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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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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


Recent developments in polarized solid targets

  • 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


Recent developments in polarized solid targets

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


Recent developments in polarized solid targets

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


Recent developments in polarized solid targets

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


Recent developments in polarized solid targets

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


Recent developments in polarized solid targets

DNP in the Picture of Spin Temperature


Recent developments in polarized solid targets

DNP in the Picture of Spin Temperature


Recent developments in polarized solid targets

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


Recent developments in polarized solid targets

Part I: Material Developments


Recent developments in polarized solid targets

  • 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


Recent developments in polarized solid targets

Example 2: Electron irradiated deuterated Butanol

Trityl


Recent developments in polarized solid targets

Example 3: Trityl doped deuterated alcohols and diols

@ B = 2.5 T


Recent developments in polarized solid targets

Part II: Magnet Developments


Recent developments in polarized solid targets

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


Recent developments in polarized solid targets

  • 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


Recent developments in polarized solid targets

  • 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


Recent developments in polarized solid targets

  • 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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