Idea: thin SiN membrane (100 nm) · LBDP Rb vapor Pros: • one single thin membrane on the...

Idea: thin SiN membrane (100 nm)

e- beam

p+ beamlaser beam

SiN membrane

LBDP

Rb vapor

Pros: • one single thin membrane on the electron beam path (small scattering angle) • LBDP stops both laser pulses

laser beamx

~1m

B

SM’or ACC’or

Check beam optics• Multiple scattering calculations may not be valid

because thickness << X0

• Check scattering angles with FLUKA simulations

• Agreement between simulations and MCS theory

Beam size at the foil• Calculate σ at the foil

• According to beamline design, the distance foil-waist can’t be < 1m (dipole dimensions constraints)

• Maximum window size: 10x10 mm^2

thickness cannot be > 100 nm

Betatron function• Calculate β* given initial normalized

emittance (20 mm*mrad) and longitudinal position of the waist w.r.t. the foil

• According to beamline design, the distance foil-waist can’t be < 1m (dipole dimensions constraints)

• First cons: β_in < β*

𝛽∗ =𝜀𝑜𝑢𝑡𝜀𝑖𝑛

∙𝑧 𝑜𝑢𝑡𝑧𝑖𝑛

∙ 𝛽𝑖𝑛

>1 <1

Emittance• Calculate εN given initial normalized

emittance (2 mm*mrad) and longitudinal position of the waist w.r.t. the foil

• According to beamline design, the distance foil-waist can’t be < 1m (dipole dimensions constraints)

• Second cons: emittance growth is higher than in the two-foil setup

𝜀𝑜𝑢𝑡2 = 𝜀𝑖𝑛

2 + 𝜎𝑓2𝜗2

Beam envelope• According to beamline design, the distance

foil-waist can’t be < 1m (dipole dimensions constraints)

• According to beamline design, quadrupole magnet is positioned ~2 m away from the dipole magnet

• Third cons: beam size at the magnet > quadrupole aperture

Conclusion• Even if it simplifies the setup, it is not feasible for the beam optics

Conclusion• Even if it simplifies the setup, it is not feasible for the beam optics• Two-foil setup is technically more complicated but feasible

Other solutions:

• One single foil acting as vacuum window and LBDP

• Only one LBDP, SiN membrane upstream at a waist• meaning: last part of the beamline has to be hot

LBDP1

VACUUM WINDOW 1

VACUUM WINDOW 2 + LBDP2

e- beam

p+ beam

LBDP

e- beam

p+ beam

hν hν

SM’or ACC’or

SM’or ACC’or