P. Muggli, 5th GLS, 10/02/10
ThePlasma Wakefield Accelerator
as aLight Source Driver
Patric MuggliUniversity of Southern California, Los Angeles
Work supported by US DoE
P. Muggli, 5th GLS, 10/02/10
OUTLINE
Introduction to the PWFA
PWFA Milestones
PWFA challenges
Drive/witness bunch generation
PWFA experiments at SLAC
Conclusions
P. Muggli, 5th GLS, 10/02/10 3
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 gainCan be optimized for acceleration, focusing, radiation, …
Plasma Wakefield Accelerator (PWFA): high-frequency, high-gradient, strong focusing beam-driven, colinear accelerator
PWFA
++++++++++++++ ++++++++++++++++
----- --- ----------------
--------------
-
-------- ------- --------------------
- --
---- - -- ---
------ -
- -- ---- - - - - - ------ -
-- - - - -
-- --
- -- - -- - -
---- - ----
----- electron
bunch
+ + + + + + + + + + ++ + + + + + + + + + + + + + +
+ + + + + + + + + + + + + + +
+ + + + + + + + + + + + + + +-
- --
--- --
Accelerating Decelerating (Ez)
+ + + + + + + + + + + + + + +
+ + + + + + + + + + + + + + +
Focusing (Er)Defocusing
+ +
+ +
P. Muggli, 5th GLS, 10/02/10
PWFA CHARACTERISTICS
Relativistic, short, dense bunch(es):
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Ez , accel (V /m) ≅ 2×10−9 Nσ z2
Accelerating gradient: with
€
σ z
λ pe≅12π
and
€
σ r
λ pe<< 2π
Typically for 1GV/m:
€
N = 2×1010
€
σ r <<137μm
€
ne =1.4 ×1015cm−3
€
σ z ≅ 200μm in
Blowout, nonlinear regime:
€
nbne>1
€
σ r < 67μm( )
Pure ion column focusing:
€
Bθr=12neeε 0c
≅ 42kT /m free of geometric aberrations
Combination of large transverse focusing gradient and large accelerating fieldleads to large energy gain
All the beam particles and the wake are ultra-relativistic no dephasing!
High energy (per particle) drive bunch
€
EWB = 3.6GV /mWavebreaking field:
(max., single bunch, lin.)
P. Muggli, 5th GLS, 10/02/10
Rosenzweig, PRL 61, 98–101 (1988)
Q=2.1nCE0=21-15MeVsz=2.4mmne=1012-1013cm-3
Lp=20-35cm
PWFA MILESTONES
The demonstration!
PWFA proposed: Chen, PRL 54 (1985)
P. Muggli, 5th GLS, 10/02/10
Muggli PRL 93, 014802 (2004)
Rosenzweig, PRL 61, 98–101 (1988)Q=3nCE0=28.5GeVsz=700µmne=1014cm-3
Lp=1.4m
PWFA MILESTONES
e-
e+
Blue PRL90, 214801 (2003).
1.5x1014cm-3
1.8x1014cm-3
P. Muggli, 5th GLS, 10/02/10
Hogan PRL 95, 054802 (2005)
Muggli PRL 93, 014802 (2004)
Rosenzweig, PRL 61, 98–101 (1988)
Q=3nCE0=28.5GeVsz=20µmne=2.7x1017cm-3
Lp=10cm
PWFA MILESTONES
e-
€
Eacc . max ∝Nσ z2
€
ne ∝1σ z2
P. Muggli, 5th GLS, 10/02/10
Hogan PRL 95, 054802 (2005)
Muggli PRL 93, 014802 (2004)
Rosenzweig, PRL 61, 98–101 (1988)
PWFA MILESTONES
e-
Significant progressLarge energy gain with a single bunch, particle acceleration
Lp=0, 13, 22, 31 cmMuggli et al., NJP 12, 045022 (2010)
+4
+8
+14Scaling with length!
P. Muggli, 5th GLS, 10/02/10
Hogan PRL 95, 054802 (2005)
Muggli PRL 93, 014802 (2004)
Rosenzweig, PRL 61, 98–101 (1988)
PWFA MILESTONES
e-
42 to 84GeV in 85cm of plasma!
Lp=0, 13, 22, 31 cmMuggli et al., NJP 12, 045022 (2010)
+4
+8
+14Scaling with length!
Q=3nCE0=42GeVsz=20µmne=2.7x1017cm-3
Lp=85cm
Energy doubling of an FEL drive bunch?
P. Muggli, 5th GLS, 10/02/10 10
Focusing (Er)
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
Optimize for acceleration and/or focusing (plasma lens)
Plasma Wakefield Accelerator (PWFA): high-frequency, high-gradient, strong focusing beam-driven accelerator
PWFA NEXT STEP
++++++++++++++ ++++++++++++++++
----- --- ----------------
--------------
-
-------- ------- --------------------
- --
---- - -- ---
------ -
- -- ---- - - - - - ------ -
-- - - - -
-- --
- -- - -- - -
---- - ----
----- electron
beam
+ + + + + + + + + + ++ + + + + + + + + + + + + + +
+ + + + + + + + + + + + + + +
+ + + + + + + + + + + + + + +-
- --
--- --
Accelerating Decelerating (Ez)
+ + + + + + + + + + + + + + +
+ + + + + + + + + + + + + + +
Focusing (Er)Defocusing
+ +
+ +
+
+ ++
Bunch train (D+W) for bunch acceleration (∆E/E<<1)
Single bunch for particle acceleration (∆E/E~1)
P. Muggli, 5th GLS, 10/02/10
PWFA CHALLENGES
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)
Demonstration of bunch acceleration (FACET)
Generation of drive/witness bunch train (ATF, FACET)
Beam-plasma matching for low emittance beams
P. Muggli, 5th GLS, 10/02/1012
Correlated energy chirp from linac
To Plasma
Choose microbunches spacing and widths with mask and beam parameters: N, ∆z, z, Q
Emittance selection
e-
Detector
PLD
∆z=434 µm
∆z=226 µm
Muggli et al., PRL 2008
DRIVE/WITNEES BUNCH TRAIN GENERATION
P. Muggli, 5th GLS, 10/02/10
DRIVE/WITNEES BUNCH TRAIN GENERATION @ SLAC FACET
Train for proof-of-principle experiments only, ne≈1016cm-3 plasma
Use the same masking method
WitnessN=3.3x109 e-
sz=13µm
DriveN=6.7x109 e-
sz=44µm
Need independent control of D and W bunch parameters
P. Muggli, 5th GLS, 10/02/10 14
DriveBunch
WitnessBunch
DriveBunch
WitnessBunch
IonBubble
Beam loading @ 37GV/m (z=0)Wake evolution due to bunch head erosion, but no dephasing
QuickPIC simulation, D: z=30µm, N=3x1010e-
W: z=10µm, N=1x1010e-, r0=3µm
FACET @ SLAC: BUNCH ACCELERATION
z=0
∆z=115µm, ne=1017cm-3
Hogan, New J. Phys. 12, 055030 (2010)
z=0
2855
83 cm
P. Muggli, 5th GLS, 10/02/10 15
QuickPIC simulation, D: z=30µm, N=3x1010e-
W: z=10µm, N=1x1010e-, r0=3µm ∆z=115µm, ne=1017cm-3, E0=25GeV
Lp=80cm, gain 25GeV, ∆E/E0≈3%, BUNCH ACCELERATION!
D to W energy transfer efficiency ≈30%
WitnessBunch
DriveBunch
Wake evolution “bends” energy gain
FACET @ SLAC: BUNCH ACCELERATION
E0
Hogan, New J. Phys. 12, 055030 (2010)
e-/e-
W
No bunch shaping, bunches carved out of a single SLAC bunch
P. Muggli, 5th GLS, 10/02/10 Tzoufras, Phys. Rev. Lett 2008
NARROW ENERGY SPREAD
Effective beam loading with bunch shaping
No W bunch
Witness bunchwith linear density rampperfect beam loading!
Very narrow energy spread with linear ramp in witness bunch charge.
P. Muggli, 5th GLS, 10/02/10
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, …)
