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

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

3. 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

4. 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

5. 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= cm-3
Lp=20-35cm

6. e- e+ PWFA MILESTONES Muggli PRL 93, 014802 (2004)
Blue PRL90, (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

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

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

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

10. 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

11. PWFA CHALLENGES Generation of drive/witness bunch train (ATF, FACET)
Demonstration of bunch acceleration (FACET)
Long plasma source for energy doubling (m-scale, ne≈ cm-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

12. 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

13. 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

14. 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 37GV/m (z=0)
Wake evolution due to bunch head erosion, but no dephasing
Hogan, New J. Phys. 12, (2010)

15. 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, (2010)

16. 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

17. 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, …)