K.Honkavaara, LCLS ICW06 LCLS Injector Commissioning Workshop, SLAC, October 9-11, 2006 Linac Experience at FLASH Katja Honkavaara University of Hamburg

K.Honkavaara, LCLS ICW06

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


Present layout of FLASH Linac

250 m

bypass5 MeV 127 MeV 370 MeV

Bunch Compressor

UndulatorsCollimator

Bunch Compressor

Accelerating StructuresDiagnostics

FEL diagnostics400…730 MeV


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 →


Linac commissioning steps

First beam to dump via by-pass 31-Oct-2005

Adjustments• LLRF (phases, gradients, feedback) • Magnets (polarity, optics)• Commission diagnostics (toroids, screens+cameras, BPMs, loss monitors)

Adjustments and optimization

• Beam parameters• Beam optics and transport• Diagnostics• LLRF• Stability• SASE

First beam through ACC2/315-Oct-2004

First SASE 14–Jan-2005

First beam through ACC4/525-Oct-2004

First beam through collimator3-Dec-2004

First beam through undulator13-Dec-2004

Start of linac operation1-Sep-2004

First user experiments June 2005

Injector commissioningFeb-May, 2004

Beam operation• Gun section• Injector

Commissioning• Modules (cavities, couplers)• Cryo measurements• Klystrons + Modulators• Magnets

Operation• SASE delivery• Change of photon wavelengths• Long bunch trains• Bunch train pattern

User facility


• 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)

Start of linac commissioning, Sep-Oct-2004

Beam operation in injector


First beam through ACC2/3

• 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

First unaccelerated beam through ACC2/3,

October-15-2004

First beam at entrance of ACC4, chicane off, October-16, 2004,

Screen 5DBC3 Screen 3UBC3

First accelerated beam through ACC2/3, October-16-2004

2nd bunch compressor = BC3

Screen 3UBC3


Beam through the 2nd bunch compressor

Screen 11BC3 Screen 5DBC3

First beam through BC3 chicane, October-21, 2004

Typical beam images before and after BC3 in SASE operation

Screen 3UBC3 Screen 5DBC3

• 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 3UBC3

Screen 11UBC3

Screen 5DBC3


First beam to dump via by-pass

• 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 collimator, October-25, 2004

First beam up to dump via by-pass, October-31, 2004


First beam downstream of collimator

• 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

Collimator Energy collimator dipole

Collimators with adjustable gap: 4 mm, 6 mm, 12 mm, or open (30 mm)

Dipoles for energy collimation

First beam through collimator Dec-3, 2004

Screens between collimator and undulator


First beam through undulator to dump

• 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

Quadrupole doublet between undulator modules. Fine adjustment of quad

position using a micromovers (hor & vert)


First lasing (32 nm)

• 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

First lasing: January-14, 2005


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


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


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

Users

FEL studies

Accelerator studies

Off

User

39%

FEL studies

37%

Accel. studies

17%

Off

7%

(Maintenance)

Beam

Development

Tuning

Down

Off

SASE beam for users

69%

Down 8%

Off 4%

Tuning

18%

Statistics of user runs in Spring/Summer 2006

(7 weeks)

Scheduled distribution of beam time in

Spring/Summer 2006 17 weeks, 7days/week,

24h/day


Downtime statistics 2006

Trendline

(8 weeks average)

Maintenance

UsersFEL studyAccel. study


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


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


Selected topics

• Charge• Feedbacks• Energy server• Beam loss monitoring• Electromagnetic interference• PETRA ramps• HOM measurements• Long bunch trains

1 MHz

599 bunches


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)


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


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 %


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


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


PETRA ramps

Field changes of 1-2 µT explain observed orbit deviations

800 um

Orbit movement at PETRA proton ramp

• 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


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 of ACC5 raw HOM signalsExample for vertical steering and dipole mode response in C1 of ACC1


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)

50 kHz

100 kHz

500 kHz

1 MHz

599 bunches


Schedule and milestones

2006

2005

2004Commission RF gun at PITZ finishedCommission RF gun at PITZ finished

Commissioning injector startedCommissioning injector started

first beam to dumpfirst beam to dump

first lasing at 32 nmfirst lasing at 32 nm

saturation at 32 nm achievedsaturation at 32 nm achievedFEL experiments startFEL experiments start FLASH is a user facilityFLASH is a user facility

First lasing at 13 nmFirst lasing at 13 nm

Lasing with long bunch trains (>30)Lasing with long bunch trains (>30)Variation of wavelength on shift-to-shift basisVariation of wavelength on shift-to-shift basis

Shutdown: installation 6Shutdown: installation 6thth module etc module etc

1 GeV beam energy1 GeV beam energy

2007now

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Documents

K.Honkavaara, LCLS ICW06 LCLS Injector Commissioning Workshop, SLAC, October 9-11, 2006 Linac Experience at FLASH Katja Honkavaara University of Hamburg