Beam tilt studies at FLASH - DESY · 2007-10-28T105016-V2GUN-TILT-SCAN.mat 280 300 320 340 360 380 400 420 440 34 36 38 40 42 44 46 48 50 52 54 Beam tilt for no bump is not zero (For

FEL Beam Dynamics Meeting - 19/11/07 Eduard Prat, DESY

Beam tilt studies at FLASH

FEL studies – Autumn 2007People involved: Kirsten Hacker, Christopher Gerth, Eduard PratFEL Beam Dynamics Meeting19th of November of 2007, Hamburg


Contents

• Overview of the measurements• Orbit response measurements• Beam tilt

– Measurements and simulations of beam tilt and emittance– Measured and simulated dispersion

• C-shape– Simulation of a possible source– Measurements

• Summary and next steps


Overview of the measurements

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BEAM TILT MEASUREMENTS (23-10-07 & 28-10-07)A vertical offset through ACC1 (running off-crest) tilts the beam at BC2 and generates an emittance increase.Using the gun steerers, we generated different vertical bumps at BPM9ACC1. For each bump we measured:-Dispersion from ACC1-Beam tilt at BC2 using SR camera-Emittance at DBC2 using 4 OTR stations at DBC2

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C-SHAPE MEASUREMENTS (28-10-07 & 29-10-07)Running ACC1 on-crest, beam at BC2 can have a C-shape (for some optics and gun phase)We have analyzed the C-shape for different iris & mirror positions and as a function of the orbit

Complementary measurements- Orbit response for gun steerers (23 & 28-10-07)- Beam energy and energy spread after the gun (29-10-07)


Orbit response measurements23-10-07

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Wrong calibration sign of BPM9ACC1 (changed)Wrong calibration constant of BPM1/2UBC2 (changed)Wrong polarity of V3GUN (changed)


Orbit response measurements28-10-07

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After the changes ~ good agreement ☺ ✔


Beam tilt measurements – 28-10-2007Beam tilt

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Beam tilt for no bump is not zero(For no bump, orbit at BM9ACC1 was -2.8mm)

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Bump amplitude at BPM9ACC1 [mm]

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SR Camera BC2: Bunch tilt measurement 28-Oct-2007


Beam tilt measurements – 28-10-2007Emittance at DBC2 (90% values)

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90% horizontal emittance90% vertical emittancehorizontal mismatchvertical mismatch

ACC1 9 degrees off crest

Emittance is not minimum for no bump(For no bump, orbit at BM9ACC1 was -2.8mm)


Beam tilt simulations

Steerer currents of the measurements for V1/2/3GUN (& bump artificially closed)

Parameters of initial distribution:Emittance=1.3μmMomentum chirp = -4%Bunch Length=1.7mm,Energy spread = 0.4%

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simulationmeasurement

Simulated vs measured orbit difference [mm]

105 particlesWakes included (structure and coupler)0.62nC9 degrees off crest at ACC1Optics of the measurements


Beam tilt simulationsBasic case (zero bump = zero orbit, no wakes)

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bump at BPM9ACC1 [mm]

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No bump corresponds to no tilt and to optimum emittance


Beam tilt simulationsReal case (no bump=-2.8mm at BPM9ACC1)

Initial orbit misalignment of 3.5mm reproduces the initial orbit at BPM9ACC1 (-2.8mm)

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Beam tiltMeasurements vs simulations

Beam tilt: if some initial offset good agreementEmittance: qualitative good agreement

EmittanceBeam tilt

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measured emittancemeasured mismatchsimulated emittance

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measurements fitmeasurement pointssimulations


Beam tilt: Dispersion from ACC1 Measurements and simulations

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[mm

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MEASURED HORIZONTAL DISPERSION

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SIMULATED VERTICAL DISPERSION

ref-1.9mm-4.9mm+1.6mm+3.2mm+4.3mm+5.9mm


Comparison between measured and simulated dispersion for each bump

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Good agreement ☺


C-shape simulations: a possible sourceEnergy chirp coming from the gun + vertical dispersion

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Initial kick of 20mrad compensated with V2/3GUN, E=4.5MeVenergy chirp=6%wakes included

What can generate such a kick? Solenoid misalignment?


Simulations of the C-shapeMoving ACC1 phase

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Same effect observed in measurements


C-shape measurements

After adjusting gun phase and optics …

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… C-shape is there


Moving ACC1 phase

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-Same effect observed during measurements before the shutdown-Same effect predicted by simulations

-1 degree

+ 1 degree reference


Pseudo solenoid misalignment

Moving both iris and mirror positions the beam is misaligned respect to the gun.


Moving vertically

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↑0.85mm reference

↓0.60 mm ↓1.80 mm

C-shape does not change significantly when moving up and down


Moving horizontally

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Movement to the right enhances C-shapeMovement to the left reduces the effect

→2.00mm →0.88mm

reference ←0.83mm


Orbit correction

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→2.00mm

←0.83mm

Orbit as →2.00mm

Correcting the orbit without moving iris and mirror has a similar impact to the C-shape as moving iris and mirror

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Orbit as ←0.83mm


Summary and next steps

SummaryGood agreement between model and measured orbit response for gun steerersBeam tilt:

Measurements of beam tilt, emittance and dispersion are in a good agreement with simulations. Initial conditions (without gun steering) were not optimal.

C-shape:Correcting the orbit has a similar effect as moving iris and mirror positions.Vertical dispersion created upstream ACC1 would generate the C-shape (simulated and ~ confirmed by measurements)

Next stepsAnalyze beam energy measurementDo more precise simulations (using initial distribution from ASTRA, using same way to determine beam tilt for measurements and simulations, etc.)

Documents

Beam tilt studies at FLASH - DESY · 2007-10-28T105016-V2GUN-TILT-SCAN.mat 280 300 320 340 360 380 400 420 440 34 36 38 40 42 44 46 48 50 52 54 Beam tilt for no bump is not zero (For