45 th ICFA Beam Dynamic Workshop June 8–12, 2009, Cornell University, Ithaca New York First Results on the Introduction of the Rediffused SEY Component.

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Presentation transcript:

45 th ICFA Beam Dynamic Workshop June 8–12, 2009, Cornell University, Ithaca New York First Results on the Introduction of the Rediffused SEY Component in ECLOUD Jim Crittenden Cornell Laboratory for Accelerator-Based Sciences and Education Electron Cloud Simulations Meeting 7 October 2009

First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 2/13 See also slides presented on 22 April 2009 in preparation for PAC 2009 and the followup on 20 May 2009 Figure 3 of Studies of the Effects of Electron Cloud Formation at CESRTA PAC 2009 J.A.Crittenden, J.Calvey, G.Dugan, D. L.Kreinick, J. A.Livezey, M.A.Palmer, D.L.Rubin (Cornell), K.C.Harkay (ANL), R.L.Holtzapple (CalPoly), K.Ohmi (KEK), M.Furman, G.Penn, M.Venturini (LBNL), M.T.F. Pivi, L.Wang (SLAC) Problems with ECLOUD tune shift calculation for long bunch trains

7 October 2009 First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 3/13 Relative Drift and Dipole Contributions Fluctuations set in for late bunches in long trains in dipole regions. Frank suggested testing numerical approximations. Time step size, field calculation frequency – no help (see 20 May). Problem resolved by increasing number and reducing charge of macroparticles (see 2 Sep).

7 October 2009 First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 4/13 Replacement for figure 3 following resolution of the fluctuation problem Next step: Does POSINST exhibit a similar problem if the rediffused component is removed?

7 October 2009 First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 5/13 Compare ECLOUD Result to POSINST with Rediffused SEY Component Removed YES ! And very precisely. ( See D.L.Kreinick talk of 9 Sep) Physics lesson: Long bunch trains (>20) are sensitive to cloud energy spectrum/SEY curve near E peak /multipacting ECLOUDPOSINST without rediffused SEY component

7 October 2009 First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 6/13 20 mA simul, red line Er 35 eV simul, red line Er 5 eV δ max ? 10 mA Er 35 eV δ max 3.1 RFA vs. POSINST: Peak at 20 ns bunch spac. (7 bkt) sensitive to true secondary electron spectrum Amplitude (max current) sensitive to δ max Peak width sensitive to rediffused component APS RFA Studies and Modeling, Kathy Harkay, CesrTA Webex 13 November 2008 Sensitivity to the Rediffused Component Also Reported by Kathy Harkay/ANL Found consistency with Er =35 eV (ss), inconsistent with Er=5 eV (Cu). The APC chamber is Al. NB: Our POSINST simulations use Cu parameters for our Al chamber.

7 October 2009 First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 7/13 Introduction of Rediffused SEY Component in ECLOUD (This is not the first time. Previously done for stainless.) Substantial modification of ECLOUD SEY routines finished 24 Sep 09. Removed redundant code, introducing new subroutines. Comments, citations. ECLOUD Furman & Pivi, PRSTAB 5, (2002)  rediffused = P red ( 1 – exp ( -( E - E red ) / r red )) ( ( 1- cos 2  ))  rediffused =  incident ran** ( 1 / ( 1 + q red ) ) Copper (used for Al in POSINST) P red = 0.2 E red = eV r red = q red = 0.5

7 October 2009 First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 8/13 Rediffused SEY Component in ECLOUD -- SEY Curve Population -- The charge of the generated secondary is Q tot = Q el + Q ts + Q red. The energy of the secondary is determined by the type generated. The frequency of type i is given by Q i /Q tot. P red = 0 P red = 0.2 (Cu)

7 October 2009 First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 9/13 Rediffused SEY Component in ECLOUD -- Energy Distribution -- Rediffused parameter E r = 0.04 eV means there is negligible energy dependence for E>0.04 eV. ECLOUD true secondary energies are limited to 12*1.8=21.6 eV max. P red = 0 P red = 0.2

7 October 2009 First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 10/13 Modelling Tune Shift Measurements of Jan e+ bunches, 0.75 mA/bunch, GeV -- Dipole Region Cloud density averaged over beampipe volume P red = 0 P red = 0.2

7 October 2009 First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 11/13 Modelling Tune Shift Measurements of Jan e+ bunches, 0.75 mA/bunch, GeV -- Dipole Region Cloud density averaged over beam P red = 0 P red = 0.2

7 October 2009 First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 12/13 Modelling Tune Shift Measurements of Jan e+ bunches, 0.75 mA/bunch, GeV -- ECLOUD vertical tune shift calculation with and without rediffused SEY component P red = 0 P red = 0.2

7 October 2009 First Results from the Introduction of the Rediffused SEY Component in ECLOUD / J.A.Crittenden 13/13 Conclusions The qualitative differences between POSINST and ECLOUD in the vertical tune shift calculation for long bunch trains are largely resolved by introducing the rediffused SEY component in ECLOUD. The SEY parameters are likely to be somewhat different since the SEY models differ. Parameter tuning must be done taking into account the range of bunch currents for which measurements are available. Next Steps Test the ECLOUD model against the wealth of tune shift measurements with long bunch trains obtained in early Develop further the RFA model in ECLOUD. Derive SEY information from the RFA measurements. Revisit the chicane data to see if realistic modelling is possible.