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Electron Cloud Diagnostics in the SPS Machine

Electron Cloud Diagnostics in the SPS Machine. G. Arduini 1 , V. Baglin 3 , P. Collier 1 , B. Dehning 2 , G. Ferioli 2 , B. Henrist 3 , N. Hilleret 3 , B. Jenninger 3 , L. Jensen 2 , J.M. Jimenez 3 , J.M. Laurent 3 , K. Weiss 3 , F. Zimmermann 4 1 SL/OP, 2 SL/BI, 3 LHC/VAC, 4 SL/AP

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Electron Cloud Diagnostics in the SPS Machine

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  1. Electron Cloud Diagnosticsin the SPS Machine G. Arduini1, V. Baglin3, P. Collier1, B. Dehning2, G. Ferioli2, B. Henrist3, N. Hilleret3, B. Jenninger3, L. Jensen2, J.M. Jimenez3, J.M. Laurent3, K. Weiss3, F. Zimmermann4 1SL/OP, 2SL/BI, 3LHC/VAC, 4SL/AP CERN, Geneva, Switzerland

  2. Beam effects: bunch intensity, threshold Reminder • Intensity threshold : • August 1999: 4.3x1010 p/b  April 2000: 6.4x1010 p/b • Pressures do not vary appreciably up to a threshold bunch intensity and then, increase with the bunch intensity. • Amplitude of the signals measured on the pick-up also increase with the bunch intensity. • Influence of a magnetic field • Threshold in magnetic field free regions: 6.0 to 7.0x1010 p/b • Threshold in dipole magnetic fields: 3.0 to 4.0x1010 p/b  Cannot be attributed to systematic errors since the gauges do not resent the magnetic field. One explanation could come from the simulations which showed that the electrons of the e- cloud are confined in the vertical plane in a dipole magnetic field (F. Zimmerman).

  3. Beam effects: bunch intensity- No magnetic field - Reminder threshold

  4. Beam effects: bunch intensity- Dipole magnetic field - Reminder

  5. Beam effects: bunch intensity- No magnetic field - Reminder LHC-type beam characteristics: 1 batch of 72 bunches 6.9x1010 p/b 21 bunches visible 8.3x1010 p/b 41 bunches visible

  6. Beam effects: bunch intensity, threshold Reminder Magnetic field free region

  7. Beam effects: bunch intensity, threshold Reminder Dipole magnetic field region

  8. Scrubbing effect Reminder • Scrubbing effect observed in the SPS • Pressure rises decrease with time  30 times after about 2.5 integrated days of LHC-type beam  e- cloud activity no longer affect pressures • Threshold bunch intensity increased from 4.0x1010 in August 1999 up to 6.6x1010 in June 2000 • Clear indication of a modification of the characteristics of the surface • N2 glow discharge against e- cloud • First cycle of experiments showed no difference between the non-treated and treated chambers • After air exposure, treated chamber showed a memory of the scrubbing • Scrubbing effect is effective up to the bunch intensity used for the commissioning. Pressure will rise for higher bunch intensities

  9. Scrubbing effect Reminder

  10. Scrubbing effect Reminder

  11. “Strip” detector 300 Strip detector Vacuum chamber Holes Beam

  12. “Strip” detector - Holes distribution - Transparency of 7.5 % to avoid the extinction of the multipacting holes

  13. “Strip” detector Connecting wires Strips

  14. Triangle detector - Holes distribution - Transparency of 42 % to avoid the extinction of the multipacting

  15. Triangle detector Vacuum chamber Beam Holes Filtering grid Detecting plates

  16. Triangle detector Vacuum chamber Beam Holes Filtering grid Detecting plates

  17. “Triangle detector” Grid to avoid an extinction of the e- cloud Beam axis Reference plate Measuring plate

  18. Strip detector calibration Varying the bump amplitude to see the effect of the holes on the vacuum chamber

  19. Beam effects: Bunch intensity, threshold Threshold before (April 2000) and after venting (July 2001)

  20. Beam effects: Bunch intensity, threshold Threshold before (April 2000) and after venting (July 2001)

  21. Beam effects: Bunch intensity, threshold Measurements made with 48 bunches in the batch

  22. Beam effects: Bunch intensity, threshold Measurements made with 48 bunches in the batch

  23. Beam effects: Bunch intensity, threshold Appearance of two strips for high intensity beam (>6.0 1010 p/b)

  24. Beam effects: Bunch intensity, threshold Two strips at high intensities Pumping holes in the LHC beam screen

  25. Beam effects: Bunch intensity, threshold Energy distribution of the electrons in the cloud

  26. Beam effects: Bunch intensity, threshold Energy distribution of the electrons in the cloud 75 eV

  27. Beam effects: Bunch intensity, threshold Effect of the magnetic field on the energy distribution of the electrons in the cloud

  28. Beam effects: Bunch length Effect of the bunch length on the electrons in the cloud Bunch length: 5ns -> 2ns Bunch length: 5ns -> 2ns 2100 Gauss 150 Gauss

  29. Beam effects: Filling pattern Effect of the injection of three batches in the SPS

  30. Beam effects: Filling pattern Effect of the injection of three batches in the SPS

  31. Beam effects: Filling pattern Effect of an increase of the batch spacing

  32. No e- cloud detected -200 G +200 G Dipole field effect: Bunch intensity, threshold Magnetic field passing through 0 Gauss

  33. Dipole field effect: Bunch intensity, threshold Magnetic field passing through 0 Gauss

  34. Dipole field effect: Bunch intensity, threshold e- cloud intensity as a function of the dipole magnetic field Starting from 200 G Starting from 1200 G Starting from 2200 G

  35. Dipole field effect: Bunch intensity, threshold e- cloud intensity as a function of the dipole magnetic field

  36. Dipole field effect: Bunch intensity, threshold Strip width as a function of the dipole magnetic field 1100 Gauss 2100 Gauss 550 Gauss 200 Gauss

  37. Dipole field effect: Bunch intensity, threshold Strip width as a function of the dipole magnetic field

  38. Conclusions • Beam effects: bunch intensity, threshold, bunch length • Dipole field regions: threshold measured at 2.0x1010 p/b • 3.0x1010 p/b in 2000 • Field free regions: threshold measured at 5.0x1010 p/b • 6.0x1010 p/b in 2000 • lower threshold measured could be explained by the venting of the whole SPS to air during the long shutdown. • Below the threshold of the field free region, when the dipole magnetic field is switched off, the e- cloud signal immediately disappeared. • The bunch length affects strongly the e- cloud, decreasing the bunch length from 5ns to 2ns increase the intensity by 50%. • Current density • Above the threshold, the current increases linearly, up to 5.5x1010 p/b, no saturation effect was observed

  39. Conclusions • Width of the e- cloud • The width of the e- cloud strip increases with the beam intensity. At 6.0x1010 p/b, the width is already bigger than 20mm and therefore, the first line of holes (7.5 mm from the axis) in the beam screen sees the e- cloud. With the present design of the beam screen, the e- cloud will see the second line (11.5mm from the axis) at an intensity of 7.0x1010 p/b. • Effect of the magnetic field strength on the e- cloud • A strong effect of the dipole field strength on the e- could behavior was shown, mainly for field below 200 G. • Below 20 Gauss, the electron cloud disappears and a maximum was found around 50 gauss. • This effect does not affect the LHC since the field at injection is about 5500 Gauss

  40. Conclusions • Beam scrubbing • After 7h of LHC-type beam (integrated time above the threshold of 2.0x1010 p/b in the dipole field region), no cleaning effect is visible. • This result is consistent with the measurements of last year presented in EPAC. • Only low intensities <5.0x1010 p/b with small duty cycle (~ 5-10%) were used. This limitation was imposed by the fixed-target beam blow up induced by the e- cloud pressure rises

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