gradient Acceleration Schemes, Results of Experiments

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1 Review of Ultra High-gradient gradient Acceleration Schemes, Results of Experiments R. Assmann,, CERN-SL Reporting also on work done at SLAC, as member of and in collaboration with the Accelerator Research Department B (ARDB) under R. Siemann. Thanks to my former co-workers and colleagues M. Hogan (SLAC), C. Joshi (UCLA), T.Katsouleas (USC), W. Leemans (LBNL), J. Rosenzweig (UCLA), R. Siemann (SLAC) F. Amiranoff (Ecole Polytechnique) for help and advice with this talk. RA EPAC02 1 Picture courtesy T. Katsouleas

2 1) Why ultra-high gradients? The Livingston plot Limits for new particle accelerators Basic requirements for particle physics The promise of ultra-high gradients 2) How to get ultra-high gradients? Overview on schemes being followed Principles (plasma and vacuum concepts) 3) Experimental results - Highlights Plasma wakefield acceleration Laser wakefield acceleration Laser acceleration 4) Moving towards usage in a linear collider Considerations The plasma booster for the Higgs? 5) Conclusion RA EPAC02 2

The Livingston plot The Livingston plot shows a saturation effect! Practical limit for accelerators at the energy frontier: Project cost increases as the energy must increase! Cost per GeV C.M.

3 The Livingston plot The Livingston plot shows a saturation effect! Practical limit for accelerators at the energy frontier: Project cost increases as the energy must increase! Cost per GeV C.M. proton has decreased by factor 10 over last 40 years (not corrected for inflation)! M. Tigner: Does Accelerator-Based Particle Physics have a Future? Physics Today, Jan 2001 Vol 54, Nb 1 Not enough: Project cost increased by factor 200! New technology needed RA EPAC02 3

4 Basic requirements beyond next generation e + e - linear colliders Beam energy c.m. >5 TeV Luminosity > cm -2 s -1 Beam power(consequence): ~ 100 MW New technologies for high energy colliders must be compatible with reasonable beam power: Example: Energy = 2.5 TeV Luminosity = cm -2 s -1 IP spot size = 10 nm Bunch population = Good efficiency Low emittance (beam size) High bunch charge RA EPAC02 4

5 The promise of ultra-high gradients Final energy = Active acceleration length Accelerating gradient Exponential increase in energy without exponential increase in accelerating gradient: 1. Accelerators become longer. 2. Without cheap technology they become more expensive. 3. They do not fit on the sites of existing laboratories (more difficult approval, additional infrastructure cost). Ultra-high gradients of up to 100 GV/m have been observed (gain of 3 orders of magnitude). What is the status of this technology? Can we build ultrashort high-energy colliders? RA EPAC02 5

6 What are ultra-high accelerating gradients? Feasible gradients in metallic structures: Collider Gradient SLC 20 MeV/m SLAC ILC MeV/m SLAC, KEK TESLA MeV/m DESY CLIC 150 MeV/m CERN See talk by W. Wuensch Ultra-high accelerating gradients: GeV/m obtained with various new technologies! RA EPAC02 6

7 1) Why ultra-high gradients? The Livingston plot Limits for new particle accelerators Basic requirements for particle physics The promise of ultra-high gradients 2) How to get ultra-high gradients? Overview on schemes being followed Principles (plasma and vacuum concepts) 3) Experimental results - Highlights Plasma wakefield acceleration Laser wakefield acceleration Laser acceleration 4) Moving towards usage in a linear collider Considerations The plasma booster for the Higgs? 5) Conclusion RA EPAC02 7

8 Advanced accelerator research Two types of advanced accelerators: 1. Wakefield accelerators Dielectrics and microstructures (RF and two beam) Plasma 2. Laser accelerators Vacuum Plasma RA EPAC02 8

9 Concepts For Plasma-Based Accelerators Pioneered by J.M. Dawson! Plasma Wake Field Accelerator(PWFA) A high energy electron bunch! Laser Wake Field Accelerator(LWFA) A single short-pulse of photons! Plasma Beat Wave Accelerator(PBWA) Two-frequencies, i.e., a train of pulses! Self Modulated Laser Wake Field Accelerator (SMLWFA) Raman forward scattering Instability evolves to Courtesy T. Katsouleas RA EPAC02 9

10 Basic principle and scaling rules 1 I) Generate homogeneous plasma channel: Laser Gas Plasma II) Send dense electron beam towards plasma: = ion = electron Beam density n b > Gas density n 0 Beam excited plasma. Also lasers can be used (laser wakefield acceleration). RA EPAC02 10

11 Basic principle and scaling rules 2 III) Excite plasma wakefields: Electrons are expelled r Ion channel z Space charge force of beam ejects all plasma electrons promptly along radial trajectories Pure ion channel is left: Ion-focused regime, underdense plasma RA EPAC02 11

12 Basic principle and scaling rules 3 Equilibrium condition: Ion charge neutralizes beam charge: a n = σ SLC: n b /n 0 = 10 r n b n 0 Beam size n n 0 Ion channel Drive beam Quasineutral plasma a n (neutralization radius) Beam and plasma densities determine most characteristics of plasma wakefields! r RA EPAC02 12

Basic principle and scaling rules 4 Electron motion solved with... driving force: restoring force: Space charge of drive beam displaces plasma electrons.

13 Basic principle and scaling rules 4 Electron motion solved with... driving force: restoring force: Space charge of drive beam displaces plasma electrons. Plasma ions exert restoring force Space charge oscillations (Harmonic oscillator) Ez electron beam Longitudinal fields can accelerate and decelerate! RA EPAC02 13

14 Basic principle and scaling rules 5 Wavelength: Accelerating field λ p 1mm cm n 0 N e σ z r e 1 (SLC: 0.2) W 100 z n 0 V/ m (roughly) Plasma density n to N b σ 2 z λ p ~ mm ~ GV/m RA EPAC02 14

15 Basic principle and scaling rules 6 Plasma ions move relatively little Constant focusing gradient W r r 2 T n = n e = m 0 2π 0 960π cm β = 2γ c ϖ p Plasma structures are also super-strong quadrupoles! (many thousand T/m)... need to handle acceleration and focusing! RA EPAC02 15

16 Basic observations Plasma based acceleration: High accelerating gradients (many GV/m) Short wavelengths (< mm) Short bunches (< 100µm) Strong transverse focusing (> kt/m), small β (< cm) Small matched beam size Rigid tolerances Availability of short bunches for experiments is limited! RA EPAC02 16

17 1) Why ultra-high gradients? The Livingston plot Limits for new particle accelerators Basic requirements for particle physics The promise of ultra-high gradients 2) How to get ultra-high gradients? Overview on schemes being followed Principles (plasma and vacuum concepts) 3) Experimental results - Highlights Plasma wakefield acceleration Laser wakefield acceleration Laser acceleration 4) Moving towards usage in a linear collider Considerations The plasma booster for the Higgs? 5) Conclusion RA EPAC02 17

18 Ultrahigh-gradient acceleration of injected electrons by laser-excited relativistic electron plasma waves UCLA C.E. Clayton et al., Phys. Rev. Letters 70, 37 (1993) Cloud chamber photograph Resonance curve 3.4 cm Accelerated electron track Low energy noise B ext e- Electron Signal (AU) } 3.5 MeV 4.1MeV 6.5MeV 5.0MeV 7.3MeV 8.6MeV 5.2 MeV, Cloud Chamber Calculated trajectory 7.25 cm Pressure (mtorr) Conclusive evidence of injected electron acceleration. First evidence of resonant acceleration. RA EPAC02 18 Courtesy C. Joshi, UCLA

19 UCLA Trapped electron acceleration by a laser-driven relativistic plasma wave M. Everett et al. Nature 368, 527 (1994) % model 25% model 10 5 Trapping Energy Electrons/MeV Injection Energy Electron energy (MeV) 30 First observation of energy gain beyond trapping threshold Evidence for energy loss as well as energy gain by plasma wave RA EPAC02 19 Courtesy C. Joshi, UCLA

20 UCLA Observation of electron energies beyond the linear dephasing limit from a laser-excited relativistic plasma wave D. Gordon et al., Phys. Rev. Letters 80, 2133 (1998) Observation of energy gain: 100 MeV over 0.6 mm => at least 160 GeV/m acceleration gradient Done at Rutherford Laboratories, UK RA EPAC02 20 Courtesy C. Joshi, UCLA

UCLA Laser-oscillator room The NEPTUNE Facility for 2nd Generation Advanced Accelerator Experiments C. Joshi, J. Rosenzweig, C. Pellegrini, K.A. Marsh, S. Tochitsky, and C.E. Clayton Amplifier hall Experiment hall Control room Plasma accelerator Injector linac Goals: Acceleration of injected, high-current beam to 100 MeV.

21 UCLA Laser-oscillator room The NEPTUNE Facility for 2nd Generation Advanced Accelerator Experiments C. Joshi, J. Rosenzweig, C. Pellegrini, K.A. Marsh, S. Tochitsky, and C.E. Clayton Amplifier hall Experiment hall Control room Plasma accelerator Injector linac Goals: Acceleration of injected, high-current beam to 100 MeV. Acceleration of a pre-bunched electron beam. Beam-physics studies. RA EPAC02 21 Courtesy C. Joshi, UCLA

22 Table-top Laser-Driven Electron Acceleration (via self-modulated laser wakefield in plasma) D. Umstadter, S.-Y. Chen, A. Maksimchuk, R. Wagner, RA EPAC02 Courtesy T. Katsouleas, USC 22

23 NRL EXPERIMENTAL PROGRAM Antonio C. Ting, Chris I. Moore, Rich Fischer, Dmitri Kaganovich, Ted Jones Self-Modulated Laser Wakefield Accelerator: Production of up to 100 MeV electrons at >100 GV/m gradient has been observed (over ~ mm). Relative # of electrons/mev/steradian Shot 12 (10 kg) 10 6 Shot 26 (10 kg) Shot 29 (5 kg) Shot 33 (5 kg) Shot 39 (2.5 kg) 10 5 Shot 40 (2.5 kg) SM-LWFA electron energy spectrum Electron energy (in MeV) A. Ting, et al, Phys. Plasmas, 4, 1889 (1997) D. Kaganovich, et al, PRE, 59, R4769 (1999) Injection and channel guiding for the GeV range (longer). RA EPAC02 Courtesy T. Katsouleas, USC 23

24 Laboratoire pour l Utilisation des Lasers Intenses (LULI) CNRS - CEA - Ecole Polytechnique - Université Paris TW LULI laser facility LPNHE - LSI LPGP - IC - LOA - CPTH Self-modulated wakefield experiments - 1 single laser pulse focused in a gas jet 100 MeV in E >100 GV/m FewnC> 4 MeV Divergence : few mrad Number of electrons [/MeV/sr] n e = cm -3 n e = cm -3 detection threshold Electron energy [MeV] T=8.1 MeV T=2.6 MeV 35 fs, 600 mj, W/cm 2, 10 Hz RA EPAC02 24

25 Some laser guiding scheme is necessary to reach high energy gains The potential energy gain is huge l 0 = 1 µm, n e = e-/cm 3, g = 100 : W = 20 GeV over L = 1 m The effective acceleration length is limited by diffraction of the laser beam Laser beam Plasma wave E L=2Z R What about guiding the laser beam over 1 m? Laser guiding in dielectric capillary tubes RA EPAC02 25

Colliding pulse injector Production of electron beams with low energy spreads and pulse-to-pulse energy stability in a plasma-based accelerator requires: Injection of femtosecond electron bunches

26 Colliding pulse injector Production of electron beams with low energy spreads and pulse-to-pulse energy stability in a plasma-based accelerator requires: Injection of femtosecond electron bunches Injection with femtosecond timing Laser triggered injection of background plasma electrons into a plasma wake by beating of two colliding pulses [E. Esarey et al., PRL, 79, 2682 (1997)] Reference: E.Esarey et al., PRL '97 C.B. Schroeder et al., PRE '99 Normalized potentials a0 a1 a ψ = plasma wake phase = k p z ω t p RA EPAC02 26 Courtesy W. Leemans LBNL

27 Plasma Wakefield Acceleration in Meter-long Plasmas E-157 & E-162 & E-164 Collaborations R. Assmann, F.-J. Decker, P. Emma, M. J. Hogan *, R.H. Iverson, C. O Connell, P. Krejcik, P. Raimondi, R.H. Siemann, D. Walz Stanford Linear Accelerator Center B.E. Blue, C.E. Clayton, C. Huang, C. Joshi *, K.A. Marsh, W.B. Mori, S. Wang University of California at Los Angeles UCLA T. Katsouleas *, S. Lee, P. Muggli University of Southern California Extraordinarily high fields developed in beam plasma interactions Many questions related to the applicability of plasmas to high energy accelerators and colliders Address these questions via experiments " E-157: First experiment to study Plasma Wakefield Acceleration (PWFA) of electrons over meter scale distances Physics for positron beam drivers qualitatively different (flow-in vs. blow-out) "E-162 Opportunity for dramatically shorter bunches in the FFTB in 2003 with correspondingly higher gradients (> GeV/m) " E-164 RA EPAC02 27 Courtesy M. Hogan, T. Katsouleas

Experimental Layout UCLA Located in the FFTB e - or e + N=2 10 10 σ z =0.

1.4 m Optical Transition Radiators Streak Camera (1ps resolution) Bending

28 Experimental Layout UCLA Located in the FFTB e - or e + N= σ z =0.6 mm E=30 GeV Ionizing Laser Pulse (193 nm) Li Plasma n e cm -3 L 1.4 m Optical Transition Radiators Streak Camera (1ps resolution) Bending Magnet 12 m Cerenkov Radiator X-Ray Diagnostic Dump RA EPAC02 28 Cdt FFTB

29 Beam Propagation Through A Long Plasma UCLA Smaller matched beam size at the plasma entrance reduces amplitude of the betatron oscillations measured at the OTR downstream of the plasma Allows stable propagation through long plasmas (> 1 meter ) σ X DS OTR (µm) s x (µm) σ 0 Plasma Entrance =50 µm ε N = (m rad) β 0 =1.16m Plasma OFF σ x (µm) L=1.4 m σ 0 =14 µm E-157 E-162 Run 2 ε N = m-rad β 0 =6.1 cm α 0 =-0.6 Plasma OFF Plasma ON Envelope cedFIT.graph Phase ψ=k*l n Advance 1/2 e ΨL n 1/2 e L 0 BetatronFitShortBetaXPSI.graph Phase Advance Ψ Ψ n 1/2 e L C. E. Clayton et al., PRL 1/2002 E-157/E-162 collaboration RA EPAC02 29

30 Electron Beam Steering: Refraction At Plasma Gas Boundary Symmetric Channel Beam Focusing Asymmetric Channel Beam Steering r c =α(n b /n e ) 1/2 r b e Plasma, n e θ φ Head Core UCLA Vary plasma e - beam angle φ using UV pellicle Beam centroid BPM6130, 3.8 m from the plasma center P. Muggli et al., Nature 411, 2001 θ (mrad) -0.3 E-157 collaboration RA EPAC θ 1/sinφ o φ (mrad) θ φ BPM DATA Impulse Model

$Refraction of an Electron Beam: Interplay Between Simulation & Experiment UCLA Experiment (Cherenkov images) Laser off Laser on 3-D$

31 Refraction of an Electron Beam: Interplay Between Simulation & Experiment UCLA Experiment (Cherenkov images) Laser off Laser on 3-D OSIRIS PIC Simulation 1 to 1 modeling of meter-scale experiment in 3-D! P. Muggli et al., Nature 411, 2001 E-157 collaboration RA EPAC02 31

32 Betatron Radiation of X-rays UCLA Plasma focusing strength of 6000T/m acts as a strong undulator l Peak brightness ~ photons/sec-mm 2 -mrad 2 -.1%bw! E-157 collaboration RA EPAC02 32

33 E-162: Use Imaging Spectrometer To Measure Energy Loss & Gain UCLA Preliminary Picosecond Gaussian Slice Analysis of Many Events Average energy loss (slice average): 159 ± 40 MeV Relative Energy (MeV) n e = (cm -3 ) n e = (cm -3 ) n e =(2.3±0.1) (cm -3 ) SliceEnergyGain3curves.graph -2σ z -σ z +σ z +2σ z +3σ z τ (ps) Average energy gain (slice average): 156 ±40 MeV ( e - /slice) E-164: > 1 GeV/m (2003) RA EPAC02 33 E-162 collaboration

34 Other schemes Laser acceleration in vacuum (LEAP): Two crossed laser scheme: Only tantalizing of the interaction signature. Power source: Laser. New proposal Inverse free electron laser (STELLA): Power source: Laser. Successful staging. 90 MeV/m goal. Limit from synchrotron radiation at ~ 200 GeV. Bunches of femto-second length. Di-electric wakefield accelerator: Possible gradients: 100 MeV 1GeV Power source: Drive beam. RA EPAC02 34

35 1) Why ultra-high gradients? The Livingston plot Limits for new particle accelerators Basic requirements for particle physics The promise of ultra-high gradients 2) How to get ultra-high gradients? Overview on schemes being followed Principles (plasma and vacuum concepts) 3) Experimental results - Highlights Plasma wakefield acceleration Laser wakefield acceleration Laser acceleration 4) Moving towards usage in a linear collider Considerations The plasma booster for the Higgs? 5) Conclusion RA EPAC02 35

Efficiency 1 High beam power requires: Efficient power generation Progress in the field of lasers: High peak power is possible (~ 100 TW ) Wall-plug-to-photon efficiency:

36 Efficiency 1 High beam power requires: Efficient power generation Progress in the field of lasers: High peak power is possible (~ 100 TW ) Wall-plug-to-photon efficiency: % Better stability (pointing stability in sub µrad regime) Efficiency of beam-driven PWFA: ~ 30% LEAP at the ORION Center Robert L. Byer & Robert H. Siemann RA EPAC02 36

37 Efficiency 2 C. D. Barnes et al, SLAC PROPOSAL E-163 Accelerating Microstructures: Re-use the laser beams for increasing efficiency! RA EPAC02 37

38 High quality beam transport 1 Short accelerator, but what about emittance? R. Assmann, K. Yokoya, NIM 1997 Parameter PWFA LWFA Acceleration 1 GeV/m 30 GeV/m Wavelength 2 mm 100 µm Focusing field 6,000 T/m 600,000 T/m Module length 6 m 1 m Injection energy 1 GeV 1 GeV Final energy 1 TeV 1 TeV Acc. length 1 km 33 m RA EPAC02 38

39 High quality beam transport 2 Matched beam size at injection energy: σ 0 [µm] PWFA LWFA NLC 0 1e-08 1e-07 1e-06 1e-05 γε [m-rad] SLC NLC type emittance requires sub-micron spot size! m rad RA EPAC02 39

40 High quality beam transport 3 Tolerance for alignment beam - plasma wakefield: emittance m rad with 200% emittance growth Number of plasma cells: 167 or 33 (LWFA) RMS alignment tolerance: < 300 nm (PWFA) 30 nm (LWFA) High energy plasma-wakefield accelerator will have difficult alignment problems, but... New ideas: Hollow plasma channels No ions on axis, no focusing! Acceleration still works... RA EPAC02 40

41 Hollow plasma channels with e + and e - Positron longitudinal wake amplitude is comparable to e- in a hollow plasma: e - e channel Radius R wp/c T. Katsouleas, USC RA EPAC02 41

42 The first step: A plasma afterburner? A 100 GeV-on-100 GeV e - e + Collider at SLAC based on Plasma Afterburners SLAC facilities 3 km 30 m LENSES Afterburners 50 GeV e - e - WFA e + WFA 50 GeV e + IP E-157 collaboration RA EPAC02 42

43 Afterburner vs. E157 Comparison E-157 Afterburner Bunch: Number: 1 - σ z =.65mm Plasma Density: 0-5e14 cm -3 Length: 1.4 m Betatron Oscillations: 0-5 Bunches: Number: 2 - σ z =.065mm,.033 mm Separation:.019 mm Plasma Density: 2e16 cm -3 Length: 7 m Betatron Oscillations: 100 Can we control 7 m of plasma? Studies are ongoing for this idea RA EPAC02 43

44 1) Why ultra-high gradients? The Livingston plot Limits for new particle accelerators Basic requirements for particle physics The promise of ultra-high gradients 2) How to get ultra-high gradients? Overview on schemes being followed Principles (plasma and vacuum concepts) 3) Experimental results - Highlights Plasma wakefield acceleration Laser wakefield acceleration Laser acceleration 4) Moving towards usage in a linear collider Considerations The plasma booster for the Higgs? 5) Conclusion RA EPAC02 44

45 Conclusion Advanced accelerator concepts have made impressive progress: High gradient acceleration up to 160 GV/m demonstrated. Beam-plasma interaction of 30 GeV SLAC beam in 1.4m long plasma. Experimental results in excellent agreement with predictions. New applications (fsec science, plasma wiggler, kicker, lens, ). Many problems still to be addressed for building a high energy collider but no fundamental show stopper!? Accelerator physics moves into the right direction (small emittance, short bunches). Can a plasma afterburner on a conventional accelerator be the first step? RA EPAC02 45

46 Plasma Accelerator Progress and the Livingston Curve 7 6 Livingston Current status future T. Katsouleas, USC Log of Energy in MeV LEP? SLAC/USC/UCLA/LBL E-162 RAL/IC/UCLA/LULI NRL, UM UCLA E-164/ORION Year UCLA Port J. LLNL/UCLA RA EPAC02 46

E-162: Positron and Electron Dynamics in a Plasma Wakefield Accelerator

E-162: Positron and Electron Dynamics in a Plasma Wakefield Accelerator Presented by Mark Hogan for the E-162 Collaboration K. Baird, F.-J. Decker, M. J. Hogan*, R.H. Iverson, P. Raimondi, R.H. Siemann,