1. Operational Experience at ELBE
SPIE, Advances in X-ray Free-Electron Lasers Instrumentation
13-16 April 2015, Praque
Peter Michel, Ulf Lehnert, Wolfgang Seidel
Helmholtz-Zentrum Dresden-Rossendorf
Outline
Introduction into ELBE radiation source & IR beams
User facility aspects & operational experience
FEL applications at ELBE

2. ELBE Beams electron beam coherent THz 100 µm - 3 mm
coherent IR 4 – 250 µm
coherent THz 100 µm - 3 mm
X-rays keV
materials research
semiconductor physics
biophysics, biochemistry
environment
(polarized) Bremsstrahlung
0 – 17 MeV
CTR/CDR
Superradiant
undulator
Free Electron Laser
nuclear physics
nuclear astrophysics
Thomson
radiator
foil
quasi mono- chromatic X-rays
10 – 100 keV
Gamma induced
Positron Spectroscopy
(GiPS)
electron beam
channeling
radiation physics
radiobiology
W moderator
Pb target
pulsed, mono-energetic
positrons 0.2 – 30 keV
(MePS)
electrons 0 – 40 MeV
radio biology
detector studies
materials research
pulsed neutrons 0 – 30 MeV
solid state physics:
material defects research
fusion & materials research
nuclear physics
transmutation research

3. ELBE Beamlines

4. ELBE Electron Linac max current 1.6 mA ! 250 kV DC gun 80 pC (…120)
10 mm mrad
RF bunch
compressor
magnetic bunch
compressor
1.3 GHz sc linac
18 MeV
1.3 GHz sc linac
18 MeV
5 MeV SRF photo gun
< 500 pC
3 mm mrad
max current 1.6 mA !

5. ELBE Free Electron Laser

6. Free Electron Lasers - Parameter
FEL Properties
FEL 1 - U27
FEL2 - U100
undulator period
27.3 mm
100 mm
design
2 x 34 periods
vacuum chamber
38 periods
waveguide
undulator param.
0.3…0.7
0.3…2.7 µm
wavelength µm µm
max. power (out)
30 W
65 W
max. pulse energy
2 µJ
5 µJ
pulse length
0.5…4 ps
1…10 ps
U27
U100

8. FEL diagnostic table IR-Diagnostic average power measurement
spectrum measurement
attenuation

9. Spectral width and duration of the IR-pulses
a: L= -2 m, FWHM= 2.5 ps, /= 1.5 %
b: L= -14 m, FWHM= 4.4 ps, /= 0.9 %
c: L= -24 m, FWHM= 5.8 ps, /= 0.6 %
Top: L= -1 m; below: ΔL= -20 m
The calculated time-bandwidth product is about 0.4 which indicates Fourier-transform limited operation

10. Temporal structure of the ELBE-FEL
high duty cycle (100%)
13 (26) MHz, cw
low duty cycle
macropulse structure Hz
single pulse selection
photo-induced reflection
1 Hz – 2 kHz
single
pulse
selector

11. Energy stabilization feed-back system
### Mathias
RF amplifier
detector: strip-line BPM + PXI data acquisition
PLC: Simatic S7-400 (cycle time 10 ms)
Profibus transmission and DAC output 4.2 ms
actuator: LL RF control + semiconductor amplifier (µs)

12. long term energy stability < 1%
Energy stabilzation feed-back : results
feed-back on
long term energy stability < 1%

13. Power stabilization feed-back system
detector: Bruker FIR-DTGS D210/3 PE window
PLC: ADC input 400 µs delay time Simatic S7-400 (cycle time 10 ms)
Profibus transmission and DAC output 4.2 ms
gate: voltage controller delay time 1.8 ms
limited bandwith

14. ELBE power stabilization feed-back: results
IR sensor
gun current
Feedback on
Feedback off
feed-back on
feed-back bandwidth limit ~ 5 Hz
many experiments improved

15. FEL tuning times new l change Krms change energy
get lasing with new energy:
- change acceleration gradient
- adjust magnets
- adjust position, b, dE, dt @ FEL
- get lasing (scan cavity length)
- optimize transmission (no Beam loss)

16. Importance of acurate accelerator tuning for stable operation
Noise diagnostics near the experiment
FEL cavity length tuning
RF phase tuning at the accelerator
Advantages of the full cw operation
- High radiation intensity
- High stability
- Feed-back loops usable

17. FEL beam parameters in practical user operation
Wavelength overlapp not sufficient
due to limited electron energy range
and low netgain of both FELs arround
22 µm !
U27
U100
l > 21µm &
l< 25 µm
Low gain at

18. Beam time statistics 2013/2014 hours in total:
scheduled 6672
used 5969
effiency 91.4%
24/7 regime , four 11-week-runs/year
/COM
Beam efficiency =
scheduled beam time
user evaluated „good“ beam time

19. ELBE user Experiments:
IR spectroscopy of semiconductors, quantum
structures, bio-molecules
IR near field microscopy & spectroscopy
pump-probe experiments in the sub-ps range
spectroscopy under high, pulsed magnetic fields
migration spectroscopy of radioactive compounds

20. High Magnetic Field Lab & ELBE
HLD
High Field Lab Dresden
ELBE
High Field Lab Dresden ms ms ms
Wavelength: 4 – 230 µm
Transmission over 70 m: 20 % - 50 %
Combination of ELBE FEL (4 … 250 m) and High Magnetic Field Lab   IR spectrosocopie at high magnetic fields
2B · 100 T » h·c / 100 m

21. Pulsed-field ESR with FELBE
Electron Spin Resonance (ESR) is known for ist remarkable resolution and the accessibility of large zero-field spin-level splitting in magnetic materials
no synchronization of the FEL with the magnetic field pulses is needed, since the FEL runs continuously at 13 MHz
> 106 FEL pulses during one magnetic-field pulse of 100 ms length provide excellent measurement conditions

22. Zeroth Landau level (LL0) loses electrons while it is optically pumped !
Reason: strong Auger scattering.
Courtesy of S.Winnerl, H.Schneider

23. Nano Lett. 15, 1057 (2015)
Courtesy of H.Schneider
By scanning near-field infrared microscopy (SNIM)

24. Summery ELBE and ELBE FELs work succesfully in routine user operation
with multiple beams for a wide range of applications altghrough
it is based on high complicate technologies like superconducting
accelerator technology, cryogenics, high average beam power,
multiple beam facility
CW operation and flexible temporal puls structure open
attractive oppertunities for user experiments
Further improvements need to be done
eg. reducing beam arrival time jitter, U27 will be replaced by
U37 in 2015 due to insufficient wavelength overlap

25. Thank you for attention

26. ELBE FEL power instabilies in very low frequency range
Cavity length / mm
~ 4%
~ 15%
Dxp-p ~100µm

27. Pulse picking with a laser-based semiconductor plasma switch
Decreasing the average power as required for certain experiments, high pulse energies but moderate or low average power
First request of a 1 kHz FEL-user beam for „Vibration control of quantum phases in complex oxides“ by A. Cavalleri et al., MPSD-CFEL Hamburg/University Oxford
Parameter: λ= 17, 29, 50 m; rep. Rate 0.5 – 1 kHz; energy/pulse 1 J
Ratio signal/dark pulses  400
Future: FEL with macropulses 1–100 kHz, duration 20–50 s
FEL pulse at 32 m in two different amplitude scales
Dependence of reflectivity on the pump-laser power (FEL ~0.5 mm2, YAG ~3 mm2)
E.H. Haselhoff et al., Nucl. Instr. and Meth. A358 (1995)ABS28
P. Haar, Ph.D. Thesis, Stanford University (1996)
W. Seidel and S. Winnerl, FEL Conference 2010, Malmö
F.A. Hegmann and M.S. Sherwin, SPIE Vol (1996)
G.M.H. Knippels et al., Nucl. Instr. and Meth. B144 (1998) 32-39