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The COMPASS polarized target

The COMPASS polarized target. N.Doshita University of Bochum, Germany Symmetries and Spin, Prague July 9 2004. Contents. The COMPASS experiment Requirement of polarized target Target material Dynamic nuclear polarization Polarized target system Polarization result.

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The COMPASS polarized target

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  1. 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

  3. 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

  4. 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 ??

  5. 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

  6. 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 %

  7. 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

  8. Dilution refrigerator 3He Pumping line Magnet Beam

  9. n+ - n- B n- P = n+ + n- n+ n+ - n- P = n+ + n0 + n- Polarization and Target Material Definition of polarization Spin 1/2 Granules 6LiD Spin 1 6Li D 6LiD Polarized target material • 6LiD -> polarizable nucleons : about 50% 4×10-10 m • Possibility of high polarization

  10. 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-dependence of dilution factor should be considered.

  11. Material loading Material Funnel Dilution refrigerator Target holder Beam Liquid N2 bath Liquid N2 Bath Target cell

  12. Electron fast relaxation Electron fast relaxation Dynamic nuclear polarization Paramagnetic centers are needed Spin status Dipolar-dipolar interaction Polarization @2.5T and 0.3K Electron: 99.9% Deuteron: 0.17% Transfer the high electron polarization to deuteron polarization

  13. Electron fast relaxation Electron fast relaxation Dynamic nuclear polarization Paramagnetic centers are needed Spin status Dipolar-dipolar interaction Polarization @2.5T and 0.3K Electron: 99.9% Deuteron: 0.17% Transfer the high electron polarization to deuteron polarization

  14. 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

  15. microwave guide target material microwave stopper microwave cavity 70 mm 1600 mm mixing chamber upstream downstream Calibrated sensors Non-calibrated sensors TTH4: RuO TTH7: speer 220 ohm TTH1: speer 220 ohm TTH6: RuO TTH2: speer 220 ohm Mixing chamber Beam  30mm 600 mm

  16. Performance of the dilution refrigerator MC Temperature [mK] 0% DNP 50% Frozen mode 3He flow rate [mmol/sec]

  17. 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 PLC LabVIEW

  18. Ethernet module PC CPU 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

  19. Superconducting magnet Solenoid magnet longitudinal (horizontal) 2.5T - field homogeneity : DB/B < 3.5 x 10-5 with 16 correction coils Dipole magnet transverse (vertical) 0.5T - field rotation (changing the spin orientation) - transverse physics program

  20. 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)

  21. 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

  22. 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 trigger signal gain selection signal bus extender VME-MXI PC in the control room Windows 2000 data acquisition program (LabVIEW) data storage NI MXI-2 cable

  23. 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

  24. Calibration With several different temperature points Preliminary in 2004 S0 T-1 NMR signal area S0 [K-1] Temperature 1/T

  25. Polarization measurement errors (in 2003) relatively

  26. Polarization build up Polarization [%] Day

  27. Enhanced NMR signals

  28. Average polarization in the whole physics runs in 2003 Red : Upstream Green : Downstream

  29. Polarization results 2004 polarizations almost have same values as 2003.

  30. 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??

  31. Equal Spin Temperature

  32. Roles of the LabView and PLC

  33. Principle of cooling 300 K Concentrated phase Dilution phase Evaporator 1.5 K < 0.1 K 0.8 K Still Main heat exchanger Mixing changer

  34. 103 Upstream (TTH1) 102 Cooling power [mW] Downstream (TTH2) 101 Still heater 6V 1 200 400 600 800 1000 Mixing chamber temperature [mK] Cooling power measurement

  35. 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 > 80% Diffusion pump recovered • - small volume pumping • powered by 48V UPS

  36. Liquid nitrogen filling system Present nitrogen level If you press here, …. Alarm

  37. C D0K- + p+ D0K+ + p- ー C

  38. Dynamic nuclear polarization With Microwave 電子スピンの 高偏極 (> 99 %) を核子スピン に移す

  39. μ μ μ μ μ μ 偏極方向 Superconductive Magnet 垂直方向磁場を用いた 磁場回転 偏極度を減らさずに 磁場方向を変えて 核子スピンを反転させる

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