Plasma Wakefield Accelerator The Plasma Wakefield Accelerator as a Light Source Driver Patric Muggli University of Southern California, Los Angeles muggli@usc.edu Work supported by US DoE

OUTLINE Introduction to the PWFA PWFA Milestones PWFA challenges Drive/witness bunch generation PWFA experiments at SLAC Conclusions

PWFA Focusing (Er) Defocusing Decelerating (Ez) Accelerating + - electron bunch Accelerating Decelerating (Ez) Focusing (Er) Defocusing 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 Can be optimized for acceleration, focusing, radiation, … Plasma Wakefield Accelerator (PWFA): high-frequency, high-gradient, strong focusing beam-driven, colinear accelerator

PWFA CHARACTERISTICS Relativistic, short, dense bunch(es): Accelerating gradient: with and (max., single bunch, lin.) Typically for 1GV/m: in Blowout, nonlinear regime: Pure ion column focusing: free of geometric aberrations Wavebreaking field: Combination of large transverse focusing gradient and large accelerating field leads to large energy gain All the beam particles and the wake are ultra-relativistic no dephasing! High energy (per particle) drive bunch

PWFA MILESTONES PWFA proposed: Chen, PRL 54 (1985) The demonstration! Rosenzweig, PRL 61, 98–101 (1988) The demonstration! Q=2.1nC E0=21-15MeV sz=2.4mm ne=1012-1013cm-3 Lp=20-35cm

e- e+ PWFA MILESTONES Muggli PRL 93, 014802 (2004) Blue PRL90, 214801 (2003). Rosenzweig, PRL 61, 98–101 (1988) Q=3nC E0=28.5GeV sz=700µm ne=1014cm-3 Lp=1.4m e- e+ 1.5x1014cm-3 1.8x1014cm-3

e- PWFA MILESTONES Q=3nC E0=28.5GeV sz=20µm ne=2.7x1017cm-3 Lp=10cm Hogan PRL 95, 054802 (2005) Muggli PRL 93, 014802 (2004) Rosenzweig, PRL 61, 98–101 (1988) e- Q=3nC E0=28.5GeV sz=20µm ne=2.7x1017cm-3 Lp=10cm

e- PWFA MILESTONES Lp=0, 13, 22, 31 cm Scaling with length! +14 +8 +4 Muggli et al., NJP 12, 045022 (2010) Lp=0, 13, 22, 31 cm Hogan PRL 95, 054802 (2005) Scaling with length! +14 Muggli PRL 93, 014802 (2004) +8 Rosenzweig, PRL 61, 98–101 (1988) e- +4 Significant progress Large energy gain with a single bunch, particle acceleration

e- PWFA MILESTONES Lp=0, 13, 22, 31 cm Scaling with length! Q=3nC Muggli et al., NJP 12, 045022 (2010) Lp=0, 13, 22, 31 cm Q=3nC E0=42GeV sz=20µm ne=2.7x1017cm-3 Lp=85cm Hogan PRL 95, 054802 (2005) Scaling with length! +14 Muggli PRL 93, 014802 (2004) +8 Rosenzweig, PRL 61, 98–101 (1988) e- +4 42 to 84GeV in 85cm of plasma! Energy doubling of an FEL drive bunch?

PWFA NEXT STEP Focusing (Er) Focusing (Er) Defocusing Decelerating (Ez) Accelerating - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + - - - - - - - - - - - - - - - - - - - + + - - - - - - - - - - - - + - + + - - - - - - - - + + - - + + + + + - - - + + - + + + - - + + + + + + + + + - - - + + + + + + + + + + + + - - + + + + + + + + + + + - + + - - - - - - - - - - - - - + - - - - - - - - - electron beam - - - - - - + + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Plasma wave/wake excited by a relativistic particle bunch Plasma e- expelled by space charge forces => energy loss + focusing Single bunch for particle acceleration (∆E/E~1) Plasma e- rush back on axis => energy gain Bunch train (D+W) for bunch acceleration (∆E/E<<1) Optimize for acceleration and/or focusing (plasma lens) Plasma Wakefield Accelerator (PWFA): high-frequency, high-gradient, strong focusing beam-driven accelerator

PWFA CHALLENGES Generation of drive/witness bunch train (ATF, FACET) Demonstration of bunch acceleration (FACET) Long plasma source for energy doubling (m-scale, ne≈1016-1017cm-3 range?) Low energy spread, careful beam loading, longitudinal bunch shaping? Low emittance, preserved over m-scale plasma (linear focusing, low scattering) Beam-plasma matching for low emittance beams

DRIVE/WITNEES BUNCH TRAIN GENERATION Correlated energy chirp from linac To Plasma e- Detector PLD Muggli et al., PRL 2008 ∆z=434 µm ∆z=226 µm Emittance selection Choose microbunches spacing and widths with mask and beam parameters: N, ∆z, z, Q

DRIVE/WITNEES BUNCH TRAIN GENERATION @ SLAC FACET Use the same masking method Drive N=6.7x109 e- sz=44µm Witness N=3.3x109 e- sz=13µm Train for proof-of-principle experiments only, ne≈1016cm-3 plasma Need independent control of D and W bunch parameters

FACET @ SLAC: BUNCH ACCELERATION QuickPIC simulation, D: z=30µm, N=3x1010e- W: z=10µm, N=1x1010e-, r0=3µm ∆z=115µm, ne=1017cm-3 Witness Bunch z=0 28 55 83 cm Drive Bunch Witness Ion Bubble z=0 Drive Bunch Beam loading @ 37GV/m (z=0) Wake evolution due to bunch head erosion, but no dephasing Hogan, New J. Phys. 12, 055030 (2010)

FACET @ SLAC: BUNCH ACCELERATION QuickPIC simulation, D: z=30µm, N=3x1010e- W: z=10µm, N=1x1010e-, r0=3µm ∆z=115µm, ne=1017cm-3, E0=25GeV Witness Bunch Drive e-/e- W E0 Wake evolution “bends” energy gain Lp=80cm, gain 25GeV, ∆E/E0≈3%, BUNCH ACCELERATION! D to W energy transfer efficiency ≈30% No bunch shaping, bunches carved out of a single SLAC bunch Hogan, New J. Phys. 12, 055030 (2010)

NARROW ENERGY SPREAD Effective beam loading with bunch shaping Witness bunch with linear density ramp perfect beam loading! No W bunch Very narrow energy spread with linear ramp in witness bunch charge. Tzoufras, Phys. Rev. Lett 2008

CONCLUSION High gradient PWFA is a good candidate as a compact light source driver Physical parameters have been reached in proof of principle experiments Energy doubler (or more) concept attractive Challenges to produce required bunch quality (energy spread, …)