Narrow plasma & electron injection simulations for the AWAKE experiment A. Petrenko, K. Lotov, October 11,

Narrow plasma simulations Baseline simulation from CDR (4 mm wide plasma): 2 mm wide plasma (r = 1 mm): 2

Electrons start to leave plasma after SMI develops: Large Er 200 keV/cm (20 MeV/m) Plasma electrons Proton beam Single particle trajectory: 3

Electron beam transport parallel to plasma/proton beam Plasma section entranceAfter 1 m:After 2 m: Electron energy = 15 MeV Close-up of Er field map: Just some very small noise Er 4 Electron beam is too sensitive to small fields over long distances. Even small numerical noise-level Er completely destroys parallel electron beam over 2 m distance. It is very difficult to calculate Er outside plasma with enough accuracy for accurate beam transport simulation.

Plasma wave acceptance Metal screen (first 6 m) 15 MeV electron beam protons plasma Initial beam configuration: Energy of electrons after 1.2 m: xi-r & xi-r’ acceptance: 5

Captured particles (animation) 6

Typical trajectory of captured particle 7

15 MeV electron beam with realistic emittance (ε n = 2 mm*mrad) n(Rb) = cm -3 In vacuum 5 m of plasma section n(Rb) = 0 In the middle of plasma section (5 m): 8

r-r’ acceptance: Beam r·pϕ distribution: r·pϕ acceptance: 9 Electron beam after scattering vs plasma wave acceptance

2.2 % of e-beam is captured Np = 3.0e11 (Baseline variant) 10

1.1 % of e-beam is captured Np = 3.0e11 11

1.1 % of e-beam is captured Np = 3.0e11 12

0.6 % of e-beam is captured Np = 3.0e11 13

(Preliminary) Effect of dipole magnetic field on side-injection 50 MeV e - dipole 14 L = 20 cm, B = 70 Gs

Conclusions Large number of electrons are ejected from plasma as a result of SMI (may be useful for diagnostic of SMI). Metal screen between electron and proton beam/plasma will probably be required for electron beam transport inside plasma section. Typical injection efficiency with realistic 15 MeV e-beam is 1-2 % (Preliminary) Dipole magnetic field (approx 50 Gs) at the injection point increases the side-injection efficiency and makes it possible to inject higher-energy electron beam (50 MeV for example). 15

Additional slides 16

Transverse acceptance17 17

Angular momentum acceptance e-beam 15 MeV r*pϕ is conserved For r = 3 mm:18 18

Energy acceptance19 19

In vacuum: n(Rb) = cm -3 :20 20

Options for electron transport line Difficult to simulate (though may actually work) Easier to simulate, should work, but the number of captured electrons will probably be reduced due to scattering on neutral gas (which induces large r*pϕ) The best control over beam parameters, and the best capture efficiency, (with longitudinally compressed beam might be possible to capture all electrons). Metal screen 2 mm wide channel Fast valve 1 m21 21