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Beam Emittance

G A Blair 1 st DITANET School, at Royal Holloway Univ. London 2 nd April 2009. Beam Emittance. Introduction Mathematical treatment Proton emittance H - machines ILC emittance measurement Laser-wire – practical considerations Summary. Luminosity - Emittance.

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Beam Emittance

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  1. G A Blair 1st DITANET School, at Royal Holloway Univ. London 2nd April 2009 Beam Emittance • Introduction • Mathematical treatment • Proton emittance • H- machines • ILC emittance measurement • Laser-wire – practical considerations • Summary

  2. Luminosity - Emittance Luminosity is dominated By the spot-sizes

  3. Conjugate Variables View from the top: Instantaneous motion is described by a point in “phase space”:

  4. Motion on a horizontal plane

  5. Consider a parabolic groove: View from the top: Individual particles will travel on elliptical trajectories in phase space

  6. General Solution where with a similar result for y constants to be determined from initial conditions determined by the beam-line

  7. Beam Ellipse H. Braun

  8. Beam Transport H. Braun

  9. Transport of Twiss Parameters H. Braun

  10. Effect of Acceleration on ε Normalised emittance: is preserved during acceleration “geometric” emittance H. Braun

  11. Common Units for ε H. Braun

  12. ε Measurement - I H. Braun

  13. Derivation of Twiss params: H. Braun

  14. ε Measurement - II H. Braun

  15. Change quad strength: H. Braun

  16. Need 3 or more measurements: H. Braun

  17. Formalism H. Braun

  18. H. Braun

  19. Pepperpot

  20. Principle and technical set up of the pepper pot emittance instrument. Copper block Scintillator screen Fast CCD Camera H- Ion Beam H- Beamlets Tungsten screen The linear shift mechanism mounted to the main flange. Adjustable camera mount. C. Gabor

  21. Longitudinal Emittance Conjugate variables E (→p), z

  22. Measurement in linac H. Braun

  23. Measuring the Transverse Beam Profile • Traditional method is to sweep a solid wire across the beam. • Measure background vs relative position of wire and beam. • Micron-scale precision required for LC • Solid wires would not stand the intense beams of the LC • Solid wires could ablate, harming SC surfaces nearby. • So: replace wire with a laser beam. • Count Comptons downstream.

  24. Laserwire

  25. y u x Skew Correction: x-y coupling ILC LW Locations Eb = 250 GeV Error on coupling term:

  26. Linac ILC

  27. Laser wire : Measurement precision Phys. Rev. ST Accel. Beams 10, 112801 (2007) I. Agapov, G. B., M. Woodley The Goal: Beam Matrix Reconstruction NOTE: Rapid improvement with better σy resolution Reconstructed emittance of one ILC train using 5% error on σy Assumes a 4d diagnostics section With 50% random mismatch of initial optical functions The true emittance is 0.079 m rad

  28. H- Neutralisation The process has threshold energy ~0.75 eV so it can be driven by a Nd:YAG laser operating at 1060 nm. A focussed laser beam can thus be used to • Measure emittance of H- beam • Enable proton production by laser-induced stripping. All the previous technical issues apply…

  29. Schematic Operation Front End Test Stand (RAL) – electrons + neutrals SNS (detect electrons)

  30. SNS laser-wire system Laser e- detector dipole to extract e-

  31. Higher Order Modes TM01 Their presence increases the effective “emittance” of the laser (M2>1) pure TM00 property of a realistic laser

  32. Summary • Emittance is an important parameter for accelerators • Determines the final luminosity of a collider • Determines the quality of a beam in a light source • Determines the aperture of a beam at any location, given a known set of optics. • Measurement: • Pepperpot for low energy protons • Transverse beam profile plus knowledge of optics: e.g. quad scans • Laser-wires for electron/positron and H- • Shintake monitor for 10s nm scale beams

  33. Thanks to: • A. Assadi • H. Braun (CAS 2008) • P. Forck • K. Wittenburg • C. Gabor Whose ideas I have used and whose slides I have borrowed! Enjoy the problem set !

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