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Photoinjector

Photoinjector. A. Cianchi for SPARC Collaboration. Outline. Brief introduction to the SPARC Project Hardware description The Emittance-Meter Running experience and problems Results and comparison with simulations. Collaboration. Gun. Solenoids. RF sections. Undulator.

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Photoinjector

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  1. Photoinjector A. Cianchi for SPARC Collaboration A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  2. Outline • Brief introduction to the SPARC Project • Hardware description • The Emittance-Meter • Running experience and problems • Results and comparison with simulations A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  3. Collaboration A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  4. Gun Solenoids RF sections Undulator 1.5 m 20º 6.0 m 1.5m 10.0 m 14.5 m SPARC Working Point GUN PARAMETERS LINAC PARAMETERS FEL PARAMETERS Frequency: 2856 MHz Frequency: 2856 MHz Wavelength: 530 nm Peak Field: 120 MV/m Accelerating Field: 25-12.5-12.5 MV/m Coop. Length: 300 mm Solenoid Field: 0.27 Tesla Solenoid Field: 0.1 Tesla Beam Energy: 5.6 MeV Beam Energy: 155 MeV Charge: 1.1 nC Laser: 11.5 ps x 1 mm (Flat Top with <1 ps rise time) A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  5. Magnets e-meter steerers Faraday cup Spectrometer cross SPARC installation Beam dump ICT A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  6. Solenoid The SPARC solenoid uses four different coils that can be powered by different power supplies. It gives the ability to change the Larmor rotation angle independently from the focusing power of the solenoid A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  7. Solenoid different configurations * * current values set for constant focusing power A strong dipolar component in the configuration A (already foreseen of the order of 10 gauss by the analysis of the magnetic field map measurements) was found. It results compensated in configuration C. A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  8. Solenoid experience • Actual configuration (--++)preserves the horizontal and vertical axes through the system • gives a reduction of steering coils current (compensation of dipolar component) • simplifies the beam based alignment procedure • Drawback: requires higher current in the coils (at 1 nC with a 10 psec FWHM gaussian pulse a current more than 200 A is needed) • Problem with cooling water. We use a thermo stick that turn off the current when the temperature is too high. It works, we tested it !!! A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  9. RF general layout A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  10. Phase feedback Double gaussian distribution of the RF gun phase with feedback ON, due to the residual error for positive and negative phase slope. Total standard deviation is inside the project specifications. A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  11. Control System Operating system Data storage Data base CONSOLE LEVEL server gigabit switch Electronic logbook Web information Automatic acquisition service SERVICE LEVEL server MAGNET VACUUM DIAGNOSTIC OTHER FRONT-END LEVEL A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  12. The emittance measurement To measure the emittance for a space charge dominated beam the used technique is the well know 1-D pepper-pot YAG To eliminate the depth of field the YAG screen is mounted at 90 degrees respect to the beam line. A mirror is placed on the back side. Mirror A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  13. 6.0 5.0 Emittance 4.0 3.0 Envelope 2.0 Bz field 1.0 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Importance of a movable diagnostic The possibility to move the measuring position along the beam line give the opportunity to study the emittance compensation process A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  14. The Emittance-Meter Rev.Sci.Instr. Vol.77, Issue 8 - 2006 A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  15. Slits holder 7X 50 mm 500 mm spaced 1X 50 mm 1X 100 mm Photochemical machining Mechanical machining A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  16. Running experience A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  17. E-Meter @ PITZ Thanks to Desy-Zeuthen team A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  18. Installation @ PITZ from ~8÷9 m away from cathode beam • A good chance to debug and test the system on the field. • Cross-check results with PITZ EMSY measurements. • Energy too high (with booster on) to have some changes of emittance vs. z A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  19. Gun • The conditioning of the Gun was quite fast. Less than 100 hrs to arrive to 120 MeV/m • Later Never vent the GUN • Only two minor problem • Too much power in the GUN due to a software problem • Some activity after two months of forced stop just after the movements of the e-meter. • In both cases about 10-20 hrs to come back in normal operation. Laser alignment Laser is aligned varying the RF phase and moving the laser position on the cathode, looking a fluorescent screen at 60 cm from the cathode A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  20. Phase scan with the Faraday cup • Two methods: • Identify the 90 degrees • Identify the zero crossing P. Musumeci A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  21. LASER PORT For the insertion of the mirror for the normal incidence the Faraday cup was removed in the first cross because there was not enough room for it Phase scan with the spectrometer Now we’re using the spectrometer to measure the energy and the energy spread vs phase. A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  22. Single slit vs multislits • Emittance measures with both single slits and multi slits • Multi slits is a single shot measure, single slit gives more sampling points • Excellent agreement between single slit and multi slits • Multi slit not so good with convergent and too small beams (fixed distance between slits), and too large beam (understimation of ) • Excellent the agreement between the measured ( with a screen) RMS beam size and the estimated from A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  23. Algorithm for phase space reconstruction Author D. Filippetto • The target of the algorithm is to identify the correct rms parameters of every beamlets. • Identify a baseline averaging the point on the far left and right sides • Subtract this value and try a gaussian fit • Use the baseline for another subtraction and the sigma to estimate a starting RMS value • Discharge the point outside a window of +/- 3 sigma. • Calculate again the RMS • Go to point n.4 • The algorithm converges in few iteration After the estimation of the RMS parameters the phase space is reconstructed with interpolation A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  24. Phase space evolution With single slit method phase space reconstruction is possible Using the e-meter one can investigate the phase-space evolution. A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  25. Emittance meter measurements Problem Make all the measure by operators is long, boring, and sometimes not precise Two measures are usually done with the e-meter (envelope and emittance) Usually only in few points along z (usually 5) there are emittance measure and in few more the envelope measure Solution Make the measure more automatic as possible A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  26. Envelope automated measures The emittance-meter moves and stops in several position when the CCD collects several images and a program calculate the RMS parameters and the error bars A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  27. A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  28. Automatic emittance scan The idea is using the results of the envelope scan : beam center position vs z and RMS size vs z. The program put the single slit in the center of the beam at the starting z position, and move it 4 sigma away from one side, then move for 8 sigma in opposite direction recording images Now all the system moves in other z position Maybe the beam center is not anymore in the same position. The program move the slit in the new center position using the data of the envelope scan. Problem: if the charge distribution is strongly asymmetric the center of mass is not the center of the image. The amplitude of 4 sigma in both direction is enough to solve this problem but it means that there are a lot of empty images A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  29. Result of an automatic emittance scan A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  30. A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  31. Measurement error bars The emittance is a small different between two big quantities The error that comes from the propagation gives a result that is meaningless when a is much greater than 1. For this reason we ‘re going to make statistic repeating several time the measures. A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  32. Comparison measure with Parmela simulation C. Ronsivalle A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  33. Emittance: Comparison simulations-measurements C. Ronsivalle INPUT BEAM: Q=1 nC, uniform transverse beam R=0.9 mm, gaussian pulse =4.5 psec A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  34. compare measurements-computations Last minute measurement dependence on longitudinal rise time A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

  35. Conclusion • Solenoid in --++ configuration to kill dipole component • Phase scan both with Faraday cup than with spectrometer • Automatic envelope measure along z • Just started automatic emittance measure along z • Emittance scans vs gun parameters are foreseen • Comparison between Gaussian and flat top longitudinal laser distribution • Good agreement between measures and simulations • The work is in progress… A. Cianchi LCLS Injector Commissioning Workshop SLAC October 9-11, 2006.

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