
17. Measure acceptance angle and beam position at PAX
1 week
18. Vacuum break: Install openable target cell
19. Calibrate Spin Flipper
20. Prepare three cycles (Filtering, Spin Flip Efficiency, Polarization Lifetime)
11.
2011
28.October
September
SPIN 2010
Folie 30
Polarization build-up cross section
For the determination of the polarization build-up cross section
several parameters have to be measured.
Here is a list of the most important ones:
➢ Acceptance angle at polarized H-Target (PAX-IP)
➢ Target density
➢ Target polarization
➢ Beam polarization after filtering
➢ Filtering time
11.
2011
28.October
September
SPIN 2010
Folie 31
Control signals
➢ Voltage of pickup coil at RF-solenoid magnet to detect each spin flip individually
➢ Target density
Baratron to measure pressure in storage cell &
Schottky method
➢ Control signal for storage cell position opened / closed
➢ Currents of holding field coils
➢ Beam polarization bits
➢ Beam current
➢ Target polarization from BRP and ABS status
11.
2011
28.October
September
SPIN 2010
Folie 32
FILTEX at TSR (1992)
Observed polarization build-up:
dP/dt = ± (1.24 ± 0.06) x 10-2 h-1
P(t)=tanh(t/1)
1/1=σ1· Q · dt · frev
σ1 = 72.5 ± 5.8 mb
F. Rathmann. et al.,
PRL 71, 1379 (1993)
Spin filtering works! But how?
11.
2011
28.October
September
SPIN 2010
Motivation
Folie 33
Mitglied der Helmholtz-Gemeinschaft
Spin Filtering at COSY - First Results
Double ratio
FILTEX at TSR (1992)