Review of the European XFEL Bunch Compression System

Summary

Torsten Limberg

Topics and Speakers

• Introduction and Concept T. Limberg• Optic and Tolerances       W. Decking• Simulation Calculations M. Dohlus• Tuning                                    T. Limberg• Bunch Compression Options     M. Dohlus• Diagnostic Overview & FB         H. Schlarb• Diagnostic Sections Lay Out      C. Gerth• Diagnostic Tools and Optical Replica      B. Schmidt & M. Yurkov • Vacuum                                    N. Mildner,

T. Wohlenberg, K. Zapfe

Design Goals and Considerations

Electron bunches out of the gun: 50 A peak current, small energy spread

BC system has to convert that to:

– 5 kA peak current

– < 25 m Bunch Length (shorter pulses?)

– < 1.4 mm-mrad slice emittance

– < 1 MeV slice energy spread (stay about a factor of two below that from synchrotron radiation in undulator)

– Compensate rf structure wake field induced correlated energy spread as good as possible with rf induced energy chirp for compression (mimimize laser bandwidth)

– avoid high gain for micro-bunch instability

– avoid big projected emittance (> 2.5 mm-mrad)

– < 10% peak current jitter (SASE jitter <10 %)

– arrival time jitter has mainly to be measured and taken care of by the experiments

Bunch Compression Scheme (TADR)

Gun

Gun R56 = 100 mm R56 = 15-25mm

: L-Band Module: 3rd harmonic rf Module: Bending Magnet

: Vertical Deflection Cavity Section

: Wire Scanner Section

s

peak

= mmI : 5 kA

0.02

Undulator

0.4 - 0.5 GeV 2.0 GeV(at 15 MeV/m in booster)

17.5 GeV

Booster Linacwith 3x4 Modules

MainLinac

Injector Linac

3rd harmonicRF section

s

peak

= mm

I : kA

0.1 - 0.15

0.7 - 1

s

peak

= 2 mmI : 50 A

Bunch Compressor Beam Line Optics

Diagnostic Section

Drift throughshielding

Dogleg (R56 ≈ - 0.015 m)

18 deg deflection to commissioning dump

W. Decking: To Do List Optics and Tolerances

• Include BC Diagnostic Sections in Master Deck• Increase BC chicane middle dipoles distance to include

diagnostics• Calculate transverse wakefield effects of 3rd harmonic

cavities• Adjust phase advance between BC1 and BC2 to n*pi• Magnet tolerance studies (field quality and alignment of

dipoles)

‘laser heater’

(LCLS layout)

kVE

rms = 2 keV(Gaussian)

rms = 10 keV(Gaussian)

rms = 10 keV(from laser heater)

slice energy distribution P(E) EdEjkEP exp

k

M. Dohlus: Simulation Calculations

gain curves

A 44rmsnoise, I

A 260rmsnoise, I

“real” heater:rms = 10keV

A 29rmsnoise, I

mmentrance

after BC1after BC2

after dogleg

dogleg, r56 = 0.84mm 0

TDR: gaussian distributionrms = 10 keV

shot noise

0

2

rmsnoise,

dGeI

I

TDR:

“real” heater:

energy to current modulation: “real” heater:rms = 10keV

TDR: gaussian distributionrms = 10 keV

mmentrance

after BC1

after BC2

after doglegeV

M

ASTRA simulation:5% modulation at cathode, = 0.2 mm injector dogleg (~45m after cathode):

~2keV

energy / eV5% current / A

s / mm

0.5%

cathode

after 45m (130 MeV)

Setup Using ‘Multiknobs’

• Make knobs to change independently the first, second and third derivative of the combined accelerating voltage of Injector Linac and 3rd harmonic RF, using linac and 3rd harmonic phase and 3rd harmonic amplitude.

– V(s) = V1cos(k1s+1) + V3cos(k3s + 3)

= V + g ∙ s + x1∙ 1010 ∙s2 + x2∙ 1012 ∙s3 + o(s4)

Use gradient knob for peak current, 2nd derivative to balance beam distribution in the center region and 3rd derivative knob for adjusting the tails.

• Linac Amplitude is still used to keep beam energy constant.

Things to Do

• Practical design of multi-knobs for FLASH• Prepare detailed tuning scheme for FLASH• Test it and learn…

BC System – ReviewOptions

● BC2 working point (energy-charge-compr.)

● 2BC (rf-rf-bc-rf-bc-rf)

● table: 2BC (rf-rf-bc-rf-bc-rf)

dogleg + 2BC (rf-dog-rf-rf-bc-rf-bc-rf)

n3BC (rf-bc-rf-rf-bc-rf-bc-rf)

3BC (rf-rf-bc-rf-rf-bc-rf-bc-rf)

rollover compression

● laser heater

● cases in detail

peak current

projected emittance

slice emittance

uncorrelatedenergy spread

remaining chirp

µ-bunch stability

parameter-sensitivity

arrival time stability

M. Dohlus bc system optimization sheet

rf knobsr56 knobscompression

factors

absolute tolerances(amplitude & phase_deg)

µ-bunching gain

chirp

minimal relative tolerances

0

2

rmsnoise,

dGeI

I

shot noise dueto µ-bunching gain

mmBC156r

deg

L2

inverse tolerance noise: Irms/A

Balancing the micro-bunch instability strength vs. the rf jitter sensitivity

inverse tolerance

noiseIrms/A

…continued

20,500

10,500

10,400

20,400

5,400

C1, E1/MeV

inverse tolerance

noise

Irms/A

E1 = 400 MeVr56BC1 = 90mm, C1=5r56BC2 = 75mm, C2=20L2 = 10 degmin(ampl_tol) = 0.1%min(phas_tol) = 0.023 degnoise: Irms = 147 A

min(phas_tol) = 0.016 degnoise: Irms = 260 A

2BC

rf(1+3)-bc-rf-bc-rf-c

rollover compr.

rf(1+3)-bc-rf-bc-rf-c

dogleg+2BCrf-d-

rf(1+3)-bc-rf-bc-rf-c

n3BCrf-bc-

rf(1+3)-bc-rf-bc-rf-c

3BCrf(1+3)-bc-

rf(1+3)-bc-rf-bc-rf-c

E=400MeV2GeV

17.5GeV

C=520

0.98

r56=-90mm-75mm

0.84mm

ampl_tol=0.1%ph_tol=0.023deg

noise= 147 A

L2 = 10 deg

E=500MeV2GeV

17.5GeV

C=1010

0.98

r56=-100mm-200mm0.84mm

ampl_tol=0.2%ph_tol=0.055deg

small

L2 = 40.5 deg

E=130MeV400MeV

2GeV17.5GeV

C=1.24.17

200.98

r56=40mm-90mm

-87.2mm0.84mm

ampl_tol=0.11%ph_tol=0.040deg

noise= 270 A

e’=1%@ 130MeVL2 = 10 deg

t566_dog=1m

E=130MeV500MeV

2GeV17.5GeV

C=1.456.90

100.98

r56=-30mm-90mm

-45.0mm0.84mm

ampl_tol=0.09%ph_tol=0.048deg

noise= 95 A

e’=2.5%@ 130MeVL2 = 10 deg

E=130MeV400MeV

2GeV17.5GeV

C=1.254

200.98

r56=30mm-80mm

-83.7mm0.84mm

ampl_tol=0.11%ph_tol=0.045deg

noise= 93 A

e’=1.6%@ 130MeVL2 = 10 deg

t566_dog=1m

Diagnostics overview BC1

• proposed beam line design:

SRF 1.3GHzSRF 1.3 GHz

Bunch compressor TDSX&Y

Diagnosticsection

SRF 3.9 GHz

SpectrometerDump

Standard diagnostics:

TOR toroid system for transmission measurements (1,3&4 for interlock)

DC dark current monitors (upstream BC1, downstream BC1)

BPM beam position monitor ~ 20 (not yet determined … every quad?)purpose: orbit correction, transfer measurements, dispersion correction

OTR optical transition screen (with wire scanners WS?)

Diagnostics overview BC1

• proposed beam line design:

SRF 1.3GHzSRF 1.3 GHz

Bunch compressor TDSX&Y

Diagnosticsection

SRF 3.9 GHz

SpectrometerDump

Special diagnostics:

TDS transverse deflecting structure X & Y

EO electro-optic longitudinal beam profile monitor

BCM bunch compression monitors (CSR at D4 and CDR/CTR)

SR synchrotron radiation monitor (energy and energy spread)

BAM beam arrival time monitor

-> B Schmidt

Diagnostics overview BC1

• proposed beam line design:

SRF 1.3GHzSRF 1.3 GHz

Bunch compressor TDSX&Y

Diagnosticsection

SRF 3.9 GHz

SpectrometerDump

Additional devices:

COL collimators (1st & 2nd to remove dark current, 3nd & 4th for kicked e-)

KIC fast kicker to off-axis screens (2 x and 2 y)

Align laser for optics alignment

BLM beam loss monitors (about 8-10 sufficient)

Horizontal kicker

Vertical kicker

FODO lattice 6 off-axis OTR screens (y and x)

3 cells = 11.4 m

OTR1 OTR3 OTR5OTR2 OTR4 OTR6

VK2

HK2

VK1

Horizontal slice emittance / vertical streak Vertical slice emittance / horizontal streak

HK1

Screen / Kicker arrangement (2)

45deg 76degHK1 OTR1 OTR1HK1 OTR2 OTR3HK2 OTR4 OTR4HK2 OTR6 OTR6

45deg 76degVK1 OTR1 OTR2VK1 OTR2 OTR3 VK2 OTR4 OTR4VK2 OTR6 OTR5

Bend plane of BCs defines the OTR arrangement

VK1

HK1 VK2 HK2

CSR

T1

T2

EOSD

BAM

ABCM TDS-x TDS-y

ABCM2.5m

Booster Linac

FODO lattice

SR

Alignmentlaser

RES10 modules

3.8 m

5 modules

7.6 m

Lattice can be divided into modules:

Diagnostic Section Engineering layout (3)

Conclusions (1):

Conclusions

For which bunch rep rate, 5MHz or 1MHz, shall the on-line slice emittance diagnostics be designed in BC1:

• Desired resolution can easily be reached at 1 MHz but is just at the theoretical limit for 5 MHz.

• Kickers with the required kick strength for 1MHz are in operation in several machines at DESY (‘off-the-shelf’). 5 MHz would requires new design and prototype development.

• If standard FEL operation will be 5 MHz slice emittance diagnostics cannot be operated parasitically if designed for 1 MHz (or might not be used if resolution is not sufficient).

• If standard FEL operation will be 1 MHz one would lose at least a factor of 1.6 in resolution if designed for 5 MHz

Conclusions (2):

Conclusions

Dump defines the horizontal streak direction in BC2.If the BCs are installed vertically slice emittance could be measured in the bend plane of BCs.

Number of quads in current layoutBC1 was 22 now 22BC2 wsa 13 now 19

Layout of the dignostics sections can be arranged in modules. Components can be prealigned and tested.This saves time during installation and commissioning.

Layout of BC1 diagnostic section almost finalized.After beam dynamic and sensitivity studies (2 months) the vacuum and engineering layout could be started

New lattice layout requires slightly more space BC1: 1.5 m in BC + 0.9 m in diag section = 2.4 mBC2: 1.0 m in BC + 1.5 m in diag section* = 2.5 m*Additional FODO cell for 45 deg lattice requires 7.6 m more space

Coherent radiation

Status : - spectrally resolving single shot instrument developed(multi stage grating spectrograph with parallel read out)-Advanced prototype running at FLASH (THz beam-line)- Existence of spectroscopic fingerprints shown down to µm scale

To be done : - develop compact monlithic version - explore and establish feedback capabilities- detailed planning of station lay-out

Zur Anzeige wird der QuickTime™ Dekompressor „TIFF (LZW)“

benötigt.

existing detector unit

Potential layout for 4-stage spectrograph

Electro-optical monitors

Status : - different methods under study at FLASH- integrity and validity of data largely explored - spectral decoding method proven to be sufficiently simple- dedicated fiber-laser version under construction

To be done : - step from ‘experiment’ to ‘on-line tool’- more robust and reliable laser system (fiber-laser)- fast (parallel) read-out system (line camera)- direct (optical) coupling to optical timing system

Requirements / implications :

- EO crystals inside beam pipe (r ~ 2-5 mm), retractable- optical ports for laser in/out

space underneath beam pipe : ~ 2 m2 optical table (laser +spectrometer + camera).

beamlaser

~0.6 m

T. Wohlenberg: Bunch compressor section BC1 and BC2

General remarks

• Lengths of the vacuum system BC1 and BC2:• BC1: total length ~ 69m → chicane length ~ 27m → deflection of the chicane ~

0.68m• BC2: total length ~ 90m → chicane length ~ 25m → deflection of the chicane ~

0.33m

• Vacuum requirements: Pressure needs to be in the range of 10-10 mbar (next to cold sections) Pump system: sputter ion pumps and titan sublimations pumps

• Both sections are particle free : The design of all vacuum components needs to be according to the particle free

conditions. Early discussion of concept of all components including beam diagnostic is necessary!

All vacuum components have to be cleaned under particle free condition (clean room).

Installations needs to be done under local clean room conditions.

Bunch compressor section BC1 and BC2General remarks

From the point of view of vacuum technology both BC sections should be treated similar. This should be valid for the aspect of material choice, joining technology, support for the chambers etc..

The design concept for the flat chamber in the chicane is similar to FLASH!

Bunch compressor section BC1 and BC2 Schedule

• Draft:

Components layout + girder and frames concept including electronics/diagnostics units concept ~ 1 year

Design of BC1 and BC2 ~ 1 year Fabrication of all components ~ 1.5 years

2007, A rough concept should be settled for the girders/frames concept including electronics and diagnostics as well as part of the layout of the components.→ layout for the arrangement of the components should be available!

2008, The detailed concept for the layout of the components, electronic concept and the girder and frames concept should be finished.

Bunch compressor section BC1 and BC2open issues

Do we have the BC‘s chicane to be installed vertically or

horizontally? → we prefer vertical installation! Do all components need to be copper coated in both BC’s? Can the RF-shielding remain the same as for FLASH or

do we have to design a new concept for the flange connections,

bellows, valves and pump connections? Is a massive lead shielding necessary ?

→ need to be included into the girder and frame design! How does the dump section for BC1 and BC2 look like? What diagnostic installations will be needed next to the beam

line?