1. BROOKHAVEN SCIENCE ASSOCIATES BIW ’ 06 Lepton Beam Emittance Instrumentation Igor Pinayev National Synchrotron Light Source BNL, Upton, NY

2. 2 BROOKHAVEN SCIENCE ASSOCIATES 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. 3 BROOKHAVEN SCIENCE ASSOCIATES Emittance Definition Emittance is a measure of area occupied by a beam in phase space It affects major operational parameter: brightness, luminosity, gain length, coherency, etc. x’x’ Area =  For uncoupled beam x The invariant emittance ellipse is given by

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

5. 5 BROOKHAVEN SCIENCE ASSOCIATES Three Screens Method Requires long drift space Sensitive to optical magnification errors Space charge effects can be significant Shot-to-shot variations S0S0 S1S1 S2S2

6. 6 BROOKHAVEN SCIENCE ASSOCIATES Wire Scan

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

8. 8 BROOKHAVEN SCIENCE ASSOCIATES 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 Quadrupole (  0,  0,  0 ) beam Screen (  S )

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

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

11. 11 BROOKHAVEN SCIENCE ASSOCIATES 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 Iris LensBandpass filter Neutral filter Camera Mirror Source length should be accounted for Mirror should provide minimal distortion under the heat load

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

13. 13 BROOKHAVEN SCIENCE ASSOCIATES Imaging with Fresnel Zone Plate source double crystal monochromator zone plate screen 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. 14 BROOKHAVEN SCIENCE ASSOCIATES Laser “ Wire ” Replaces solid “ wire ” with laser beam Can reach micron level resolution (waist 12 μ)

15. 15 BROOKHAVEN SCIENCE ASSOCIATES 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. 16 BROOKHAVEN SCIENCE ASSOCIATES Interference Method Similar to Michelson stellar interferometer Measures dependence of contrast of interference fringes on slit separation For Gaussian beam

17. 17 BROOKHAVEN SCIENCE ASSOCIATES Set-up KEK-ATF

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

19. 19 BROOKHAVEN SCIENCE ASSOCIATES Undulator Spectrum

20. 20 BROOKHAVEN SCIENCE ASSOCIATES Calculated vs. Measured SRW Calculations Measured 3 45

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

22. 22 BROOKHAVEN SCIENCE ASSOCIATES 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. 23 BROOKHAVEN SCIENCE ASSOCIATES mrad = meter · radian

24. 24 BROOKHAVEN SCIENCE ASSOCIATES 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 1 Undulator 2 Buncher

25. 25 BROOKHAVEN SCIENCE ASSOCIATES

26. 26 BROOKHAVEN SCIENCE ASSOCIATES wire beam scan bend beam detector WS  a) b) S0S0 S1S1 S2S2 x’x’ Area =  x source screen mask L