140 likes | 250 Vues
On-axis injection simulations. Petrenko , K. Lotov, 10 / 04 /2014 AWAKE collaboration meeting at CERN. On-axis injection of electron beam (15 MeV, 2 mm* mrad ) into the proton-driven SMI wake-fields. Injected electron beam:15 MeV, σ r = 0.3 mm, ε n = 2 mm·mrad
E N D
On-axis injection simulations Petrenko, K. Lotov, 10/04/2014 AWAKE collaboration meeting at CERN
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
On-axis injection of electron beam (15 MeV, 2 mm*mrad) into the proton-driven SMI wake-fields
On-axis injection of electron beam (15 MeV, 2 mm*mrad) into the proton-driven SMI wake-fields
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
On-axis injection of initially parallel 15 MeV electron beam into the SMI wake-fields (first 1 meter)
Individual injection trajectories for some electrons along 1 m of plasma:
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?
On-axis injection of narrow initially parallel electron beam into the SMI wake-fields (first 1 meter)
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
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
Baseline proton beam after 10 m plasma: Proton distribution in the interacting part of the beam (s<0):
Electron & proton beam envelopes after plasma: Laser beam size? Plasma exit
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)