P. Muggli, 5th GLS, 10/02/10

ThePlasma Wakefield Accelerator

as aLight Source Driver

Patric MuggliUniversity of Southern California, Los Angeles

muggli@usc.edu

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):

€

Ez , accel (V /m) ≅ 2×10−9 Nσ z2Accelerating 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=21-15MeVσz=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=28.5GeVσz=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=28.5GeVσz=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=42GeVσz=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, σz, Q

Emittance selection

e-

DetectorPLD

∆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-

σz=13µm

DriveN=6.7x109 e-

σz=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: σz=30µm, N=3x1010e-

W: σz=10µm, N=1x1010e-, σr0=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: σz=30µm, N=3x1010e-

W: σz=10µm, N=1x1010e-, σr0=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, …)