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Recent Developments in Polarized Solid Targets

Recent Developments in Polarized Solid Targets. H. Dutz, S. Goertz Physics Institute, University Bonn J. Heckmann, C. Hess, W. Meyer, E. Radke, G. Reicherz Institute for Experimental Physics, Ruhr-University Bochum. Contents: Luminosities of experiments with polarized targets

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Recent Developments in Polarized Solid Targets

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  1. Recent Developments in Polarized Solid Targets H. Dutz, S. Goertz Physics Institute, University Bonn J. Heckmann, C. Hess, W. Meyer, E. Radke, G. Reicherz Institute for Experimental Physics, Ruhr-University Bochum

  2. Contents: • Luminosities of experiments with polarized targets • The quality factor of a polarized target: The Figure of Merit • Polarized target Basics: Concept and components • The DNP process • The idea of spin temperatures • The role of the electron spin resonance line • The problem of polarizing deuterons • Three examples for an optimized preparation • The special challange of a large solid angle experiment • Developments concerning internal superconducting magnets • Summary

  3. Polarized Luminosities in Different Beams Lunpol = 1036 – 1037 cm-2s-1 Polarized Solid Targets: Frozen Spin Mode in dilution fridges: up to 107 1/s Continuous Mode in dilution fridges: up to 1 nA Continuous Mode in 4He- evaporators: up to 100 nA Gas Targets: Compressed 3He for external experiments: up to 30 mA H, D storage cells for internal experiments: up to 50 mA COMPASS E155 CB-ELSA < 100nA E154,3He L = 1036 cm-2s-1 < 30mA 1034 1032 1030 1028 HERMES 3He HERMES H,D < 50mA

  4. The Figure of Merit in Asymmetry Experiments - transverse target asymmetry in the case of spin-1/2 - H-Butanol: H H H H     H - C – C – C – C –OH     H H H H f=10/74~13.5% Measured counting rate asymmetry: Physics asymmetry for a pure target: Dilution factor: = fraction of polarizable nucleons Physics asymmetry for a dilute target: Absolute error of A: small

  5. Measuring time for DA = const : Target Figure of Merit: Typical FoM‘s (continuous polarization at B = 2.5 T, COMPASS like dilution fridge) increasing radiation hardness increasing dilution factors

  6. The Basic Concept of Dynamic Nuclear Polarization Doping and transfer of polarization Cryogenics: 1 K 100 mK NMR: 10 200 MHz Refrigerator Microwaves: 50 200 GHz Magnet: 2 7 T DAQ

  7. DNP in the Picture of Spin Temperature

  8. DNP in the Picture of Spin Temperature

  9. The special problem of low m nuclei (e.g. deuterons) DE • Minimize DE while maintaining the thermal contact: DE ~ O(nn) • Find a chemical radical with a narrow EPR line width • Try radiation doping if only low m nuclei present

  10. Part I: Material Developments

  11. Example 1: Electron irradiation of 6LiD • Idea: A. Abragam 1980, Saclay • Refinement of preparation: • Since 1991 in Bonn,from 1995 in Bochum  COMPASS D • F-Center: • s-wave electron • no g-anisotropy • weak HF interaction + Li 20 MeV at T = 185 K B 7Li (large m) impurity has considerable influence on Pmax 1 liter for COMPASS: Synthesized from highly enriched 6LiD (2000 Bochum)  Pmax = 55 % at 2.5 T

  12. Example 2: Electron irradiated deuterated Butanol Trityl

  13. Example 3: Trityl doped deuterated alcohols and diols @ B = 2.5 T

  14. Part II: Magnet Developments

  15. CB/ELSA @ Bonn: A 4p double polarization experiment in the frozen spin mode

  16. Disadvantages of the frozen spin mode: • Polarization decays while data taking • Pmax (frozen) ~ 0.8 · Pmax (cont.) • 3) Changing between polarization / measuring modes time consuming and dangerous ! Peff (frozen) ~ 0.7 · Pmax (cont.) • Ways out: • Huge polarizing magnet enclosing the detector • Thin polarizing magnet as part of the refrigerator Already realized as internal holding magnets since middle of 1990 (GDH @ Mainz & Bonn, CB/ELSA) 120mm • Challanges: • High field (B > 2T) with only a few layers  120A current: HT superconductors ! • Mechanical stability of the thin carrier structure  Stability of magnet operation • Homogeneous magnetic field (DB/B < 10-4) in a volume comparable to the field volume

  17. Status of the project: Collaboration together with IKP FZ-Jülich and IAM Bonn • Homogeneous volume can not be achieved just by correction coils !!! • Result extremely sensitive to positioning errors of the individual wires • But: Achieveable by a slightly non-cylindrical • shape plus correction coils (DB/B << 10-4 ?) • Theoretical work successfully finished • (patent application) • Test coil to be manufactored in the workshops • of the FZ-Jülich • Internal magnet for transverse polarization: • Saddle coil type with 7 layers • B = 0.5 T @ 30 A • Only problem: Mechanical stability • Order given to a company •  Delivery forseen during 2008

  18. Summary: • Due to the limited luminosity a successfull polarization experiment • demands an optimally working polarized target: • Choice of a suitable target material: • Dilution factor • Maximum polarization • Long relaxation times (frozen spin) • Sufficient radiation hardness (more intense beams) • Optimized operating conditions: • Cryostat: Suitable design / high perfomance and reliability • Magnet technology: • Magnets enabling a continuous polarization mode • Magnets for longitudinal AND transverse spin orientation

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