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PULSE LASER WIRE Laser pulse storage in an optical cavity as a beam monitor & an X-ray source

PULSE LASER WIRE Laser pulse storage in an optical cavity as a beam monitor & an X-ray source. Kaori Takezawa Kyoto Univ. 2nd Mini-Workshop on Nano Project at ATF 12 th Dec. / 2004. OVERVIEW PRINCIPLE OPTICAL CAVITY EXPERIMENTAL SETUP CONCLUSION FUTURE PLAN. 2. 1.OVERVIEW. 3.

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PULSE LASER WIRE Laser pulse storage in an optical cavity as a beam monitor & an X-ray source

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  1. PULSE LASER WIRELaser pulse storage in an optical cavity as a beam monitor & an X-ray source Kaori Takezawa Kyoto Univ. 2nd Mini-Workshop on Nano Project at ATF 12th Dec. / 2004

  2. OVERVIEW • PRINCIPLE • OPTICAL CAVITY • EXPERIMENTAL SETUP • CONCLUSION • FUTURE PLAN • 2

  3. 1.OVERVIEW • 3 Pulse Laser Wire (Storage laser pulses in optical cavity ): The systems for New X-ray source & New bunch length monitor at a storage ring

  4. 1.OVERVIEW 714MHz Cavity • 3 Scattered Gamma beam Laser Repetition rate : 357MHz laser pulses Phase Scan Compton Scattering in every 357MHz Electron repetition rate : 357MHz Electron bunches As an X-ray source : An optical cavity store higher peak power and get higher flux X-ray with pulse CW laser than CW laser. As Beam monitor : By scanning the laser pulse’s phase in the cavity and measuring the Compton signal count rate ; an electron bunch length profile is obtained.

  5. 2.PRINCIPLE : Storage of laser pulse Resonance condition : • 4 Perfect resonance : L = L laser cavity The relationship with laser and cavity : Imperfect Resonance : L ～ L laser cavity The ext. cavity’s parameters ; enhancement factor , reflectivity , …. is the function of Δl and laser pulse width. Not resonance : L ≠ L laser cavity

  6. 2.PRINCIPLE : Enhancement factor • 5 The reflectivity is bigger at resonance point with Δl ≠0,.this means that enhancement factor is smaller . And data says laser pulse width.

  7. 2.PRINCIPLE :Count rate& Measurement Signal flux • 6 2 σ= σ+σ 2 2 - Laser beamwaist e v-beamwaist Phase Suppose both electron bunch and laser pulses have a Gaussian intensity distribution, The measured profile is also a Gaussian shape. Vertical position 2 2 2 2 2 σ= σ+σ+σ+σ ～σ - - Laser pulse width e bunch length Laser beamwaist e h-beamsize 2 The electron bunch length is 20 ～ 40 psec (10mm) > Laser pulse width ( FWHM =7 psec ; 1 mm) >> Laserwire beamwaist( 120um ), electron’s horizontal beamsize ( 100um ) Laser pulse width

  8. 3.OPTICAL CAVITY • 7

  9. 3.OPTICAL CAVITY : The design • Cavity length : 714 MHz +/- 2 kHz ( from PZT dynamic range ) • Mirrors • The radius of curvature : 250 mm • The reflectivity : 0.997 +/- 0.001 • Beamwaist > 200 um • 8 Cavity length is 210mm. It is easy to adjust cavity length with short cavity. For cavity’s dynamic range , long PZT is used ( 10um ). Finesse is ～ 1000 . But Maximum finesse is ～500 ,when the cavity , the length is 714MHz , stores laser pulses, which repetition rate is 357MHz. For enhanced laser pulses in the cavity , Next pulse come after 4times reflection It is difficult to make thin laserwires at long cavity length . ρ= 250mm R = 0.997 Adjustment with PZT 714MHz

  10. 3.OPTICAL CAVITY : feedback circuit • 9 Transmission PZT voltage PI circuit DC Mode locked Laser Laser Rep.rate feedback Shoulder feedback system ( OFF : background) A trombone for a signal delay 357MHz Ring RF standard 10MHz Signal Generator By a phase detector, the signal is synchronized with Ring 357MHz ← Feedback ON/OFF

  11. 4.EXPRIMENTAL SETUP : Layout • 10

  12. 4.EXPERIMENTAL SETUP : Optics • 11 λ/2 λ/4 Isolator Reflection Injection mirrors Transmission Cavity Laser head

  13. 5.CONCLUSION : Timing scan ← Compton signal • 13 In timing scan, we detect Compton signals and the laser pulse’s phase in cavity when signals come. Enhanced laser pulses 2times go and back in the cavity , and are scattered 4times every 2.8 nsec. 2.8 nsec Bunch length

  14. 5.CONCLUSION : count rate • 14 σ=laser beamwaist Calculated maximum count rate is～ 2500 [Hz/mA] . Actual count rate is ～ 1500 because of imperfectly adjustment cavity length with shoulder feedback system.

  15. 5.CONCLUSION : VS. RF voltage • 15 Data at 19th Nov. had a sharp peak , but There was no peak at 01st Dec. ( Because of the change Ring tune ? )

  16. 5.CONCLUSION : VS. the beam current • 16 Count rate [Hz/mA] When the number of electron per bunch is bigger , The Gauusian shape of scattered photons count rate change. (The life time of low current electron beam at ring is long ) Phase [psec]

  17. 6. FUTURE PLAN • For high count rate : • Problems as a bunch length monitor : • And now • 17 We plan the higher finesse cavity (mirror R=0.999) and thin laserwire with beamwaist 50um. In the plan , the enhancement factor is 10 times as much as current systems. New feedback system, Tilt locking can adjust cavity length at resonance peak . We will test those systems in this winter. In current systems, It takes about 20 seconds for data taking . Data can be taken at low current electron beam , but at high current beam cannot . Next week, we will measure bunch length with pulse laser wire timing scan and streak camera. If I can, we will test tiltlocking feedback system.

  18. Kyoto Univ. KEK Thanks ! NIRS ISSP Jaeri And you !! 2nd Mini-Workshop on Nano Project at ATF12th Dec. / 2004

  19. 1. 企画書の目的と概要 • 1

  20. 1. 企画書の目的と概要 • 1

  21. 4.EXPERIMENTAL SETUP : Data taking • 12

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