1. LLRF'15 Workshop, Shanghai, Nov. 4, 2015
Low Level RF Control Implementation and Simultaneous Operation of Two Undulator Beamlines at FLASH
V.Ayvazyan, S.Ackermann, J.Branlard, B.Faatz, M.Grecki, O.Hensler, S.Pfeiffer, H.Schlarb, C.Schmidt, M.Scholz, S.Schreiber, DESY, Hamburg, Germany; A.Piotrowski, Fast Logic, Lodz, Poland
LLRF'15 Workshop, Shanghai, Nov. 4, 2015

2. Outline FLASH and the FLASH II project
Layout of the facility
Pulsed operation mode and timing aspects
LLRF control for multi-beamlines
Requirements and functionality extension
Regulation performance
Simultaneous operation and results
Summary

3. Free-electron Laser in Hamburg - User Facility since 2005
TESLA type superconducting accelerating modules 1.3 GHz
3rd harmonic sc module 3.9 GHz
FLASH1 fixed gap undulators
FLASH1 Experimental Hall
315 m
5 MeV
150 MeV
1250 MeV
Bunch Compressors
450 MeV
Accelerating Structures
RF Stations
Lasers
RF Gun
Soft X-ray Undulators
sFLASH
FEL Experiments
Photon Diagnostics
Beam Dump
THz
FLASH1
FLASH2
Normal conducting 1.3 GHz RF gun
Two photocathode lasers
Extraction to FLASH2
FLASH2 variable gap undulators
FLASH2 Experimental Hall

4. The FLASH II Project RF Control Requirements for Multi-Beamlines
Separation of FLASH and FLASH2 beamlines behind the last accelerating module
Tunability of FLASH2 by undulator gap change
Extend user capacity with SASE (Self-Amplified Spontaneous Emission)
RF Control Requirements for Multi-Beamlines
Amplitude and phase can – in certain limits – be independently chosen for both FELs
Ability of phase tuning at injector for variation in compression FLASH1 and FLASH2
Ability of gradient tuning of last two RF stations for wavelength scans
Handling different beam loading scenarios
Bunch repetition rate, number of bunches and charge

5. Temporal Structure (An Example)
– Bunch charge FLASH1
– Bunch charge FLASH2
– RF signal (amplitude/phase)
– Kicker amplitude
filling
FLASH1
transition
FLASH2
decay
500 µs
500 µs
50 µs
250 µs
500 µs
98.2 ms t
Kicker pulse:
rise
flattop
fall
Next pulse train
SC machine 1 flattop, many bunches
100 ms,10 Hz
Same optics setup for both beamlines, limitations of the bunch parameter range
Energy acceptance in dispersive sections, slow magnet changes
Two lasers operating on one cathode (alignment, orbit)

6. The Low Level RF System Overview
In 2013 was the last major LLRF control hardware/software upgrade to a MicroTCA.4 based system
Digital feedback - based on vector sum control group of cavities gradients
MIMO controller
Learning feed forward
Beam based feedback
Application software
Description of the signal flow
See talk by U. Mavric: Operational experience with the MicroTCA based LLRF system at FLASH

7. RF Control Functionality Extension for FLASH2
Main Timing
RF Settings
LLRF
3rd BL F1 F2
Kicker, BPM, BLM, MPS, Laser ctrl., …
Transmission F1
Besides LLRF, all machine timing triggered systems receive a priori beam information => no manual synchronization
LLRF control tables are generated from the operational setting according to the provided timing information
Independent RF operational parameters adjustment (defined limits) F2
Globally controlled by main timing system, expected bunch pattern, start and stops
Distribution to other subsystems
Colored indications for all aspects
Operator must be capable to distinguish
Extandable for a 3rd beamline

8. RF Control Performance
Vector-sum amplitude and phase stability fulfills given requirements
min e for all t FB
LFF
We can achieve the given requirements on the Amplitude and phase stability
Transition time is mainly determined by the kicker
However there is space for improvements at the transitions steps, already smooth
Kicker given minimum transition time can be achieved
Smooth transition steps to avoid broadband excitation

9. Lasing with Two Independent Bunch Trains
FLASH features two injector lasers to produce electron bunch trains with different numbers of bunches, charges and repetition rates
It has been shown that for the same charge the same amount of SASE is present (top), while for different charges the difference in SASE is as theoretically expected (bottom)

10. First Lasing FLASH2
Most of the commissioning for FLASH2 was done in parallel with FLASH1
First lasing FLASH2: August 20, 2014
FLASH1 lasing in parallel 250 bunches with about 50 µJ
First lasing FLASH2 was also first parallel operation
After the demonstration of the first lasing at FLASH2 SASE operation was established at various wavelengths
FLASH2: 1 bunch
SASE Energy [µJ]
FLASH1: 250 bunches
FLASH: The first soft X-ray FEL operating two undulator beamlines simultaneously

11. Parallel SASE Operation
Separate panels for FLASH1 and FLASH2
Fast kicker
FLASH1
FLASH1
FLASH2
Two injector lasers
FLASH2
SASE pulse energy (in a.u.)
Two operators controlling two “virtual” machines
Parameters affecting both BL are blocked from individual panels

12. Achieved Photon Wavelengths during Parallel SASE Operation
Achieved photon wavelength during parallel SASE operation in the period from August 2014 to August 2015
Variable gap undulators in FLASH2 allow different photon wavelengths at fixed beam energies

13. Thanks for your attention!
Summary and Outlook
Low Level RF control functionality has been extended which makes simultaneous RF operation of multi-beamlines possible
Can operate with different compressions, charges and bunch patterns
Maintaining RF field amplitude and the phase stability requirements
Achieved simultaneous operation and lasing of two undulator beamlines
SASE operation at various wavelengths was established
LLRF commissioning for multi-beamlines at European XFEL in progress
Operations of alternating RF pulses (from pulse to pulse)
Requires additional changes in firmware/software structure, e.g. extending the amount of control tables
Thanks for your attention!