1. Design and Experimental Considerations for Multi-stage Laser Driven Particle Accelerator at 1μm Driving Wavelength Y.Y. Lin( 林元堯）, A.C. Chiang （蔣安忠）, Y.C. Huang （黃衍介） Department of Electrical Engineering, National Tsing Hua University, Hsinchu,300, Taiwan ORION Workshop Feb.18-20,2003 NTHU Relativistic Photon- Electron Dynamics Laboratory

2. OUTLINE Motivation Review on the multi-stage CO 2 -laser- acceleration Project at ATF BNL Scaled to 1-μm Wavelength A Proposed Muti-stage Experiment at ORION NTHU Relativistic Photon- Electron Dynamics Laboratory

3. MOTIVATION 10-μm Wavelength using 70 MeV beam at ATF BNL a. large structure size b. high-power CO 2 laser available at ATF c. easier for alignment d. good for proof-of-principle experiment 1-μm Wavelength using 350 MeV beam at ORION a. higher material damage field with 1-μm wavelength b. higher laser damage threshold with ~100 fs laser pulse c. smaller phase slip with 350 MeV beam d. smaller beam size for electron transmission aperture e. higher acceleration gradient f. solid-state laser stability and efficiency NTHU Relativistic Photon-Electron Dynamics Laboratory

4. Lens-array structure (I): Accelerating Stages 2/3*z 0 f=5z 0 /3=3.81cm 24 cm = 15cm x 16 1.5cm Each lens’ temperature is varied independently by a TE cooler Electron transit on each lens is 100μm in diameter NTHU Relativistic Photon- Electron Dynamics Laboratory Ref: E.J. Bochove, G.T. Moor, ad M. O. Scully, Phy. Rev. A, Vo. 46, No. 10,pp. 6640-53,Nov. 1992 CO 2 -laser-acceleration Project at ATF BNL Laser beam waist ~280μm

6. Lens-array structure (II): System setup of the multi-stage lens array accelerator structure TEM 00 TEM 01 Mode filter f=10” f=2” f=3”f=0.5” Accelerator cell 24 cm5.32 cm9.19 cm2 cm 120  m 100  m 120  m 30.48 cm Si detector (movable) 48.15 cm W 0 = 280  m W 0 = 10 4  m W 0 = 2000  m Phase offset Iris & mirror iris Chamber E_max=132M V/m Energy gain=240 keV NTHU Relativistic Photon-Electron Dynamics Laboratory CO 2 -laser-acceleration Project at ATF BNL

7. NTHU Relativistic Photon- Electron Dynamics Laboratory CO 2 -laser-acceleration Project at ATF BNL Numerical simulation for 1st stage

8. CO 2 -laser-acceleration Project at ATF BNL Numerical simulation for 2nd stage NTHU Relativistic Photon- Electron Dynamics Laboratory

9. Lens-array structure (III): Energy Gain along axis Damage threshold: 0.45 J/cm 2 for ZnSe and 1.2 J/cm 2 for CVD diamond Total energy Gain over 24 cm: 240 keV (ZnSe) 400 keV (CVD diamond) NTHU Relativistic Photon- electronics dynamic Laboratory CO 2 -laser-acceleration Project at ATF BNL

10. Lens-array structure (IV): The Design Parameters for the Multistage Accelerator at ATF BNL Single-stage length1.5 cm Total linac length24 cm Number of accelerator stages16 Electron transit hole diameter 100  m Laser beam waist in each stage 280  m Laser damage threshold (ZnSe)2.25 GW/cm 2 (0.45 J/cm 2 ) Laser wavelength 10.6  m Laser ModeTEM 01 Phase tuning by temperature π over 93  C Total energy gain240 keV NTHU Relativistic Photon- Electron Dynamics Laboratory CO 2 -laser-acceleration Project at ATF BNL

11. Lens array structure at (V): Temperature phase tuning laser HeNe B.S. Mirror L1: ZnSe lens temperature controlled by TE cooler L1 TE cooler Si detector (det210) iris NTHU Relativistic Photon- Electron Dynamics Laboratory CO 2 -laser-acceleration Project at ATF BNL

12. Lens array resonator structure at (V): Phase tuning over temperature experiment,where d is the thickness of lens(~0.98mm), and λ 0 is the wavelength of He-Ne laser in vacuum (~632.8nm) For 10.6 um NTHU Relativistic Photon- Electron Dynamics Laboratory CO 2 -laser-acceleration Project at ATF BNL Or

13. Scaled to 1  m wavelength at ORION 1.Formation/coherence length ~ γ 2 λ 2.Acceleration field ~ √(damage threshold) ORIONATF Wavelength1μm1μm10.6 μm Beam energy350MeV (  small phase slip and beam size) 70MeV Laser pulse width100 fsec200 psec Damage threshold2J/cm 2 0.45J/cm 2 advantagesuitable for high- gradient experiment Suitable for proof- of-principle experiment NTHU Relativistic Photon- Electron Dynamics Laboratory

14. Lens-array structure (I): The Design Parameters for the Multistage Accelerator High-gradient, small structure design Low-gradient, large structure design Single-stage length1 mm5 mm Total linac length1.3 cm6 cm L π ( Coherent length )9.8 mm260 mm Number of accelerator stages1312 beam waist (W 0 ) 18.4  m( with z r =1mm) 87.3  m ( with z r =2.25cm) Laser damage threshold2J/cm 2 Laser wavelength 1  m Laser ModeTEM 01 Total energy gain3.6 MeV4MeV Acceleration gradient280 MeV/m66 MeV/m A Proposed Muti-stage Experiment at ORION NTHU Relativistic Photon- Electron Dynamics Laboratory

15. A Proposed Muti-stage Experiment at ORION Quantities to be Measured 1. Coherent transition radiation by tuning the optical phase on individual lens  wake field impedance 2. Multistage phase control 3. Acceleration energy gain and gradient

16. A Proposed Muti-stage Experiment at ORION NTHU Relativistic Photon- Electron Dynamics Laboratory Energy350MeV Pulse length100 fsec Particles~10 9 Energy Spread0.1% Normalized Emittance~1 mm-mrad Timing Stability100 fsec Energy Stability0.1% Pointing Stability1μm1μm Electron beam parameter Summary Table of Laser Acceleration Project at ORION (I)

17. NTHU Relativistic Photon- Electron Dynamics Laboratory Pulse Energy 0.3 mJ Wavelength1 μm Pulse width100 fsec ModeTEM 10 Timing Stability100 fsec Pointing Stability1μm1μm Laser beam parameters A Proposed Muti-stage Experiment at ORION Summary Table of Laser Acceleration Project at ORION (II)

18. Energy Spectrometer0.1% Charge10 pC/pulse (10 8 electrons) Positioning resolution1 μm Emittance resolution0.05 μm rad Pulse timing resolution < 0.1 psec NTHU Relativistic Photon- Electron Dynamics Laboratory Electron Beam Diagnostics Laser Beam Diagnostics: power, pulse width, wavelength etc. A Proposed Muti-stage Experiment at ORION Summary Table of Laser Acceleration Project at ORION (III)

19. Summary The 1 MeV/m Multi-stage CO 2 -laser-acceleration Project at ATF BNL is a proof-of-principle experiment for vacuum acceleration ORION facility is suitable for high-gradient, small-size vacuum acceleration. With 350 MeV beam, 1 μm wavelength, and 100 fsec laser pulse width, an acceleration gradient of 280 MeV/m can be obtained near the material damage. The electron energy gain from the proposed 14 accelerator stages is 3.6 MeV over a overall accelerator length of 1.3 cm. NTHU Relativistic Photon- Electron Dynamics Laboratory