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Emittance Measurement for LCLS

Emittance Measurement for LCLS. Emittance Measurement Basics. Measure different beam sizes “Three screen” At different locations (WS, OTR) with same accelerator setup “Quad scan” At same location (WS, OTR) with different accelerator setups

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Emittance Measurement for LCLS

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  1. Emittance Measurement for LCLS

  2. Emittance Measurement Basics • Measure different beam sizes • “Three screen”At different locations (WS, OTR)with same accelerator setup • “Quad scan”At same location (WS, OTR)with different accelerator setups • Obtain transport (R)-Matrix from common starting point in accelerator for each measurement • Least square fit for emittance • Display results

  3. Three Screen Flow Chart User Select predefined set of locations (WS, OTR) Display online beam size/ profile/ image data (optional) Display results from emittance fit Control System Fit Emittance Control system inserts or scans each location consecutively Calculate beam size at each location Obtain R-Matrix for each location

  4. Quad Scan Flow Chart User Select predefined location (WS, OTR) and quadrupole Display online beam size/ profile/ image data (optional) Display results from emittance fit Control System Fit Emittance Control system inserts location and scans quadrupole Calculate beam size for each quad setting Obtain R-Matrix for each location

  5. Software • User front end • Measurement sequence • Beam data analysis • R-Matrix generation • Emittance calculation

  6. Emittance Algorithm • Input • List of beam sizes and their standard variations • List of R-matrices corresponding to each measurement • Output • σ-matrix at start of beamline • Twiss parameters, emittance • Best fit beam sizes • Standard deviations of all parameters

  7. Emittance Calculation • Three independent values in σ-matrix, σ1, σ2, σ3 • Related to measured beam size σxwith R-matrix by σx2 = R112 σ1 + 2R11R12 σ2 + R122 σ3 • Form linear equations for measurement i:σx,i2 = ΣkMik σk • Find σk by least squares fit • Emittance is ε2 = σ1 σ3 - σ22 • Twiss parameters are β = σ1/ε, α = -σ2/ε • Plus error calculation

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