1. Towards CO2-laser-driven wake-field accelerator with external injection
V.N. Litvinenko, H. Li, N. Vafaei Stony Brook University
M. Babzien, M. Fedurin, Y. Jing, K. Kusche, Brookhaven National Lab
I. Pogorelsky, M. Polyansky, C. Swinson
C. Joshi, W.B. Mori UC Los Angelis
M.C. Downer, J. Welch, R. Zgadzaj UT Austin
W. Lu, Ch. Zhang Tsinghua University
DoE HEP grant # support activities by SBU/BNL/UCLA/UTA
Collaborators: J. Byrd , L. Doolittle , G. Huang , R. Wilcox (LBNL)
August 4, 2016, ACC 2016, National Harbor, MD

2. Main points
Final goal: generating high quality electron beam in LPWA with energy stability and energy spread reaching towards Our final goal will require completions of the CO2-laser power upgrades in progress at ATF, BNL
to explore large (e.g. psec ) length of “bubble” in CO2-laser driven plasma wake-field accelerator
to inject an external high quality matched electron bunch with duration and synchronization ~ 10 fsec
Plasma source with ramp-up and ramp-down density profiles
Electron bunch compressor to 10 fsec with emittance preservation
Visible/near IR laser and e-beam diagnostics for the plasma
Current research: while waiting for the CO2-laser power upgrades to be completed, we are developing and testing the key components necessary for such experiment:
Exciting plasma by self-modulated CO2-laser pulses
Near IR and visible laser diagnostics for the plasma
Electron bunch compressor to ~10 fsec with emittance preservation
Using fsec electron bunches for plasma diagnostics

3. It is a real team work mm rad -0.5 0 0.5 ps 1.5 - 0.5 1.0 - 1.0 0.5 ps
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4. Team expertise High power CO2-lasers Plasma sources Plasma diagnostics
Laser diagnostics
e-beam diagnostics
LPWA and PWFA theory
LPWA and PWFA simulations
Generation / acceleration of high brightness electron beams
Compression of high brightness electron beams to fsec durations
Suppression of CSR effects on the beam dynamics ……

5. 2 ps 10 mJ 3 ps 6 J SOLID-STATE OPA INJECTOR REGENERATIVE
2 TW BNL CO2 laser system
SOLID-STATE
OPA INJECTOR
REGENERATIVE
ISOTOPIC AMPLIFIER
MAIN AMPLIFIER 12
400 fs
40 µJ
2 ps
10 mJ
3 ps
6 J
I. Pogorelsky 5

6. Collection of innovations:
New concept of 100TW CO2 laser
Collection of innovations:
35 µJ
350 fs
Amplifier 1
OPA: fs seed
Stretcher + compressor = Chirped pulse amplification
High-pressure, isotopic amplifiers
Nonlinear compressor
10 µJ
100 ps
Ti:Al2O3
OPA
Stretcher
100 mJ
Amplifier 2c
Amplifier 2b
Amplifier 2a
70 J
Non-linear compressor (patent)
50 J
2 ps
25 TW
10 J
100 fs
100 TW
Vacuum grating compressor
I. Pogorelsky

7. What ATF II with the 100TW CO2 would offer
CO2 laser will drive bubble-regime wakes
Experiments will be conducted in 10 to 100 cm long plasma source with density 5 x 1015 < ne < 1017 cm-3 (to be built by UCLA team)
Two parameter sets for LWFA at ATF II. (C. Joshi)
Laser Intensity Dephasing Energy Gain Spot Matched-spot Rayleigh
a (W/cm2) Length (cm) MeV w0 (μm) wm (μm) Length (mm) x x
External injection of ~ 10fs x ~ 3μm bunches from the linear accelerator into the plasma accelerator below its self-injection threshold (SBU/BNL)
Simulations of all key LWFA/ injection processes (Tsinghua U/UCLA/SBU)
Diagnostics (UT Austin/ Tsinghua U / BNL)
What ATF II with the 100TW CO2 would offer

8. Example of the CO2-laser driven bubble
The “bubble”, or ion cavity, will have typical lateral dimension ~ 300+ μm, time duration ~1+ psec for ne = 1016 cm-3.
Its large size will allow unprecedented detail in the visualization of the bubble structure, its shot to shot variations, and evolution.
Example of the CO2-laser driven bubble
Simulated bubble in plasma density 1.1 x 1016 cm-3 ,driven by 500 fsec CO2 laser with a0 =1.4
Wei Lu

9. ATF II ZigZag compressor Taking care of CSR Y. Jing Energy, MeV 150
Bunch length, fsec
≤10
Y. Jing

10. What’s going on
Current ATF CO2 laser pulse parameters are ~ 3 psec, ~ 1-2 TW
Pulse is too long for direct excitation of plasma, but power is sufficient for exciting self-modulated wakes
Detailed simulations were done by Chaojie Zhang (Tsinghua University)
We used a 2 mm gas jet to test this using IR laser
Plan to repeat with green diagnostic laser
With special vacuum vessel, 5 mm gas jet we will test this mode of exitation with both lased and fsec e-beam diagnostics
N.Andreev
Normalized laser field
Normalized plasma density

11. Quasi-3D simulation for SMLWFA by CO2 laser
w0 = 50 μm
t = 1 ps
plasma mm
t = 1 ps
plasma mm
plasma mm
t = 2 ps
plasma mm
t = 2 ps
Chaojie Zhang

12. Energy spectrum of injected bunch
Injection and acceleration occurs for proper laser and plasma parameters.
laser:
plasma:
1ps, mm
1ps, mm
Chaojie Zhang
7/3/2014

13. Self-modulation vs. plasma density
For a given 2 ps, 1 TW laser with 100 um spot size, higher plasma density leads to stronger modulation and more intense accelerating fields.
laser:
Chaojie Zhang

14. Details of current experiment just were presented by James Welch
We used existing chamber for ion acceleration using CO2 laser (thanks!)
CO2 laser were hitting gas jet and generated self-modulated instability and plasma wake
Nd:YAG laser was used as Collective Thompson Scattering Probe
Good results, which are in a good agreement with simulation by Chaojie Zhang at Tsinghua University
I. Pogorelsky, M. Polyansky
R. Zgadzaj, J. Welch

15. Next steps
Repeat the self-induced modulation experiment with green laser probe to (in next two months)
Measure energy of electrons generated by this SMLWFA
Finish design of a dedicated set-up and build it up and install at ATF beam-line
Characterize SMLWFA using fsec laser and e-beam diagnostics

16. Sketch for electron probe
electron trajectory (zoomed in)
plasma
transverse
momentum
driver
b field
Probe
e field
Chaojie Zhang

17. Electron probe snapshot of self-modulated wake
The 80 MeV linac can be used to study the self-modulated wake generation and evolution.
plasma density lineout
electron probe parameters:
E=80 MeV, T=100 fs, Q=20 pC
snapshot of the wake
(probe density projection)
E1 field after 3mm evolution
laser:
t=2ps-
Chaojie Zhang

18. e-bunch We have multiple options for bunch compression
Compressing bunch to ~ fs RMS is possible with current ATF and a simple chicane - we plan to start with this simplest option
If necessary, we will modify system to a proper Zig-Zag chicane compression, which is more robust, emittance-preserving and is suitable for large charges – this is most likely scenario for the injecting bunch

19. Bunch Compression: existing ATF beam
With new Zig-Zag type compressor could be installed in ATF to compress bunches to 12fs
Energy, MeV 70
Bunch length, mm
0.06
Chirp, m-1 20
Bunch length, rms, fsec 12
Y. Jing, VL

20. Proposed layouts for CO2 SFLWFA experiment on ATF beamline 1
e-beam from ATF
Charge
100 pC
RMS bunch length
1 ps
RMS energy spread
1e-3
Normalized emittance
1 μm
Energy
60 MeV
Compressor location
“Box”
Simple bunch compressor
M. Fedurin

21. 100 pC, CSR shielding using polished plates
Compression with simple chicane
100 pC, CSR shielding using polished plates
10 pC, no CSR shielding
M. Fedurin

22. Conclusions
Our Final goal: generating high quality electron beam in LPWA with energy stability and energy spread reaching towards Our final goal will require completions of the CO2-laser power upgrades in progress at ATF, BNL
to explore large (e.g. psec ) length of “bubble” in CO2-laser driven plasma wake-field accelerator
to inject a high quality matched electron bunch with duration and synchronization ~ 10 fsec
Current research: waiting for the CO2-laser power upgrades to be completed, we are developing and testing the key components necessary for such experiment:
SMLWFA: Exciting plasma by self-modulated CO2-laser pulses
Near IR and visible laser diagnostics for the plasma
Electron bunch compressor to ~10 fsec with emittance preservation
Using fsec electron bunches for plasma diagnostics
We acknowledge support by US DoE HEP office - grant #215125

23. And it is always the team work ps
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24. Thank you for your attention