Narrow plasma & electron injection simulations for the AWAKE experiment

A. Petrenko, K. Lotov, October 11, 2013

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Narrow plasma simulationsBaseline simulation from CDR (4 mm wide plasma):

2 mm wide plasma (r = 1 mm):

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Electrons start to leave plasma after SMI develops:

Large Er200 keV/cm(20 MeV/m)

Plasmaelectrons

Protonbeam

Single particle trajectory:

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Electron beam transport parallel to plasma/proton beam

Plasma section entrance After 1 m: After 2 m:

Electron energy = 15 MeV

Close-up of Er field map:

Just some very small noise Er

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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 MeVelectronbeam

protonsplasma

Initial beam configuration:

Energy of electrons after 1.2 m:

xi-r & xi-r’ acceptance:

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Captured particles (animation)

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Typical trajectory of captured particle

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15 MeV electron beam with realistic emittance (εn = 2 mm*mrad)

n(Rb) = 1015 cm-3In vacuum

5 m of plasma section

n(Rb) = 0

In the middle of plasma section (5 m):

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r-r’ acceptance:

Beam r·pϕ distribution:r·pϕ acceptance:

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Electron beam after scattering vs plasma wave acceptance

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

1.1 % of e-beam is capturedNp = 3.0e11 11

1.1 % of e-beam is capturedNp = 3.0e11 12

0.6 % of e-beam is capturedNp = 3.0e11 13

(Preliminary) Effect of dipole magnetic field on side-injection

50 MeV e- 50 MeV e-dipole

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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).

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Additional slides

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Transverse acceptance17

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Angular momentum acceptance

e-beam15 MeV

r*pϕ is conserved For r = 3 mm:

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Energy acceptance19

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In vacuum:

n(Rb) = 1015 cm-3:

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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 m

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