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 #215125 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

Main points Final goal: generating high quality electron beam in LPWA with energy stability and energy spread reaching towards 10-4. 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

It is a real team work mm rad -0.5 0 0.5 ps 1.5 - 0.5 1.0 - 1.0 0.5 -0.5 0 0.5 ps - 2.0 rad - 1.5 - 1.0 - 0.5 0.5 1.0 1.5 mm

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 ……

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

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

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 a0 (W/cm2) Length (cm) MeV w0 (μm) wm (μm) Length (mm) 2 4x1016 10 666 200 150 12.6 4 1.6x1017 14 1332 100 212 3.1 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

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

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

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

Quasi-3D simulation for SMLWFA by CO2 laser w0 = 50 μm t = 1 ps plasma density @2.77 mm t = 1 ps plasma density @2.77 mm plasma density @4.80 mm t = 2 ps plasma density @4.80 mm t = 2 ps Chaojie Zhang

Energy spectrum of injected bunch Injection and acceleration occurs for proper laser and plasma parameters. laser: plasma: 1ps, 1TW, @5.4 mm 1ps, 2TW, @4.8 mm Chaojie Zhang 7/3/2014

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

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

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

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

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

e-bunch We have multiple options for bunch compression Compressing bunch to ~ 10-20 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

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

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

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

Conclusions Our Final goal: generating high quality electron beam in LPWA with energy stability and energy spread reaching towards 10-4. 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

And it is always the team work -0.5 0 0.5 ps - 2.0 rad - 1.5 - 1.0 - 0.5 0.5 1.0 1.5 mm

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