1. Emittance Partitioning between x (or y) and z dimensions
Y. Jiao

2. Motivation 1
Hard X-ray FEL facility for Matter and Radiation in Extremes (MaRIE).
Requirements for the emittances:
enx / eny / enz = 0.14/0.14/180 mm, 6D phase space volume 3.5 mm3.
Typical emittances produced at cathode: enx / eny / enz = 0.7/0.7/1.4 mm, volume 0.7 mm3.
Emittances at the LCLS cathode: enx / eny / enz = 0.5/0.5/3 mm, volume mm3
Where should we go for LCLS II (photon wavelength 2.5 nm ~ 1.2 angstrom)?
1, N. Yampokky, et al., Controlling electron-beam emittance partitioning for future X-ray light sources,
2018/12/30

3. Emittance partitioning
Main idea:
1,Change the eigen emittances by non-symplectic transformations (eigen emittances are constants within linear Hamiltonian dynamics)
2, Recover the emittance by special beamline sections.
Difficulty
1,The proposal is correct only within linear dynamics aspects, so far the nonlinearities have not been well explored.
2,Conventionally the eigen emittances is only able to be modified at the birth of the beam with low energy (cathode), strong space charge.
2018/12/30

4. Option one: tilting the incident laser front pulse
~100 MeV
Space charge, solenoid,
acceleration
Subsequent Linac
cathode
Correlation removing beam line section
Problem:
1, beam parameters with nonzero correlations evolution under nonlinearities of strong space charge and RF acceleration. There are not yet well established codes to treat such case.
2, It requires incident laser with elliptical transverse profile to produce electron beam with 25:1 ratio between x and y radius.
2018/12/30

5. Option two: tapered foil at a relatively high energy
~135MeV
Acceleration and emittance compensation
Wedged shape foil (x dimension)
Wedged shape foil (y dimension)
Cathode
enx / eny / enz = 0.7/0.7/1.4 mm
enx / eny / enz = 0.14/0.7/7mm
enx / eny / enz = 0.14/0.14/35mm
Advantage: avoid strong space charge region.
Problem: Multiple scattering in foil leads to transverse emittance growth and energy spread. one should well control the emittance growth. It requires detailed simulations.
2018/12/30

6. Time table of milestone
See word file.
2018/12/30