1 / 11

ZS with LHC-type beams

Brief review on electron cloud simulations for the SPS electrostatic septum (ZS) G. Rumolo and G. Iadarola in LIU-SPS ZS Review, 20/02/2013. ZS with LHC-type beams Study of electron cloud build up thresholds in a ZS-like geometry with LHC25 beams : Without external fields

vea
Download Presentation

ZS with LHC-type beams

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Brief review on electroncloudsimulationsforthe SPS electrostaticseptum (ZS)G. Rumolo and G. Iadarola in LIU-SPS ZS Review, 20/02/2013 • ZS withLHC-typebeams • Study of electroncloudbuild up thresholds in a ZS-likegeometrywith LHC25 beams: • Withoutexternalfields • Withthevoltagefromtheion traps • Someconclusions New simulations run with PyECLOUD with the correct model/geometry

  2. Some practical information on the ZS From J. Wenninger, Introduction to Slow Extraction to the North Targets Anode Cathode -3kV -6kV Ion-traps 20mm V=-220kV • 2000 W.75Re.25 septum wires. • Wire diameter 50 mm (first ZS) to 100 mm. • Wire spacing 1.5 mm.

  3. ZS during SPS operation with high intensity LHC beams • Instructions when high intensity LHC beams are in the SPS: • Retracted girder (not anymore after 2010 to allow || MDs & conditioning) • HV 0 kV (not anymore after 2010, 20-100 kV applied, reduces outgassing) • Ion traps on • Observations at the ZS with 25 ns high intensity beam (see also talks from Bruno and Karel): • Above certain intensities (nominal beam, more than 1 batch injected) vacuum spike in the ZS observed • The increased vacuum levels can provoke a vacuum interlock, which stops the ion traps and hence the beam in the machine. In this sense, “ZS limits the LHC beam” • By increasing the bunch length the vacuum does not degrade. • Sparking occasionally occurs (ramp, ejection) • Ion trap voltage drop and current measured off the plates • Does not appear to be the principal problem, rate decreasing • Some hints that e-cloud could build up in the ZS, even if the presence of a voltage should clear electrons….

  4. Electron cloud simulationsthe ZS geometry without external fields lec = 1010e-/m 46 mm 140 mm • In absence of voltage from the ion traps • significant electron cloud builds up for dmax > 1.5 • the electron cloud between bunches is uniformly distributed over the chamber cross section

  5. Electron cloud simulations including the voltage from the ion traps lec = 103e-/m E 46 mm 140 mm • Assuming a voltage of 3 kV between the bottom and top plates • the electron cloud is suppressed at least up to dmax =2.0 (different build up curves are all below the one for dmax =2.0)

  6. Electron cloud simulations including the voltage from the ion traps Zoom of previous plot in the first 0.3 ms E 46 mm 140 mm • Assuming a voltage of 3 kV between the bottom and top plates • the electron cloud is suppressed at least up to dmax =2.0 (different build up curves are all below the one for dmax =2.0) • the electrons are fully cleared between subsequent bunches and there is no visible dependence on the SEY of the plate.

  7. Electron cloud simulationsscanning the voltage values V = 100 V • For V=100 V the SEY threshold lies also around 1.5 • Assuming dmax =1.7 and scanning the voltage between the bottom and top plate • the electron cloud is found to be fully suppressed for 500 V ≤ V < 4 kV • V=100 V is not sufficient and a strong electron cloud is formed (with a faster rise time than V=0 but a faster decay, too, due to the clearing voltage)

  8. Electron cloud simulationsscanning the voltage values dmax =1.7, zoom on the first 50 ns • Changing the voltage, we actually change the clearing efficiency • electrons are cleared more efficiently (i.e. more quickly) with higher voltages • However, if the voltage becomes • too low (<500 V), the intra-bunch clearing is insufficient and multipacting cannot be avoided • the quoted clearing voltage values also depend on having assumed in the model a maximum SEY at Emax=230 eV and R0=0.7

  9. Electron cloud simulationselectron dynamics and distribution No voltage applied

  10. Electron cloud simulationselectron dynamics and distribution V = 3 kV

  11. Summary and conclusions • All the simulations have been re-run with the PyECLOUD, which allows for the use of the correct chamber shape (both correct geometric and electromagnetic boundary conditions) • The geometry of the ZS is confirmed to be prone to electron cloud build up with LHC25 beams at nominal intensity • in absence of the voltage from the ion traps, there is electron cloud build up for maximum SEY above 1.5 • A difference of potential between top and bottom plate is certainly effective to clear the electrons from residual gas ionization between bunches • voltage should be at least a few hundreds V (100V certainly not enough)

More Related