1. 1 Preliminary Analysis of GTF Longitudinal Emittance Experiment D. Dowell SLAC July 18, 2001

2. 2 I. Description of Experimental Technique II. Data Analysis III. Experimental Results IV. Summary and Conclusions Talk Outline

3. 3 Booster Gun Spectrometer Energy Screen Description of the Experimental Technique  booster Determine Longitudinal  -Space at Exit of Gun Longitudinal : Measure Energy Spectra Vs.  booster Transverse: Measure Beam Size Vs. Quad Current Technique similar to quadrupole scan of transverse emittance

4. 4 Longitudinal Beam Ellipse:    ttEE 22 2  Longitudinal Beam Matrix:                     1112 22  11  Uncorrelated BunchLength  22  Uncorrelated Energy Spread Definition of Initial Phase Space Parameters, Including Correlations Include correlated emittance by distorting the ellipse boundary using quadratic and cubic terms:  Ett t atbt                   2 2 23  EEE booster 10 booster  (cos(   t 0booster  )cos( ))  ;  tt 10  Uncorrelated Bunch Length Uncorrelated Energy Spread Randomly populate and ray-trace down the booster:

5. 5 May, 2001 Longitudinal Emittance Scan

6. 6 20 Quadratic Distortion  12 = 0 a > 0, b = 0 Cubic Distortion  12 = 0 a = 0, b > 0 Undistorted Phase Space  12 = 0 a = 0, b = 0  E (keV)  t (ps) Distortions of the Longitudinal Phase Space Ellipse

7. 7 Curvature Terms are Needed to Fit Ends of Energy Spectra Head Tail

8. 8 On Crest Min Energy Spread

9. 9 Fits to Longitudinal Emittance Scan Fit Data

10. 10 Phase Space Out of Gun Correlated Length and Energy Spectrum 2.9 ps fwhm Tail Head

11. 11 Uncorrelated Energy Spread 15 keV

12. 12 The Uncorrelated Longitudinal Emittance Grows Linearly with Surface Charge Density Below the Space Charge Limit -Results from 1994 Experiment for 144 MHz Gun- Ref: D. H. Dowell, S. Joly and A. Loulergue, “The Dependence of Longitudinal Emittance Upon Surface Charge Density in a RF Photoinjector”, Proc. Of 1997 Particle Accelerator Conf., Vancouver, BC, Canada

13. 13 In These Experiments Most of the Emittance Growth Results From Increased Energy Spread -Results from 1994 Experiment for 144 MHz Gun- 1  Spread Ref: D. H. Dowell, S. Joly and A. Loulergue, “The Dependence of Longitudinal Emittance Upon Surface Charge Density in a RF Photoinjector”, Proc. Of 1997 Particle Accelerator Conf., Vancouver, BC, Canada

14. 14 Summary and Conclusions -Curvature Terms Needed to Fit Energy Spectra -Fits Poor for Large Phases--> More careful analysis -Large Energy Correlation for 50 deg Launch Phase (Relative to Peak Field) -Compression Observed from 4 ps to 2.9 ps -Model-Independent Analysis (Tomography) Needed