Demonstration of Energy Gain Larger than 10GeV in a Plasma Wakefield Accelerator

Transcription

1 Demonstration of Energy Gain Larger than 10GeV in a Plasma Wakefield Accelerator Patric Muggli University of Southern California Los Angeles, USA muggli@usc.edu

2 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 and of the E157/162/164/164X Collaborations THANK YOU to SLAC

3 OUTLINE Motivation Introduction to plasma wakefield accelerator (PWFA) Experimental setup e energy gain Summary/Conclusions

4 MOTIVATION Could an accelerating structure with a gradient significantly larger ( 10,, 1000) than that reached in present rf cavities (<200 MV/m) be created and can it lead to large energy gain (1100 GeV)? Plasmas can sustain very large electric fields (10100 GV/m) Relativistic plasma waves or wakes: E//k, electrostatic No fabricated structure Operation a very high frequency (THz), high gradient Laserdriven plasma accelerator: high charge, control and stability (V. Malka, Monday) beamdriven, plasma wakefield accelerator or PWFA

5 PLASMA WAKEFIELD ACCELERTAOR (e ) PWFA = beamdriven plasma accelerator Defocusing Focusing (E r ) Accelerating Decelerating (E z ) Relativistic electron bunch 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 Extract energy from the front, transfer to the back Focusing + acceleration = large energy gain Single bunch => particles at all phases

6 PWFA SCALING PWFA = beamdriven plasma accelerator Linear theory (n b <<n e ) scaling: When k pe σ z =(2π/λ p )σ z 2 (with k pe σ r <<1) N E acc 110(MeV /m) 1/σ 2 ( σ z (µm) /600) 2 z Focusing strength: (n b >n e ) B θ Defocusing Relativistic electron λ p bunch r = 1 n e e 2 ε 0 c = 3kT / m n e (1014 cm 3 ) Focusing (E r ) Accelerating Decelerating (E z ) N= σ z (µm) n e (cm 3 ) E acc (GV/m) f (GHz) λ p (µm) B θ /r (kt/m) Long Short >

7 SLAC 3 km Final Focus Test Beam (FFTB) parameters: E 0 =28.5 or 42 GeV N= e /bunch σ z =1440 µm (ultrashort bunches) σ x,y 10 µm

8 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

9 PLASMA SOURCE Lithium vapor in a heatpipe oven e Be Window Pressure He Heaters Cooling Jackets Boundary Layers Li Plasma Light Diagnostic Wick He 20 n 0 = cm 3 T= C L= cm P He 140 T P. Muggli et al., IEEE TPS (1999) Li Vapor Tunnelionization: Lithium: low Z, low IP (5.4 ev) Ultrashort bunch E r field > 6GV/m n e =n o, Li Plasma very reproducible L r/σ r 10 0 Plasma z/σ z

10 e N= σ z =2012µm E=28.5 GeV Xray Chicane E EXPERIMENTAL SET UP (GENERIC) Energy Spectrum Coherent Transition Radiation and Interferometer Energy resolution 60 MeV IP0: Li Plasma n e 03x10 17 cm 3 L 1020 cm Plasma light Optical Transition Radiators (OTR) Compare events with similar incoming longitudinal characteristics Cherenkov Gas Cell Imaging Spectrometer 25m y IP2: x z Cherenkov Radiator Cdt XRay Diagnostic, e/e + Production Dump Cherenkov (aerogel) Spatial resolution 100 µm Energy resolution 30 MeV y,e x

11 ENERGY GAIN VS. PLASMA LENGTH E 0 =28.5 GeV, 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!

12 ENERGY GAIN VS. PLASMA LENGTH Energy Gain (GeV) n e = (cm 3 ) (cm 3 ) (cm 3 ) EnergyGainvslength Plasma Length FWHM (cm) Accelerating Gradient (GV/m) AccGradientvsDensity n e (cm 3 ) Largest gain with n e = cm 3 ( L p, for σ z 20 µm) Accelerating gradient of 36 GV/m over L p =31 cm (unloaded: 7% accelerated charge)

13 e Energy Spectrum Xray EXPERIMENTAL SET UP Li Plasma n e 03x10 17 cm 3 L cm Plasma light y Cherenkov Gas Cell x z Loss Gain N= σ z =2012µm E=28.5 GeV Xray Chicane E Coherent Transition Radiation and Interferometer Energy resolution 60 MeV Optical Transition Radiators (OTR) High Energy GainLoss Measurements FOV 3 GeV to >100 GeV Spectrometer 3m y,e Cherenkov Radiators Cherenkov (air) Loss x y,e Dump Gain x

14 Energy (GeV) ENERGY GAIN E 0 =42 GeV, N= e, n e = cm 3, L p =90 cm No Plasma Final Focus Test Beam E 0 Gain Loss x10 8 e 154 pc 3 km e /e + LINAC 90 cm Energy gain 38 GeV over 90 cm of plasma! or 42GV/m! PWFA = extremely simple and compact accelerator x (mm) e

15 Defocusing FUTURE EXPERIMENT 2Bunch PWFA Focusing (E r ) Accelerating Decelerating (E z ) Witness Bunch: Driver Bunch: E 0 => 2E 0 E 0 => 0 Driver bunch: highcharge (3N), modest emittance, shaped? Witness bunch: lower charge (N), good emittance beam loading for E/E<<1 Typical 2 bunch PWFA parameters: n e cm 3, f pe 900 GHz, λ pe 300 µm G 1020 GeV/m N e σ D 60 µm, σ W 30 µm, t 150 µm

16 SUMMARY / CONCLUSIONS First plasma accelerator with >1GeV energy gain Energy gain up to 38 GeV in 90 cm, 42 GV/m over 90 cm Measured important scalings: Bunch length: σ z =730 µm W=200 MV/m, σ z 20 µm W=42 GV/m Optimum plasma density: n e =1.8x10 14 cm 3 n e = 2.6x10 17 cm 3 Plasma length: 13.6 GeV 31 cm (E 0 =28.5 GeV), 38 GeV, 85 cm, (E 0 =42 GeV) Energy gain increases linearly with plasma length Stable and reproducible acceleration Next steps: Twobunch experiment ( E/E<1) Highgradient positrons acceleration

17 FUTURE RESEARCH? PLASMA AFTERBURNER S. Lee et al., PRSTAB (2001) Large Gradient Plasma Accelerators 10 s km 100 s m Plasma Lenses Double the gradient and reduce size? Double the energy and extend the energy frontier?

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19 Neutral Density (10 17 cm 3 ) EnergyGain_3profiles ENERGY GAIN VS. PLASMA LENGTH 3D Simulations using QuickPIC E 0 =28.5 GeV, N= e, n e = cm 3 Position (cm) Energy Gain (GeV) Energy Gain (GeV) Energy gain increases with plasma length (L p ) Gradient 53 GV/m 20 AccelGradQuickPIC 18 W 53 GV/m Plasma Length (cm)

20 FUTURE RESEARCH e + wake gradient, emittance growth in plasma e + σ z 730 µm, N= e + Plasma Off n e = cm 3 Front Back Hollow plasma channel More stringent beam parameters Loss 70 MeV Gain 75 MeV Excellent agreement with simulations! PRL 90, , (2003) (over 1.4 m) Plasmas do accelerate e +

21 FUTURE RESEARCH Plasma ions motion (J. B. Rosenzweig, et al. PRL. 95, (2005)) Synchrotron radiation, beam plasma matching Significant when n b /n e >>1 Degrades beam emittace and focusing Improves with: larger σ r, higher ε, higher A, etc. Preservation of emittance and polarization (<<X 0 ) Evolution, stability of the bunch/wake over long plasma lengths Real accelerator: beam loading, optimization,

22 Linear Theory: Simulation using OSIRIS, for nonlinear regime: n b >n 0 ACCELERATING GRADIENT SCALING E acc 110(MeV / m) Electric Field (GV/m) AccDeccFields(sigmaz) 106 N σ z / 0.6mm ( ) 2 1/σ z 2 k pe σ z 2 (with k pe σ r <<1) Accel. (Useful) σ r =20 (µm) Accel. (Useful) σ r =10 (µm) Deccel. σ r =20 (µm) Deccel. σ r =10 (µm) GeV/m Measure energy gain! 0.01 E164X E167 E σ z (µm) E157 E162

23 ENERGY GAIN VS. BUNCH LENGTH Peak Energy (GeV) EnergyGain(pyro)26e16(EPAC) n e = cm 3 L p =31 cm L p =22 cm L p =13 cm E 0 =28.5 GeV CTR Energy I peak 1/σ z (a.u.) Energy gain increases bunch peak current or σ z 1 Energy gain reaches 13? GeV with L p =31 cm!

24 FUTURE RESEARCH Synchrotron radiation e beam K = γω β c r o = f n e,r o,γ Xrays ω c = 3ω 2 βγ 3 2c ( ) = r o = f ( n e,r o,γ 2 ) = 64 MeV de dz = 1 3 r em e c 2 γ 2 k 2 β K 2 = f ( n 2 e,r 2 o,γ 2 ) = 334 MeV /m n e =2x10 16 cm 3 r 0 =10 µm E=125 GeV Decreases with beam radius r 0 (compromise with ions motion) Negligible when compared to accelerating gradient ( 10 GV/m) Interesting as a source of gamma rays for positron production? (D.K. Johnson, PAC 05 and PRL to come)

25 Relative Energy (MeV) n e = cm 3, σ z 700 µm Front E MeV τ n e = (cm 3 ) n e =1.8± (cm 3 ) 3σ z σ z σ z +σ z +2σ z +3σ z Time (ps) Gain 280 MeV, L p =1.4m Gradient 200 MV/m PRL 93, (2004) e ACCELERATION Relative Energy (GeV) Pre Self Ionized n e = cm 3, σ z 2030 µm GeV! 7.9 GeV Scaling with bunch length and plasma length Energy (GeV) Energy Loss X (mm) Gain 4 GeV, L p =10cm Gain 14 GeV, L p =32cm Gradient 40 GV/m PRL 95, (2005) 0 +5 X (mm)

26 e ENERGY DOUBLING EXPERIMENT L p 60cm, n e = cm 3, σ z 2030 µm Highdispersion Image for Energy Gain Measurement Lowdispersion Image for Energy Loss Measurement Final Focus Test Beam 3 km e /e + LINAC Energy (GeV) E 0 E cm e x x Large energy loss and gain, as expected

27 CONCLUSIONS Next E167 run: Double the energy of 43GeV e Beyond energy doubling? Twobunch experiment SABER will be a great facility to study: e + beamplasma physics Ionization/wake excitation by e +, hollow plasmas γray source/e + source, polarized? Radiation from e + in plasmas? Possible new experiments at SABER : Focusing/plasma lens Ion channel laser Ion motion in PWFA Beam loading (ε?, E/E?, ) and much more (to be discussed in the WG)

28 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)

29 e + PLASMA FOCUSING E150: J.S.T Ng et al., PRL 2001 Plasmas lens experiment x: B θ /r 0.7T/µm, f=34mm y: B θ /r 4T/µm, f=1.6mm L p =3 mm n e =5x10 17 cm 3 >n b =2x10 16 cm 3 Plasmas do focus e +

30 e + Propagation Triangle FWHM (µm) σ x0 =σ y0 =25µm, ε Nx = , ε Ny = mrad, N= e +, L=1.4 m Experiment 12230clnmd4TriangOTR.kg Downstream OTR xlaser OFF ylaser OFF xlaser ON ylaser ON FWHM@otr (µm) Simulations PE390by80resultsOTR FWHMx@otr (µm) FWHMy@otr (µm) UV UV Energy (mj) OFF (mj) σ x (µm) Plasma OFF Plasma ON Envelope Equation Fit σ=30 µm ε N = mrad β=0.11 m α= n e ( cm 3 ) 0 No βtron oscillations Plasma Density ( cm 3 ) Excellent experimental/simulation results agreement! 07250cwMatchedBetatron.graph 100

31 FOCUSING OF e /e + OTR images 1m from plasma exit (ε x ε y ) 50 n e =0 n e cm 3 2mm 50 e Ideal Plasma Lens in BlowOut Regime e mm Plasma Lens with Aberrations Qualitative differences

32 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)

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

35 TRAPPING OF PLASMA e Interference of Coherent Radiation from Trapped Bunches Clear threshold at ~7 GV/m τδω = 2π Bunch Spacing = cτ 70 µ, plasma wavelength, λ p = 64 µ. Trapping above a threshold wake amplitude 7GV/m Excess charge of the order of the beam incoming charge (1.6x10 10 e ) Evidence for two (or more) short bunches of trapped particles Courtesy Erdem Oz, USC

36 TRAPPING OF PLASMA e Cherenkov Cell Image Highenergy Trapped e E 28.5GeV Beam 2 nd Cher. Ring Energy (MeV) L p =32cm, n e =2.6x10 17 cm ct CTR Energy (a.u.) 1/σ z Highenergy, narrow E/E trapped particle bunches

37 SCIENCE TOPICS FOR SABER SABER: Topics: Short (σ z <30µm) e and e + bunches High peak current (>10kA, N 2x10 10 /bunch) Small (σ x,y <10µm) transverse size e + beam/plasma physics Beyond energy doubling? Ionization/wake excitation by e +, hollow plasmas Transport/acceleration in long plasmas (e /e + ) Beam quality (ε?, E/E?, ), ion motion Beam/plasma matching γray source/e + source Radiation from e + in plasmas Focusing/plasma lens 2bunch experiments/head erosion/stability Hollow plasmas for e + beams Experiments fo early SABER?

38 e + PLASMA FOCUSING E150: J.S.T Ng et al., PRL 2001 M.J. Hogan et al., PRL 2006 Plasmas do focus e +

39 PROPAGATION OF e OTR Images 1m downstream from plasma σ x (µm) K 1/β 0 L=1.4 m σ 0 =50 µm ε N = mrad β 0 =1.16 m α 0 =0.5 PRL 88, (2002) PRL 93, (2004) 600 Plasma OFF Plasma OFF Plasma ON Plasma ON Envelope 500 Envelope Equation Fit σ=30 µm 400 ε N = mrad σ x (µm) 300 K 1/β 0 β=0.11 m α=0 K 1/ β n e, matched = cm 3 0 BetaronFitLongBeta.graph Plasma Density ( cm 3 ) cwMatchedBetatron.graph Plasma Density ( cm 3 ) Focusing of the beam well described by a simple model (n b >n e ): Plasma = No emittance growth observed as n e is increased Ideal Thick Lens Stable propagation over L=1.4 m up to as n e = cm 3 Channeling of the beam over 1.4 m or >12β 0 => Matched Propagation over long distance!

40 Relative Energy (MeV) n e = cm 3, σ z 700 µm Front E MeV τ n e = (cm 3 ) n e =1.8± (cm 3 ) 3σ z σ z σ z +σ z +2σ z +3σ z Time (ps) Gain 280 MeV, L p =1.4m Gradient 200 MV/m PRL 93, (2004) e ACCELERATION Relative Energy (GeV) Pre Self Ionized 3 GeV! 7.9 GeV Gain 4 GeV, L p =10cm Gain 14 GeV, L p =32cm Gradient 40 GV/m PRL 95, (2005) n e = cm 3, σ z 2030 µm Scaling with bunch length and plasma length X (mm)

41 MOTIVATION / QUESTIONS Could an accelerating structure with a gradient significantly larger ( 10,, 1000) than that reached in present rf cavities be created and can it lead to large energy gain (1100 GeV)? ILC: 3545 MV/m 2823 km for 1 TeV! CLIC: 150 MV/m 7 km for 1 TeV! Could such a structure be used to produce highquality e /e + beams? E GeV/TeV, E/E<<1, ε<<1, Could such a structure be made of PLASMA?

42 WHY PLASMA? Plasmas can sustain very large electric fields (10100 GV/m) Relativistic plasma waves or wakes: E//k, electrostatic Exist for a a short time (few wave periods) Already ionized ( H I: 13.6 ev, Li I: 5.4 ev, Li II: 75 ev) Accelerating structure or wake is sustained by the plasma No fabricated structure Operation a very high frequency (THz) No damage to the structure beamdriven, plasma wakefield accelerator or PWFA

43 PLASMA AFTERBURNER (SLC EXAMPLE) GeV, e /e + Collider 50 GeV e e and e + : Driver bunches: IP σ z =63 µm, σ r =5 µm, N= e /e +, 50 > 0 GeV Witness bunches: σ z =32 µm, σ r =5 µm, N= e /e +, 50 > GeV Delay: d=200 µm Plasma: n e = cm 3, L=7, 21 m Accelerating gradient: 8, 3 GV/m 3 km e PWFA 7m PLASMA LENSES e + PWFA 21m S. Lee et al., PRSTAB (2001) 50 GeV e +

44 σ r (µm) PROPAGATION OF e Beam Envelope Model for Plasma Focusing 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: Multiple foci (betatron oscillation) within the plasma Synchroton betatron radiation 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

45 PROPAGATION OF e OTR Images 1m downstream from plasma σ x (µm) K 1/β 0 PRL 93, (2004) Plasma OFF Plasma ON Envelope Equation Fit σ=30 µm ε N = mrad β=0.11 m α=0 K 1/ β n e, matched = cm cwMatchedBetatron.graph Plasma Density ( cm 3 ) Matching condition: σ 2 n e εγ = ε 0m e c 2e 2 Focusing of the beam well described by a simple model (n b >n e ): Plasma = No emittance growth observed as n e is increased Ideal Thick Lens Stable propagation over L=1.4 m up to as n e = cm 3 Channeling of the beam over 1.4 m or >12β 0 => Matched Propagation over long distance!

46 Positron Production from Betatron Xrays Plasma ion column acts as a Plasma Wiggler lead to Xray synchrotron radiation. Xray synchrotron radiation from electrons betatron oscillations. e beam N p =3e17 cm 3,γ=56000, r 0 =10 µm, B θ /r= 9 MT/m, λ β = 2cm 1) Wiggler strength: γω K = β ro =173 c 2) Critical frequency onaxis (K>>1): 2 3 3ω βγ ωc = ro = 49. 6MeV 2c 3) Particle energy loss: de dz 1 2 = β Xrays re mec γ k K = 4.3GeV / m r 3 02 γ 2 n 2 e Courtesy of Devon Johnson, UCLA Figure 1: Measured vs. Computed e + Spectra: N p =1E17, R x =7µm and R y =5µm with N b =7.2E9 electrons in the ion column Measured e + Spectrum Computed e + Spectrum

47 Notch Collimator 2BUNCH GENERATION Notch collimator in the dispersive region of the FFTB dogleg Energy (%) Energy (%) Notch Position Number e (a.u.) Current (ka) z (mm) Energy Gain Suppressed E Before Plasma Drive Bunch z (mm) Witness Bunch Work in progress, transferred to SABER? E After Plasma Litrack, K. Bane, P. Emma