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The HERMES Polarized H&D Gas Target: 10 Years of Operation

The HERMES Polarized H&D Gas Target: 10 Years of Operation. Erhard Steffens University of Erlangen-Nürnberg and HERMES Collaboration (DESY-Hamburg). Introduction and history Polarized gas targets in a high energy storage ring Overview of HERMES H&D target

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The HERMES Polarized H&D Gas Target: 10 Years of Operation

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  1. The HERMES Polarized H&D Gas Target: 10 Years of Operation Erhard Steffens University of Erlangen-Nürnberg and HERMES Collaboration (DESY-Hamburg) • Introduction and history • Polarized gas targets in a high energy storage ring • Overview of HERMES H&D target • Summary of runs 1996 to 2005 (H║, D║ H┴) • Conclusions E. Steffens – Spin 2006

  2. The Clue to High Density: Storage Cells • Storage Cell proposed by W. Haeberli • Proc. Karlsruhe 1965, p. 64 • Proc. Workshop IUCF 1984, AIP Conf. Proc.#128, p.251 • Ballistic flowfrom AtomicBeam Source (H, D) • Flow driven by pressure gradient Laser Driven Sources (H, D, 3He) Polarized atoms from source Target areal density given by t = L ro with ro = It / Ctot and Ctot = S Ci Note:Conductance of tube proportional to d3/L T-shaped storage cell Density gain compared to Jet of same intensity can be up to several hundred! E. Steffens – Spin 2006

  3. 1st Test of a Storage Cell in a 2 GeV Electron Storage Ring: VEPP-3 at BINP • Storage cell surface is coated to inhibit recombination and depolarization • Coatings like Teflon or Drifilm are sensitive to Synchrotron Radiation (= hard X-rays) • First test of storage cell (uncooled, Drifilm coating) performed by BINP-ANL collaboration in 1988: R.A. Gilman et al, PRL 65 (1990) 1733 • Results show that the coating is stable on the time scale of ½ year! Aymmetry for electro-disintegration of the deuteron as function of running time for a polarized deuterium storage cell target in the VEPP-3 storage ring at BINP Found later: In the cooled HERMES storage cell (T = 100 K) a water surface is formed with superior quality E. Steffens – Spin 2006

  4. Expectations Paris 1990 Talk on: ‚Experiments with Dense Polarized Internal Targets‘ I E. Steffens – Spin 2006

  5. Expectations Paris 1990 II E. Steffens – Spin 2006

  6. Past History: FILTEX • Goal: spin filtering of antiprotons (proposal 1985) • Tool: dense polarized H target in p_bar storage ring LEAR (CERN) • Test experiment with protons in the Heidelberg test storage ring TSR 1992 E. Steffens – Spin 2006

  7. Past History: FILTEX E. Steffens – Spin 2006

  8. Past History: FILTEX W. Korsch, F. Rathmann, K. Zapfe, P. Schiemenz † 1014/cm2 demon- strated! High polari- zation in weak field! • View into the FILTEX target chamber • rear: last 6-pole (SmCo) • center: T-shaped storage cell • right: cryopump with hole for beam E. Steffens – Spin 2006

  9. HERMES experiment proposed for the HERA 30 GeV polarized electron ring - Letter of Intent 1988 - Proposal 1990 - Technical Design Report 1993 - First Operation in April 1995 (with pol. 3He target) The HERMES Experiment Physics: see talk by E. Aschenauer (Wedn.) • Requirements on the target: • - Areal density t = 1014/cm2 in two substates OK • - Sampling polarimeter with DP/P = 3% ? • - Coating stable wrt synchrotron radiation (OK?) • - Suppression of Wake Fields in the target Simulations OK • - Suppression of beam-induced (rf) depolarization „ „ „ Several open questions left... E. Steffens – Spin 2006

  10. HERMES Target- Overview Target chamber E. Steffens – Spin 2006

  11. HERMES Target 1996 H-Target installed in early 1996 Erlangen Liverpool Madison Marburg Munich Yerevan F. Stock B. Braun G. Graw G. Court T. Wise et al E. Steffens – Spin 2006

  12. Collimated cold atomic beams produced by disso-ciator with cold nozzle (100K) and differential pumping system (SSi ~104 l/s) Spin-dependent focussing of H and D atomic beams by 6-pole magnets: mJ= +1/2 Nuclear polarization Pz,Pzzproduced by means of rf transitions with ~100% effi-cieny; rapid switching enabled Atomic Beam Source (ABS) Heidelberg-Marburg-Munich-Madison Bc = 50.7 mT E. Steffens – Spin 2006

  13. Design of Target Chamber G. Court – Liverpool T. Wise – Madison H&D Collimator C2 e± Target Cell 400mm Wake Field Suppr. SC Coils E. Steffens – Spin 2006

  14. Cell optimized for operation in an electron storage ring Conducting surface with smooth variation of cross section excitation of wake fields! System of W collimators for protection against beam and SR Cooled via cooling rails by cold He gas to 60-100K 75mm Al walls with Drifilm coating - Radiation damage visible! But: Very effective wall coating due to ice layer maintained by small fraction of water in the atomic beam ! Storage Cell Design Liverpool-Madison-Ferrara E. Steffens – Spin 2006

  15. Diagnostics B. Braun, Ch. Baumgarten, P. Lenisa, et al • Target gas analyzer (TGA) • -measures degree of dissociation a to 1% in few minutes • - molecules (with polarization fraction b) dilute nuclear polarization • - enters the final values of target polarization Sketch of the TGA: E. Steffens – Spin 2006

  16. Diagnostics • Target gas analyzer (TGA) • -measures degree of dissociation a to 1% in few minutes • - molecules (with polarization fraction b) dilute nuclear polarization • - enters the final values of target polarization Temperature scan on new cell (hydrogen 1997) E. Steffens – Spin 2006

  17. Diagnostics • Target gas analyzer (TGA) • -measures degree of dissociation a to 1% in few minutes Temperature scan on used cell (deuterium 2000) after formation of water layer no T-dependence visible no recombination in the cell! E. Steffens – Spin 2006

  18. Diagnostics • Sampling polarimeter (BRP) • -measures substate population ni of sample beam to Dn/n = 1% in few minutes • - BRP polarizations Pe (electrons) and Pz , Pzz (nuclei) calculated • - Sampling corrections applied to calculate PTarget seen by the beam! Erlangen-Heidelberg-Munich-Ferrara-Yerevan D. Braun, Ch. Baumgarten, G. Graw, D. Reggiani, P. Lenisa et al Detector Sample Beam Schematic view of Sampling Polarimeter E. Steffens – Spin 2006

  19. Diagnostics • Sampling polarimeter (BRP) • -measures substate population ni of sample beam to Dn/n = 1% in few minutes Hydrogen hfs-population as function of holding field Detector Sample Beam B. Braun Thesis, Munich 1995 E. Steffens – Spin 2006

  20. Diagnostics • Sampling polarimeter (BRP) • -measures substate population ni of sample beam to Dn/n = 1% in few minutes • - BRP polarizations Pe (electrons) and Pz , Pzz (nuclei) calculated BRP polarization for the deuterium run 2000 top: vector pol. Pz bottom: tensor pol. Pzz E. Steffens – Spin 2006

  21. Beam-induced Depolarization • HERA-e: • Bunch frequency nBunch = 10.4 MHz • Bunch length st = 38 ps Harmonics nn = n·nB up to very high harmonics! (nmax≈ 103 corr. to 10 GHz) h·nn Resonance condition: DE(Bn) = h·nn → resonant guide fields Bn exist! Bn E. Steffens – Spin 2006

  22. Beam-induced Depolarization • blue:p resonances (DmF = ± 1) • red:s resonances (DmF = 0) narrow-spaced! • Transverse target only s24 p34 E. Steffens – Spin 2006

  23. Beam-induced Depolarization Ferrara-Erlangen-Peking BRP used to detect the resonances induced by harmonics of the bunch field! Shown: the widely spaced p resonances • HERA-e: • Bunch frequency nBunch = 10.4 MHz • Bunch length st = 38 ps Harmonics nn = n·nB up to very high harmonics! (nmax≈ 103 corr. to 10 GHz) Resonance condition: DE(Bn) = h·nn → resonant guide field Bn exists! p 3-4 p 1-2 B-scan of p-resonances E. Steffens – Spin 2006

  24. Beam-induced Depolarization Ferrara-Erlangen-Peking BRP used to detect the resonances induced by harmonics of the bunch field! Shown: the narrow s resonances • HERA-e: • Bunch frequency nBunch = 10.4 MHz • Bunch length st = 38 ps Harmonics nn = n·nB up to very high harmonics! (nmax≈ 103 corr. to 10 GHz) Correction coil For optimum setting of correction current: Small change of BRP detector current by the bunch field → Beam-induced depolarization is low! No beam B-scan of s-resonances E. Steffens – Spin 2006

  25. Target Performance recombination spin exchange wall depol. beam induced calculated target polarization → target areal density → Figure Of Merrit E. Steffens – Spin 2006

  26. Conclusions • Polarized H&D target successfully operated over 10 years in a HE electron storage ring more or less continuesly • Several problems solved during commissioning phase(s) thanks to many enthousiastic collaborators – impossible to name them all! • Nature was kind to us (no show-stopper)  • Technology ready to be used for other projects! www.fz-juelich.de/ikp/pax E. Steffens – Spin 2006

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