Staging of Laser Plasma Accelerators (LPAs) Sven Steinke* J. van Tilborg, C. Benedetti, C. G. R. Geddes, C. B. Schroeder, J. Daniels, K. K. Swanson, A. J. Gonsalves, K. Nakamura, B. H. Shaw, H.-S. Mao, D. Mittelberger, C. Toth, E. Esarey and W. P. Leemans BELLA Center, LBNL *ssteinke@lbl.gov Work supported by Office of Science, Office of HEP, US DOE Contract DE-AC02-05CH11231, by NNSA DNN R&D, US DOE and by NSF 0917687 & 0935197 Office of High Energy Physics Science
High gradient LPAs offer path to colliders • Plasma provides a structure to sustain high field gradients (GeV/m) • High field gradients require high peak power: laser driven, particle beam driven Z R v beam laser bunch v phase wave v group laser Limits to single stage energy gain • Laser Diffraction (~Rayleigh range) o mitigated by transverse plasma density tailoring (plasma channel) • Beam-Plasma Wave Dephasing o mitigated by longitudinal plasma density tailoring (plasma taper) • Laser Energy Depletion: energy loss into plasma wave excitation For high gradient, laser depletion necessitates staging laser-plasma accelerators 2
Vision: LPA linear collider concept Scaling laws indicate E. Esarey, plenary, Mon., 11am: operation at n e ~ 10 17 cm -3 “Roadmap towards a future o plasma-based collider “ Quasi-linear regime ( a 0 ~1): e + and e - , o focusing control Staging & laser coupling into plasma o channels • ~10 J laser/energy per stage • multi-GeV energy gain/stage Leemans & Esarey, Phys Today (2009) BELLA PW Multi-GeV expts. BELLA Center Staging expts. Required laser technology development tens of kHz o ~100-200 kW avg. power/laser o High wall-plug efficiency o Office of 3 Science
Scaling towards 10 GeV requires lower densities C.B. Schroeder, tutorial, Mon., 5pm: LPA scaling laws Schroeder et al., Phys. Rev ST, 13, 101301 (2010). o Laser-plasma interaction length: LBNL 2006 Beam energy (MeV) 3/2 RAL 2009 L deplete n 1 LLNL 2010 n o Accelerating gradient: (require > GV/m) MPQ 2007 E z ~ m e c p e n U.Mich 2008 LOA 2006 o APRI 2008 Energy gain (per LPA stage): RAL 2004 LBNL 2004 E z L int 1 n plasma density, n (cm -3 ) Office of 4 Science
ns-scale Heater Pulse enables deeper channels with better mode matching Decoupling of Ignitor and Heater 9cm discharge capillary Volfbeyn et al., PoP 6 , 2269 (1999) Durfee and Milchberg PRL 71 , 2409 (1993) Inverse Bremsstrahlung heating o Testing underway with guiding Density (10 18 cm -3 ) 0.58 0.33 of a 10ns, 2J heater laser 0.08 o Indication of heating (few eV) observed J. Daniels, WG1, Wed., 11:10am: “ Plasma control & diagnostics for 10 GeV on BELLA “ Bobrova et al., PoP 20 , 020703 (2013) Office of 5 Science
Simulations using measured top hat laser pulses indicate ~10 GeV beams can be obtained in ~ 40 cm capillary Non-linear regime with ideal, Quasi-linear regime with realistic, Gaussian laser pulse shape measured laser pulse shape Laser: U=36 J, w 0 =60 um, Laser: U=40 J, w 0 =64 um, INF&RNO simulations by Carlo Benedetti T=66 fs (FWHM of intensity) T=27 fs (FWHM of intensity) Plasma: n 0 =1.6x10 17 cm -3 , R cap =200 um, Plasma: n 0 =2.7x10 17 cm -3 , R cap =250 um, laser heater (2.3 J, 10 ns) laser heater (2.3 J, 10 ns) z = 10 cm z = 43 cm E [GeV] E [GeV] Q = 200 pC Q = 96 pC E average = 9 GeV E average = 8.4 GeV (dE/E) rms = 7 % (dE/E) rms = 7 % ( σ z ) rms = 1 μm ( σ z ) rms = 2 μm ( σ x' ) rms = 0.45 mrad ( σ x' ) rms = 0.33 mrad k p (z-ct) k p (z-ct) C. Benedetti, WG2, Mon., 4:10pm: 6 “ Efficient modeling of LPAs with INF&RNO ”
Multistage Coupling of two independent LPAs Stage ge I: gas jet - injector Coupling II: tape-driven plasma mirror Stage ge II: discharge capillary- accelerator Coupling I: active plasma lens TREX EX: laser 1: 1.3J, 45fs laser 2: 0.6J, 45fs dipole magnet C.G.R. Geddes, WG7, Tue., 11:15am: “Narrow bandwidth Thomson photon source development using LPAs“ 7
Multistage Coupling of two independent LPAs Stage ge I: gas jet - injector Coupling I: active plasma lens Coupling II: tape-driven plasma mirror Stage ge II: : discharge capillary- accelerator 8
Stage I : Turnkey gas jet operation in ionization injection regime provides tunable injector beams of excellent stability Steering possible Stable energy and charge charge density Avg. mean energy (115 ± 3) MeV (arb. units) Avg. charge (37 ± 4) pC Stable E-beam pointing 10mrad 10mrad o Pointing stability ± 0.3 mrad o Divergence FWHM (2.3 ± 0.3) mrad Phosphor screen Phosphor screen 9
Multistage Coupling of two independent LPAs Stage ge I: gas jet - injector Coupling I: active plasma lens Coupling II: tape-driven plasma mirror Stage ge II: : discharge capillary- accelerator 10
Developed Active Plasma Lens for efficient e-beam coupling to the 2 nd stage and emittance measurement Emittance measurement: Tunable, ultra-high field source size of 5 μ m Plasma lens Magnetic spectrometer: Model Experiment J. van Tilborg et al., PRL 184802 (2015) Discharge pulse enables gradients of >3000 T/m: I r 0 dis B 2 2 R Scintillator screen: Office of 11 Science
Active Plasma Lens enables transport of 15% of the injector charge to a spotsize ≤ the wakefield acceptance Beam profiles at Stage 2 entrance Beam spectra within wake acceptance without lens: with lens : efficiency <1% efficiency 15% w/o lens Broad energy spread of the injector beam with lens limits charge coupling to the 2 nd stage wakefield due to the chromaticity of the plasma lens. J. van Tilborg, plenary, Fr., 9:05am: “FELs d riven by LPAs” S. Barber, WG5, Mon., 4:30pm: “ Transport and phase space manipulation of LPA beams“ S. Steinke, WG6, Thu., TBA: “Isochoric heating with PW -laser- driven Ion beams” Office of 12 Science
Multistage Coupling of two independent LPAs Stage ge I: gas jet - injector Coupling I: active plasma lens Coupling II: tape-driven plasma mirror Stage ge II: : discharge capillary- accelerator 13
Tape-driven Plasma Mirror (PM) to couple in the 2 nd stage laser pulse at cm-scale to maintain the overall acceleration gradient Plasma Mirror design Plasma mirror performance • High reflectivity (80%) Sokollik et al. AAC proc. (2010) • Excellent mode quality (Strehl ratio >0.8) beam2 • Small pointing fluctuation (~9µm) f=2m 0 mm +2 mm -2mm Shaw et al. PoP 23 , 063118 (2016) tape probe • Active feedback control s, plastic • Stable operation over hours of run time s, metallic p, plastic p, metallic S. Steinke, WG6, Tue., 4:20pm “ Plasma mirrors as diagnostic for basic plasma parameters ” Optimize material and laser polarization 14
Multistage Coupling of two independent LPAs Stage ge I: gas jet - injector Coupling I: active plasma lens Coupling II: tape-driven plasma mirror Stage ge II: : discharge capillary- accelerator Relative delay of both laser arms is controlled by an optical delay stage with fs-precision 15
Staging Experiment: Energy gain of witness beam by timing of second laser (wake phase) Modulation period of 80fs consistent with a plasma frequency at a density of 2x10 18 cm -3 reference (g) (d) ref. S. Steinke et al., Nature 530 , 190 (2016) subtracted reference Previous plasma lens calculation suggest that 1.2pC of trapped charge corresponds to a wake trapping efficiency of 30%, but it’s not that easy (unfortunately) Office of 16 Science
Simulation reproduce staging signatures at correct magnitude Comparison of experiment and simulation S. Steinke et al., Nature 530 , 190 (2016) reference subtracted • Recurring post acceleration (100 MeV) at the plasma frequency • ~1pC of charge at energies >200MeV • Analysis of simulation results unravels details of the acceleration/ deceleration processes 17
Mismatched laser guiding leads to 2 phases of acceleration & deceleration Energy & Spotsize of electrons focused to stage2 entrance S. Steinke et al., Nature 530 , 190 (2016) 18
Mismatched laser guiding leads to 2 phases of acceleration & deceleration Energy & Spotsize of electrons focused to stage2 entrance S. Steinke et al., Nature 530 , 190 (2016) 19
Mismatched laser guiding leads to 2 phases of acceleration & deceleration Energy, Spotsize and laser a 0 of electrons focused to stage2 entrance S. Steinke et al., Nature 530 , 190 (2016) 20
Mismatched laser guiding leads to 2 phases of acceleration & deceleration Energy, Spotsize and laser a 0 of electrons accelerated to energies >200 MeV S. Steinke et al., Nature 530 , 190 (2016) spotsize evolution w/o laser 21
~10 GeV electron beams from STAGING experiment using BELLA: simulations show high efficiency capturing and acceleration in LPA2 of the bunch produced by LPA1 Energy ← injector 10 cm 8 cm 1 cm 20 cm ~30 cm ~30 cm spectra cap lens after LPA1 LPA2 LPA1 Laser1 [n 0 =(2-3)x10 17 cm -3 ] [n 0 =(2-3)x10 17 cm -3 ] =BELLA/2 after LPA2 bunch (15 J, 80 fs) Laser2 injector =BELLA/2 (15 J, 80 fs) Bunch dynamics in LPA1 Bunch transport LPA1 → LPA2 Bunch dynamics in LPA2 delay=-434.6 fs delay=-430.8 fs delay= -426.9 fs Bunch energy Bunch energy Relative energy spread Relative energy cap spread lens 22
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