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Electron Cloud Modeling for CesrTA Daniel Carmody Mentors: Levi Schächter, David Rubin August 8th, 2007.

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Presentation on theme: "Electron Cloud Modeling for CesrTA Daniel Carmody Mentors: Levi Schächter, David Rubin August 8th, 2007."— Presentation transcript:

1 Electron Cloud Modeling for CesrTA Daniel Carmody Mentors: Levi Schächter, David Rubin August 8th, 2007

2 8/8/2007Daniel Carmody2 Overview Topic\Theory Goals Methods Future Work

3 8/8/2007Daniel Carmody3 The ILC - CESR’s role CesrTA proposed to investigate factors that limit the performance of the ILC http://www.interactions.org/imagebank/search_detail.php?image_no=OT0052

4 8/8/2007Daniel Carmody4 The Electron Cloud Effect Beam particles emit synchrotron radiation Synchrotron radiation generates photoelectrons

5 8/8/2007Daniel Carmody5 The Electron Cloud Effect Positrons travel in bunches/trains Bunches generate a cloud of electrons build-up equilibrium decay lifetime

6 8/8/2007Daniel Carmody6 Measurements April 2007 Tune extrapolated from BPM measurements Approximate decay time of 170ns

7 8/8/2007Daniel Carmody7 The Issue Characterize the development and decay of the electron cloud in CESR: magnetic fields beam parameters vacuum chamber design primary/secondary electron emission yields

8 8/8/2007Daniel Carmody8 The ECloud Program Models a single magnetic chamber of the accelerator Hundreds of macro-particles representing billions of electrons Carry a variable amount of charge More introduced every bunch passage Charge may change when particle reflects off wall

9 8/8/2007Daniel Carmody9 ECloud Input/Output Variables bunch grouping bunch current bunch separation photoelectron yield secondary emission

10 8/8/2007Daniel Carmody10 The Analytic Model Each bunch contributes a number of new electrons to the cloud (∆) The cloud is reabsorbed by the wall according to an exponential decay law (lifetime,  )

11 8/8/2007Daniel Carmody11 Matching the Data

12 8/8/2007Daniel Carmody12 Mathematica Modeling time density lifetime

13 8/8/2007Daniel Carmody13 ECloud Modeling 10 bunches14ns bunch spacing 2.085 GeVdipole magnetic field

14 8/8/2007Daniel Carmody14 Mathematica Fitting Time (s) Density (particles/m 3 ) Varying: PEEFF = Primary Photoemission Yield REFL = Photoelectron Distribution SEY = Secondary Emission Yield B Field = Magnetic Field Chamber

15 8/8/2007Daniel Carmody15 Parameter Search What are realistic values for parameters to have? materials research tabletop experiments

16 8/8/2007Daniel Carmody16 Issues Many parameters  many possible sets that fit Which most accurately represents the situation?

17 8/8/2007Daniel Carmody17 ibeam = 0 Ibeam = 1 Energy Spread Average Energy Energy (eV) 179ns204ns

18 8/8/2007Daniel Carmody18 The Best Fit Many parameters  many possible sets that fit Which most accurately represents the situation?

19 8/8/2007Daniel Carmody19 Where does it go from here? See what parameters can be changed to help mitigate the ECE Determine the instability thresholds Implement diagnostic tools for more direct measurement of EC

20 8/8/2007Daniel Carmody20 Sources [1] K. Harkay, Prepared for 31st ICFA Beam Dynamics Workshop: Electron Cloud Effects (ECLOUD04), Napa, California, 19-23 Apr 2004 [2] M. A. Palmer, R. W. Helms, D. L. Rubin, D. Sagan, J. T. Urban and M. Ehrlichman, Prepared for European Particle Accelerator Conference (EPAC 06), Edinburgh, Scotland, 26-30 Jun 2006 [3] G. Rumolo and F. Zimmermann, CERN-SL-2001-067-AP-D [4] ”Electron Cloud in the LHC” web page, http://ab-abp-rlc.web.cern.ch/ab-abp-rlc-ecloud/ [5] G. Rumolo and F. Zimmermann, CERN-SL-Note-2002-016 (AP) [6] D. Schulte and F. Zimmermann, Proc. 31st ICFA Advanced Beam Dynamics Workshop on Electron-Cloud Effects ECLOUD04, 2004


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