Jim Crittenden Electron Cloud Meeting 4 December 2013

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Presentation transcript:

Jim Crittenden Electron Cloud Meeting 4 December 2013 Updated Status of the Modeling of Electron Cloud Trapping in Q48W -- Slides of 27 November updated and augmented -- -- Updated following meeting with corrected wall profile on slide 7 as used by Synrad3D -- Jim Crittenden Electron Cloud Meeting 4 December 2013

Single bunch at 490-ns delay provides increased clearing. Clearing trapped electrons using intermediate bunches (JPS measurements 11/5 and 11/19) About 15-20% signal reduction for 6-bunch trains at 490 and 980 ns delay Single bunch at 490-ns delay provides increased clearing.

Present Status of ECLOUD Model Without witness train With 6-bunch witness train starting at bunch 91 (994-ns delay) 3.52e10 2.83e10 0.35/7.96 = 4.4% of cloud is trapped with no witness train. Model of cloud buildup shows clearing effect at 20% (1-2.83/3.52). Consistent with signal reduction. (Delay still wrong, should have been 980 ns)

Present status of ECLOUD model Without witness train With 6-bunch witness train starting at bunch 91 (994-ns delay) Secondary yield model (stainless steel) improved. Statistical uncertainties to be added. Signal reduction is found, but statistics still insufficient for 20% effect (4-day job).

What about single bunch vs 6-bunch? (Bunch 56, 504-ns delay) With 6-bunch witness train starting at bunch 56 (504-ns delay) With single witness bunch At bunch 56 (504-ns delay) 3.10e10 1.90e10 Single bunch is more effective. Density reduced to 54%, rather than 88%, somewhat more than the measured signal.

Modeled signal for single bunch vs 6-bunch With 6-bunch witness train starting at bunch 56 (504-ns delay) With single witness bunch At bunch 56 (504-ns delay) Modeled signal also shows increased clearing effect of single bunch.

Questions about Synrad3D for CESRTA Layout Why does it give a factor of about 50 high number of reflected photons at Q48W? Upstream of Q48W (for positrons) there is a wide vacuum chamber where a vertical separator used to be. This was roughly modeled in the wall profile file that I have been using for Synrad (2D) calculations of s.r. photon fluxes. Yesterday I learned from DCS that the program PROFILER_SYNRAD uses the detailed work of S. Milashuk et al to make BOTH 2D and 3D wall profile files. So I ran Synrad with the 2D version, since Synrad provides plots of the wall position. The detailed model shows a big vacuum chamber in the soft bend B48W (1.25 kG, EC = 2.4 keV). Is Synrad3D correctly handling this complicated geometry? Also, the modeled Q48W v.c. is wrong. Beginning in January, 2013, it is cylindrical with radius 4.7752 cm. Wall file status as of June, 2010 Rudimentary with some detail added in L3 Wall file status as of June, 2011 S. Milashuk, D.C. Sagan, Y. Li Extremely detailed throughout CESR