Post-Linac Beam Lines - Deutschlands größtes … MAC_20… · · 2010-01-21W. Decking, DESY,...

W. Decking (DESY)1st XFEL Machine Advisory Committee

Meeting26.01.2010

Post-Linac Beam Lines

2

26.01.2010, 1st XFEL MACW. Decking, DESY, XFEL Machine Layout Coordinator

Post Linac Beam Lines

� Overview� Basic Requirements� Sections� Collimation� Feedback� Beam Switchyard� Undulators� Beam Dumps

� Hardware Components� Summary

3



Overview

SASE 1 tunable, planar

0.1 nm


0.1 – 0.4 nm

U 2

U 1

e-

electrons 17.5 GeV

Exp

erim

ents

SASE 3 tunable, helical

0.4 – 1.6 nm

e-

Transport and distribute electrons to undulators an d beam dumps

4



Overview


0.1 nm


0.1 – 0.4 nm

U 2

U 1

e-

electrons 17.5 GeV

Exp

erim

ents

SASE 3 tunable, helical

0.4 – 1.6 nm

e-

Transport and distribute electrons to undulators an d beam dumps� 2920 m of electron beam line (including 714 m of undulator section)� At present 388 main magnets� Three 300 kW beam dumps� Intra-bunch switching system� Collimation and feedback section

5



Basic Requirements� Hardware protection

� Collimation section withstanding impact of 100 bunches� Beam halo collimation down to 20 σ transverse and ± 2.5%

longitudinal� Trajectory launch correction

� Intra-bunch feedback with about 1 MHz bandwidth and up to 2 σcorrection amplitude

� Beam switchyard with maximum bunch pattern flexibility� Flexible undulator beam optics match� Variable gap undulator section with FODO lattice � Beam dumps accepting 300 kW (½ of available beam power)

6



Basic Requirements (cont.)� Beam optics should be

� Robust and easy tunable� Allow ± 1.5% energy variation with no beam perturbation

� Deflection sections have to be isochronous to prevent further bunch compression and micro-bunch gain

� Vacuum system impedance optimized� Maximum beam energy 22 GeV

7



Collimation Section� Hardware protection for miss-steered beam

� Beam size large enough (> 80 µm) to withstand impact of 100 bunches in TiAl collimators

� Beam Halo collimation� Combined energy and betatron collimation required proper

adjustment of dispersion and betatron function ratio� Large energy bandwidth and tune able R56

� arc consists of four 90 deg FODOS in mirror symmetry� reverse bends for R56 tune ability� Sextupoles improve energy bandwidth and allow larger collimator

apertures

8



Collimation Section (cont.)Optical functions� System can be tuned to simple

FODO channel for commissioning or diagnostics purposes

� Beta-function value can be varied to tune energy and betatron collimation depth independently

� Primary collimators with three different apertures foreseen

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Collimation Section (cont.)� Beam Dynamics

� 3 σ ellipses with 0 and ±1.5% energy deviation

� Collimator aperture radius to protect 3 mm (XFEL=4mm) undulator chamber

3 mm

10



Intra-bunch Feedback� Expected Perturbations (realistic/pessimistic assumption)

� Train-To-Train:

� 10/43 µm random: mainly magnet vibration� Intra-Train:

� ~2 µm random: beam distribution kicker jitter, dispersion and energy chirp

� 10/85 µm repetitive: wake fields, beam distribution kicker drift, dispersion and large energy chirp

� Expected Performance� Trajectory correction at undulator < 3 µm

� BPM resolution < 1 µm

� Latency 1 µs� Max. kick 2 µrad (scaleable)

� Adaptive feed-forward for repetitive perturbations

� Integration of additional (undulator, photon) BPMs for enhanced resolution and slow feedback

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Intra-bunch Feedback (cont.)

SASE 1

e-beamLINAC

SASE 2

Digital Signals (Duplex Fiber Optic Cables)

- - - - - - - - - - - Analog Signals (Coax Cables) - - - - - - - - - -

IBFB UpstreamBPM Pickups

IBFB Kicker Magnets(Horizont. & V ertical)

IBFB DownstreamBPM Pickups

V1H1 H2 V2

IBFB Electronics

Daisy-Chain 2 of BPM Units

Daisy-Chain 1 of BPM Units

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Beam Switchyard� Kicker-Septum Scheme� Stable flat-top kicker distributes between beam lines� Fast burst kicker deflects into dump for arbitrary bunch pattern and

emergency beam abort� Linac operates with constant beam loading

13



Beam Switchyard cont.

300 µs

200 ns •high accuracy(< 0.01 %)

•10 Hz operation

•low accuracy(>1 %)

•5 MHz burst operation

example: pulser prototype measurement

example: pulser prototype measurement

5 MHz Dump Kicker(pulse pattern)

600 µs

5MHz Dump Kicker(Pulse pattern)

a)

650us

Gun Linac

Flat Top Kicker (pulse width 290 µs)Dump

290 µs

5 MHz Dump Kicker(pulse pattern)

600 µs

Dump Gap< 20 µs

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Beam Switchyard cont. ‘Slow’ flat top pulser

DESY in-house development� Capacitor discharge� Stability measurements

� At FLASH: < 4e-3 RMS (resolution limited)� Laboratory: < 2e-4 RMS

Fast dump pulser

Company built pulser and in-house kicker� Stability measurements

� At FLASH: estimated stability about 1%, but measurement hampered by large residual kick

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Beam Switchyard cont.

� Stability goal at undulator < 1/10 σ� Kick strength approx 300 σ => rel. amplitude stability < 3e-4� Septum deflection approx 4000 σ => rel. amplitude stability < 2.5e-5

� Horizontal deflecting Lambertson DC septum (requires vertical kick)

� Simultaneous correction of horizontal and vertical dispersion

� Isochronous (R56=0) arc

16



Undulators

total number of undulators 96 (116 TDR)

length of undulator system 586 m

total available straight length 1500 mlength of FODO cell 12.2 m

17



Undulators cont.

•absorber for spontaneous radiation

•cavity BPM•Quadrupole on mover

•phase shifter•air coils for undulator ∫Bdl correction

•Intersection on a common granite girder

•Total length 1.1 m

•length of undulator segments 5 m

•movable gap

18



Undulator cont.

Simulation of beam based alignment procedure (dispersion free steering)

� SASE simulations for quadrupole misalignments resulting from BBAprocedure with various ‘dispersion’ resoultions

�need BPM resolution < 100 nm or energy change > 30%

19



Beam Dumps

main beam dumpsup to 25 GeVPave= 300 kW 1/2 max beam powerbeam magnifiedslow sweep to distribute heat

injector dumps130 MeVPave= 12 kW max. beam power

bunch compressor diagnostic dumps0.5 and 2.5 GeVsmall fraction of max. beam power

20



Beam Diagnostics

beam position, beam intensity, beam losseswithin bunchwithin bunch trainfrom train to train

projected emittanceoptics matchenergyenergy spreadrel. peak currentslice emittancelong. bunch shapearrival time

projected emittanceoptics matchenergyenergy spreadrel. peak currentarrival time

projected emittance

Photon diagnostics

21



Beam Diagnostics

BPM, Toroids, Fibers, loss monitors, screens within bunchwithin bunch trainfrom train to train

wire scannerOTR screensBPMSR monitorscoherent diffraction radiationtransverse deflecting structureelectro-optical methods

wire scannerBPMSR monitorscoherent diffraction radiationelectro-optical methods

wire scanner

Photon diagnostics

22



Vacuum System� Undulator beam pipe 15 mm x 8.8 mm ellipsoid extruded Al

� Impedance Budget:� Criteria for max. roughness and oxide layer

roughness [nm] + 50 x oxide layer [nm] < 500 nm

23



Vacuum System� Standard beam pipe Ø 40.5 mm Cu or Al

� Diameter and Material selected to minimize resistive wall and surface roughness wake contribution

� Criteria: contribution of beam lines to energy spread should be < 20% of undulator chamber contribution

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Vacuum System cont.� All elements collected in impedance database

� wake field represented by Green’s function� folded with arbitrary bunch shape to obtain wake potential� calculates energy loss and spread contribution

Example:Impedance Budget from Linac up to SA1

25



Optical Synchronization� Master Laser Oscillator� Free Space Distribution

� Fiber Links based on optical cross-correlation (~ 20)

� End-stations (arrival time/BPM, laser synchronization, RF generation) (~30), ∆t~10 fs� Large system with many sub-components

� Reliability and operability main issue today

� Future R&D: simplify system, 10fs -> 1fs, low charge operation

FLASH Setup

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Optical Synchronization cont.

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Summary Hardware Contributions� Accelerator Magnets

� Construction, Fabrication: Efremov Institute� Fiducialization of Undulator quadrupoles: Uni Stockholm� Movers for Undulator quadrupoles: Ciemat

� Vacuum System: � Collimators, Undulator Intersections, Standard Pipes: BINP� Kicker chambers, Switchyard, Undulator Chambers: DESY

� Beam Dumps: IHEP� Diagnostics:

� BPM electronic: PSI� BPM pickup: DESY� OTR/WIRE/Screens: DESY� BLM: IHEP� Transverse Deflecting Structure: INR

� Transverse Feedback: PSI

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Summary

� Post-linac beam lines design has to fulfill many demanding requirements

� Solutions to exploit unique beam properties of E-XFEL� Expandable for future upgrades� Conceptual designs finished, lots of work in the detailed

design phase

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