On-axis injection simulations

1. On-axis injection simulations Petrenko, K. Lotov, 10/04/2014 AWAKE collaboration meeting at CERN

2. On-axis injection of electron beam (15 MeV, 2 mm*mrad) into the proton-driven SMI wake-fields Injected electron beam:15 MeV, σr= 0.3 mm, εn = 2 mm·mrad 27% of injected beam is captured These electrons will be captured Distance from laser pulse

3. On-axis injection of electron beam (15 MeV, 2 mm*mrad) into the proton-driven SMI wake-fields

4. On-axis injection of electron beam (15 MeV, 2 mm*mrad) into the proton-driven SMI wake-fields

5. On-axis injection of initially parallel 15 MeV electron beam into the SMI wake-fields (first 1 meter) This artificial rectangular electron beam initially has zero angular spread In order to minimize nose this first meter of injection is simulated here using the fliud mode of LCODE

6. On-axis injection of initially parallel 15 MeV electron beam into the SMI wake-fields (first 1 meter)

7. Individual injection trajectories for some electrons along 1 m of plasma:

8. On-axis injection of narrow initially parallel electron beam into the SMI wake-fields (first 1 meter) Does it make sense to inject very narrow electron beam in order to get low emittance? Will the electrons always stay near the axis during the capture process?

9. On-axis injection of narrow initially parallel electron beam into the SMI wake-fields (first 1 meter)

10. Typical electron beam distributionsafter10 m plasma: Injected electron beam: (15 MeV) σr = 0.3 mm, εn = 2 mm·mrad, bunch length = 2.7 mm (uniform). 27% of injected beam is accelerated If initial Ne= 109 then final Ne = 3·108. 4

11. Typical electron beam distributionsafter10 m plasma: Estimate of final e-beam emittance: εn ~ (0.1 mm)*(2 mrad)*γ = = 0.1*2*1300 MeV/0.5 MeV = = 500 mm·mrad >> initial εn

12. Baseline proton beam after 10 m plasma: Proton distribution in the interacting part of the beam (s<0):

13. Electron & proton beam envelopes after plasma: Laser beam size? Plasma exit

14. Conclusions • On-axis injection of 15-20 MeV e-beam should be the primary option. In the case of baseline 2 mm*mrade-beam capture efficiency is 30 %, energy gain is 1-2 GeV (If initial Ne= 109 then final Ne = 3·108). • Injected electron beam should be focused to σr = 0.2--0.5 mm. • Wakefield focusing/defocusing quickly (over first 20-50 cm) gives large transverse angles (5-10 mrad) to captured electrons. Therefore on-axis injection is not sensitive to e-beam emittance. Electron beams with 20-30 mm*mrademittancecould also be injected with 10-15% capture efficiency. • Typical angular spread in the accelerated beam is ±2 mrad (if spectrometer screen is 3 m downstream plasma section => transverse beam size = ±6 mm)