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e-cloud in 800mm chamber @ IP2

e-cloud in 800mm chamber @ IP2. G. Iadarola , O. Dominguez, G. Rumolo. Thanks to: V. Baglin , G. Papotti. LHC Background Study Group meeting 19/03/2012. 800mm vacuum chamber @ IP2.

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e-cloud in 800mm chamber @ IP2

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  1. e-cloud in 800mm chamber @ IP2 G. Iadarola, O. Dominguez, G. Rumolo Thanks to: V. Baglin, G. Papotti LHC Background Study Group meeting 19/03/2012

  2. 800mm vacuum chamber @ IP2 • Vacuum team has reported pressure rise in 800mm common vacuum chambers on both sides of ALICE, with significant impact on background Ø 80cm Ø 20cm 27m

  3. Vacuum observations • Pressure measurements in the 800mm chambers on both sides of ALICE • Number of bunches per beam 1236 1092 1380 ALICE polarity flip seems to cause further worsening of vacuum quality followed by a slow conditioning

  4. Vacuum observations Ramp • Fill 1960 19-20/07/2011

  5. Vacuum observations Ramp • Fill 1960 19-20/07/2011 Pressure rise is strongly correlated to the injection of the last two batches from the SPS and already appears at 450GeV

  6. Vacuum observations Ramp • Fill 1960 19-20/07/2011 Pressure rise is strongly correlated to the injection of the last two batches from the SPS and already appears at 450GeV Does electron cloud explain this kind of behavior?

  7. Electron cloud build-up • Beam pipe transverse cut • In the LHC at 450GeV the Electron Cloud Effect is triggered by free electron generation due to beam induced residual gas ionization

  8. Electron cloud build-up • Beam pipe transverse cut • During the bunch passage the electrons are accelerated by the beam “pinched” at the center of the beam pipe

  9. Electron cloud build-up • Beam pipe transverse cut • During the bunch passage the electrons are accelerated by the beam “pinched” at the center of the beam pipe

  10. Electron cloud build-up • Beam pipe transverse cut • During the bunch passage the electrons are accelerated by the beam “pinched” at the center of the beam pipe

  11. Electron cloud build-up • Beam pipe transverse cut • During the bunch passage the electrons are accelerated by the beam “pinched” at the center of the beam pipe

  12. Electron cloud build-up • Beam pipe transverse cut • After the bunch passage the electrons hit the chamber’s wall (with E~100eV) • If the Secondary Electron Yield (SEY) of the surface is large enough, secondary electrons can be generated and growth of the total number of electrons is observed

  13. Electron cloud build-up • Beam pipe transverse cut • After the bunch passage the electrons hit the chamber’s wall (with E~100eV) • If the Secondary Electron Yield (SEY) of the surface is large enough, secondary electrons can be generated and growth of the total number of electrons is observed

  14. Electron cloud build-up • Beam pipe transverse cut • After the bunch passage the electrons hit the chamber’s wall (with E~100eV) • If the Secondary Electron Yield (SEY) of the surface is large enough, secondary electrons can be generated and growth of the total number of electrons is observed

  15. Electron cloud build-up • Beam pipe transverse cut • After the bunch passage the electrons hit the chamber’s wall (with E~100eV) • If the Secondary Electron Yield (SEY) of the surface is large enough, secondary electrons can be generated and growth of the total number of electrons is observed

  16. Electron cloud build-up • Beam pipe transverse cut • After the bunch passage the electrons hit the chamber’s wall (with E~100eV) • If the Secondary Electron Yield (SEY) of the surface is large enough, secondary electrons can be generated and growth of the total number of electrons is observed

  17. Electron cloud build-up • Beam pipe transverse cut • After the bunch passage the electrons hit the chamber’s wall (with E~100eV) • If the Secondary Electron Yield (SEY) of the surface is large enough, secondary electrons can be generated and growth of the total number of electrons is observed

  18. Electron cloud build-up • Beam pipe transverse cut • After the bunch passage the electrons hit the chamber’s wall (with E~100eV) • If the Secondary Electron Yield (SEY) of the surface is large enough, secondary electrons can be generated and growth of the total number of electrons is observed

  19. Electron cloud build-up • Beam pipe transverse cut • After the bunch passage the electrons hit the chamber’s wall (with E~100eV) • If the Secondary Electron Yield (SEY) of the surface is large enough, secondary electrons can be generated and growth of the total number of electrons is observed

  20. Electron cloud build-up • Beam pipe transverse cut • After the bunch passage the electrons hit the chamber’s wall (with E~100eV) • If the Secondary Electron Yield (SEY) of the surface is large enough, secondary electrons can be generated and growth of the total number of electrons is observed

  21. Electron cloud build-up • Beam pipe transverse cut • After the bunch passage the electrons hit the chamber’s wall (with E~100eV) • If the Secondary Electron Yield (SEY) of the surface is large enough, secondary electrons can be generated and growth of the total number of electrons is observed

  22. Electron cloud build-up • Beam pipe transverse cut • After the bunch passage the electrons hit the chamber’s wall (with E~100eV) • If the Secondary Electron Yield (SEY) of the surface is large enough, secondary electrons can be generated and growth of the total number of electrons is observed

  23. Electron cloud build-up • Beam pipe transverse cut • Secondary electrons are emitted with smaller energies (E~1eV) and, if they hit the wall before the following bunch passage, they are absorbed without generation of further secondaries • Decay of the total number of electrons can be observed in this stage

  24. Electron cloud build-up • Beam pipe transverse cut • Secondary electrons are emitted with smaller energies (E~1eV) and, if they hit the wall before the following bunch passage, they are absorbed without generation of further secondaries • Decay of the total number of electrons can be observed in this stage

  25. Electron cloud build-up • Beam pipe transverse cut • Secondary electrons are emitted with smaller energies (E~1eV) and, if they hit the wall before the following bunch passage, they are absorbed without generation of further secondaries • Decay of the total number of electrons can be observed in this stage

  26. Electron cloud build-up • Beam pipe transverse cut • Secondary electrons are emitted with smaller energies (E~1eV) and, if they hit the wall before the following bunch passage, they are absorbed without generation of further secondaries • Decay of the total number of electrons can be observed in this stage

  27. Electron cloud build-up • Beam pipe transverse cut • Secondary electrons are emitted with smaller energies (E~1eV) and, if they hit the wall before the following bunch passage, they are absorbed without generation of further secondaries • Decay of the total number of electrons can be observed in this stage

  28. Electron cloud build-up • Beam pipe transverse cut • Secondary electrons are emitted with smaller energies (E~1eV) and, if they hit the wall before the following bunch passage, they are absorbed without generation of further secondaries • Decay of the total number of electrons can be observed in this stage

  29. Electron cloud build-up • Beam pipe transverse cut • Secondary electrons are emitted with smaller energies (E~1eV) and, if they hit the wall before the following bunch passage, they are absorbed without generation of further secondaries • Decay of the total number of electrons can be observed in this stage

  30. Electron cloud build-up • Beam pipe transverse cut • Another bunch passage can interrupt the decay before reaching the initial value • In these cases avalanche multiplication is observed between bunch passages, and an exponential growth of the number of electrons happens during the bunch train passage

  31. Electron cloud build-up • Beam pipe transverse cut • Another bunch passage can interrupt the decay before reaching the initial value • In these cases avalanche multiplication is observed between bunch passages, and an exponential growth of the number of electrons happens during the bunch train passage

  32. Electron cloud build-up • Beam pipe transverse cut bunch spac. • Electron cloud effect is strongly dependent on bunch spacing!

  33. Electron cloud build-up Let us observe the electron number evolution at a certain section of the machine • LSS2

  34. Electron cloud build-up Let us observe the electron number evolution at a certain section of the machine • LSS2

  35. Electron cloud build-up Let us observe the electron number evolution at a certain section of the machine • LSS2

  36. Electron cloud build-up Let us observe the electron number evolution at a certain section of the machine • LSS2

  37. Electron cloud build-up Let us observe the electron number evolution at a certain section of the machine • LSS2

  38. Electron cloud build-up Let us observe the electron number evolution at a certain section of the machine • LSS2

  39. Electron cloud build-up The electron number grows during the passages of batches while a small decay is observed in the gaps between them • LSS2

  40. Electron cloud build-up The electron number grows during the passages of batches while a small decay is observed in the gaps between them • LSS2

  41. Electron cloud build-up The electron number grows during the passages of batches while a small decay is observed in the gaps between them • LSS2

  42. Electron cloud build-up The electron number grows during the passages of batches while a small decay is observed in the gaps between them • LSS2

  43. Electron cloud build-up The electron number grows during the passages of batches while a small decay is observed in the gaps between them • LSS2

  44. Electron cloud build-up The electron number saturates at a certain value due to the spacecharge forces inside the cloud • LSS2

  45. Electron cloud build-up The electron number saturates at a certain value due to the spacecharge forces inside the cloud • LSS2

  46. Electron cloud build-up The electron number saturates at a certain value due to the spacecharge forces inside the cloud • LSS2

  47. The electron number saturates at a certain value due to the spacecharge forces inside the cloud • LSS2

  48. Electron cloud build-up The electron number saturates at a certain value due to the spacecharge forces inside the cloud • LSS2

  49. Electron cloud build-up The electron number saturates at a certain value due to the spacecharge forces inside the cloud • LSS2

  50. Electron cloud build-up The electron number saturates at a certain value due to the spacecharge forces inside the cloud • LSS2

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