1. BE-ABP-HSC Electron cloud simulations in the LHC MKI Electron Cloud meeting 4-12-14 A. Romano, G. Iadarola, G. Rumolo Many thanks to: M. Barnes, M. Taborelli

2. BE-ABP-HSC Electron Cloud meeting 4-12-14 Outline LHC MKI ceramic tube Numerical challenge for high SEY Analysis of simulation results Summary and conclusions

3. BE-ABP-HSC LHC Injection Kicker Magnets Electron Cloud meeting 4-12-14 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

4. 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 4-12-14

5. BE-ABP-HSC Realistic model of the LHC MKI chamber x [m] y [m] D=42.0 mm Nickel-Chrome conductors Electron Cloud meeting 4-12-14  Suitable alumina data measured by TE/VSC (M. Taborelli): SEY = [7.0-13] Emax=[700-2000] eV  SEY of Nickel- Chrome conductors: SEY = [1.0-1.4] Alumina

6. BE-ABP-HSC EC simulations in PyECLOUD Electron Cloud meeting 4-12-14 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!!!!!

7. BE-ABP-HSC MPs size management in PyECLOUD Electron Cloud meeting 4-12-14 The regeneration of the set of MPs is applied only once per bunch passage!!!!!

8. BE-ABP-HSC Numerical challenge for high SEY (1/4) Electron Cloud meeting 4-12-14 size of allocated arrays Passage 0 1 2 3 Why? regeneration threshold Simulation crashes here

9. BE-ABP-HSC Numerical challenge for high SEY (1/4) Electron Cloud meeting 4-12-14 Passage 0 1 2 3 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

10. BE-ABP-HSC Numerical challenge for high SEY (2/4) Electron Cloud meeting 4-12-14 Passage 0 1 2 3  1 st Attempt The splitting factor is modified and it becomes function of the SEY: from 1.5 δ max + 0.5

11. The splitting factor is modified and it becomes function of the SEY: from 1.5 δ max + 0.5 BE-ABP-HSC Numerical challenge for high SEY (2/4) Electron Cloud meeting 4-12-14 Passage 0 1 2 3 the number of MPs decreases only another passage is completed …. but it’s not enough!!!  1 st Attempt

12. Passage 0 1 2 3 BE-ABP-HSC Numerical challenge for high SEY (3/4) Electron Cloud meeting 4-12-14  2 nd Attempt Also the size of bunch slot is modified. Before was: Bunch slot = 25 ns Few check points for regeneration

13. BE-ABP-HSC Numerical challenge for high SEY (3/4) Electron Cloud meeting 4-12-14  2 nd Attempt Also the size of bunch slot is modified. Now is: Bunch slot = 2.5 ns More check points for regeneration

14. BE-ABP-HSC Numerical challenge for high SEY (4/4) Electron Cloud meeting 4-12-14  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

15. 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 4-12-14

16. 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 4-12-14

17. 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 4-12-14

18. 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 4-12-14

19. 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 4-12-14

20. BE-ABP-HSC Electron Cloud meeting 4-12-14 At beginning of the simulation

21. BE-ABP-HSC Conclusions: Electron Cloud meeting 4-12-14 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

22. BE-ABP-HSC Thanks for your attention! Electron Cloud meeting 4-12-14

23. BE-ABP-HSC Electron Cloud meeting 4-12-14 Just before the saturation