the e166 experiment k. peter schüler e+ source options for the ilc undulator source scheme for ilc...
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The E166 Experiment K. Peter Schüler
• e+ source options for the ILC• undulator source scheme for ILC• E166 – proof-of-principle demonstration of the undulator method• undulator basics• transmission polarimetry• results & conclusions
The E166 Experiment: Undulator-BasedProduction of Polarized Positrons
K. Peter Schüler (DESY) - on behalf of the E166 Collaboration
PSTP 2007 at BNL 10-14 Sep. 2007
The E166 Experiment K. Peter Schüler
e+ source options for the ILC
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existing/proposed positron sources:
← ILC
3 Concepts:
large amount ofcharge req‘d !
• ‚conventional‘• laser Compton based (see M. Kuriki‘s talk)• undulator-based (this talk)
PSTP 2007 at BNL 10-14 Sep. 2007
The E166 Experiment K. Peter Schüler
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conventional positron source (as used with SLC at SLAC)
PRO: established technology (although not at req‘d level)CON: pushing technical limits of target materials; req‘s multiple targets and beamlines; very high activation levels no polarization option
PSTP 2007 at BNL 10-14 Sep. 2007
thick W-Re target:strong multiple scattering,less efficient e+ capture
The E166 Experiment K. Peter Schüler
undulator source scheme for ILC
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PRO:• photoprod. in thin target 0.4 X0 Ti-alloy lower e+ beam emittance• less energy deposition in target (1/5) and AMD (1/10)• less neutron induced activation (1/16)• polarized positrons
CON:• need high-energy electron drive beam (coupled e+/e- operation)• long undulator (150-300 m) req‘d
positron beam profile
PSTP 2007 at BNL 10-14 Sep. 2007
The E166 Experiment K. Peter Schüler
undulator source scheme for ILC
5PSTP 2007 at BNL 10-14 Sep. 2007
auxiliary keep-alive source
The E166 Experiment K. Peter Schüler
E166 – proof of principle demonstrationof the undulator method
6PSTP 2007 at BNL 10-14 Sep. 2007
7The E166 Experiment K. Peter Schüler
PSTP 2007 at BNL 10-14 Sep. 2007
The E166 Experiment K. Peter Schüler
undulator basics
8PSTP 2007 at BNL 10-14 Sep. 2007
E166 ILC (RDR) electron beam energy (GeV) 46.6 150 field (T) 0.71 0.86 period (mm) 2.54 11.5 K value 0.17 0.92 photon energy 0
max (MeV) 7.9 10.0 beam aperture (mm) 0.89 5.85 active length (m) 1 147 M (no. of periods) 394 12800
The E166 Experiment K. Peter Schüler
undulator basics
9PSTP 2007 at BNL 10-14 Sep. 2007
E166 Photon Spectrum E166 Photon Polarization
Spectrum: Angular Distribution: Polarization:
first harmonic (dominating) expressions:
E166 Photon Yield: = no. of photons per high-energy beam electron
0max = 7.9 MeV
The E166 Experiment K. Peter Schüler
The E166 Experiment
10PSTP 2007 at BNL 10-14 Sep. 2007
2004/2005 setup and checkout
Oct. 2005 4 weeks of data taking
The E166 Experiment K. Peter Schüler
E166 experimental setup
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46.6 GeV
4 – 8 MeV
C1 – C4: photon collimationAG1, AG2: aerogel detectorsAG1Si, AG2Si: silicon detectorsGCAL: Si/W-calorimeter
DM: electron beam dump magnetsT1: g e+ prod. target (0.2 X0 W)T2: e+ g reconv. target (0.5 X0 W)PosSi: e+ flux monitor (Silicon)CsI: Cesium Iodide calorimeterSL: solenoid lensJ: movable jaws
< 8 MeV
The E166 Experiment K. Peter Schüler
E166 photo gallery
12PSTP 2007 at BNL 10-14 Sep. 2007
The E166 Experiment K. Peter Schüler
transmission polarimetry
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1. Compton Transmission Polarimetry for Low-Energy Photons relies on spin dependence of Compton effect in magnetized iron:
2. Positron Polarimetry: (a) transfer e+ polarization to photon via brems/annihilation process (b) then infer e+ polarization from measured photon pol. as in method 1.
PSTP 2007 at BNL 10-14 Sep. 2007
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analyzer magnets: overview
active volumePhoton Analyzer: 50 mm dia. x 150 mm longPositron Analyzer: 50 mm dia. x 75 mm long
The E166 ExperimentK. Peter Schüler
Pe ≈ 0.07
ΔPe/Pe < 0.05 (aim of experiment)
electron polarization of the iron:
M = (B–B0)/0 magnetization n = electron densityμB = Bohr magneton g‘ = magneto-mechanical factor
PSTP 2007 at BNL 10-14 Sep. 2007
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spin and magnetization
The E166 ExperimentK. Peter Schüler
g‘ = magneto-mechanical factor: obtained from Einstein - de Haas type experiments, related to gyromagnetic ratio: γ = (g‘/2) ∙ (e/m)
the principle … and its ultimate implementation (Scott 1962) g‘ = 1.919 ± 0.002 for pure iron i.e. orbital effects contribute about 4%
Note: g‘ = 2 Ms / M = 1 (pure spin magnetization) γ = e/m g‘ = 1 Ms / M = 0 (pure orbit magnetization) γ = ½ (e/m)
PSTP 2007 at BNL 10-14 Sep. 2007
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analyzer magnets
The E166 ExperimentK. Peter Schüler
CsI-Detector
e+ Analyzer
Pickup Coils
e+ Analyzer Analyzer
PSTP 2007 at BNL 10-14 Sep. 2007
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field distribution modeling(Vector Fields OPERA-2d)
The E166 ExperimentK. Peter Schüler
R = 0 mm
1015
22.5
Bz (T)
Z (mm)
longitudinal field distribution: Bz (R,Z)field drops gradually towards the ends: Leff / L < 1
center
end
PSTP 2007 at BNL 10-14 Sep. 2007
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5
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field distribution in 2d(Vector Fields OPERA-2d)
The E166 ExperimentK. Peter Schüler
longitudinal field distribution: Bz (R,Z)(shown for one quadrant)
R (mm)
Z (mm)
PSTP 2007 at BNL 10-14 Sep. 2007
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flux measurements:
The E166 ExperimentK. Peter Schüler
measure voltage transients in pickup coils upon current reversals
Positron Analyzer (-60 +60 amps)
PSTP 2007 at BNL 10-14 Sep. 2007
voltage transient
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flux and field measurements: results
The E166 ExperimentK. Peter Schüler
Note: polarimetry was always done at full saturation over the central region (±60A)
Z = 0 (center)
PSTP 2007 at BNL 10-14 Sep. 2007
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electron polarization of the iron
The E166 ExperimentK. Peter Schüler
PSTP 2007 at BNL 10-14 Sep. 2007
Pe/Pe ~ 2%
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photon asymmetries
The E166 ExperimentK. Peter Schüler
PSTP 2007 at BNL 10-14 Sep. 2007
detector asymmetry (%) (%) AG2Si (silicon) 3.883 0.062 AG2 (aerogel) 3.307 0.123 GCAL (Si/W-calo) 3.665 0.071
AG2Si
AG2
GCAL
measured photon asymmetries are in reasonable agreementwith simulation results (3.2-3.5%) based on the theoreticalundulator polarization spectrum and detector response functions, but no detailed spectral shape analysis is possible.
The E166 Experiment K. Peter Schüler
e+ analysis: energy deposition in CsI crystals
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• good signal/background separation in central crystal • background comes from beam halo hitting the undulator• undulator on/off measurements were taken on alternating machine pulses for effective background separation
PSTP 2007 at BNL 10-14 Sep. 2007
undulator on: signal + backgroundundulator off: background
The E166 Experiment K. Peter Schüler
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central crystal asymmetry vs. run cycle numberfor e+ spectrometer setting at 140 A
positron asymmetries
PSTP 2007 at BNL 10-14 Sep. 2007
data samples and spectrometer settings
The E166 Experiment K. Peter Schüler
positron asymmetries & beam polarizations
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e+ / e-e+ / e-
results for the central CsI crystal
= analyzing power from simulations = electron polarization of the iron
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conclusions• successful demonstration of the undulator method• undulator functioned as predicted• successful polarimetry of low-energy and e+ • confirmed expected γ e+ spin-transfer mechanism • measured high positron polarization with ~ 80% max.
The E166 Experiment K. Peter Schüler
PSTP 2007 at BNL 10-14 Sep. 2007