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Motivation Polarized 3 He gas target Solenoid design and test 3 He feasibility test

Johannes Gutenberg-Universit ä t Mainz Institut f ü r Kernphysik. Study for the use of the polarized 3 He target at the photon beam of MAMI. Motivation Polarized 3 He gas target Solenoid design and test 3 He feasibility test Summary and outlook.

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Motivation Polarized 3 He gas target Solenoid design and test 3 He feasibility test

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  1. Johannes Gutenberg-Universität Mainz Institut für Kernphysik Study for the use of the polarized 3He target at the photon beam of MAMI • Motivation • Polarized 3He gas target • Solenoid design and test • 3He feasibility test • Summary and outlook Patricia Aguar Bartolomé

  2. Motivation • Test of the GDH sum rule on the neutron • Double polarization experiments • 3He gas as neutron target for real photon beams • Number of neutrons • 2 cmD-butanol target • 20 cm 3He gas target (p = 6 bar) Patricia Aguar Bartolomé

  3. Polarized 3He gas target • 3He is made of two protons and one neutron • In the ground state the two protons couple together cancel their spin contribution to the nuclear magnetic moment • 3He spin is carried by the unpaired neutron Patricia Aguar Bartolomé

  4. 3He Polarization Metastability Exchange Optical Pumping(Colegrove et al., Phys. Rev. 132 (1963) 2561) • Electronic optical pumping in the 2 3S1 • State + transfer of polarization to the • Nucleus by hyperfine coupling • Metastability collisions transfer of • Nuclear polarization to the 1 1S0 state Result Nuclear polarization of the 1 1S0 ground state Patricia Aguar Bartolomé

  5. 3He polarization relaxation The polarization decays with a time constant, The overall relaxation time, is given by The relaxation is caused by • Magnetic dipole-dipole interactions between 3He atoms ( ) • Wall relaxation on the inner surface of the cell ( ) Gas stored in special ironfree glass vessels. Patricia Aguar Bartolomé

  6. 3He polarization relaxation (cont.) Transport in homogenous magnetic field • Magnetic field gradients ( ) The required relative field gradient is • Interactions with gas impurities ( ) The cell and gasses must be very clean. • Ionization due to the experimental photon beam ( ). Patricia Aguar Bartolomé

  7. Solenoid design Polarized targets require a magnetic holding field, B0, to provide a quantization axis. SOLENOID The strength and uniformity of the field play an important role in obtaining long polarization relaxation times. Depolarization effects due to field gradients should be smaller than the relaxation due to surface effects. • Main constraints • Produce magnetic holding field of 7G with a relative field gradient of 10-3 cm-1for 6 bars in the target cell area. • Appropriate outer radius to fit inside the Crystal Ball detector. • Target cell dimensions determine the inner radius. • The outgoing particles have to pass the coil minimization of the wire thickness. Patricia Aguar Bartolomé

  8. Magnetic field calculation • Numerical calculation of the field and gradients with a finite • element code (FEMM) • Geometric parameters for the solenoid Parameter Value Longitud solenoide No vueltas Corriente Diámetro interior Diámetro exterior Diámetro conductor 80 cm 1457 0.3 A 82.0 mm 83.06 mm 0.53 mm • Coil wound on a CFK-tube with cross section of 82 x 1 mm2 and 120 cm • length. • B magnitude determined using the three axis magnetometer MAG-03 MS • (Bartington Instruments Ltd.) Patricia Aguar Bartolomé

  9. Solenoid test Patricia Aguar Bartolomé

  10. 3He feasibility test • Goal:Study the ratio of nuclear scattering events produced on the windows • of the target cell compared to that produced on the gas. • Detectors • Scattering experiment performed with the 855 MeV polarized photon beam at MAMI. • Main detector was CB. • Vertex detector consisting of two coaxial • MWPCs with cathode readout. • PID coaxial with the MWPCs used to identify charged particles. Patricia Aguar Bartolomé

  11. Experimental setup 20 cm • Quartz • 100 cm3 • 0.4 cm wall • Pressure up 10 bar • kapton windows • Entrance cell window placed 2 cm downstream • from CB center • Leak test performed in the whole system Patricia Aguar Bartolomé

  12. Data analysis and results Analysis focused on identifying hadronic events from the particles scattered in the target cell. Nw / Ng = 0.93 Experiment is possible!!! Patricia Aguar Bartolomé

  13. Summary and outlook • Conclusions • A solenoid produced to provide the holding field for the 3He target • was designed and tested • First measurements of the homogeneity give values of • 3He feasibility test was successfully performed giving a 0.93 ratio which is in good agreement with the 0.89 theoretical prediction EXPERIMENT IS POSSIBLE!!! • Future • Production of a new cylindrical target cell aluminosilicate materials present better relaxation times • New measurements for the relaxation time in a polarized cell placed • inside the solenoid Patricia Aguar Bartolomé

  14. 3He PolarizationSpin-exchange optical pumping(Bouchiat et al., Phys. Rev. Lett. 5 (1960) 373) • Circularly polarized light at 795 nm • optically pumps an alkali-metal • vapor optical electron spins • aligned along the quantization axis. • Spin-exchange collisions between • Rb and the 3He transfer of • angular momentum from Rb to 3He • nuclei Patricia Aguar Bartolomé

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