institut für kernphysik bosen 2010 30th august 2010 andreas thomas polarised targets for...
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Institut für Kernphysik
Bosen 201030th August 2010
Andreas Thomas
Polarised Targets for Photoproduction Experiments
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Polarisation Observables
Disentangle broad, overlapping resonances,Measure meson threshold production, quark mass ratios,Determine fundamental properties: Spin Polarisibiltities,
GDH sumrule.
BeamTarget
s
ppp
g ggg
EGP
PTP
FHP
dd
P
PPP
z
y
x
unpol
circlinlinunpol
- -
- -
- -
- -
4,
4
2,0 Target
Beam
S÷øö
çèæ
W
÷øö
çèæ -+÷
øö
çèæ
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Polarised Target
Polarisation = Orientation of Spins in a magnetic field
NNNNP Ideally: All spins in field direction
P=100%
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P=100% in reality not so easy to realise:Complicated interplay between
Polarising force ~ magnetic field Band
Depolarising force ~ thermal motion of spin particles(temperature T – relaxation)
B = 10-5 Tesla (earth magnetic field)T = 25° Celsius (room temperature)
B = 5 Tesla (superconducting magnets)T = -273° Celsius (refrigerators)
P = 10-12%
B = 1 Tesla (superconducting magnets)T = 37° Celsius (body temperature)
P = 100%DNP (particle physics)
P = 10-8% MRI (medicine)
Examples:
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Thermal equilibriumBoltzmann distribution
kT
B
NN
NNP
tanh
kT
E
eEN
EEN
)(
)(
Trick: Transfer of the high electron polarization to the nucleon via m-wave irradiation (DNP)
electron proton
Magnetic moment in magnetic field: mBgBE o
B=0T B=0T B=2.5TB=2.5T
DE GHzh
Ee 70
MHzp 106
B [Tesla]
T [mK] e- [%] p [%] d [%]
2,5 100 99,8 0,51 0,10
1000 93,3 0,25 0,05
5,0 100 100,0 5,09 1,05
1000 99,8 1,28 0,11
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Model: Solid State Effect (SSE)
ssIIISIZSZ HHHHHH
k
kee BSg j
jpp BIg
Zeemann
small660
pp
eeg
g
small distance e-
big (~r-3)
Dipol-Dipol :
ki ik
ikkikikiikppeeIS
r
rSrISIrggH
,2
3 ))((3
Mixing of the energylevels 210B
Bl3r
SB kel
We
Wp
Wp
Wep+
Wep-
Magnetic Dipole transition allows Spin flip (Dm=+-1) of electrons or protons.Probability to pump forbidden transitions Wep+ or Wep- ~ e2
P| > + e| >
P| > + e| >
P| > + e| >
P| > + e| >
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He3/He4 Roots4000m3/h
Vacuum system
Mikrowaves70GHz
Dynamic Nuclear
Polarization
NMR-Apparatus
106MHz
Polarisation meas.
Components of the polarized target
for the Crystal Ball detector
Horizontal He3/He4 Dilutionrefrigerator
(30mKelvin)with internalHolding coil
SuperconductingPolarization magnet
5Tesla
Targetmaterial
H-ButanolD-Butanol
Similar to Bonn Target [C.Bradtke et al., NIM A436, 430 (1999)]
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Polarized Target for Crystal Ball
Tagged CW photon beam 4p- detector
Frozen spin target (30 mKelvin achieved)Pproton ~ 95%Pdeuteron~70%All directions of polarization
sec105 7
New 3He4He-Dilution refrigerator(in collaboration with JINR Dubna)
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Cryogenics
Evaporation cooling
2 Precooling stages:
Separator (4.2Kelvin pot)
Evaporator (1.5Kelvin)
Dilution circuit(0.03Kelvin)
3He4He-Dilution refrigerator
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Alignment thermal radiation shieldsHigh temperature heat exchanger
Alignment still and evaporator
Impressions from the technical realisation
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Transverse
And
Longitudinal
Internal
Holding coil
1.3 Kelvin
1Tesla at 46A
achieved
Mainz/Dubna Dilution refrigerator
Separator (4.2Kelvin)
Evaporator (1.5Kelvin)
Mixing chamber(0.03K)
Still (0.7K)
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Holding Coil
Coil has to be as thin aspossible to allow lowenergetic particlesto punch through.
Subcooled Superconductor
F54-1.35(0.20)TV
jcrit
B
T
@4.2Kelvin
@1.3Kelvin
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• Copper/scandium wire with 54 Nb-Ti filaments embedded in it.
• Cu:Sc=1.35:1• Alloy composition:
Nb47wt.%Ti• Diameter=0.222mm• It achieves currents up
to 50A at 4.2K and 1T.
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Coil winding by TBM Mainz (Herr Kappel) Glueing by TBV Mainz (Herr Kauth)
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Simulation and Optimisation Transverse Field
cos)(JIdeal case for dipole magnet:
4-layer dipole:
N1=N2=138
N3=N4=78
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Production
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150mm
4-layer dipole:
N1=N2=138
N3=N4=78
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High Field 1T
Threshold Production
Transverse Field
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Polarizingmagnet
He4(liq)
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Rotation of the Holding Field
1) Bz=2.5Tesla
2) Bz=0.5Tesla
Superconducting 2.5Tesla Magnet for polarising in z-direction
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Rotation of the Holding Field
2) Bz=0.5Tesla
3) By=0.5Tesla
Superconducting 2.5Tesla Magnet for polarising in z-direction
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Rotation of the Holding Field
4) Bz=0.0Tesla
By=0.5Tesla
Superconducting 2.5Tesla Magnet for polarising in z-direction
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410#
# protons
radicals
Free electrons Radicals in material by chemical or radiative doping
Saturated electrons of target material not polarized (Pauli principle)
Butanol Ammonia LiD
30mm
HHHH
HOCCCCH
HHHH
N
H
H
HN
O
CH3
CH3CH3
CH3
Tempo
Target material
Dilution factor (e.g. fButanol=10/74)determines quality of target material.
Typically 1023 pol. protons
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2cm
HHHH
HOCCCCH
HHHH
Butanol
Target material
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Cryostat
Polarizingmagnet
Crystal Ball
Frozen Spin Target Waltz
1. External magnet 2.5 T2. Polarize with microwaves3. Internal holding coil 0.7 T4. Remove external magnet5. Move CB detector in. 6. Data taking.7. Repolarization
Polarizingmagnet
MicrowavesMicrowaves
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New Frozen Spin Target offers all directions of polarization.
Data taking with CBall TAPS detector system started February 2010.
Spin observables with focus to P11(1440), S11(1535), and D33(1700) resonance regions. Complete Experiment.
First Measurement of 4 Vector Spin Polarisabilities and T inp-threshold region planned.
Conclusions
Outlook
Production of an internal polarising coil avoids FST waltz. FoM better.
R&D for polarised active szintillator target for threshold production.
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Loading of the target material
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Microwave system
70 GHz
Diploma Martinez 2003
NMR system
106 MHz
Diploma Frömmgen 2009
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Testrun in December 2009
Thermal Equilibrium-Signal0.5% Polarisation2.5Tesla,1KelvinTo be improved:HF-Lab Mainz (F.Fichtner)and Bochum
Enhanced Signal at 70% Polarisationafter spin rotation
Transverse polarised target ready for data taking run in February
TE
dynTEdyn AU
AUPP
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Vacuum
C4H10O – 60%30mm
3He/4He – 6%
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Holding Coil
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1.- Longitudinal PT: a) Helicity Dependence E of Meson Photoproduction b) Measurement of the G in single pion production
2.- Transverse PT: a) Transverse asymmetries T and F in -h photoproduction in the S11(1535) regionb) Spin observables in ph photoproduction in the D33(1700) region
Double Polarised Experiments
Excitation Spectrum
Fundamental Properties
1.- Long. and trans. PT: Spin Polarisibilities
2.- Transverse PT: Transverse asymmetries T and F in -p photoproduction in the threshold region mu - md