45 th ICFA Beam Dynamic Workshop June 8–12, 2009, Cornell University, Ithaca New York Recent Studies with ECLOUD Jim Crittenden Cornell Laboratory for.

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Presentation transcript:

45 th ICFA Beam Dynamic Workshop June 8–12, 2009, Cornell University, Ithaca New York Recent Studies with ECLOUD Jim Crittenden Cornell Laboratory for Accelerator-Based Sciences and Education Electron Cloud Meeting 11 November 2009 I. ECLOUD/POSINST comparison for Feb 2009 tune shift data II. Improvement using  x,y -weighted photon rates III. Sensitivity to vertical beam size IV. Predictions for 4 GeV wiggler-on/wiggler-off lattices

11November 2009 Recent Studies with ECLOUD / J.A.Crittenden 2/8 POSINST simulations with nominal parameters 45 bunch trains, 14 ns spacing, Feb mA=1.6x10 10

11November 2009 Recent Studies with ECLOUD / J.A.Crittenden 3/8 Resolving the remaining discrepancies exhibited in our PAC2009 beam dynamics paper required: Reducing fluctuations due to large individual macroparticle charges Introducing the rediffused SEY component Using the more realistic 2-mm beam offset rather than 5 mm Refining the space charge grid 41x41 --> 81x81 over the 45mm x 25mm vacuum chamber ellipse. I. ECLOUD/POSINST Comparison for the February 2009 Measurements 2.1 GeV e+ 45-bunches, 14 ns spacing 0.4 mA 0.8 mA1.2 mA

11November 2009 Recent Studies with ECLOUD / J.A.Crittenden 4/8 The ECLOUD and POSINST calculations on the previous slide were done with the same input parameters for photon rates, beta functions, SEY parameters and beam sizes. The photon rates were 0.28 (0.57) photons/m/beam particle for the drift (dipole) region averages. The lattice synchrotron radiation tables can provide separate horizontal and vertical beta-averaged rates as well. For this lattice, they turned out to be 0.217/0.220 (0.482/0.482) for the drift (dipole) regions. This correction preferentially affects primary-related phenomena. II. Effect of linear correction for independent horizontal and vertical beta-weighting of synchrotron radiation rates 0.4 mA 0.8 mA1.2 mA With Correction Without Correction

11November 2009 Recent Studies with ECLOUD / J.A.Crittenden 5/8 The modelled vertical tune shifts appear to depend strongly on this parameter, perhaps owing to the varying number of cloud particles in the beam region. The nominal rms vertical beam sizes in our data sets range widely from 30 m (Feb 2009) to 160 m ( April 2007). III. Remarkable Sensitivity to Vertical Beam Size 0.4 mA 0.8 mA1.2 mA  V = 29.7  nominal  V = 40  This example indicates that the tune shift measurements can exclude a vertical beam size larger than 40 m.

11November 2009 Recent Studies with ECLOUD / J.A.Crittenden 6/8 We should consider whether such effects can be produced by other input parameters. The dependence on photon rate appears to decouple in cases where multipacting becomes significant. This sensitivity may present an opportunity to provide useful information to the LET effort. The sensitivity to vertical beam size is asymmetrical, with less sensitivity to smaller beam sizes 0.4 mA 0.8 mA1.2 mA  V = 29.7  nominal  V = 20  The discrimination power of the vertical tune shift data appears to be greater for larger vertical beam sizes.

11November 2009 Recent Studies with ECLOUD / J.A.Crittenden 7/8 IV. Predictions for 4 GeV lattices Wigglers on ( e V = 23 nm) Wigglers off ( e V = 42 nm) 0.4 mA 0.8 mA1.2 mA Wigglers on s H = 843 m s V = 65 m s Z = 13.4 mm The photon rates are about a factor of 2 higher than at 2.1 GeV. The tune shifts are inversely proportional to the beam energy. So the wiggler-off prediction is about what one might have expected. The prediction for the wiggler-on lattice is surprising, especially since the model input parameters are so similar. The culprit turns out to be s V = 88 m --> 65 m. What is the physics? Is it physics? Wigglers off s H = 887 m s V = 88 m s Z = 7.1 mm

11November 2009 Recent Studies with ECLOUD / J.A.Crittenden 8/8 ECLOUD's explanation of the suppressed vertical tune shift in the 4 GeV wiggler-on lattice (e+ beam, 0.8 mA/bunch) 4 GeV Wigglers on ECLOUD finds that the pinch effect suppresses the vertical tune shift at a precise vertical beam size. 4 GeV Wigglers off2.1 GeV Vertical Field Difference (2D averages) All bunches Vertical Field Difference (2D averages) Bunches 42-45