The hermes polarized target
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The HERMES polarized target. Paolo Lenisa – Universita’ and INFN – Sez. Ferrara, Italy. Principle of operation Target polarization Performance Discussion. The target in the HERMES experiment. Atomic Beam Source NIM A 505, (2003) 633. Principle of operation.

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The HERMES polarized target

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The hermes polarized target

The HERMES polarized target

Paolo Lenisa – Universita’ and INFN – Sez. Ferrara, Italy

  • Principle of operation

  • Target polarization

  • Performance

  • Discussion


The hermes polarized target

The target in the HERMES experiment


Principle of operation

Atomic Beam Source

NIM A 505, (2003) 633

Principle of operation

Y. Ye :“Direct measurement of Intrabeam

Scattering in Atomic Beam Sources”


The hermes polarized target

Atomic Beam Source

NIM A 505, (2003) 633

Principle of operation

Pz+ = |1> + |4>

Pz- = |2> + |3>


The hermes polarized target

Atomic Beam Source

NIM A 505, (2003) 633

Storage cell

NIM A 496, (2003) 277

Diagnostics:

  • Target Gas Analyzer

    NIM A 508, (2003) 265

  • Breit-Rabi Polarimeter

    NIM A 482, (2002) 606

Principle of operation


The hermes polarized target

Target operation

Longitudinal Polarization (B=335 mT)

  • 1996 - 1997 Hydrogen

  • 1999 - 2000 Deuterium

TransversePolarization (B=297 mT)

  • 2002 - … Hydrogen


The storage cell

The storage cell

Material:75 mm Al with Drifilm coating

Size: length: 400mm, elliptical cross section (21 mm x 8.9 mm)

Working temperature: 100 K ( variable 35 K – 300 K)


The hermes polarized target

The storage cell

  • Advantages:

    • No diluition

    • Rapid inversion of polarization

    • Increase in density respect free jet (~100)

(Supposed) drawbacks


Beam induced depolarization

  • Resonance condition:

Depolarization

Beam induced depolarization

Hera e-beam time structure:

  • 220 bunches

  • Spacing: Dt = 96 ns

  • Width: st = 37.7 ps

Fourier analysis of e-bunch:


Resonance conditions

DB magnet 0.15 mT

Resonance conditions

p transitions (BST  BRF)long.&trans.

s transitions (BST  BRF)trans. only

DB s2-4 = 0.37 mT


Transverse hydrogen running holding field

Transverse hydrogen running: holding field

B = 297 mT DB  0.15 mT


S resonance measurements

s resonance measurements

Spin flip measurement

  • e-beam current: > 20 mA

  • Injection: state |4>

  • Target field: scanned around working point (297 mT)

  • Detection: states |1> and |2>

    A peak in the signal indicates a resonance

D. Reggiani:

“Beam Induced Depolarization

in the HERMES polarized target”


Target polarization

Eur. Phys. J. D 29 (2004) 21

Target polarization

  • PT = total target polarization

  • a0 =atomic fractionin absence of recombination

  • ar=atomic fractionsurviving recombination

  • Pa= polarization of atoms

  • Pm = polarization of recombined molecules

  • Relation to measured quantities:

    • Sampling corrections

      • ar=caarTGA

      • Pa= cPPaBRP


The hermes polarized target

Target performance

Longitudinal Polarization (B=335 mT)

  • 1996-1997 Hydrogen

1999-2000 Deuterium

Pt = 0.845 ± 0.028


The hermes polarized target

Target performance

Longitudinal Polarization (B=335 mT)

  • 1996-1997 Hydrogen

  • 1999-2000 Deuterium

Pt = 0.845 ± 0.028


The hermes polarized target

Target performance

Transverse Polarization (B=297 mT)

  • 2002 - … Hydrogen

PT = 0.795  0.033


Summary of target performance since 1997

HERMES Coll.: submitted

Summary of target performance since 1997


The hermes polarized target

Conclusions

  • The HERMES H/D polarized target is stably and reliably running since 1996.

    • High-polarization (P>80 %)

    • The systematics is fully under control (DP = 3%)

  • It expresses the work of:

    • 10 PhD thesis

    • 7 Diploma thesis

    • 17 senior scientists

  • It will be decommissoned in sommer 2005 (?)

    but this is not the end of the story…

The target is ready for new challenges:

F. Rathmann : “Spin-physics at GSI”


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