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ECLOUD Calculations of Coherent Tune Shifts for the April 2007 Measurements - Thanks to Marco for clarifying the drift/dipole weighting - - Thanks to Gerry.

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Presentation on theme: "ECLOUD Calculations of Coherent Tune Shifts for the April 2007 Measurements - Thanks to Marco for clarifying the drift/dipole weighting - - Thanks to Gerry."— Presentation transcript:

1 ECLOUD Calculations of Coherent Tune Shifts for the April 2007 Measurements - Thanks to Marco for clarifying the drift/dipole weighting - - Thanks to Gerry for updating comparisons of 11 Feb 2009 - Jim Crittenden Cornell Laboratory for Accelerator-Based Sciences and Education Electron Cloud Simulations Meeting Wilson Lab 4 March 2009

2 2 Conversion of Space-charge Field Values to Tune Shifts ECLOUD Coherent Tune Shifts/ J.A.Crittenden I. ECLOUD input parameters 1.Sync rad photon rate per meter per beam particle at primary source point (Drift R=0.23, Dipole R=0.53) 2.Quantum efficiency (12%) 3.Beam particles per bunch (0.75 mA/bunch -> 1.2e10 e/bunch). 4.Eleven bunches filled, followed by nine empty. ● In the POSINST calculations, only the first ten bunches and the witness bunch for which the tune is calculated are filled. 5.Contribution of reflected sync rad photons uniform in azimuth (15%). ● This contribution is also subtracted from the primary source point. 6.The primary p.e. generation model is identical to POSINST's (panghel=1). 7.Secondary emission peak yield (SEY=2.0) at peak energy (E peak = 310 eV) ● These values are also used by POSINST, but the POSINST SEY model is very different from ECLOUD's. II. Field difference or gradient --> tune shift conversion parameters 1.E beam = 1.885e9 eV 2.f rev = 390 kHz 3.Ring circumference C=768 m (C f rev = c = 2.998e8 m/s) 4. Ring-averaged b values (from sync rad summary tables, see my presentation 18 Feb 09) ● e+ beam: Drift b X ( b Y )= 19.6(18.8), Dipole b X ( b Y ) = 15.4(18.8) ● e- beam: Drift b X ( b Y ) = 19.4(19.3), Dipole b X ( b Y ) = 15.3(19.4) III. Relative drift/dipole weighting (from sync rad summary tables) 1.Ring length fraction ● Drift: (174.9/768) = 0.228 ● Dipole: (473.9/768) = 0.617 (MV used 377.99 m. I weight his tune shift by 473.9/377.99 in this talk.) 2. b -averaged photon rate values ● e+ beam: Drift R X (R Y ) = 0.987(1.061), Dipole R X (R Y ) = 1.100(0.911) ● e- beam: Drift R X (R Y ) = 0.957(1.030), Dipole R X (R Y ) = 1.098(0.911)

3 3 4 March 2009 Example Tune Shift Calculation ECLOUD Coherent Tune Shifts/ J.A.Crittenden Example: D E/ D Y = 1000 V/m 2, b Y = 20 m => D f = 253 Hz April 2007 Conditions Positron beam beam-averaged field values for vertical offsets +- 5 mm D E/ D Y averaged over bunch 11 Drift: 9.038e3 V/m 2 Dipole: 2.610e3 V/m 2 (Omit b -weighted photon rate correction for purposes of this comparison)

4 4 4 March 2009 ECLOUD Vertical Tune Shift Calculations ECLOUD Coherent Tune Shifts / J.A.Crittenden GD LBNL/Cornell POSINST Comparison 11 Feb 09 (update 3 Mar 09) 11 bunches offset, bunch 11 Drift Δ Y=+5mm E Y Δ f Y Cornell: 42.35 V/m 0.426 LBNL: -41.06 V/m 0.445 ECLOUD: 48.05 V/m 0.490 Dipole Δ Y=+5mm E Y Δ f Y Cornell: 13.77 V/m 0.406 LBNL: -13.71 V/m 0.41 ECLOUD: 9.62 V/m 0.383 Note that the tune shifts are derived from the differences of fields calculated for two different beam offsets. The above fields are for the positive beam offset only.

5 5 4 March 2009 ECLOUD Tune Shift Calculations -- Positron Beam -- ECLOUD Coherent Tune Shifts / J.A.Crittenden

6 6 4 March 2009 ECLOUD Tune Shift Calculations -- Electron Beam -- ECLOUD Coherent Tune Shifts / J.A.Crittenden

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