1. Using ionization injection to get high quality electron beam in laser wakefield acceleration
M. Chen,1 M. Zeng,1 Z.M. Sheng,1,3 L.L. Yu,1 W.B. Mori,2 S. Li,1 N. Hafz,1 M. Mirzaie,1 B. Hidding,3 D. A. Jaroszynski,3 and J. Zhang1
1 Laboratory for Laser Plasmas, Department of Physics and Astronomy
Shanghai Jiao Tong University，Shanghai
2 University of California, Los Angeles, California 90095, USA
3 SUPA, Department of Physics, University of Strathclyde,
Glasgow G4 0NG, UK
2nd EAAC, 13-19/ La Biodola, Isola d'Elba, Italy

2. 25
Laboratory for Laser Plasmas at SJTU

3. Outlines
Fundament of Ionization injection in Laser WakeField Acceleration
Laser evolution induced self-truncated ionization injection (theory and experiment)
Extreme low energy spread of electron beams from two-color laser ionization injection (theory)

4. Outlines
Fundament of Ionization injection in Laser WakeField Acceleration
Laser evolution induced self-truncated ionization injection (theory and experiment)
Extreme low energy spread of electron beams from two-color laser ionization injection (theory)

5. A new Technology for Accelerator and Radiation Source
Laser Wakefield—Acceleration cavity in plasma
High quality beam needs high quality injection

6. Introduction to LWFA Surfing Wakefield Acceleration
Laser
e- beam
Wake
50GeV 3.2km
SLAC linear accelerator
Ultrahigh acceleration gradient: 1GV/cm 1000 times larger than the conventional RF accelerator
2GeV, X. M. Wang,et al., Nature Communication, 4, 1988
DOI: /ncomms2988 (2013)
In 2004, 3 Nature Papers show the mono-energetic electron beams accelerated from LWFA.
50GeV 1.07m
Applications：1. Table top accelerator；2. TeV e+e- collider；3. Table top radiation source（smaller than traditional device by 1000 times）

7. New world record 4.2 GeV 9cm, 310TW, 15J, 43fs, 6X1017/cm3
BELLA, LBNL, Wim Leemans, Phys. Rev. Lett. 113, (2014)

8. Current Main Challenges of LWFA
Laser Guiding– Diffraction
Velocity matching- Dephasing
Staging– Depletion
Direction 1：High Energy
Direction 2: High Quality
Electron injection
Transverse acceleration structure control
Longitudinal control
New generation of collider
New generation of
Radiation Source 加速 减速

9. Wake & Surfing
Well done!
Late!
Too slow
or late!

10. Difficulties of e- injection in LWFA
Duration: s
Precision: mm
Dose: cm3
Requirement of injection
Duration: fs
Precision: 10mm
Dose：10pC~nC

11. Existed main injection schemes
Make the e- catch up with wave
Make the wake wait for e-
Ponderomotive injection
D. Umstadter et al. PRL 76, 2073 (1996) …
Colliding pulse injection
E. Esarey et al. PRL 79, 2682 (1997)
J. Faure et al., Nature 444, 7120 (2006) …
Density down ramp injection
S.V. Bulanov et al., PRE 58, R5257 (1998)
C.G.R. Geddes et al., PRL 100, (2008)…
Density transition injection
H. Suk et al., PRL 86, 1011 (2001)…
Plasma lens injection
A. Gonsalves et al., Nature Phys. 7, 862 (2011)
Put new e- at appropriate phase of the wake
Ionization injection
E. Oz, PRL. 98, (2007)
A. Pak et al., PRL. 104, (2010)
B. C. McGuffey et al., PRL. 104, (2010)
C.E. Clayton et al., PRL. 105, (2010)
B. B. Pollock et al., PRL. 107, (2011)
B. Hidding et al., PRL. 108, (2012)
N. Bourgeois, et al., PRL. 111, (2013)
M. Chen et al., J. Appl. Phys., 99, (2006)
M. Chen, et al., Phys. Plasmas, 19, (2012)
M. Zeng et al., Phys. Plasmas, 21, (2014)
M. Chen et al., PRSTAB 17, (2014)
Y. Xi, et al., PRSTAB 16, (2013)
C. Xia, et al., Phys. Plasmas 18, (2011)
J.S. Liu, et. al., PRL. 107, (2011)
F. Li, et al., PRL. 111, (2013)
L.-L. Yu et al., PRL. 112, (2014)
There are a lot of other mechanisms…

12. Using inner shell ionization to e- injection
Principle：using the atomic potential to protect the electrons from deceleration by the wakefield and directly injected into the acceleration phase.
The concept was mentioned by Umstadter in 1996 (PRL, 76, 2073).
The PIC simulation was demonstrated by M.Chen, Z.M. Sheng, Y.Y. Ma and J. Zhang, “Electron injection and trapping in a laser wakefield by field ionization to high-charge states of gases”J. Appl. Phys. 99, (2006)
Only when the laser is strong enough, ionization happens 12
-12
kpx 15 5 -5
n/n0
Ez/E0
Deceleration
Acceleration

13. Recent progresses of ionization injection
M. Chen et al., J. Appl. Phys., 99, (2006)
E. Oz, PRL. 98, (2007)
Pak et al., PRL. 104, (2010)
B. C. McGuffey et al., PRL. 104, (2010)
C.E. Clayton et al., PRL. 105, (2010)
B. B. Pollock et al., PRL. 107, (2011)
C. Xia, et al., Phys. Plasmas 18, (2011)
J.S. Liu, et. al., PRL. 107, (2011)
M. Chen, et al., POP 19, (2012)
B. Hidding et al., PRL. 108, (2012)
N. Bourgeois, et al., PRL. 111, (2013)
Y. Xi, et al., PRSTAB 16, (2013)
F. Li, et al., PRL. 111, (2013)
M. Chen et al., PRSTAB 17, (2014)
L.-L. Yu et al., PRL. 112, (2014)
M. Zeng et al., Phys. Plasmas 21, (2014)
M. Zeng, et al., PRL, 114, (2015)
Ionization injection has attracted a lot of attentions recently!

14. Ionization injection tends to high energy spread
Two stages: injection and acceleration leads to improved energy spread.
dE=Ewake*L
~GeV/cm*mm
~100MeV
Energy spread
comes from two ways
J.S. Liu, et. al.,Phys. Rev. Lett. 107, (2011).
Injection length is limited to mm.
M. Chen, et al., POP 19, (2012)
Optical cutting?
Or optical stopping!
Can we make the injection length even shorter?
Less than the mechanical operation limitation? 100mm?

15. Outlines
Fundament of Ionization injection in Laser WakeField Acceleration
Laser evolution induced self-truncated ionization injection (theory and experiment)
Extreme low energy spread of electron beams from two-color laser ionization injection (theory)

16. Laser self-evolution controlled injection
Principle
Ming Zeng et al., Phys. Plasmas 21, (2014).

17. Effective injection length is controlled by changing the laser spot size
Injection charge VS laser propagation legnth
Charge [pC mm-1] -3 -6 -9
Propagation distance [mm]
400
800
1200
Injection and suppression
Injection
suppression
Injection
Continuous injection
The first stage injection length is only 250mm！

18. Acceleration structure and final spectrum
Laser evolution leads to injection suppression
Continuous injection leads 100% energy spread
Minimum absolute energy spread in simulation is only 5 MeV
a0=3.2, kp W0=2.96
a0=2.4, kp W0=5.27
Control the laser initial focus,  control the injection and final energy spread.

19. Three dimensional PIC simulations
Laser evolution in 3D case
Injection process in 2D and 3D simulaitons.
2D:nHe=2.8e18/cm3, nN=8.5e15/cm3, a0=2.9, and W0=11.69um,14.58 pC, 383MeV 3.33% Energy spread
3D:nHe=8e-4nc, a0=2.3, and kpW0=4.066.
25.5 pC
Ming Zeng et al., Phys. Plasmas 21, (2014).

20. Experiment demonstration of self-truncated ionization injection
M. Mirzaie, et al., Scientific Reports (in press) 2015
30TW 30fs laser
4mm gas
5 % energy spread
at 412 MeV
118TW 30fs laser
1cm gas
7% energy spread
at 1.2 GeV
acceleration

21. Experiment demonstration of self-truncated ionization injection
A typical energy spectrum
30TW
0.5%N2 case: 41210 MeV, 80 pC electron 7.1mrad
M. Mirzaie, et al., Scientific Reports (in press) 2015

22. Experiment demonstration of self-truncated ionization injection
Self-injection
ionization-injection
118TW
103TW
0.5%N2
6.5 (0.5)1018 cm-3
114TW
0.3%N2
1.81018 cm-3
(a) E 3004.5 MeV, Q =21 pC E/E  25% divergence angle of 7.6 mrad
(b) EQME  5308 MeV, Q (charge) =25 pC, E/E  8 %, divergence angle of 5.2 mrad
(d) EQME  1.20.03 GeV, Q (charge) =16 pC, E/E  7 %, divergence angle of 4.7 mrad

23. 3D PIC simulations for GeV level self-truncated ionization injection
a0 =1.11, 30 fs
40200200 µm3
1280200200
M. Mirzaie, et al., Scientific Reports (in press) 2015

24. Outlines
Fundament of Ionization injection in Laser WakeField Acceleration
Laser evolution induced self-truncated ionization injection (theory and experiment)
Extreme low energy spread of electron beams from two-color laser ionization injection (theory)

25. Laser pulses with different frequency have different vp.
Two color laser ionization injection to get extreme low energy spread electron beam
Laser pulses with different frequency have different vp.
Ionization happens locally within tens of mm and local wake phase.
M. Zeng， M. Chen*, et al., PhysRevLett (2015)

26. One dimensional PIC simulation results
Injection VS final beam energy
Combined field
evolution & injection
Energy fluctuation due
to phase unlocking
FWHM energy
spread0.29%

27. Comb like energy spectrum
Multi-chromatic X-ray source from Thomson scattering!
0.2%

28. Single electron beam with shorter mixed gas
1.5%, 12.6 pC
Initial 3D Simulation with short mixed gas length shows single electron beam with 1 percent energy spread possible.
M. Zeng， M. Chen*, et al., PhysRevLett (2015)

29. Summary
Laser self-evolution can introduce self-truncated Ionization injection and GeV level mono-energetic electron beam acceleration by this mechanism has been experimentally demonstrated.
Two color ionization injection can be used to get high energy electron beams with extreme low energy spread (less than 0.5%) and comb like spectrum.
Refences:
1. Ming Zeng, et al., Phys. Plasmas 21, (2014).
2. M. Mirzaie, et al., Scientific Reports (in press 2015).
3. M. Zeng , et al., PhysRevLett (2015)
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30. Thanks a lot for your Attention!