Proposal for an experiment at the Brookhaven Accelerator Test Facility

Submitted by TMU, KEK, SUNY Stony Brook, and NSLS/ATF

Proposal Submission Date: March 30, 1998


Study of Compton Scattering of Picosecond Electron and CO2 Laser Beams to Prototype the Polarized Positron Source for Japan Linear Collider


Principal Investigators:


  Tachishige Hirose

  Physics Department, TMU, Japan


Ilan Ben-Zvi

National Synchrotron Light Source, BNL, USA and

Department of Physics and Astronomy, SUNY Stony Brook, USA




                             Akira Tsunemi, KEK, Japan


                             Igor Pogorelsky, NSLS/ATF, USA


·       The high intensity polarized positron source proposed for the Japan Linear Collider (JLC) is based on the production of electron-positron pairs when the polarized gamma-quanta are stopped at the foil target. Compton scattering between the relativistic electrons and polarized laser beams is the source of the polarized gamma-quanta.

·       The requirements for the high peak flux and short pulse duration of the polarized gamma rays specify the high-brightness photocathode electron accelerator and the picosecond subterawatt CO2 laser as essential components of the projected Compton source.

·       The BNL-ATF is the only users facility worldwide that features such a combination of equipment.

·       Partial funding for the experiment is available from grant for Japan/US collaborative research in high energy physics.


2-year Schedule


1st year (1998-1999)

1.1    Develop the experimental chamber including off-axis parabolic mirrors with remote alignment.

1.2    Prepare the x-ray detector.

1.3    Modify the laser transport system for the Compton experiment.

1.4    Perform Stage I of Compton scattering experiment.

1.5    Evaluate the results of the Stage I experiment.

Required beam time: 7 days


2nd year (1999-2000)

2.1    Modify the optics and the experiment design to use the TW-CO2 laser.

2.2    Perform Stage II of Compton scattering experiment.

2.3    Evaluate the results of the Stage II experiment.

Required beam time: 12 days

1st year (1998-1999)

1.1                 Done


1.2                 Large-area Si diode. Will use also phosphors in the next run

1.3                 Done

1.4                 Done in September 99

1.5                 Done (4 talks, 2 publications)


Two runs: ~10 days


2nd year (1999-2000)

2.1                 In progress

2.2                 Plan for this Fall

2.3                 Modeling of the Stage II experiment is in progress

Required beam time: 12 days


3rd year (2000-2001)


Initially proposed



3.1    Develop and test the picosecond CO2 laser in the multi-pulse configuration.

3.2    Perform Stage III of Compton scattering experiment.

3.3    Evaluate the results of the Stage III experiment.

3.4    Design the positron source modeling experiment at the KEK-ATF

Required beam time: 10 days





3.1                 Develop and tests of a plasma channel for CO2 laser and e-beam transport

3.2                 Perform Compton scattering experiment in a plasma channel.

3.3                 Evaluate the results of the Stage III experiment.

3.4                 Prepare proposal for next stages if necessary

Required beam time: 12 days

Diagram of the ATF Thomson scattering experiment


Interaction Cell for ATF Compton Scattering Experiment

Production and focusing of “donut”-shaped laser beam


Kirhchoff simulations of the Gaussian and “Donut” focusing

 “Donut” focus

0 mm, 1.5 mm and 3.5 mm from focus


Gauss focus

0 mm, 1.5 mm and 3.5 mm from focus



7 mm from focus


Electron and laser focus size measured        in the ATF Thomson scattering experiment


A – transverse wire scan of the e-beam focus shows sb=32 mm

B – laser/electron cross-correlation indicates closely matched focal spots sL»sb=32 mm


Laser and electron temporal structure in the ATF Thomson scattering experiment


3.5 ps electron bunch counter-propagating with the 180 ps laser pulse radiates 3.5 ps x-ray pulse,

shaded is a portion of the laser pulse that is utilized for the x-ray production (fits into the laser waist length)


Thomson x-rays detected in 5-6.5 keV window



Detected:        3x106 photon/pulse (based on detector calibration).

Simulated:      2.8x107 photon/pulse produced in the entire spectrum.

Correction for detector acceptance angle, absorption in Be window and air gives that 3.4x106 photon/pulse in the 5-6.5 keV window can reach the detector.

Proof-of-principle Laser Synchrotron Source experiments










Solid. St.

Solid. St.






Photon energy (keV)





Pulse length

3.5 ps

350 fs

300 fs

300 fs

Photon yield





Peak Bright. (/0.1%)






Nonlinear Thomson scattering

       @ I=1016 W/cm2 for CO2 laser

------- 0.2 J,      180 ps,    s=32 mm,        a=0.02

------- 10 J,       30 ps,      s=32 mm,        a=0.43

------- 30 J,       30 ps,      s=32 mm,        a=0.75





Prospective Compton Scattering Experiment in      Plasma Channel







1.     I.V. Pogorelsky, “Ultra-bright x-ray and gamma sources by Compton backscattering of CO2 laser beams”, Nucl. Instrum. and Methods in Phys. Res. A, 411, 172-187 (1998)

2.     A. Tsunemi, A. Endo, I. Pogorelsky, I. Ben-Zvi, K. Kusche, J. Skaritka, V. Yakimenko, T. Hirose, J. Urakawa, T. Omori, M. Washio, Y. Liu, P. He, D.  Cline, “Ultra-Bright X-Ray Generation Using Inverse Compton Scattering of Picosecond CO2 Laser Pulses”, Proc. of the 1999 Particle Accelerator Conference, 2552, (1999)

3.     S. Kashiwagi, M. Washio, T. Kobuki, R. Kuroda, I. Ben-Zvi, I. Pogorelsky, K. Kusche, J. Skaritka, V. Yakimenko, X.J. Wang, T. Hirose, T. Muto, T. Okugi, A. Tsunemi, D. Cline, Y. Liu, P.He, and Z. Segalov, “observation of high intensity x-rays in inverse compton scattering experiment”, presented at symposium “New Visions in Laser – Beam Interactions”, Tokyo, October 10-13, 1999; to be published in Nucl. Instrum. and Methods in Phys. Res. A

4.     I.V. Pogorelsky, I. Ben-Zvi, X.J. Wang, T. Hirose, “femtosecond laser synchrotron sources based on compton scattering in plasma channels”, ”, presented at symposium “New Visions in Laser – Beam Interactions”, Tokyo, October 10-13, 1999; to be published in Nucl. Instrum. and Methods in Phys. Res. A  

5.     I.V. Pogorelsky, I. Ben-Zvi, T. Hirose “LASER-ELECTRON COMPTON INTERACTION IN PLASMA CHANNELS” 10/14/1998

6.     I.V. Pogorelsky, “ATF SETS NEW STANDARD IN RELATIVISTIC THOMSON SCATTERING”, NSLS Newsletter, March 2000, p.7

7.     I.V. Pogorelsky, “LASER SYNCHROTRON SOURCE FOR FEMTOSECOND X-RAY SCIENCE”, NSLS Users Meeting, May 23, 2000

8.     I.V. Pogorelsky, “High x-ray yields in CO2 laser driven relativistic Thomson scattering”, APS Annual Meeting, Long Beach, CA, April 28-May 2, 2000

9.     I.V. Pogorelsky, I. Ben-Zvi, T. Hirose, S. Kashiwagi, V. Yakimenko, K. Kusche, P. Siddons, J. Skaritka, T. Kumita, A. Tsunemi, T. Omori, J. Urakawa, M.Washio, K. Yokoya, T. Okugi, Y. Liu, P. He, and D. Cline. “Demonstration of 8´1018 photons/second peaked at 1.8 Å in relativistic Thomson scattering experiment” submitted to Phys. Rev.