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

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Idea: thin SiN membrane (100 nm) e- beam p+ beam laser 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 beam x ~1m B SM’or ACC’or

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

Page 1: Idea: thin SiN membrane (100 nm) · LBDP Rb vapor Pros: • one single thin membrane on the electron beam path (small scattering angle) • LBDP stops both laser pulses laser beam

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

Page 2: Idea: thin SiN membrane (100 nm) · LBDP Rb vapor Pros: • one single thin membrane on the electron beam path (small scattering angle) • LBDP stops both laser pulses laser beam

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

Page 3: Idea: thin SiN membrane (100 nm) · LBDP Rb vapor Pros: • one single thin membrane on the electron beam path (small scattering angle) • LBDP stops both laser pulses laser beam

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

Page 4: Idea: thin SiN membrane (100 nm) · LBDP Rb vapor Pros: • one single thin membrane on the electron beam path (small scattering angle) • LBDP stops both laser pulses laser beam

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

Page 5: Idea: thin SiN membrane (100 nm) · LBDP Rb vapor Pros: • one single thin membrane on the electron beam path (small scattering angle) • LBDP stops both laser pulses laser beam

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

Page 6: Idea: thin SiN membrane (100 nm) · LBDP Rb vapor Pros: • one single thin membrane on the electron beam path (small scattering angle) • LBDP stops both laser pulses laser beam

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

Page 7: Idea: thin SiN membrane (100 nm) · LBDP Rb vapor Pros: • one single thin membrane on the electron beam path (small scattering angle) • LBDP stops both laser pulses laser beam

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

Page 8: Idea: thin SiN membrane (100 nm) · LBDP Rb vapor Pros: • one single thin membrane on the electron beam path (small scattering angle) • LBDP stops both laser pulses laser beam

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