BE-ABP-HSC Electron cloud simulations in the LHC MKI Electron Cloud meeting A. Romano, G. Iadarola, G. Rumolo Many thanks to: M. Barnes, M. Taborelli

BE-ABP-HSC Electron Cloud meeting Outline LHC MKI ceramic tube Numerical challenge for high SEY Analysis of simulation results Summary and conclusions

BE-ABP-HSC LHC Injection Kicker Magnets Electron Cloud meeting MKIs deflect the incoming particle beams onto the accelerators closed orbits To limit the longitudinal beam coupling impedance of the MKI, a ceramic tube with screen conductors on its inner wall is placed within the aperture of the magnet …but during 2012 operation, significant pressure rise due to the electron cloud occurred in and nearby the MKIs

BE-ABP-HSC Realistic model of the LHC MKI chamber x [m] y [m] D=42.0 mm Nickel-Chrome conductors Alumina Electron Cloud meeting

BE-ABP-HSC Realistic model of the LHC MKI chamber x [m] y [m] D=42.0 mm Nickel-Chrome conductors Electron Cloud meeting  Suitable alumina data measured by TE/VSC (M. Taborelli): SEY = [7.0-13] Emax=[ ] eV  SEY of Nickel- Chrome conductors: SEY = [ ] Alumina

BE-ABP-HSC EC simulations in PyECLOUD Electron Cloud meeting Due to the multipacting effect, the number of electrons increases exponentially The reference size of macroparticles ( MPs) is dynamically adapted during the simulation to keep reasonable computation burden When the number of MPs become larger than a certain threshold, a regeneration algorithm is applied After the MP’s impact N emitted < 1.5 N ref  the size of MP is rescaled according to SEY N emitted > 1.5 N ref  ‘true’ secondary MPs are generated with size as close as possible to N ref 1.5 is an arbitrary factor of splitting!!!!!

BE-ABP-HSC MPs size management in PyECLOUD Electron Cloud meeting The regeneration of the set of MPs is applied only once per bunch passage!!!!!

BE-ABP-HSC Numerical challenge for high SEY (1/4) Electron Cloud meeting size of allocated arrays Passage Why? regeneration threshold Simulation crashes here

BE-ABP-HSC Numerical challenge for high SEY (1/4) Electron Cloud meeting Passage MPs number at the end of 2 nd passage MPs number when it is exactly stopped The simulation is stopped because the number of MPs goes beyond size of allocated arrays Since this happens before of the end of the passage, the regeneration is not applied!!!!!!!!!!! size of allocated vectors regeneration threshold

BE-ABP-HSC Numerical challenge for high SEY (2/4) Electron Cloud meeting Passage  1 st Attempt The splitting factor is modified and it becomes function of the SEY: from 1.5 δ max + 0.5

The splitting factor is modified and it becomes function of the SEY: from 1.5 δ max BE-ABP-HSC Numerical challenge for high SEY (2/4) Electron Cloud meeting Passage the number of MPs decreases only another passage is completed …. but it’s not enough!!!  1 st Attempt

Passage BE-ABP-HSC Numerical challenge for high SEY (3/4) Electron Cloud meeting  2 nd Attempt Also the size of bunch slot is modified. Before was: Bunch slot = 25 ns Few check points for regeneration

BE-ABP-HSC Numerical challenge for high SEY (3/4) Electron Cloud meeting  2 nd Attempt Also the size of bunch slot is modified. Now is: Bunch slot = 2.5 ns More check points for regeneration

BE-ABP-HSC Numerical challenge for high SEY (4/4) Electron Cloud meeting  2 nd Attempt …. simulation complete!!! Also the size of bunch slot is modified. Now is: Bunch slot = 2.5 ns More check points for regeneration

BE-ABP-HSC SEY threshold – Nickel Chrome SEY 1.4 The SEY threshold of the Electron Cloud (EC) build up is around 2.0. The high SEY of the alumina induces a strong electron multipacting. Electron Cloud meeting

BE-ABP-HSC SEY threshold – Nickel Chrome SEY 1.3 The SEY threshold of the Electron Cloud (EC) build up is around 2.0. The high SEY of the alumina induces a strong electron multipacting. Electron Cloud meeting

BE-ABP-HSC SEY threshold – Nickel Chrome SEY 1.2 The SEY threshold of the Electron Cloud (EC) build up is around 2.0. The high SEY of the alumina induces a strong electron multipacting. Electron Cloud meeting

BE-ABP-HSC SEY threshold – Nickel Chrome SEY 1.1 The SEY threshold of the Electron Cloud (EC) build up is around 2.0. The high SEY of the alumina induces a strong electron multipacting. Electron Cloud meeting

BE-ABP-HSC SEY threshold – Nickel Chrome SEY 1.0 The SEY threshold of the Electron Cloud (EC) build up is around 2.0. The high SEY of the alumina induces a strong electron multipacting. Electron Cloud meeting

BE-ABP-HSC Electron Cloud meeting At beginning of the simulation

BE-ABP-HSC Conclusions: Electron Cloud meeting The implementation of the LHC MKI model in PyECLOUD represented an interesting numerical challenge As expected, the high SEY value of the alumina induces a strong electron multipacting. According to this, a different simulation set-up had to be found: - different MPs splitting criterion - more regeneration check points along the simulation The results obtained show that the presence of the alumina inside the chamber strongly affects the EC build-up

BE-ABP-HSC Thanks for your attention! Electron Cloud meeting

BE-ABP-HSC Electron Cloud meeting Just before the saturation