1. October 3, 2006E. Steffens – Spin 2006 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

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

3. October 3, 2006E. Steffens – Spin 2006 3 1 st 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

4. October 3, 2006E. Steffens – Spin 2006 4 Expectations Paris 1990 Talk on: ‚Experiments with Dense Polarized Internal Targets‘ I

5. October 3, 2006E. Steffens – Spin 2006 5 Expectations Paris 1990 II

6. October 3, 2006E. 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

7. October 3, 2006E. Steffens – Spin 2006 7 Past History: FILTEX

8. October 3, 2006E. Steffens – Spin 2006 8 Past History: FILTEX View into the FILTEX target chamber - rear: last 6-pole (SmCo) - center: T-shaped storage cell - right: cryopump with hole for beam 10 14 /cm 2 demon- strated! High polari- zation in weak field! W. Korsch, F. Rathmann, K. Zapfe, P. Schiemenz †

9. October 3, 2006E. Steffens – Spin 2006 9 The HERMES Experiment 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. 3 He target) Physics: see talk by E. Aschenauer (Wedn.) Requirements on the target: - Areal density t = 10 14 /cm 2 in two substatesOK - Sampling polarimeter with  P/P = 3% ? - Coating stable wrt synchrotron radiation(OK?) - Suppression of Wake Fields in the targetSimulations OK - Suppression of beam-induced (rf) depolarization „ „ „ Several open questions left...

10. October 3, 2006E. Steffens – Spin 2006 10 HERMES Target- Overview Target chamber

11. October 3, 2006E. 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

12. October 3, 2006E. Steffens – Spin 2006 12 Atomic Beam Source (ABS) Collimated cold atomic beams produced by disso- ciator with cold nozzle (100K) and differential pumping system (  S i ~10 4 l/s) Spin-dependent focussing of H and D atomic beams by 6-pole magnets: m J = +1/2 Nuclear polarization P z, P zz produced by means of rf transitions with ~100% effi- cieny; rapid switching enabled B c = 50.7 mT Heidelberg-Marburg-Munich-Madison

13. October 3, 2006E. Steffens – Spin 2006 13 Design of Target Chamber H&D e±e± Collimator C2 SC Coils Wake Field Suppr. G. Court – Liverpool T. Wise – Madison Target Cell 400mm

14. October 3, 2006E. Steffens – Spin 2006 14 Storage Cell Design 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 75  m 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 ! Liverpool-Madison-Ferrara

15. October 3, 2006E. Steffens – Spin 2006 15 Diagnostics Target gas analyzer (TGA) - measures degree of dissociation  to 1% in few minutes - molecules (with polarization fraction  ) dilute nuclear polarization - enters the final values of target polarization Sketch of the TGA: B. Braun, Ch. Baumgarten, P. Lenisa, et al

16. October 3, 2006E. Steffens – Spin 2006 16 Diagnostics Target gas analyzer (TGA) - measures degree of dissociation  to 1% in few minutes - molecules (with polarization fraction  ) dilute nuclear polarization - enters the final values of target polarization Temperature scan on new cell (hydrogen 1997)

17. October 3, 2006E. Steffens – Spin 2006 17 Diagnostics Target gas analyzer (TGA) - measures degree of dissociation  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!

18. October 3, 2006E. Steffens – Spin 2006 18 Diagnostics Target gas analyzer (TGA) At T = 100 K: stable water layer, suppresses recombination (  ≈ 1) At T = 260 K: water layer partly removed!

19. October 3, 2006E. Steffens – Spin 2006 19 Diagnostics Sampling polarimeter (BRP) - measures substate population n i of sample beam to  n/n = 1% in few minutes - BRP polarizations P e (electrons) and P z, P zz (nuclei) calculated - Sampling corrections applied to calculate P Target seen by the beam! Sample Beam Detector Schematic view of Sampling Polarimeter Erlangen-Heidelberg- Munich-Ferrara-Yerevan D. Braun, Ch. Baumgarten, G. Graw, D. Reggiani, P. Lenisa et al

20. October 3, 2006E. Steffens – Spin 2006 20 Diagnostics Sampling polarimeter (BRP) - measures substate population n i of sample beam to  n/n = 1% in few minutes Sample Beam Detector Hydrogen hfs- population as function of holding field B. Braun Thesis, Munich 1995

21. October 3, 2006E. Steffens – Spin 2006 21 Diagnostics Sampling polarimeter (BRP) - measures substate population n i of sample beam to  n/n = 1% in few minutes - BRP polarizations P e (electrons) and P z, P zz (nuclei) calculated BRP polarization for the deuterium run 2000 top: vector pol. P z bottom: tensor pol. P zz

22. October 3, 2006E. Steffens – Spin 2006 22 Beam-induced Depolarization HERA-e: Bunch frequency Bunch = 10.4 MHz Bunch length  t = 38 ps Harmonics n = n· B up to very high harmonics! (n max ≈ 10 3 corr. to 10 GHz) Resonance condition:  E(B n ) = h· n → resonant guide fields B n exist! h· n BnBn

23. October 3, 2006E. Steffens – Spin 2006 23 Beam-induced Depolarization  24 - blue:  resonances (  m F = ± 1) -red:  resonances (  m F = 0) narrow-spaced! Transverse target only  34

24. October 3, 2006E. Steffens – Spin 2006 24 Beam-induced Depolarization HERA-e: Bunch frequency Bunch = 10.4 MHz Bunch length  t = 38 ps Harmonics n = n· B up to very high harmonics! (n max ≈ 10 3 corr. to 10 GHz) Resonance condition:  E(B n ) = h· n → resonant guide field B n exists! B-scan of  -resonances  3-4  1-2 BRP used to detect the resonances induced by harmonics of the bunch field! Shown: the widely spaced  resonances Ferrara-Erlangen-Peking

25. October 3, 2006E. Steffens – Spin 2006 25 Beam-induced Depolarization HERA-e: Bunch frequency Bunch = 10.4 MHz Bunch length  t = 38 ps Harmonics n = n· B up to very high harmonics! (n max ≈ 10 3 corr. to 10 GHz) B-scan of  -resonances BRP used to detect the resonances induced by harmonics of the bunch field! Shown: the narrow  resonances No beam Correction coil For optimum setting of correction current: Small change of BRP detector current by the bunch field → Beam-induced depolarization is low! Ferrara-Erlangen-Peking

26. October 3, 2006E. Steffens – Spin 2006 26 Target Performance Target/yearH ║ (1997)D ║ (2000)H ┴ (2003)  r 0.0550.0030.004  P SE 0.035≤0.0010.055  P WD 0.02≤0.010.055  P BI absent 0.015 PTPT 0.851±0.0330.845±0.0280.795±0.033 t (10 14 nucl./cm 2 ) 0.72.11.1 FOM (P T 2 ·t) 0.51.50.7 recombination spin exchange wall depol. beam induced calculated target polarization → target areal density → Figure Of Merrit

27. October 3, 2006E. Steffens – Spin 2006 27 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