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Direct Measurement of Intra-beam Scattering in Atomic Beam Sources

Direct Measurement of Intra-beam Scattering in Atomic Beam Sources. Z.Ye for the HERMES Target Group DESY 16 th International Spin Physics Symposium, SPIN 2004, October 2004; ICTP, Trieste, Italy Introduction Measurement Principle Result from the HERMES-ABS Summary.

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Direct Measurement of Intra-beam Scattering in Atomic Beam Sources

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  1. Direct Measurement of Intra-beam Scattering in Atomic Beam Sources Z.Ye for the HERMES Target Group DESY 16th International Spin Physics Symposium, SPIN 2004, October 2004; ICTP, Trieste, Italy Introduction Measurement Principle Result from the HERMES-ABS Summary

  2. Introduction • Discrepancies between measured intensity and expected • HERMES ABS: 20% less than expected, Rest Gas Attenuation accounted N.Koch, Ph.D Thesis, Univ. Erlägen-Nürnberg (1999)

  3. Introduction • Discrepancies between measured intensity and expected • HERMES ABS: 20% less than expected, Rest Gas Attenuation accounted • VEPP-3 ABS: 40% less than expected, IBS estimated ~20% M.V.Dyug et. al, NIM A 495 (2002) 8-19

  4. Introduction • Discrepancies between measured intensity and expected • HERMES ABS: 20% less than expected, Rest Gas Attenuation accounted • VEPP-3 ABS: 40% less than expected, IBS estimated ~20% • IBS could be the candidate to explain these discrepancies. • However no direct measurement has been provided yet. • Difficult to measure by detecting the scattered atoms

  5. Introduction • Discrepancies between measured intensity and expected • HERMES ABS: 20% less than expected, Rest Gas Attenuation accounted • VEPP-3 ABS: 40% less than expected, IBS estimated ~20% • IBS could be the candidate to explain these discrepancies. • However no direct measurement has been provided yet. • Difficult to measure by detecting the scattered atoms. • Using a set of high frequency transitions between the sextupole magnets of the ABS, the IBS effect can be measured directly.

  6. How to measure IBS Intra-Beam Scattering (IBS) : Particles with different velocities in the beam scatter on each other and get lost

  7. How to measure IBS Intra-Beam Scattering (IBS) : Particles with different velocities in the beam scatter on each other and get lost • The relative loss of densitydue to IBS in a parallel beam is proportional to beam density , traveled distance , scattering cross-section , velocity spread and reverse of the square of mean velocity .

  8. How to measure IBS Intra-Beam Scattering (IBS) : Particles with different velocities in the beam scatter on each other and get lost • The relative loss of densitydue to IBS in a parallel beam is proportional to beam density , traveled distance , scattering cross-section , velocity spread and reverse of the square of mean velocity • Varying the beam density while keeping the other parameters of the beam unchanged, the IBS effect can be varied and measured

  9. How to measure IBS Intra-Beam Scattering (IBS) : Particles with different velocities in the beam scatter on each other and get lost • The relative loss of densitydue to IBS in a parallel beam is proportional to beam density , traveled distance , scattering cross-section , velocity spread and reverse of the square of mean velocity • Varying the beam density while keeping the other parameters of the beam unchanged, the IBS effect can be varied and measured

  10. Measuring IBS in an ABS

  11. Measuring IBS in an ABS

  12. Measuring IBS in the HERMES ABS

  13. Measuring IBS in the HERMES ABS • ABS intensity: : intensity loss due to RGA (IBS) in the 1st (2nd) part of the ABS. : transition efficiency of an atom in state become as an atom in state after the HFTs between the sextupoles. : transmission probability of an atom through the ABS which is in state before and in state after the HFTs between sextupoles

  14. Measuring IBS in the HERMES ABS • ABS intensity: • Nucleon magnetic moment is much smaller than electron magnetic moment: • Injection mode with ideally no atoms injected:

  15. Measuring IBS in the HERMES ABS

  16. Measuring IBS in the HERMES ABS

  17. Measuring IBS in the HERMES ABS

  18. Results with the HERMES ABS

  19. Results with the HERMES ABS

  20. Results with the HERMES ABS

  21. Results with the HERMES ABS

  22. Summary • A method to directly measure the IBS effect in an ABS by using a set of transitions between sextupoles is introduced. • Results using the HERMES ABS are presented. The results explain well the discrepancy between the measured intensity and the expected one. • The study confirms further that the IBS effect is relevant for ABSs and has to be taken into account in the design of future high intensity ABSs.

  23. IBS in VEPP-3ABS M.V.Dyug et. al, NIM A 495 (2002) 8-19 • Intensity is smaller than expected, IBS is roughly estimated to be 20%. Fig 9 Intensity of the focused deuterium beam versus the currents through the coils of the magnets. Fig 10 Calculated density near the beam axis along the ABS.

  24. IBS in the HERMES-ABS Z.Ye, Intra-Beam Scattering from Monte Carlo, under preparation

  25. IBS in the HERMES-ABS N.Koch, Ph.D Thesis, Univ. Erlagen-Nuernberg, DESY-Thesis-1999-015 • Rest Gas Attenuation was measured and calculated by MC simulation. Meas. Intensity Calculated (n=2) Calculated (n=5)

  26. High Frequency Transition • The effect of a HFT which exchanging atoms in state and , on the hyperfine populations of the hydrogen atoms can be described by a matrix : • For example, for a strong field transition (SFT) 2-4: where is the transition efficiency of SFT2-4. • Transition efficiencies larger than 98% for the HFT units used in the ABS and BRP for the HERMES experiment has been reported.

  27. Sextupole Magnet • The probability for a hydrogen atom to be transmitted by the sextupole magnet system can be described by a matrix: • Row refer to the hyperfine states in the first sextupole subsystem, while columns refer to the hyperfine states in the second sextupole subsystem. For example, a hydrogen atom in state interchanged to state by an ideal SFT 2-4 ( ) between the two sextupole subsystems has an absolute probability to enter the target cell. State 0.45 0.45 0.033 0.047 0.45 0.45 0.03 0.043 0.009 0.0085 0 0 0.013 0.013 0 0

  28. Measurement with SFT2-4/WFT1-3 Meas. No. HFT empl. states inj. ABS Beam Intensity 1 - 2 SFT2-4 3 WFT1-3 4 SFT2-4 & WFT1-3 No state

  29. Measurement with SFT2-4/MFT1-3 Meas. No. HFT empl. states inj. ABS Beam Intensity 1 - 2 SFT2-4 3 MFT1-3 4 SFT2-4 & MFT1-3 No state

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