1. Paul Scherrer Institut
Sven Reiche
SwissFEL Design
PSI,
PSI,
13. September 2018
13. September 2018

2. Design Goals for SwissFEL
Compact FEL Facility , reaching 1 Ångstrom:
Low beam energy
Compact undulator
Low Emittance Gun
Short period undulator
with sufficient gap and ield strength (K>1)
lu = 15 mm, K = 1.2  E = 5.8 GeV, en = 0.43 mm mrad
PSI,

3. Design Goals for SwissFEL
SwissFEL facility covers 0.1 – 7 nm with 1- 5 nm seeded, variable polarization > 1nm
Natural cut of wavelength range by photon optics ( nm and 0.7 – 7 nm)
Tuning of hard X-ray FEL (ARAMIS) mostly by beam energy ( GeV) (K value allows only small tuning)
Tuning of soft X-ray FEL (ATHOS) by K-value and beam energy
Independence of both beamlines
ATHOS is instrumented with APPLE II type undulator modules with 4 cm period (K=1-3.5)
Self-seeding scheme preferred over EEHG and HHG seeds
PSI,

4. Expected FEL Performance of ARAMIS @ 1 A
FEL Beam Design Parameters
Nominal Operation Mode
Special Operation Mode
Long Pulses
Short Pulses
Large Bandwidth
Ultra-Short Pulses
Undulator period (mm) 15
Undulator parameter
1.2
Energy spread (keV)
350
250
17000 (FW)
1000
Saturation length (m) 47 50
Saturation pulse energy (µJ)
150 (*) 3
100
Effective saturation power (GW)
2.8
0.6 2
Photon pulse length (fs, rms) 21
2.1
0.06
Beam radius (µm)
26.1 17 26
Divergence (µrad)
1.9
2.5
Number of photons (×109) 73
1.7
7.5
Spectral Bandwidth, rms (%)
0.05
0.04
3.5 (FW)
Peak brightness (# photon/mm2.mrad2.s1.0.1% bandwidth)
7.1032
1.1032
8.1030
1,3.1033
Average brightness (# photon/mm2.mrad2.s1.0.1% bandwidth)
2,3.1021
5,7.1018
3.1019
7,5.1018
PSI,

5. Layout SwissFEL 600 m Technology choice:
RF photo-electron gun (2.5 cell), S-band
2 Stage compression at highest energy possible to minimize RF tolerances
C-band linac (less RF stations, real estate and mains power than S-band, chirp removal after BC 2)
X-band for linearizing phase space before BC 1
2 bunch operation (28 ns) with distribution to Aramis and Athos at 100 Hz
Laser Heater to mitigate microbunch instability
PSI,

6. Microbunch Instability – Gain Curve for SwissFEL
sd = 5e-5
PSI,

7. Laser Heater Layout ✜ ✜ ✜ ✜  ✜  ✜ BPM X [m] Screen ICT BAM BLM   ✜ ✜ ✜ ✜     ✜
BPM
X [m] 
Screen 
ICT 
BAM 
BLM ✜  
Steerer
Z [m]
PSI,

8. Laser Heater Schematic
PSI,

9. Laser Heater Specification/Interface
Two bunches with 28 ns separation, diagnostic must resolve both bunches and laser pulses
EPICS control system mandatory, following the PSI/SwissFEL naming convention
Actuator/Sensor of the feedback system must have a RocketIO interface (same for machine protection)
Laser position, intensity and overlap must be part of the feedback system.
Modulator undulator will be built by STFC/Daresbury
Dipole magnets will be built by PSI
Electron beam diagnostic will be built by PSI (including the overlap screens in the chicane)
Vacuum chamber within the laser heater has an inner diameter/height of 16 mm.
Undulator and Vacuum chamber will be movable between two fixed position (on/off position)
Contributed by the collaboration:
Vacuum chamber
Movers for vacuum chamber and undulator
Laser transport & laser diagnostic (arrival time, overlap, intensity for set-up & feedback)
Mechanical support and girder
PSI,

10. Time Schedule
PSI,