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Lepton Beam Emittance Instrumentation

Lepton Beam Emittance Instrumentation. Igor Pinayev National Synchrotron Light Source BNL, Upton, NY. Outline. Motivation and Definitions Invasive methods Three screens Wire scan Quadrupole and solenoid scan Non-invasive methods Visible light imaging Pinhole camera

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Lepton Beam Emittance Instrumentation

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  1. Lepton Beam Emittance Instrumentation Igor Pinayev National Synchrotron Light Source BNL, Upton, NY

  2. Outline • Motivation and Definitions • Invasive methods • Three screens • Wire scan • Quadrupole and solenoid scan • Non-invasive methods • Visible light imaging • Pinhole camera • Imaging with zone plate • Interferometric method • Undulator radiation • Optical diffraction radiation • Conclusions

  3. Emittance Definition x x’ • Emittance is a measure of area occupied by a beam in phase space • It affects major operational parameter: brightness, luminosity, gain length, coherency, etc. The invariant emittance ellipse is given by Area =  For uncoupled beam

  4. Matrix Gymnastics Particle propagating from point to another can be described by the transport matrix For drift space with length L For thin lens Twiss parameters transform as follows

  5. Three Screens Method S2 S0 S1 Requires long drift space Sensitive to optical magnification errors Space charge effects can be significant Shot-to-shot variations

  6. Wire Scan

  7. Factors Affecting Accuracy of Wire Scan • tilt angle of wire • dispersion in transfer line • beam jitter • scan non-uniformity

  8. Quadrupole Scan • Beam parameters are extracted from the dependence of observed beam size vs. quadrupole strength • Change in the upstream quadrupoles strength may be required because quadrupole focuses in one plane and defocuses in another beam Quadrupole (0, 0, 0) Screen (S)

  9. Extracting Data from the Quadrupole Scan For the thin quadrupole and drift with length L transport matrix is

  10. Solenoid Scan Screen Gun Solenoid • Similar to the quadrupole scan • Solenoid introduces beam rotation (coupling) • Low energy • Radial symmetry can be used

  11. Imaging with Visible Radiation • Used mostly for storage rings with well known -functions • Versatile and easily realized • Can be used for real-time beam measurements Synchrotron radiation Camera Mirror Lens Bandpass filter Neutral filter Iris Source length should be accounted for Mirror should provide minimal distortion under the heat load

  12. Pinhole Camera At ESRF 10 μ pinhole provides resolution of 13 μ for beam size

  13. Imaging with Fresnel Zone Plate double crystal monochromator screen zone plate source Monochromator is required due to the strong chromatic aberrations of zone plate SPring-8 achieved 4 μ resolution for beam size with the help of X-ray zooming tube Observed transient in the beam size during top-off operation

  14. Laser “Wire” • Replaces solid “wire” with laser beam • Can reach micron level resolution (waist 12 μ)

  15. Laser “Harp” • Standing wave interference pattern is generated by two crossing laser beams • Electron beam is moved across the pattern and modulation in the intensity of Compton scattered photons is observed

  16. Interference Method • Similar to Michelson stellar interferometer • Measures dependence of contrast of interference fringes on slit separation For Gaussian beam

  17. Set-up KEK-ATF

  18. Undulator Radiation l Undulator (LU) screen The nth harmonic wavelength Emittance of 0.2 nm was measured with 30 keV X-ray photons

  19. Undulator Spectrum

  20. Calculated vs. Measured SRW Calculations 3 4 5 Measured

  21. Optical Diffraction Radiation =2500 y=0, 30 μm Dependence of contrast vs. beam size at different wavelengths

  22. Conclusions • The emittance measurement technique became state-of-the-art capable to satisfy most requirements • Wide variety of methods is used • Some methods require thorough theoretical consideration • Some has experimental complexity • New methods will appear as improvements in beam quality will require more precise instrumentation

  23. mrad = meter·radian

  24. Optical Klystron Spectrum • Spectrum is interference of two wave packets • Fringes visibility is defined by energy spread • Only longer wavelength part of the spectrum is affected by non-zero emittance • Horizontal emittance is obtained Undulator 2 Undulator 1 Buncher

  25. bend detector wire  scan beam WS S0 S1 S2 beam b) a) x’ x Area =  source L mask screen

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