Laser wakefield electron acceleration to multi-gev energies

Transcription

1 Laser wakefield electron acceleration to multi-gev energies N.E. Andreev Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, Russia Moscow Institute of Physics and Technology, Russia In collaboration with CNRS - University Paris XI, France European Plasma Research Accelerator with excellence In Applications 3nd European Advanced Accelerator Concepts Workshop WG8 Advanced and novel accelerators for High Energy Physics La Biodola, Isola d'elba, September 5 9, 017 1

2 Outline Motivation and some history e-bunch energy spread in LWFA with external injection e-bunch compression and acceleration minimal energy spread at different injection schemes Laser wakefield electron acceleration in guiding structures to high (TeV) energies multistage acceleration (first accelerating stage) wakefield generation and electron acceleration with low energy spread (loading effect) emittance growth at broken cylindrical symmetry Conclusions and perspectives

3 JIHT of RAS Motivation and some history e-bunch energy spread in LWFA Electron bunch injection into LWFA at the maximum of accelerating field 1,0 e φ/mc 0,8 a= e A/mc 0,6 0,4 0, 0,0-0, Parameters of the laser pulse and electron bunch phase space of accelerated electrons ee a L 0 = = 1.0 γ ph = ω / ω p = 50 E inj = 80 mc L b = kp mcω V inj bunch ξ=k p (z-v ph t) Laser pulse P z / mc ~ E / mc V g E / E max (L acc ) CO Laser: a 0 = 0.71, k p r L = 3.8, k p R ch =14.3, L ph = 51 cm with increase in accelerating length L acc L acc = n L ph / 16, n = 0, 1,,... E mc γ ϕ max ph E mсγ kl d-0.1 φξ ( ) inj 1 ph p b0 n = 0 max max dξ without loading effect energy spread of accelerated e-buinch as a function of accelerating length initial bunch sizes: L b = r b = 0. λ p E inj / mc =100, L b = r b = 0.1λ p E/ E kl= 10% for L b 1mkm (3fs!) p b L b = r b = 0.1 λ p φ = e ϕ(ξ, r=0) / mc ξ = k p (z - V ph t) L acc / L ph

4 ОИВТ РАН Electron Bunch Injection in Front of the Laser Pulse e φ/mc boundary of focusing phase γ p =100, k p r 0 =3.35, k p l 0 =.355 laser pulse a(r=0, ξ) 0.4 E inj / mc = electron bunch ξ=k p (z-vt) For the velocity of injected electrons u = c 1 m c 4 inj E inj / < v ph : E dϕ dϕ kl p b d ϕ d ϕ = γ phkl p b + mc dξinj dξ dξ dξ inj L L b 1 β = β u / c b0 inj β = v / c ph Long low-energy electron bunch will be trapped and compressed in the wakefield N.E Andreev., S.V. Kuznezov. Electron Bunch Compression in Laser Wakefield Acceleration.// Giens Workshop Proceedings, June 4-9, 001.

5 ОИВТ РАН Electron Bunch Injection in Front of the Laser Pulse trapping and compression bunch injected in front of the laser pulse can be trapped and compressed in the wake field, if the condition ( )( ) 1/ ϕξ = γ γ 4 ( tr ) Einj mc 1 ph Einj m c 1 1/ ph is fulfilled in the focusing phase of the wakefield L c V E b, rms ph inj 4 Lb 0 Vph uinj γ phmc N.E. Andreev, S.V. Kuznetsov, et al, Plasma Phys. Control. Fusion, 5 (010)

6 ОИВТ РАН Electron Bunch Injection in Front of the Laser Pulse energy spread at the end of acceleration E max γ ph mc ϕ max E E min max 1 E ( ) kl πγ / mc 4 ( L λ) 6 inj p b, rms ph b0 0 E mc d ϕ min = γ ph( kl p b, rms ) dξmax γ = 100, 30, and 10 marked by triangles, squares and circles respectively, and for three initial bunch lengths ph L b0 = 100, 30, and 10 µm (solid, dashed and dotted lines respectively) for the laser wave length λ 0 = 1μm

7 JIHT of RAS Motivation and some history e-bunch energy spread in LWFA Electron bunch injection into LWFA at the maximum of the WF potential The compressed length of the trapped bunch can be estimated through the wakefield potential at the phases of injection and trapping: E dϕ dϕ kl p b d ϕ d ϕ = γ phkl p b + mc dξinj dξ dξ dξ inj

8 Laser Wakefield Electron Acceleration to high (TeV) electron energies, high quality bunches In guiding structures: L acc (10 100) L R 1m Staging techniques: ~ 10 GeV per stage Focusing system Plasma Accelerated electrons Electron injector Laser pulse Wake wave 8

9 JIHT of RAS Wakefield generation by guided laser pulses in dielectric capillary C n ~ E( r) = N m C n= 1 n J 0 ( k nr), k n un = a us i k a w a = ( ) ( / ), ( E r J 0 unr a rdr J 0 un [ a J1( un) ] 0 ) = 0 Laser pulse ε w >1 for the Gaussian laser pulse E(r) =E 0 exp(-r /r 0 ) Energy coupling to the main mode 98% at r 0 /a=0.645 z a Laser energy leakage: I L (z) = I 0 exp(- z / L D ) L 1 un 1+ ε w Dn, = 3 ka 0 ε w 1 9

10 JIHT of RAS Low energy electron bunch injection at the maximum of the WF potential to minimize the energy spread Computer simulation by the code LAPLAC Initial energy of electrons E inj = 1.9 mc and normalized emittance σ N = mm mrad The radial bunch dispersion was σ r,inj = 1.88 μm (k p σ r,inj = 0.148, k p R rms = 0.14) Longitudinal dispersion σ z,inj =.3 μm (FWHM bunch duration = 3 fs, k p σ z,inj = 0.18) At the entrance of the plasma channel, the laser pulse envelope was Gaussian in both longitudinal and transverse directions with laser wavelength λ 0 = 0.8 μm, amplitude a 0 =0.964 and FWHM pulse duration τ FWHM = 50 fs. and waist radius r 0 = 68. µm P 10 L =145 TW, P L /P cr =0.854, at plasma density on the axis n 0 = cm 3, γ ph = 100.

11 From 1-D theory in the stationer wakefield for test particles The compressed length of the trapped bunch can be estimated through the wakefield potential at the phases of injection and trapping: Injected RMS bunch length k p L b0 =0.41 Compressed bunch length k p L b =0.08 k p L rms =0.07 obtained in the simulations The upper estimate for the minimal electron energy spread: E rms /<E> 0.00 the maximum energy of the bunch electrons at the focusing point is limited to the value 11

12 How does it work in 3D modelling with allowance for the nonlinear laser and wakefield dynamics? The normalized by kp RMS bunch length (dotted line, left axis) and RMS bunch radius (solid line, left axis) and normalized emittance (line marked by squares, right axis) as functions of the acceleration length (a). The averaged energy (solid line) and the normalized RMS energy spread (dashed line) of the accelerated electron bunch as functions of the acceleration length (b). N.E. Andreev, V.E. Baranov and H.H. Matevosyan. Laser and Particles Beams DOI: 1

13 JIHT of RAS Loading effect (self-action of the bunch charge) in the LWFA E rms /<E> 0,05 Test particles Q b = 1 pc Q b = pc 0,04 Q b = 3 pc 0,03 0,0 N load ~ n 0 k p -3 = 3.6x > 60 pc 0,01 0,07 0, z [cm] Minimal energy spread for Q b = 3 pc: E rms /<E>= % E FWHM /<E>= 0.% N.E. Andreev, V.E. Baranov and H.H. Matevosyan. Laser and Particles Beams DOI: Energy spectrum 0,06 0,05 0,04 0,03 0,0 0,01 Q b = 3 pc z/l ph =0.36, z = 9 cm minimum of the energy spectrum width 0, E, MeV 13

14 Conclusion on the Laser WakeField electron Acceleration in guiding structures Stable and controllable laser propagation and wakefield generation over tens of Rayleigh length in guiding structures are demonstrated Acceleration of electrons to GeV energies in cm-scale capillaries is achieved Loading effect can be controlled and used to optimize electron bunch parameters for low energy spread (but it limits the bunch charge!) LWFA can provide low emittance acceleration of polarized electron bunches to high energies (next talk) Complete analysis of the multistage acceleration that preserve highquality electron bunches are needed to demonstrate the key element of the collider concept 14

15 With thanks for collaboration to all contributors: V.E. Baranov B. Cros - CNRS-Universitè Paris XI, France S.V. Kuznetsov D.V. Pugacheva - Joint Institute for High Temperatures RAS, Russia M.E. Veisman C-G Wahlström - Department of Physics, Lund University, Sweden - Joint Institute for High Temperatures RAS, Russia - Joint Institute for High Temperatures RAS, Russia - Joint Institute for High Temperatures RAS, Russia Thank You for your attention! 15