Laser Plasma Wakefield Acceleration : Concepts, Tests and Premises

Transcription

1 Laser Plasma Wakefield Acceleration : Concepts, Tests and Premises J. Faure, Y. Glinec, A. Lifschitz, A. Norlin, C. Réchatin, V.Malka Laboratoire d Optique Appliquée ENSTA-Ecole Polytechnique, CNRS Palaiseau, FRANCE Partially supported by CARE/PHIN FP6 project

2 Summary Part 1 : Laser plasma accelerator : motivation Part 2 : Laser plasma accelerator as booster Part 3 : Laser Plasma accelerator as injector : Production of monoenergetic electron beam Part 4 : New scheme of injection : toward a stable, tuneable and quasi monoenergetic electron beam. Part 5 : Conclusion and perspectives

3 Classical accelerator limitations E-field max few 10 MeV /meter (Breakdown) R>R min Synchrotron radiation Energy = Length = $$$ LEP at CERN 27 km PARIS Circle road 31 km New medium : the plasma

4 Why is a Plasma useful? Superconducting RF-Cavities : E z = 55 MV/m Plasma is an Ionized Medium High Electric Fields

5 How to excite Relativistic Plasma waves? The laser wake field Electron density perturbation F -grad I Laser pulse τ laser T p / 2 =>Short laser pulse Phase velocity v φ epw=v g laser => close to c Analogy with a boat Are Relativistic Plasma waves efficient? E ~ n z e E z = 0.3 GV/m for 1 % Density Perturbation at cc -1 E z = 300 GV/m for 100 % Density Perturbation at cc -1 Tajima&Dawson, PRL79

6 Relativistics microelectronic devices Courtesy of W. Mori & L. da Silva 100 μm Plasma cavity 1 m RF cavity

7 Interaction and dephasing lenghts electron t 1 t 2 t 3 γ e >> γ φ >> 1 L Deph. = λ p γ φ 2 =>L deph. =(λ 0 /2)(n c /n e ) 3/2 Diffraction limited Guiding : channel or relativistic L acc. =πz R L acc ΔW diff. [MeV] 580 (λ/λ p )/(1+a 02 /2) 1/2 P [TW] ΔW ch [MeV] 60 (λ p /w 0 ) P [TW] W. P. Leemans et al., IEEE 24, 2 (1996)

8 Summary Part 1 : Laser plasma accelerator : motivation Part 2 : Laser plasma accelerator as booster Part 3: Laser Plasma accelerator as injector : Production of monoenergetic electron beam Part 4 : New scheme of injection : toward a stable, tuneable and quasi monoenergetic electron beam. Part 5 : Conclusion and perspectives

9 Accelerating & focusing fields in Linear RPW Small Laser amplitude a 0 =0.5 Homogeneous plasma Pulse Electron density Accelerating E z Decelerating Defocusing E r Focusing

10 Accelerating & focusing fields in plasma channel Small Laser amplitude a 0 =0.5 Parabolic plasma channel Pulse Pulse Electron density Accelerating E z Decelerating Defocusing E r Focusing

11 Accelerating & focusing fields in NL RPW Large Laser amplitude a 0 =2 Homogeneous plasma relativistic shift of ω p Pulse Electron density Accelerating Decelerating Defocusing Focusing

12 Three Injection schemes Low energy => Low charge Before the pulse High Energy => Short Bunch Low energy laser

13 τ bunch = 200 fs

14 Injecting the τ bunch = 30 fs, 170 MeV

15 3 GeV, 1% energy spread e-beam E=9 J P= 0.15 PW a 0 =1.5 Parabolic channel: r 0 =47 μm, n(r)=n 0 ( r/r 0 ) n 0 = cm GeV, with a relative energy spread FWHM of 1% and an unnormalized emittance of mm.

16 Summary Part 1 : Laser plasma accelerator : motivation Part 2 : Laser plasma accelerator as booster Part 3: Laser Plasma accelerator as injector : Production of monoenergetic electron beam Part 4 : New scheme of injection : a stable, tuneable and quasi monoenergetic electron beam. Part 5 : Conclusion and perspectives

17 Laser plasma injector Scheme of principle Experimental set up

18 Energy distribution improvements: The Bubble regime Several groups have obtained quasi monoenergetic e beam but at higher density (τ L >τ p ) *Y. Glinec et al., in preparation, NB Charge in the peak : few 100 pc According to absolute calibration of scintillator* Experiment Divergence = 6 mrad PIC At J. Faure et al. Nature (2004)

19 Quasi monoenergetic e-beam :14 groups At Lundt Mangles et al. PRL (2006) At LBNL Geddes et al. Nature (2004)

20 Laser plasma injector : GeV electron beams w 0 = 20μ m τ = 30 fs P = 200TW λ =0.8μ m a 0 = 4 n p = cm 3 f(e) (a.u.) 2.5 After 5 Z r / 7.5 mm Energy (MeV) Courtesy of UCLA& Golp groups

21 Laser plasma injector : + good efficiency : E e-beam /E laser 10 % + simple device + sub 30 fs duration : ideal as injector + with channel : GeV range is obtained 1 with moderate laser power* *But since the efficiency is conserved a compromise between charge and energy must be found -Stability not yet demonstrated! - Energy spread still too large for some applications : δe/e few % * Courtesy of S. Hoocker or F. S. Tzung PRL (2004)

22 Summary Part 1 : Laser plasma accelerator : motivation Part 2 : Laser plasma accelerator as booster Part 3: Laser Plasma accelerator as injector : Production of monoenergetic electron beam Part 4 : New scheme of injection : toward a stable, tuneable and quasi monoenergetic electron beam. Part 5 : Conclusion and perspectives

23 External injection using another laser pulse Counter-propagating geometry: pump injection Principle: Plasma wave electrons Pump beam Injection beam Ponderomotive force of beatwave: F p ~ 2a 0 a 1 /λ 0 (a 0 et a 1 can be weak )y Boost electrons locally and injects them: y INJECTION IS LOCAL IN FIRST BUCKET E. Esarey et al, PRL 79, 2682 (1997), G. Fubbiani et al. (PRE 2004)

24 Experimental set-up electron spectrometer to shadowgraphy diagnostic LANEX B Field Gas jet Probe beam Injection beam Pump beam 250 mj, 30 fs φ fwhm =30 µm I ~ W/cm 2 a 1 = mj, 30 fs, φ fwhm =16 µm I ~ W/cm 2 a 0 =1.2

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26 From self-injection to external injection pump n e = cm -3 Single beam n e =10 19 cm -3 Self-injection Threshold n e = cm -3 pump injection n e = cm -3 2 beams

27 Optical injection by colliding pulses leads to stable monoenergetic beams STATISTICS Bunch charge= 15 +/- 5 pc Peak energy= 118 +/- 7 MeV ΔE= 13 +/- 2.5 MeV ΔE/E= 11 % Divergence= 5.7 +/- 2 mrad Pointing stability= 2 mrad

28 Monoenergetic bunch comes from colliding pulses: polarization test Parallel polarization Crossed polarization

29 Controlling the bunch energy by controlling the acceleration length By changing delay between pulses: Change collision point Change effective acceleration length Tune bunchenergy Pump beam Injection beam 2 mm Gas jet

30 Tunable monoenergetic bunches pump injection Z inj =225 μm Z inj =125 μm late injection Z inj =25 μm pump injection Z inj =-75 μm Z inj =-175 μm middle injection Z inj =-275 μm Z inj =-375 μm pump injection early injection

31 Tunable monoenergetic electrons bunches: Peak Energy (MeV) δe/e E peak δe/e (%) spectrometer resolution δe/e ~ 5 % z inj (µm) 190 MeV gain in 700 µm: E=270 GV/m Compare with E max =mcω p /e=250 GV/m at n e = cm -3

32 Conclusions / perspectives SUMMARY Optical injection by colliding pulse: it works! Monoenergetic beams trapped in first bucket Enhances dramatically stability Energy is tunable: MeV Charge up to 50 pc in monoenergetic bunch δe/e down to 5 % (spectrometer resolution), δe ~ MeV PERSPECTIVES Q Combine with waveguide: tunable up to few GeV with δe/e ~ 1 % Multi/single stage accelerators Stable source: extremely important accelerator development light source development Applications (material science, radiotherapy, chemistry etc )

33 Parameter designs Laser Plasma Accelerators ELI : > 100 GeV a 0 =4 P(PW) τ (fs) n e (cm-3 ) W 0 (μm) L(m) E(J) Q(nC) E(Gev) e e e k e k Golp and UCLA Group

34 Electron beam energy and laser power evolution ELI Maximale Electrons Energy (MeV) «conventional» technology *LBNL *LUND RAL UCLA KEK *LBNL UCLA ILE LULI Years E L I *LBNL Laser Power (W)

35 Towards an Integrated Scientific Project for European Researcher : ELI ELI