Analysis of TTF Screen Data

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Analysis of TTF Screen Data
ICFA Mini-Workshop on Commissioning of X-Ray
Free-Electron Lasers DESY Zeuthen 18.-22.04.2005
Work package 2 Linac Comissioning

• Michael Abo-Bakr

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Overview

• Measurement
• Layout Diagnostics
• What has been measured?
• Data Structure
• Calculation of Emittance and Twiss-Parameters
• Emittance Estimation from Beam-size
• Extraction of Beam-sizes from OTR Screen Images
• Emittance Fit Results

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Measurement
Diagnostics OTR digital camera system
Layout TTF
E 125 MeV / 101.8 MeV
Q 0.4 nC
Images from OTRs 4DBC2 (OTR1) 6DBC2
(OTR2) 8DBC2 (OTR3) 10DBC2 (OTR4)
FODO lattice
Image format tiff x-y image of beam with 640 X
480 pixels
Quadrupoles
(Katja Honkavaara, talk on Wednesday)
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Measurement
What is measured long. projected transverse beam
pofile (no
information on sliced parameters)
Data structure 4 cases (measurement rows)
4s_20040602_21h13m terrible
beam 4s_20041212_16h57m32s mismatched 4s_200
41212_18h12m38s less mismatched 4s_20041212_18
h46m29s reasonable matched
each case with 10 beam images per OTR 10
background images per OTR
Calibration information pixel -gt m is provided
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Emittance Estimation from Beam-size
Assumption beam-sizes at OTR positions are known
Transformation matrices M0-n from first OTR to
downstream ones are known
Twiss-parameters depend on emittance e, beam-size
s and beam-divergence s
No dispersion at OTR positions!
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Emittance Estimation from Beam-size

• Assume values for the emittance and for
  beam-size and beam-
• divergence at position of the first OTR
  beam-size (and
• divergence) at the downstream OTR positions can
  be calculated!
• Compare calculated with measured/image-extracted
  beam-size values to
• build a fit function

Task minimize fit function by varying the
assumed beam parameters (at first OTR)
and emittance.

• finally calculate Twiss parameters with fitted
  values

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Extraction of Beam-sizes from OTR Images
Provided tiff-images 640 x 480, gray scale
Examples of beam (left) and background (right)
images (reasonable matched case, 4DBC2)
How to extract beam-size from such an image?
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Extraction of Beam-sizes from OTR Images
Using SDDS Toolkit for image analysis SDDS Self
describing data set ANL, M. Borland, L. Emery,
H. Shang, R. Soliday

• Transform binary, partly compressed tiff-file to
  something readable
• tiff2sdds converts to binary/ascii SDDS file
  with simple array structure

Short look to images with sddsimageconvert
sddscontour
Example left reasonable matched 4DBC2_7 (with
noise/background)
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Extraction of Beam-sizes from OTR Images

• Image processing
• first average over all beam and background images
  of one OTR (images taken sequently)
• remove averaged background from averaged beam
  images afterwards

Example reasonable matched case 4DBC2
averaged with noise/background
averaged without noise/background
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Extraction of Beam-sizes from OTR Images

• Estimate transverse beam-sizes from processed
  images
• rms value or standard deviation from a
  Gaussian-fit?
• rms suffers from residual background, quite large
  due to projection
• sophisticated procedures have
  to be applied (ROI, masks, )
• Gaussian-fit more easy, no background problems
  when baseline is fitted

B base-line H height x0 mean value s
stand. deviation
sddsimageprofiles sddsgfit
Example Gaussian-fit for reasonable matched
case OTR1 (4DBC2) white line x data red line
x fit green line y data blue line y
fit
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Extraction of Beam-sizes from OTR Images
Beam-sizes from Gaussian-fit
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Results from Emittance Fit
Terrible Beam (4s_20040602_21h13m)
calibration not included yet 26mm/pixel
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Results from Emittance Fit
Terrible Beam (4s_20040602_21h13m)
en,x 6.77 p mm mrad
en,y 5.15 p mm mrad
bx,by
bx,by
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Results from Emittance Fit
Mismatched Beam (4s_20041212_16h57m32s)
calibration not included yet 10mm/pixel
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Results from Emittance Fit
Mismatched Beam (4s_20041212_16h57m32s)
en,x 2.54 p mm mrad
en,y 1.67 p mm mrad
bx,by
bx,by
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Results from Emittance Fit
Less Mismatched Beam (4s_20041212_18h12m38s)
calibration not included yet 10mm/pixel
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Results from Emittance Fit
Less Mismatched Beam (4s_20041212_18h12m38s)
en,x 1.44 p mm mrad
en,y 1.63 p mm mrad
bx,by
bx,by
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Results from Emittance Fit
Reasonable Matched Beam (4s_20041212_18h46m29s)
calibration not included yet 10mm/pixel
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Results from Emittance Fit
Reasonable Matched Beam (4s_20041212_18h46m29s)
en,x 1.25 p mm mrad
en,y 1.59 p mm mrad
bx,by
bx,by
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Conclusion

• Method for beam-size extraction
• SDDS toolkit
• Gaussian-fit to averaged and background reduced
  images
• Calculation of emittance and Twiss parameters
• small emittances estimated 1.25 2.5 p mm mrad,
  except for the terrible beam
• expected quality of matching confirmed

?!
Thats it!