Research Topics

Femto-Science Factory (FSF)

The machine parameters of the FSF are driven by the demand of the users. The unique features of the multi-turn ERL-based light source include:

  • High peak brilliance of the beam. This feature is the result of the low emittance of the electron beam (conserved and adiabatically damped during acceleration). Both, transversal and longitudinal emittances, achieved from bright electron beam injectors can be an order of magnitude better than equilibrium emittances of 3rd generation storage rings-based light sources.
  • High temporal resolution. Low longitudinal emittance allows short radiation pulses down to tens of fs. This gives great advantage in the peak brilliance, as well as for the time-resolved experiments
  • High transversal coherence. If the transversal emittance of the electron beam is lower, than λ/4π, the radiation can be transversally coherent. Such low emittances in storage rings are unattainable.
  • Multiple beam energies at the same time in the same installation. Improves the flexibility and broadens the spectrum of user applications reducing overall working costs.
  • Multi-User Facility. Comparable to modern day storage ring facilities.

The schematic above shows the principle of the FSF light source. An injector based on the emerging Superconducting Radio Frequency (SRF) technology is used as a continuous source of high brightness electron beams. From the 10 MeV injector the electron bunch is transported to a preinjector and accelerated to an energy of 240 MeV. Following the green line in the figure, the bunch is deflected 180° through a magnetic Arc lattice and injected into the first of two long, high energy gain SRF linacs. Subsequently after each independent Arc orbit comes the alternating 960 MeV linac acceleration until a final beam energy of 6 GeV is reached. The Arcs themselves contain undulators for generating photon radiation for science but the final larger Arc (black line) transports the beam to a long undulator section to produce the ultra-bright photons.

The table below summarises the goal parameters of the FSF light source. Once through the long undulator section the beam is decelerated back, again three times through each of the two linacs (red line) and safely transported to the beam dump. On deceleration the bunch energy is recovered and reused to accelerate a fresh bunch arriving half an RF cycle later.

ParametersHigh brilliance modeShort pulse mode
Energy,  E (GeV)66
Charge, Q (pC)154
Emittance, εxn    (µm)0.1~ 0.5
Pulse length, Δt  (fs)< 2000~ 10
<B>, ph/s/mm2/mrad2/0.1% 8·10224·1021
Bpeak, ph/s/mm2/mrad2/0.1% 10261026

The  most important parameters of the FSF facility are the peak and average brilliance of the photon beam. The critical electron beam parameters are the transverse emittance, pulse length and energy spread in undulators.

The plots above shows the average brilliance expected from of the FSF light source. The curves lie in a unchartered region between the 3rd generation light sources and the new Free Electron Laser facilities (FEL). This area of high brilliance at angstrom wavelengths for a high duty cycle machine is only sustainable using an ERL based light source.

For more information on the FSF design study please do not hesitate to contact the simulation team.