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

ELBE Beams electron beam coherent THz 100 µm - 3 mm coherent IR 4 – 250 µm coherent THz 100 µm - 3 mm X-rays 12 - 20 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

ELBE Beamlines

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 !

ELBE Free Electron Laser

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 4...22 µm 20...250 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

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

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

Temporal structure of the ELBE-FEL high duty cycle (100%) 13 (26) MHz, cw low duty cycle macropulse structure 1 - 25 Hz single pulse selection photo-induced reflection 1 Hz – 2 kHz single pulse selector

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)

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

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

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

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)

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

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

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

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

High Magnetic Field Lab & ELBE HLD High Field Lab Dresden ELBE High Field Lab Dresden 60 T @ 1000 ms 70 T @ 100 ms 100 T @ 10 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

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

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

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

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

Thank you for attention

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

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. 2842 (1996) 90-105 G.M.H. Knippels et al., Nucl. Instr. and Meth. B144 (1998) 32-39