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Transverse Coherent Transition Radiation (TCTR) Experiment First Ideas for a Measurement Setup

Transverse Coherent Transition Radiation (TCTR) Experiment First Ideas for a Measurement Setup. Max-Planck-Institute for Physics Munich Olaf Reimann , Scott Mandry Geneva, October 19, 2012. Outline. Short introduction Why TCTR in frequency domain? Principle of the measurement First results

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Transverse Coherent Transition Radiation (TCTR) Experiment First Ideas for a Measurement Setup

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  1. Transverse Coherent Transition Radiation (TCTR) ExperimentFirst Ideas for a Measurement Setup Max-Planck-Institute for PhysicsMunich Olaf Reimann, Scott Mandry Geneva, October 19, 2012

  2. Outline • Short introduction • Why TCTR in frequency domain? • Principle of the measurement • First results • Probes and Probe configuration

  3. What we are looking for? • We are interested in the proton-beam modulation: • Modulation frequency • Modulation depth • Modulation frequency: •  250 GHz for a 7 1014 cm-3 plasma • Bunch-to-bunch changes? • Single-shot measurement  Electrooptic sampling

  4. A Problem! • The protons are only pushed out of axis in the plasma cell. They are not disappearing.  The E-field outside the proton-beam is not modulated • We need a “converter” Transverse coherent transition radiation is a good candidate!

  5. What is TCTR • Coherent Transition Radiation emitted radial around a charged beam along the surface of a (metallic) screen • Normal (to the screen) electric field component • Dipole-like radiation pattern • Can be modulated by beam density Picture taken from A. Pukhov paper

  6. TCTR Characteristics • Electric fields with amplitudes up to hundredths of kV at a distance of 10mm • Signal is to the first order proportional to thebeam density • High frequencies (several hundredth GHz) Make use of electrooptic sampling (EOS) • But: No simple frequency response curve Typical E-field for TCTR atdifferent radial distances

  7. Why Frequency Domain? • “Normal” time-domain single shot EOS-systems are measuring within a window of 10-20ps • Too short for our expected frequency range (250GHz) to achieve high resolution frequency information • Additional problem: too complicated to use it at different probing positions • Better: Time-Lensing EOS • But: has to be optimized for a “design“ frequency • Not for the first experimental phase, but maybe later • Measurement in the frequency domain

  8. TCTR in Frequency Domain •      -Field of a charge distribution exiting a metallic screen: with                     • In frequency domain: with retarded time results in

  9. TCTR with Constant Beam Radius • Beam density:                           for                                        for          •      -field of a beam with constant radius:

  10. Const. Beam Radius and Density Modulation • Modulation:                                   with • Resultant E-field amplitude:

  11. Constant Radius vs. Constant Current Constant radius Constant current Scott Mandry is looking todifferent configurations:- Probe placement - Foil with and without hole - …

  12. TCTR-Measurement using EO-Techniques Phase modulation: Modulation function: Optical signal (electrical field): NEW FREQUENCIES! Amplitudes for different frequencies: Maximum phaseshift (<0.5) Measured intensity

  13. Some (very old) Simulations • Some simulations (nonlinear field simulations): • 1ns optical pulse (“window”) • 100µm ZnTe probe • External E-field EZ=5MV/m 20cm bunch, 150µm micro-bunch length, 600µm spacing 100GHz sine-wave, 1ns window Base frequency 193THz (1.55µm) 1. Harmonic (signal) 2. Harmonic

  14. First Results • Fourier spectrumMeasurement of a 6GHz signal with 100ps window 0 GHz

  15. First Results • Fourier spectrum to show the resolution • Artificial (nonlinear) phase modulated spectrum • Comparison with 4-path grating spectrometer EO phase modulated spectrum with 8 GHz line separation

  16. Advantages of the System • Semiconductor laser based • Simple setup • Fiber based signal transport • Sampling-signal can be splitted und transported to many different probing positions • Make use of the same EOS system for many probing positions

  17. Probe Configuration Probe setup with a “closed” optical path using GRIN-Lenses and prisms: Possible length of probe in longitudinal (beam) direction:  5mm GRIN-Lens with prism (GRINTECH)

  18. Wishlist!!! • Probing directly before (without foil) and after (with foil) the plasma cell • At least four (maybe eight) probes at each probing position around the beam in the beam line Picture stolenfrom anothertalk

  19. What we need in the Beam Line Probing section • 20 cm per section (Length), • Metallic foil in the beam line(maybe with a hole for the beam?) • 4 or 8 motorized stages around the beam line • Radial movable probes ( 1-2cm from beam axis?) • Probe diameter:  5mm • Access with two optical fibers (SMF28?) per probe • Measurement system can be far away (10m, 100m, …) • Connected by two fibers pro probe • No Radiation ???

  20. Future Work • Simulations of different probing configurations • Increase resolution and sensitivity • Studying nonlinearities of the system • Building and testing probes • Building a TCTR probe section and test it

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