LCLS Injector Commissioning Workshop: Linac Experience at FLASH

1. LCLS Injector Commissioning Workshop, SLAC, October 9-11, 2006 Linac Experience at FLASH Katja Honkavaara University of Hamburg and DESY • Linac commissioning • Operation as a user facility • Some selected topics K.Honkavaara, LCLS ICW06

2. Diagnostics Accelerating Structures Collimator Undulators Bunch Compressor Bunch Compressor 250 m Present layout of FLASH Linac FEL diagnostics 5 MeV 127 MeV 370 MeV 400…730 MeV bypass K.Honkavaara, LCLS ICW06

3. Linac commissioning strategy • Injector commissioning run February-May, 2004 • Summer 2004 • Installations in tunnel finished (modules, waveguides, vacuum, magnets, diagnostics, cabling) • Conditioning of modules (couplers) • Experience of module conditioning and operation already from TTF1 • Commissioning of klystrons and modulators • Commissioning of the linac sector by sector as soon as a sector is ready for beam operation (modules, magnets); commissioning of other sectors continued parallel • RF-gun: 1-Sep-2004 → • Injector (ACC1+BC): 6-Oct-2004 → • Beamline up to collimator: 15-Oct-2004 → • By-pass line: 22-Oct-2004 → • FEL beam line: 1-Dec-2004 → K.Honkavaara, LCLS ICW06

4. Linac commissioning steps • Beam operation • Gun section • Injector Injector commissioning Feb-May, 2004 • Adjustments • LLRF (phases, gradients, • feedback) • Magnets (polarity, optics) • Commission diagnostics • (toroids, screens+cameras, • BPMs, loss monitors) • Commissioning • Modules (cavities, couplers) • Cryo measurements • Klystrons + Modulators • Magnets Start of linac operation 1-Sep-2004 First beam through ACC2/3 15-Oct-2004 First beam through ACC4/5 25-Oct-2004 First beam to dump via by-pass 31-Oct-2005 First beam through collimator 3-Dec-2004 • Adjustments and optimization • Beam parameters • Beam optics and • transport • Diagnostics • LLRF • Stability • SASE • Operation • SASE delivery • Change of photon • wavelengths • Long bunch trains • Bunch train pattern First beam through undulator 13-Dec-2004 First SASE 14–Jan-2005 First user experiments June 2005 User facility K.Honkavaara, LCLS ICW06

5. Beam operation in injector Start of linac commissioning, Sep-Oct-2004 • Restart RF-gun and establish beam in gun section • Beam based solenoid and laser beam alignment using a camera in the diagnostics cross • LLRF adjustments of RF-gun • Stability measurements (charge, energy) • Momentum and dark current measurements • Conditioning of ACC1 cavity 7 • Piezo-tuner studies ACC1 • Dark current studies ACC5 • Cryo measurements • LLRF preparation for modules • Commissioning magnet power supplies along the linac • 6-Oct-2004 → Beam operation in injector (up to ACC2) • ACC1 with unbalanced gradients: 4 first cavities ~12 MV/m, 4 last ~20 MV/m • Commissioning of magnet controls (cycling, control by DOOCS) and diagnostics (toroids, BPMs, BLMs, camera system) K.Honkavaara, LCLS ICW06

6. First beam through ACC2/3 First unaccelerated beam through ACC2/3, October-15-2004 • ACC2/3: Adjustment of cavity phases, gradient and phase calibration, LLRF adjustments • Polarity of magnets • Calculated nominal optics taken a start point for quadrupole settings; empirical fine tuning Screen 3UBC3 First beam at entrance of ACC4, chicane off, October-16, 2004, First accelerated beam through ACC2/3, October-16-2004 Screen 3UBC3 Screen 5DBC3 2nd bunch compressor = BC3 K.Honkavaara, LCLS ICW06

7. Beam through the 2nd bunch compressor First beam through BC3 chicane, October-21, 2004 • 2nd bunch compressor (BC3) is S-shape chicane • OTR screen in second dispersive section of the chicane to measure energy and adjust on-crest phase of ACC2/3 • No on-line monitoring of energy and phase Screen 11BC3 Screen 5DBC3 Typical beam images before and after BC3 in SASE operation Screen 3UBC3 Screen 5DBC3 Screen 5DBC3 Screen 3UBC3 Screen 11UBC3 K.Honkavaara, LCLS ICW06

8. First beam to dump via by-pass First beam up to collimator, October-25, 2004 • ACC4/5: Adjustment of cavity phases, gradient and phase calibration, LLRF adjustments, tuning cavities ACC5 • ACC4/5 operated with low gradient (~ 5 MV/m) corresponding to total beam energy of 450 MeV • First lasing planned with wavelength of 32 nm • Calculated nominal optics taken as a start point for quadrupole settings • Difficult to achieve full transmission to the dump: polarity of several quads were wrong • Optics of by-pass line still not fully understood; presently by-pass only rarely used, and therefore we have not put much effort to improve situation First beam up to dump via by-pass, October-31, 2004 K.Honkavaara, LCLS ICW06

9. Energy collimator dipole Collimator Collimators with adjustable gap: 4 mm, 6 mm, 12 mm, or open (30 mm) First beam downstream of collimator Dipoles for energy collimation • FEL beam line ready for beam operation Dec-1-2004 • Calculated nominal optics taken as a start point for quadrupole settings, empirical adjustments required • First beam through collimator dogleg (collimators open) up to undulator entrance relatively easy • But no transmission through undulator First beam through collimator Dec-3, 2004 Screens between collimator and undulator K.Honkavaara, LCLS ICW06

10. First beam through undulator to dump Quadrupole doublet between undulator modules. Fine adjustment of quad position using a micromovers (hor & vert) • Several trials to get beam through undulator without success • Complication: losses in undulator have to be kept small • Reason identified by manual check of all quadrupoles in/upstream undulator: • Two quadrupoles upstream undulator had a wrong calibration by a factor of 3.6, one had a short • Quadrupole in diagnostics block downstream first undulator module horizontally moved out of nominal position by 2 mm; micromover was not mechanically fixed • After fixing: beam through undulator quickly → start of photon diagnostics commissioning and SASE search First beam through undulator to dump, Dec-13, 2004 Screen 12EXP, downstream of undulator K.Honkavaara, LCLS ICW06

11. First lasing (32 nm) First lasing: January-14, 2005 • Over Christmas 2004 we had 2.5 weeks break in operation • Jan-6-2005 → • Start-up + beam in by-pass • LLRF adjustments • Jan-11-2005 → • Set-up beam in FEL mode • First lasing: Jan-14-2005 K.Honkavaara, LCLS ICW06

12. September - December, 2004 • Lot of studies and commissioning done during autumn 2004 parallel to establishment of beam operation through the linac • Commissioning of diagnostics tools (hardware and software) • Camera system • Emittance measurement and matching in injector • BPM • Transverse deflecting cavity LOLA • Diagnostics using coherent radiation • Beam loss monitor system • LLRF adjustments and developments • HOM measurements • Magnets: cycling, integration to DOOCS K.Honkavaara, LCLS ICW06

13. After first lasing: January – June 2005 • Beam time shared between • SASE search and characterization • Diagnostics commissioning (BPMs, coherent radiation diagnostics, camera system, toroids, beam loss monitor system, phase monitors, LOLA) • Beam optics, transportation, optimization (transverse emittance in injector, beam based alignment linac/undulator, dispersion, …) • Noise and stability studies, correlations • LLRF adjustments and developments • HOM measurements • Typically every shift has a different program • Disadvantage: machine settings often different from shift to shift • But: since lot of commissioning was still on-going, program of a shift often determined by availability of experts • May 2005 → well defined blocks for different studies and SASE optimization • Clear improvement of SASE performance K.Honkavaara, LCLS ICW06

14. Off 4% Down 8% Off 7% Accel. studies 17% Tuning 18% User 39% SASE beam for users 69% FEL studies 37% (Maintenance) User Facility • FLASH is a user facility since August 2005 • Blocks for user experiments and machine/FEL studies clearly separated: • 2-3 weeks blocks dedicated for FEL studies (machine improvements related to FLASH operation, preparation of a user run) are followed by • 4-5 weeks block of users experiments: stable SASE radiation delivery • 2-3 times per year a block of 2-4 weeks dedicated to accelerator studies, priority tor further developments (e.g for XFEL and ILC) • 1 maintenace shift per week, longer maintenance periods 2-3 times per year Scheduled distribution of beam time in Spring/Summer 2006 17 weeks, 7days/week, 24h/day Statistics of user runs in Spring/Summer 2006 (7 weeks) K.Honkavaara, LCLS ICW06

15. Users FEL study Accel. study Trendline (8 weeks average) Downtime statistics 2006 Maintenance K.Honkavaara, LCLS ICW06

16. Machine improvement continues • Improvements, especially in stability, diagnostics and understanding of beam orbit and optics continues parallel with user runs, typically during FEL study periods • Stability • Injection: stability of laser profile, alignment injector section • LLRF: feedbacks and stability • New FPGA based hardware with improved precision installed for RF-gun and ACC1 • Stabilization of ambient temperatures • Slow feedbacks: orbit, phase, and charge • Improved procedures to obtain and maintain good SASE radiation • Investigation and fixing external noise sources (EMI) • Orbit, optics, beam dynamics • Measurements of transfer functions: led to a much better understanding of optics and gave a push in BPM improvements • Dispersion measured and partially corrected • Low beta function optics tested with success: 13 nm lasing achieved within 4 h • Beam based alignment undulator section ongoing, BPM resolution now sufficient • Understanding non-linear beam dynamics started • Emittance measurements continue K.Honkavaara, LCLS ICW06

17. Other steps towards design goal • Lasing with different wavelengths and switching between wavelengths • Lasing with ~15 different wavelengths between 13 nm and 45 nm achieved • Shortest wavelength: 13.1 nm (limited by electron beam energy) • Lasing with different bunch train pattern and long pulse trains (> 30 µs) • Lasing with higher repetition rate • Currently 5 Hz running, 10 Hz to be tested • Repair and install modules • ACC3 to be replaced, ACC5 repair 4 tuners • Install new module ACC6 to reach 1 GeV (→ lasing down to ~ 6 nm) • Install 3rd harmonic cavity • after ACC1 to improve longitudinal beam profile K.Honkavaara, LCLS ICW06

18. 1 MHz 599 bunches Selected topics • Charge • Feedbacks • Energy server • Beam loss monitoring • Electromagnetic interference • PETRA ramps • HOM measurements • Long bunch trains K.Honkavaara, LCLS ICW06

19. Charge • Measured with toroids • Noise from quadrupole magnet power supplies induces large noise in the toroids • Has been mostly removed by ferrites.Work on low noise power supplies required. • Noise level now below 1% of 1 nC • Laser BBO crystal adjustment needed time to time • After adjustment charge stability 1-2% (rms) K.Honkavaara, LCLS ICW06

20. Slow feedbacks • Feedbacks used to correct slow drifts of charge, ACC1 phase, and orbit (upstream of collimator) • Charge feedback: • Sensor: Charge in 3GUN toroid • Actuator: Laser attenuator • ACC1 feedback • Sensor: Pyrosignal after BC (coherent diffraction radiation from a slit) • Actuator: ACC1 phase set-point • Orbit feedback: • Sensor: BPM signals • Actuator: Steerers K.Honkavaara, LCLS ICW06

21. Energy server • Electron beam energy determined from dipole current and orbit through collimator dogleg • Used as an input for on-line determination of SASE wavelength • More accurate energy estimation still by measuring photon wavelength • Typical discrepancy with energy server few % K.Honkavaara, LCLS ICW06

22. Beam loss monitor system • Linac: Photomultipliers • Undulator: photomultipliers + glass fibers (accumulated dose) • Beam protection system disables beam operation when too high losses detected in undulator • Long bunch trains (> 30 bunches) allowed only when losses along the whole linac are low • Crucial for undulator protection and long bunch train operation, but helps also when steering the beam through the linac K.Honkavaara, LCLS ICW06

23. Electromagnetic interference (EMI) • We do have many sources of interference • High noise level in all ADCs • Noise from magnet power supplies (choppers) in diagnostics • Pulsed power cable testing • Inappropriate grounding scheme, high currents on earth lines • Magnetic disturbance due to PETRA ramps • Temperature induced drifts (phases) • Investigation and fixing of external noise sources on-going K.Honkavaara, LCLS ICW06

24. 800 um PETRA ramps Orbit movement at PETRA proton ramp Field changes of 1-2 µT explain observed orbit deviations • PETRA proton ramps have an effect on beam orbit at FLASH → SASE production was disturbed during ramps • Now compensated: stable SASE operation possible also when PETRA is ramping K.Honkavaara, LCLS ICW06

25. HOM measurements • Signal of dipole mode in a cavity can be used as an indication of the beam position → HOM signals provides a tool for on-line monitoring of beam position in the accelerating module • Development of on-line BPM like display of HOM based beam positions on-going • Dependence of HOM signal on the module phase under study • Large collaboration: DESY, SLAC, Fermilab, KEK, CEA-Saclay Example for vertical steering and dipole mode response in C1 of ACC1 Example of ACC5 raw HOM signals K.Honkavaara, LCLS ICW06

26. 50 kHz 1 MHz 599 bunches 100 kHz 500 kHz Long bunch trains • Up to 600 bunches (1 MHz) through the undulator • 500 kHz, 100 kHz, and 50 kHz operation tested as well • Lasing with at least 450 bunches (detector limit) • Problems: • Toroid protection system not yet in operation • Beam loading compensation and other LLRF adjustments still required for 800 us flat top operation • Activation of beam line components due to darkcurrent (mostly from RF gun) K.Honkavaara, LCLS ICW06

27. • 1 GeV beam energy • Shutdown: installation 6th module etc • • 2007 Lasing with long bunch trains (>30) • Variation of wavelength on shift-to-shift basis • • First lasing at 13 nm now • • 2006 • • FEL experiments start saturation at 32 nm achieved • • 2005 first lasing at 32 nm • FLASH is a user facility first beam to dump • • Commissioning injector started 2004 • Commission RF gun at PITZ finished Schedule and milestones K.Honkavaara, LCLS ICW06