Plasma-based Acceleration at SLAC

Transcription

1 Plasmabased Acceleration at SLAC Patric Muggli University of Southern California for the E167 collaboration

2 E167 Collaboration: I. Blumenfeld, F.J. Decker, P. Emma, M. J. Hogan, R. Iverson, R. Ischebeck, N.A. Kirby, P. Krejcik, R.H. Siemann, D. Walz Stanford Linear Accelerator Center D. Auerbach, C. E. Clayton, C. Huang, C. Joshi, K. A. Marsh, W. B. Mori, W. Lu, M. Zhou University of California, Los Angeles T. Katsouleas, E. Oz, P. Muggli University of Southern California and E157/162/164/164X Collaborations THANK YOU to SLAC THANK YOU to DoE

3 OUTLINE Motivation The Plasma Wakefield Accelerator (PWFA) Propagation of e beams in plasmas e /e + energy gain Issues to be addressed Summary/Conclusions

4 WHY PLASMAS AS ACCELERATOR? Large accelerating gradients n λ pe =ω pe /2πc e ion z c E = ne ε 0 ω pe = ne ε 0 m 1 2 E = mcω pe e E=1GV/m for n=10 14 cm 3 Large focusing fields Already ionized, further ionization is more difficult H: fully ionized, Li: φ 1 =5.4 ev, φ 2 =75 ev Fields last for only a few periods of the wave No structure, no fabrication, no damage operation at high frequency and high gradient

5 PLASMA WAKEFIELD (e ) Defocusing Focusing (E r ) Accelerating Decelerating (E z ) Relativistic electron beam Plasma wave/wake excited by a relativistic particle bunch Plasma e expelled by space charge forces => energy loss + focusing Plasma e rush back on axis => energy gain Plasma Wakefield Accelerator (PWFA) = energy transformer, 2beam accelerator

6 Defocusing PLASMA WAKEFIELD (e ) PWFA: highfrequency, highgradient, strong focusing beamdriven accelerator N Linear scaling: E acc 110(MeV / m) σ z / k pe σ z 2 or n e cm 3 (with k pe σ z <<1) Focusing strength: B θ Focusing (E r ) Accelerating Decelerating (E z ) r = 1 2 ( ) 2 1/σ z 2 n e e ε 0 c = 3kT / m n e (1014 cm 3 ) Single beam: particles fill all the phases of the accelerating bucket Relativistic electron beam

7 NUMERICAL SIMULATIONS e Gradient Increases when σ z decreases (N=cst) Electric Field (GV/m) AccDeccFields(sigmaz) Accel. (Useful) σ r =20 (µm) Accel. (Useful) σ r =10 (µm) Deccel. σ r =20 (µm) Deccel. σ r =10 (µm) N=10 10 e, k p σ z GeV/m 0.01 E164X E σ z (µm) E157 E162 E167: σ z =2010 µm: >10 GV/m gradient! (σ r dependent! k p σ r 1) n e 1.4x10 17 cm 3 for k p σ z 2 and σ z =20 µm f p =2.8 THz, n e =10 17 cm 3

8 PWFA SLAC 3 km Longbunch Experiments Shortbunch experiments e /e GeV σ z 700 µm σ r 30 µm n e 2x10 14 cm 3 L p 1.4 m Preionized N x10 10 /bunch k pe σ z GV/m e 28.5, 42 GeV σ z 3020 µm σ r 10 µm n e 23x10 17 cm 3 L p 10, 20, 30, 60, 90, 120 cm Fieldionized

9 e N= σ z =2012µm E=28.5 GeV Xray Chicane E EXPERIMENTAL SET UP (GENERIC) Energy Spectrum Xray Coherent Transition Radiation and Interferometer IP0: Li Plasma n e 03x10 17 cm 3 L 1090 cm Plasma light Optical Transition Radiators (OTR) Imaging Spectrometer 25m IP2: Cherenkov Radiator Cdt XRay Diagnostic, e/e + Production Dump Coherent Transition OTR Cherenkov (aerogel) Radiation (CTR) Spatial resolution 100 µm CTR Energy I peak 1/σ z Energy resolution 30 MeV y Cherenkov Gas Cell y x z Energy resolution 60 MeV x Spatial resolution 9 µm y,e x

10 PROPAGATION OF e Beam Envelope Model for Plasma Focusing σ r (µm) Plasma Focusing Force > Beam Emittance Force (β beam =1/K> β plasma ) No Plasma n e = cm 3 Plasma Lens n e = cm 3 3 rd Betatron Pinch Plasma BeamFocusing(z).graph λ β z (m) OTR Envelope equation: 2 σ z 2 + K 2 σ = ε 2 σ 3 In an ion channel: K = ω pe 2γ c ( n e ) 1/ 2 with a focusing strength: n e e W = E r rc = B θ r = 1 2 ε 0 c =6 n e = cm 3 =6 n e = cm 3 Multiple foci (betatron oscillation) within the plasma

11 FOCUSING OF e OTR Images 1m downstream from plasma σ x (µm) L=1.4 m σ 0 =50 µm ε N = mrad β 0 =1.16 m α 0 =0.5 K 1/β 0 Plasma OFF Plasma ON Envelope σ x (µm) K 1/β 0 Plasma OFF Plasma ON Envelope Equation Fit σ=30 µm ε N = mrad β=0.11 m α=0 β 0 K BetaronFitLongBeta.graph Plasma Density ( cm 3 ) Focusing of the beam well described by a simple model (n b >n e ): Plasma = Ideal Thick Lens No emittance growth observed as n e is increased Stable propagation over L=1.4 m up to as n e = cm n e, matched = cm cwMatchedBetatron.graph Plasma Density ( cm 3 ) Channeling of the beam over 1.4 m or >12β 0

12 e N= σ z =2012µm E=28.5 GeV Xray Chicane E EXPERIMENTAL SET UP (GENERIC) Energy Spectrum Xray Coherent Transition Radiation and Interferometer IP0: Li Plasma n e 03x10 17 cm 3 L 1090 cm Plasma light Optical Transition Radiators (OTR) Imaging Spectrometer 25m IP2: Cherenkov Radiator Cdt XRay Diagnostic, e/e + Production Dump Coherent Transition OTR Cherenkov (aerogel) Radiation (CTR) Spatial resolution 100 µm CTR Energy I peak 1/σ z Energy resolution 30 MeV y Cherenkov Gas Cell y x z Energy resolution 60 MeV x Spatial resolution 9 µm y,e x

13 SLICE ANALYSIS RESULTS PREIONIZED, LONG BUNCH (σ z 730 µm) Relative Energy (MeV) 200 n e = (cm 3 ) 150 n 100 e =1.8± (cm 3 ) Front Back 150 2σ 200 z σ z +σ z +2σ z +3σ z Time (ps) Energy gain smaller than, hidden by, incoming energy spread Time resolution needed, shows the physics Peak energy gain: 279 MeV, L=1.4 m, 200 MeV/m E 0 =28.5 GeV e : P. Muggli et al., PRL 2004

14 e & e + ASYMMETRY IN PLASMAS 3D QuickPIC simulations, plasma e density: e σ r =35 µm σ r =700 µm e + Ν= d=2 mm e : n e0 = cm 3, c/ω p =375 µm e + : n e0 = cm 3, c/ω p =3750 µm Back Blow Out Back Front 3σ 0 beam Front 3σ 0 beam Uniform focusing force (r,z) Nonuniform focusing force (r,z)

15 Experiment Plasma Off ENERGY LOSS/GAIN e + σ z 730 µm N= e + n e = cm 3 n e = cm 3 Loss Gain 2D Simulation Front Back Front Back Loss 70 MeV Gain 75 MeV Excellent agreement! Plasmas do accelerate e + (over 1.4 m) Loss 45 MeV/m 1.4 m=63 MeV Gain 60 MeV/m 1.4 m=84 MeV PRL 90, , (2003)

16 Damping Ring 50 ps RTL Short Bunch Generation In The SLAC Linac Chirping 1 GeV 9 ps 0.4 ps 2050 GeV Add Add 12meter chicane compressor in in linac linac at at 1/3point (9 (9 GeV) SLAC Linac Compression FFTB <100 fs Existing bends compress to <100 fsec 1.5% 30 ka 80 fsec FWHM 28 GeV E acc 110(MeV / m) ~1 Å N σ z / 0.6mm ( ) 2 Courtesy of SPPS

17 ENERGY GAIN VS. PLASMA LENGTH E 0 =28.5 GeV, σ z 20 µm n e = cm 3 Plasma Density ( cm 3 ) PlasmaProfiles26e16 1,2,3 H 34.2 T L p =13, 22, Position (cm) Energy gain increases with plasma length (L p ) Energy gain reaches 13.6 GeV with L p =31 cm!

18 ENERGY GAIN E 0 =42 GeV, N= e, n e = cm 3, L p =90 cm No Plasma Final Focus Test Beam 9.6x10 8 e 154 pc 3 km e /e + LINAC 90 cm e Energy gain 42 GeV over 90 cm of plasma! or 46 GV/m! PWFA = extremely simple and compact accelerator (unloaded)

19 PLASMA SOURCE Lithium vapor in a heatpipe oven e Heater Wick Plasma Light Diagnostic Be Window Pressure He Cooling Jackets Boundary Layers Li He n 0 = cm 3 T= C L=10120 cm P He 140 T Extremely simple and cheap, highgradient accelerator Tunnelionization: n e =n o, Li, removes plasmarelated variations L P. Muggli et al., IEEE TPS (1999)

20 PLASMA WAKEFIELD ACCELERATOR Defocusing Focusing (E r ) Accelerating Decelerating (E z ) Witness Bunch: E 0 => 2E 0 Driver Bunch: E 0 => 0 Driver bunch: highcharge (3N), modest emittance, shaped? Witness bunch: lower charge (N), good emittance beam loading for E/E<<1 Plasma provides focusing and acceleration

21 PLASMA AFTERBURNER 50 GeV e e and e + : Driver bunches: IP σ z =63 µm, N= e /e +, 50 > 0 + GeV Witness bunches: σ z =32 µm, N= e /e +, 50 > GeV Delay: d=200 µm Plasma: n e = cm 3, L=7, 17 m Accelerating gradient: 8, 3 GV/m 3 km e PWFA 7m PLASMA LENSES e + PWFA 17m S. Lee et al., PRSTAB (2001) 50 GeV e +

22 IMPORTANT ISSUES Highgradient positron acceleration Acceleration to small E/E 2bunch experiments with e and e + Preservation of emittance and polarization Evolution, stability of the bunches over long plasma lengths Real accelerator: beam loading, optimization, luminosity

23 SUMMARY / CONCLUSIONS We have a very good understanding of high energy beam/plasma interaction We have demonstrated experimentally: Excitation of large accelerating gradients ( 45GV/m, unloaded) by e beams in meterlong plasmas, stable and reproducible Stable propagation of electron beams in long, dense plasmas Doubling of the energy of e of a collider beam Scaling of energy gain with plasma length, bunch length, and plasma density Acceleration of e + in plasmas Simulation tools have been developed to help/guide the experiment This is just the beginning e + in plasmas Acceleration of particle bunches ( E/E<<1) Preservation of collider beam parameters

24 No Plasma Gain Loss Energy (GeV) E x (mm) THANK YOU to my colleagues of the E167 Collaboration: I. Blumenfeld, F.J. Decker, P. Emma, M. J. Hogan, R. Iverson, R. Ischebeck, N.A. Kirby, P. Krejcik, R.H. Siemann, D. Walz Stanford Linear Accelerator Center D. Auerbach, C. E. Clayton, C. Huang, C. Joshi, K. A. Marsh, W. B. Mori, W. Lu, M. Zhou University of California, Los Angeles T. Katsouleas, E. Oz, P. Muggli University of Southern California THANK YOU to SLAC THANK YOU to DoE We will be back!

25 SIMULATION CHALLENGE Simulations by C. Huang, UCLA L 30 m Driver Witness >0.5 TeV Driver Witness N D =3x10 10, N w =10 10, ε Nx =ε Ny =2230x10 6 mrad, σ x =σ y =15 µm, (beam matched to the plasma) σ zd =145 µm, σ zw =10 µm, z=100 µm N e =5.66x10 16 cm 3, L p =30 m Doubling the energy of a 500 GeV bunch possible! in only 30 m ( 17 GeV/m)! (simulation)

26 SIMULATION CHALLENGE Simulations by C. Huang UCLA N D =3x10 10, N w =10 10, ε Nx =ε Ny =2230x10 6 mrad, σ x =σ y =15 µm, (beam matched to the plasma) σ zd =145 µm, σ zw =10 µm, z=100 µm N e =5.66x10 16 cm 3, L p =30 m, preionized, Gradient>17 GeV/m Doubling the energy of 500 GeV bunch possible! in only 30 m! (simulation)

27 SIMULATION CHALLENGE Head erosion Wake loading evolution E/E 5% FWHM Narrow energy spread, could be improved with optimization Stability with real beam parameters (ε x,y, σ x,y ) CPU time intensive

28 IMPORTANT ISSUES Plasma ions motion (J. B. Rosenzweig, et al. PRL. 95, (2005)) Significant when n b /n e >>1 Degrades beam emittace and focusing Improves with: higher ε, higher A, space charge, etc. e + wake gradient, emittance growth in plasma e + Hollow plasma channel More stringent beam parameters