Prospects and Directions of CO 2 Laser-driven Accelerators

Transcription

1 Prospects and Directions of CO 2 Laser-driven Accelerators Sergei Tochitsky Neptune Laboratory, Department of Electrical Engineering, AAC-2014

2 Motivation Particle Acceleration Ponderomotive force scales as I 2 a 0 =1 I=10 16 W/cm 2 (CO 2 ) W/cm 2 (1µm) Plasma Based Accelerators Overdense plasma phenomena in range n e = 1-100n cr (n cr =10 19 cm 3 ) can be easily realized in an ionized gas and probed by visible light. Vacuum Based Laser Accelerators Manipulation of longitudinal phase-space at long wavelength is relatively easy and robust. Transverse matching of electron beam is straight forward that is important for accelerating structures.

3 Outline Long-wavelength Gas Laser Drivers for Advanced Particle Accelerators. Monoenergetic Proton Beams from Plasmas Accelerated by Collisionless Shocks in Gases. Direct Laser Acceleration in Vacuum using Inverse Free Electron Laser scheme and a dielectric structure.

4 Normalized Gain O C O CO 2 Molecule Linewidth Boltzman Distribution N [N CO 2 exp( hv 3 / kt 3 )] / Q v Normalized Ampl.. 10 mm mm 1atm col =3.5 GHz x atm At 10 atm 35 GHz > 55GHz line spacing CO 2 Gain Spectrum 10atm 25atm Wavelength (mm) Wavelength (mm) ~1.2THz

5 Bandwidth, GHz Power Broadening power =2 R =2mE/h=2(6.91x10 6 m I) ac Stark Broadening at 10 GW/cm 2 ~50 GHz CO2 = col + power Intensity, GW/cm 2 Picosecond Pulse Amplification Strategy From nj to mj High-Pressure From mj to 5J High-Pressure I.Pogorelsky et al ATF BNL From mj to 100s J High-Fields S.Tochitsky et al, Optics Letters, 26, 813 (2001)

6 Neptune CO 2 MOPA Laser System Nd:Glass Laser 1 mm 3 ps Master Oscillator 10 mm 200 kw ns CS 2 Ge Switch ~nj 3 ps Pockels cell 4 mj 3 ps 8 atm Regenerative Amplifier 2.5 atm Large-aperture Amplifier 10 mm TW 3 ps

7 Picosecond CO 2 Laser Seed Pulse Nd:Glass Laser CO 2 Laser Present CS 2 Kerr Switch Polarizer CS 2 Kerr Cell Analyzer 1µm 3ps 1mJ 10µm 500ns 30mJ I 90 (1µm) = 25 GW/cm 2 Signal-to-background contrast = 10 5 Future Front End: All solid state OP CPA 2-mm Laser Fiber Laser DFG 10 mm 200ps,200 mj 1 ps, 1mJ Stretcher OPA GaAs,ZGP 100ps Compressor 10µm 3ps 1nJ 10 mm 1-5 mj

8 Normalized Amplitude Norm. Amplitude Regenerative Amplification at 8 atm 8atm TE CO 2 module col = 37GHz 50% OC Pulse train after Regenerative Amplification 3 ps 10mJ (4mJ) Frequency Spectrum CO 2 Gain Spectrum at 8atm 3ps Input Pulse Spectrum Overlapped Spectrums ~nj Pulse Train Formation ps Time (ps) Amplified Pulse Temporal Structure 18ps = 1/55GHz Modulation 18 ps=1/ 55 GHz line spacing Frequency (THz) Time (ps)

9 Norm. Amplitude Norm. Amplitude TW CO 2 MOPA System at the Neptune Laboratory In 4 mj 1 cm Out 100J 5 Electron-beam controlled Large-aperture CO 2 amplifier 20x35x250 cm 3 discharge size CO 2 :N 2 =4:1, P=2.5 atm Pulse train after Regenerative Amplification 3 ps Pulse train after Final Amplification 18 ps Time (ps) The most powerful CO 2 laser E total =100J 45J, 3ps 15 TW! Time (ps) D. Haberberger et al, Optics Express (2010)

10 Isotopic active medium Simulations Experiment Polyanskiy et al. Optics Express 19:7717 (2011)

11 CO 2 Laser Facilities for Advanced Accelerator Research NEPTUNE - 201? 50TW CO 2 Laser =10.6 mm E ~ 50J in 1 ps High-repetition rate 3 J in 3 ps=1tw CA NY ATF BNL 201? 50+TW =9.3 mm E ~ 50J in ps I W/cm 2 Vosc/c 10 Neptune Lab. ATF MARS PITER

12 Normalized Amplitude Normalized Amplitude Beyond 100 TW Dreams ~300J, 1 ps MARS ~1J, 3 ps Rabi flopping in the CO 2 amplifier at W/cm 2 I=10G W/cm I=100G W/cm ps 3ps Rabi Flopping N W 12 W 12 << Pulse length, ps Time (ps) Pulse length, ps PITER R =me/h>> W 12 = R2 / Time

13 Outline Monoenergetic Proton Beams from Plasmas Accelerated by Collisionless Shocks in Gases.

14 Medical Laser Based Accelerators Goal Cost : 20 million USD Table top laser system (developing) Transportation : Mirrors Only has focusing magnet Gantry : small, protons generated in direction of patient

15 Laser Based Accelerators Dose Radiation Beam Requirements 2 Gray in 1 liter tumor in a few minutes -Translates to protons per second Laser Driven Ion Acceleration Lasers can accelerate up to protons in a single shot Energy Energy Spread Proton energies in range of 200 MeV Energy Spread of ~5% Worlds most powerful lasers produced 100 MeV protons Vast majority of beams have continuous energy spread Focusability, Energy Accuracy, Energy Variability, Dose Accuracy, etc. Future Work

16 Optical probing of laser hole-boring in overdense plasma n e laser n c r V sh 2V sh jet foil Palmer et al, PRL, 106, (2011) 5% energy spread 5x10 6 protons within 5-mrad spectral brightness protons/mev/sr Courtesy of Igor Pogorelsky

17 1mm CR-39 Noise Floor Monoenergetic Proton Acceleration in H 2 Gas Jet Energy spreads measured to be FWHM ΔE/E ~1-10% Feb 22 th CR-39 #179 Jan 25 th CR-39 #92 Jan 25 th CR-39 #99 Haberberger et al, Nature Phys., 8, (2012)

18 Plasma Density (10 19 cm -3 ) Y-Distance (mm) Plasma Density Profile Measurements -600 Observations Laser -300 A. Strong profile modification 0 on the front side of the 300 plasma : hole boring 600 B. Sharp rise (10λ) 4 to overcritical plasma where laser 3pulse is stopped C. Long (1/e 30λ) 1 exponential plasma tail 2 Laser X-Distance (mm)

19 2D OSIRIS Simulations: CO 2 Laser Pulse Train Initial Plasma Profile Similar to one Measured in Experiment linear ramp Laser a o = 2.5 Δτ = 3ps Laser a o = 2.5 Δτ = 3ps exponential ramp ( ionized by hot electrons) 18 ps

20 Collisionless Electrostatic Shocks Generate Monoenergetic Protons Time = 17ps Time = 52ps Time = 122ps Shock Shock Formation Expansion Protons Expansion Ions SWA SWA Vi=2Vsh V i =2V sh -V o

21 2D Simulations: Proton Energy Scaling 10µm Laser H 2 Gas Jet Gas plume >200 MeV a0~ TW CO 2 Laser Extended Plasma E max ~a 0 3/2 hybrid PIC E TNSA ~ 1/L F. Fiuza et al PRL, 109, (2012)

22 Compact Picosecond Ion Source/Injector 1-10 Hz Tunable, debris free gas target at cm -3 plasma density I~ W/cm 2 a Pulsed Solenoid RF cavity 3 ps CO 2 Laser 1-3 J, 1-10 Hz PRF 1-5 MeV H..Ne E/E~1% H 2, He Ne Gas jet He H2 Ne Future facilities will need multiple ions, ideally from protons through neon to permit inter-facility comparisons of RBE and to permit combining ions for optimal patient treating DOE Workshop on Ion Beam Therapy, 2013

23 Outline Direct Laser Acceleration in Vacuum using Inverse Free Electron Laser scheme and a dielectric structure.

24 E xˆ B yˆ zˆ k Laser + electron beam Sinusoidal Modulation Seeded FEL/IFEL interactions Trapping w 2 2 ebw K 2 mc Saturation Exponential Gain Linear Gain w 2 1 K 2 2 w :undulator wavelength B w :magnet strength Initial state Typical radiation power plot Totally trapped in the pomderomotive bucket

25 Final energy (MeV) Fraction of captured particles (%) Neptune 10-mm IFEL experiment IFEL output vs. Laser Power Laser Power (GW) 5% of electrons trapped and increased kinetic energy from 12.5 to >35 MeV; Energy gain 70 MeV/m P. Musumeci et al, PRL, 94, , (2005)

26 Status of 10 mm high-gain IFEL research Present 2014 record for IFELs energy gain and acceleration gradient in helical undulator Future 1-2 GeV IFEL accelerators for soft X-ray FELs 100MeV/m 1 GeV/m 100 TW Past 2004 Diffraction dominated highgain planar 10-mm IFEL 1996 Proof of principle IFEL at ATF: Ari van Steenbergen

27 Courtesy of W. Kimura Schematic Layout of STELLA Experiment CONVEX MIRROR CO2 LASER BEAM DIPOLE MAGNET VACUUM PIPE ACCELERATOR (IFEL2) BUNCHER (IFEL1) WINDOW LENS E-BEAM SPECTROMETER VIDEO CAMERA E-BEAM FOCUSING LENSES TAPERED UNDULATOR ARRAY CHICANE E-BEAM FOCUSING LENSES VACUUM CHAMBER PARABOLIC MIRROR WITH CENTRAL HOLE

28 Comparison of Data and Model Predictions E-beam only 14% trapping 80% trapping Advantages of using 10.6 mm laser beam - For given e-beam energy, permits using longer wiggler period - Easier to maintain stable phase synchronization between electrons and laser field inside IFEL W.D. Kimura et al, PRL 92, (2004)

29 CTR energy (pj) 7th order IFEL buncher experiment at the Neptune Laboratory Microbunching in the undulator using 7th order IFEL interactions10.6 mm x 7=74.2 mm 12.4 MeVe-beam mirror with a hole ICT undulator 2 w K 1, 3,5, n 2 n CTR Harmonics of the Bunched beam Fundamental Second Harmonic Third Harmonic CO 2 Laser 1 Hz PRF P= 40 MW 4mJ, 100 ps NaCl lens F=2.5 m Undulator L=33 cm; w =3.3 cm; K=1.8 2 w K 1, 3,5, n 2 n Laser Power (MW) S. Tochitsky et al, Phys Rev. STAB, (2009)

30 Seeded 340 mm microbunching for Plasma Accelerator THz DFG seed 1 kw, 7.25 MeV electron beam in a 1-m long undulator e-beam I=30 A 15 ps FWHM OAP mirror with a hole Undulator 9.6 GHz RF Cavity 1 ps 1 kw THz seed by DFG in GaAs pumped by CO 2 laser 10.6 mm 300 kw THz pulse Electron beam is longitudinally modulated on 340 mm scale phase-locked to a Laser Wakefield at cm -3 plasma.

31 Surface wave accelerator driven by a picosecond CO 2 Laser = mm = mm Accelerating wake Deflecting wake Both accelerating (good) and deflecting (parasitic) wakes are experimentally observed Simple fabrication, macroscopic size, driven by picosecond CO 2 laser pulses B. Neuner III, D. Korobkin, G. Ferro, and G. Shvets, PRSTAB 15, (2012).33

32 Status and Future Directions Demonstrated high-peak power >10 TW, capability of wall-plug efficiency >10 %, and average power >1kW makes CO 2 laser technology a viable source for Advanced Accelerator R & D. An upgrade to 50+TW is underway at BNL. At the main interest at high-repetition rate TW class laser : 3J-3 ps or 300 mj-300 fs. Required for Radiotherapy monoenergetic ~200 MeV proton beams are predicted in CO 2 laser interaction with a gas jet plasma at a 0 =10 using SWA. A near term goal a few MeV high-brightness ion source /injector tunable from protons through neon. 10 mm Inverse Free Electron laser is a rather mature technology potentially could deliver GeV class beams of good quality or beams microbunched on the scale of mm for phase-locked injection in plasma accelerators. The United States is undoubted leader in the field of high-power CO 2 gas lasers and its applications for particle acceleration.

33 Acknowledgement Catalin Filip, Ritesh Narang, Jay Sung, Joe Ralph, Dan Haberberger, Chao Gong, Jeremy Pigeon, Brent Blue, Ken Marsh, Chris Clayton, Chand Joshi s Laser-Plasma Group Warren Mori, Frank Tsung, Oliver Williams, Pietro Musumeci, James Rosenzweig () Frederico Fiuza, Luis O. Silva, (IST Portugal) Igor Pogorelsky, Marcus Babzien, Ilan Ben-Zvi (ATF BNL) DOE Office of Science, HEP

34 Laser Power, W Long, 50-ns pulse 10-mm Power Source for Advanced Accelerators TEA CO laser 2 Canada, France NRC LANL (Laser Fusion) UL, Canada Mode-Locking, UL NRC Harvard 1 ns Pulse Amplification LEKKO, Japan TIR-1, Russia NRC -MARS LAB Production of Picosecond Pulses Year -NEPTUNE LAB 50 TW BNL-ATF Picosecond Pulse Amplification ATF BNL 201? 50 TW =10.6 mm E ~ 25J in 0.5 ps I W/cm 2 Vosc/c 10 NEPTUNE - 201? 50TW CO 2 Laser =10.6 mm E ~ 50J in 1 ps High-repetition rate 3 J in 3 ps=1tw

35 10-mm Power Source for 200 MeV Proton Beams TABLE. CO 2 laser requirements for radiotherapy source based on SWA or RPA acceleration in a gas jet. Parameter Repetition rate (spot/passive) Laser for Proton Therapy 30 Hz/10 Hz Laser Wavelength (mm) 10.6 Laser Intensity (W/cm 2 ) 1-3x10 18 Pulse duration (ps) (with compression after final amplification) <1 (0.3) Contrast (5 ps/500 ps) <10-5 /10-7 Laser energy stability < 5% Focused spot size (mm) ~50 Pulse Energy (J) Peak Power (PW) 0.1 Average Power (kw) at 10 Hz (30 Hz) (0.9-3)

36 50 TW CO 2 MOPA Laser Driver for Radiotherapy at Hz Ho:Laser Fiber Laser DFG 2.1 mm 200ps,200 mj 10 mm 1 ps, 1mJ 100ps QPM GaAs Stretcher- Compressor 5-10 mj 1 ps Front End All solid state OP CPA 10 mm 400 mj 3 ps WP 8-10 atm CO 2 Booster Amplifier 10x10x100 cm 3 3-pass 3-5 atm CO 2 Amplifier Thin Film Polarizer 30 J 1 ps

37 Normalized Amplitude Normalized Amplitude Future Developments-50 TW Rabi flopping in the CO 2 amplifier at W/cm 2 I=10G W/cm I=100G W/cm ps 3ps Rabi Flopping N W 12 W 12 << Time Pulse length, ps Time (ps) Pulse length, ps R =me/h>> W 12 = R2 / 1. Simulations show Rabi Flopping of the lasing transition at >100 GW/cm 2 2. Oscillations in population inversion shortens pulse to <1ps (FWHM) 3. For 1 ps pulses E sat is expected to increase to 300 mj/cm 2 4. Five passes may be needed to reach this regime E total =50J 1 ps 50 TW! Experiments at very relativistic powers a 0 =5 (for w 0 =60 mm, I=7x10 17 W/cm 2 ).

38 Future Prospects-1-10Hz Multiple Ion Source/Injector High-repetition rate Laser driver for the H +, He 2+ or Ne injector 8atm Regenerative Amp 4mJ w o = 4mm I = 450 MW/cm 2 8atm 2-Pass Amp L T = 1.2 m 50mJ w o = 1cm I = 1.8 GW/cm 2 3atm 3-Pass Amp L T = 3m 3-10J, 3 ps P = 1 TW H 2 Gas Jet 5x10x100 cm atm CO 2 module with UV preionization at Neptune Lab made by PaR Development of a picosecond injector for medical RF accelerators or a compact laboratory ion source!

39 Wall-Plug Efficiency For E/N=5x10-16 Vxcm 2 (I)-Elastic collisions: N 2 rotational Stretching & Bending modes-14.3% (II)-Upper laser level-54.3% (III)-Electronic excitation-31.4% (IV)-Ionization negligible P opt 250kW kW Wall plug 21.7% e-beam controlled 4atm, 20J, 50 Hz, >25% JTech.Phys.v.57,1987

40 Rubicon IFEL Helical geometry high gain high gradient IFEL First strongly tapered helical undulator Two different tapering used» Demonstrate control of the final beam properties Input e-beam energy 50 Mev Average accelerating gradient 124 MV/m Laser wavelength 10.3 μm Laser power 300 GW Laser focal spot size (w) 980 μm Laser Rayleigh range 25 cm Undulator length 54 cm Undulator period 4 6 cm Magnetic field amplitude kg

41 Energy (MeV) 1 GeV IFEL with ATF upgrade Take advantage of higher CO2 power after upgrade Demonstrate 1 m long z 0.999m - 1 GeV IFEL module Challenging tapered undulator design Parameters for BNL high gradient high energy gain IFEL experiment Input beam energy Final beam energy Laser wavelength Average accelerating gradient Laser seed power Laser size (at focus) Laser Rayleigh range Undulator length Undulator wavelength (initial-final) Undulator peak field (initialfinal) MeV 1200 MeV 10.3 mm >1 GV/m 100 TW 950 mm 25 cm 100 cm 4 cm 20 cm T Undulator period and amplitude as a function of the distance along the undulator Phase Longitudinal phase space and energy spectrum of 1 GeV IFEL module from period averaged one dimensional simulations.