The COMPASS polarized target

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The COMPASS polarized target

• N.Doshita
• University of Bochum, Germany
• Symmetries and Spin, Prague
• July 9 2004

2
Contents

• The COMPASS experiment
• Requirement of polarized target
• Target material
• Dynamic nuclear polarization
• Polarized target system
• Polarization result

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The COMPASS experiment

• Muon program
• -Nucleon spin structure --- gluon
  contribution
• -Polarized muon beam and polarized nucleon
  
• target
• Hadron program
• -Meson spectroscopy
• -hadron beam and Hydrogen, carbon target

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Motivation of muon program
Nucleon spin
1
1
DS DG Lq Lg

2
2
DS Quarks spin
DG Gluons spin
Lq, Lg Orbital angular momentum
SMC, SLAC, HERMES in 1990s
DS 0.2
DG ??
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Gluon polarization measurement in the COMPASS
Double spin asymmetry
PB Beam polarization PT Target polarization f
Dilution factor N Number of events
Direction of beam polarization
Dilution factor polarizable nucleon rate in
material
?
Direction of target polarization
Aphys ? Gluon polarization
Extraction
What kinds of events are counted?

• Open charm production events
• High-PT hadron production events

D0, D0
Low statistics
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Requirement of Polarized Target
Statistical accuracy
-High polarization -High dilution factor -Large
target -Stability during long beam period
COMPASS polarized target

• - Target material 6LiD (high
  dilution factor), 350g
• - Magnetic field 2.5T
  superconducting magnet
• Temperature less than 100mK and
  high cooling power
• dilution
  refrigerator
• - Control system LabView and PLC

?
Dynamic Nuclear Polarization with Microwave
Deuteron polarization more than 50
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COMPASS polarized target
Still pumping line
3He precooling line
Magnet 2.5 T solenoid 0.5 T
dipole
µ beam
Twin target cell Target material 350 g
Mixing chamber 6 L
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Dilution refrigerator
3He Pumping line
Magnet
Beam
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Polarization and Target Material
Definition of polarization
Granules 6LiD
Spin 1/2
Spin 1
6Li
D
6LiD Polarized target material

• 6LiD

-gt polarizable nucleons about 50
410-10 m

• Possibility of high polarization

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Figure of Merit
r density k packing factor f effective
dilution factor PT polarization
The beam time needed to achieve a certain
statistical accuracy is inversely proportional
to the FoM.
FoM rk(f PT)2
kg/m3
For the extraction of the real physics Bjorken-x-d
ependence of dilution factor should be
considered.
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Material loading
Material
Funnel
Dilution refrigerator
Target holder
Beam
Liquid N2 bath
Liquid N2 Bath
Target cell
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Dynamic nuclear polarization
Paramagnetic centers are needed
Spin status Dipolar-dipolar interaction
Polarization _at_2.5T and 0.3K Electron
99.9 Deuteron 0.17
Transfer the high electron polarization to
deuteron polarization
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Dynamic nuclear polarization
Paramagnetic centers are needed
Spin status Dipolar-dipolar interaction
Polarization _at_2.5T and 0.3K Electron
99.9 Deuteron 0.17
Transfer the high electron polarization to
deuteron polarization
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COMPASS dilution refrigerator
15-20 L/h
3He of 1400 L NTP 4He of 9200 L NTP
3He flow 30-100 mmol/sec
2000 L
13500m3/h
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Mixing chamber
Beam
?
30mm
600 mm
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Performance of the dilution refrigerator
MC Temperature mK
0
DNP
50
Frozen mode
3He flow rate mmol/sec
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Dilution Refrigerator Control and Monitoring
System
Monitor
Thermo-sensors, Pressure gauges, Flow meters,
Level gauges ? more than
50
Control
Valves, pumps
? more than 10
Location
Beam area, Pump room, Control room
Running time
6 month ? several years
LabVIEW
PLC
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PLC (programmable logic controller) System
Siemens S7-300, CPU315-2DP with 48 kByte memory
intranet
Control room

• Pressures
• Flow rates
• Gate valve control
• Needle valves control
• Interlock (still heater, MW)

Touch panel
Profibus
Pump room
Beam area

• LN2 trap level control
• 4He roots pump
• 3He pumps
• Cooling water security
• room temperature
• Air conditioning

• Isolation vacuum
• LHe valve
• Turbo pump control
• Diffusion pump
• Vertical, horizontal screens

Power 48V UPS, 49 channels are used
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Superconducting magnet
Solenoid magnet longitudinal (horizontal) 2.5T
- field homogeneity DB/B lt 3.5 x 10-5 with
16 correction coils Dipole magnet transverse
(vertical) 0.5T - field rotation (changing
the spin orientation) - transverse physics
program
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Field Rotation
In order to cancel the systematic error
Upstream
Muon
Downstream

• Spectrometer acceptance
• Time dependence variation

(a)
(b)
? Transverse program
(c)
Target material spin direction
(b)
33 minutes every 8 hours
(c)
(a)
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Microwave system
0.2W needed for both cells
Microwave cavity
Microwave stopper
holes
Mixing Chamber
2W due to long waveguide
Power control attenuators
Power supply
Microwave generator
10W output power
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NMR System
10 coils can be operated at the same time.
NMR coil
UT-85 Cable Cu jacket semi-rigid
material 6LiD
Yale card
Liverpool Q-meter
PTS 250 Microwave generator
scope
VME-bus
10 ch ADC 12 bit
DC offset subtraction
16 ch ADC 16 bit
Splitter
ADC/DAC 12 bit
96 ch digital I/O
frequency control
gain selection signal
trigger signal
bus extender VME-MXI
PC in the control room
Windows 2000 data acquisition program
(LabVIEW) data storage
NI MXI-2 cable
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NMR signal process
After subtracting Q curve
Q curve Signal
Q curve
signal
Subtract residual background by a polynomial
function
Subtract Q curve
Polarization determination with Aria method
Calculated by temperature and magnetic field
P0 polarization at thermal equilibrium
S0 NMR signal area at thermal
equilibrium
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Calibration
With several different temperature points
Preliminary in 2004
S0 ? T-1
NMR signal area S0
K-1
Temperature 1/T
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Polarization measurement errors
(in 2003)
relatively
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Polarization build up
Polarization
Day
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Enhanced NMR signals
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Average polarization in the whole physics runs in
2003
Red Upstream Green Downstream
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Polarization results
2004 polarizations almost have same values as
2003.
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Summary and Outlook
-In order to obtain high statistics Large
6LiD target with 2.5 T magnet and dilution
refrigerator -In order to cancel the systematic
error Field rotation -The system has been
working since 2001 without any big
problems. -2004 run It also has same
polarizations as 2003. -New magnet Large
acceptance -New target material test in 2005??
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Equal Spin Temperature
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Roles of the LabView and PLC
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Principle of cooling
300 K
Concentrated phase
Dilution phase
Evaporator
1.5 K
lt 0.1 K
0.8 K
Still
Main heat exchanger
Mixing changer
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Cooling power measurement
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Emergency isolation vacuum pump(Turbo pump)
Diffusion Pump

• - large volume pumping
• need cooling water
• need high-pressure air

Turbo Pump
Diffusion pump stopped
Pumping speed gt 80
Diffusion pump recovered

• - small volume pumping
• powered by 48V UPS

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Liquid nitrogen filling system
Present nitrogen level
If you press here, .
Alarm
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C
D0 K- p
D0 K p-
?
C
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Dynamic nuclear polarization
With Microwave
?????? ??? (gt 99 ) ?????? ???
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Superconductive Magnet
?????????? ????
????????? ???????? ???????????
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