Synchrotron Radiation Source R&D at BESSY II in Berlin

Synchrotron Radiation Source R&D at BESSY II in Berlin 

Ernst Weihreter 

♦ BESSY II facility overview 

♦ Generation of coherent THz radiation by low α operation 

♦ Generation of fsec X-ray beams by the fsec slicing technique 

♦ Implementation of a 7T wiggler for high energy X-rays 

♦ Higher order mode damped cavity R&D 

♦ BERLinPro, a poof of principle experiment for a future ERL based 

multi-user facility

HMI + BESSY → 

HZB: RESEARCH at two Sites 

Hahn-Meitner Institut 

• Established in 1959 at Berlin-Wannsee 

• BER II, reactor based neutron source 

• Staff: approx. 800 , from which 300 are scientists 

• Focus: 

- Structural studies of condensed 

matter using neutrons 

- Research on Solar Energy 

BESSY 

• Established in 1981 at Berlin-Wilmersdorf (BESSY I) 

• Since 1998 „large ring“ BESSY II in Berlin-Adlershof 

• Staff: 230, from which 100 are scientists 

• Focus: 

- Research with Synchrotron Radiation 

- Development of SR sources 

HMI and BESSY merged in January 2009 to form the 

Helmholtz Zentrum Berlin 

providing two probes, neutrons and photons for a large research community, 

and perform structural investigations for fundamental and applied research 

4th Nat. Congress on Particle Accelerators and Applications / Bodrum / Turkey 30.8. – 1.9. 2010 Ernst Weihreter / HZB BESSY II 

2

Metrology Light Source MLS 

Physikalisch Technische Bundesanstalt 

Task: Radiation Metrology 

MLS 

600MeV 

SR Sources in Berlin-Adlershof 

MLS BESSY II 

BESSY II 

3rd generation SR source 

1.7 GeV 

BESSY II 

Task: SR source for fundamental 

and applied research 


3

Broad spectral range 

♦ IR and coherent THz radiation 

from dipole and in low-α mode 

♦ XUV-soft X ray range, var. polarisation 

♦ 

From 12 wigglers/undulators – 

6 APPLE II type: UE112, 4 - 700eV 

Up to 100 keV photons 

from 4 superconducting WLS/ wigglers 

BESSY II Facility 

♦ 

♦ 

14 straight sections for IDs 

52 beamlines operating in 

a broad spectral range 


IRIS IR beam line 

4

Lattice – Linear Optics - Operation 

♦ 16 cell Double Bend Achromat, with 7 

sextupole families for chromatic corr. and 

optimisation of dynamic aperture 

♦ high and low beta straights with doublet or 

triplet focusing → flexible ID matching 

♦ε 0 =6·10 -9 m rad @ 1.7 GeV, L = 240m 

Peter Kuske at ELETTRA, 25 th of May 2007 


♦ 

closely spaced magnets 

♦ sextupole magnets serve as dipoleand 

skew quadrupole correctors 

♦ injection every 8 hours: 290 mA + 10 mA 

single bunch in 100 ns dark gap 

♦ 

♦ 

lifetime: 10 h @ 300 mA, sb 3 h 

Hybrid mode 

nsec 

time resolved and cw experiments in parallel 

5

Applications of Synchrotron Radiation at BESSY II 

7T multipole wiggler 

EXAFS, NEXAFS 

X-ray Fluorescence 

Residual Stress Analysis 

Femto-Second Slicing 

Magnetic studies with 

polarised X-rays 

Metrology 

PTB 

THz Imaging and Spectroscopy 

Photoemission Studies 

Spectro-Microscopy 

Low α mode 

Electronic Structure Studies 


6

Power amplification = 

Coherent Emission 

Power (λ) = pλ(N + N2gλ) incoherent coherent 

part part 

Power(�) / (P incoh ) = 1 + N g � 

10 

N�10 electrons 


7

σ→equilibrium between 

- radiation damping 

- quantum excitation 

machine optics 

BESSY II: Low alpha optics 

Bunch length σ 

momentum 

compaction 

D 

D 

ΔL/L = αΔp/p 

α 

BESSY II main parameters 

optics parameter reg.user 

optics 


low alpha 

optics 

nat. emittance / nmrad 6 ��~30 

synchrotron freq. / kHz 7.5 7.5 … 1.75 … 0.35 

mom. compaction factor �� 7.2E-4 7.2E-4 …4E-5… 1.6E-6 

nat. bunch length rms /ps 12 12 … 3 … 0.7 

For σ 

~ sqrt(α) 

= M 

� � 

User operation for coherent THz generation 

l 

c 

� 

2� � E �E0 

0 

heV 

= 3 ps, α= 4. 10 -5 : very stable machine operation, 

I = 20 mA and 20 h lifetime 

E 

0 

rf 

cos� 

s 

8

BRILLIANCE W/mm/sr/(0.1% bdw) 

brilliance of the BESSY II THz spectrum 

10+1 

10-4 

10-9 

BESSY II: Coherent radiation 

10-14 

power spectrum analysis 

0.1THz 1THz 

user optics bursting 

CSR, SB 15 mA 

low alpha stable 

CSR, 18 mA 

incoherent radiation 

250 mA, user optics 

black body, 1200 K, 10 mm^2 

1 10 100 1000 10000 

wave number cm -1 

chamber 

cut off 

Very versatile radiation source in the THz range 


9

e 

Motivation: many structural changes and magnetic phenomena 

occur on fsec scale 

electron bunch → psec scale, lasers → fsec scale 

Principle: ♦ modulate electron energy by the field of a fsec laser pulse 

co-propagating with the electron bunch in a wiggler 

♦ separate energy in a dispersive section 

♦ generate fsec X-rays in the radiator 

Laser pulse 

50 fsec 

� 

laser 

�mod 

� 2 

2� 

modulator 

wiggler 

E - field 

transverse velocity 

2 

k 

( 1� 

2 

mod 

Electron bunch 

30 psec 

) 

dipole 

120 mrad 

Femtosecond Slicing 

� 

X �ray 

radiator 

elliptical undulator 

(tunable) 

2 

�rad 

krad 

� ( 1� 

2 

2� 

2 

Laser pulse 


) 

aperture 

Laser: λ = 800 nm 

E = 1.5 mJ / pulse 

Δt = 50 fsec 

frep = 3 kHz 

10 -4 I tot 

Radiator beam 

Φ ≈ 3. 103 ph/pulse/0.1%bw 

S/N ≥ 10:1 

Δt = 30 fs rms 

10

„Femtoslicing“ – Technical realisation at BESSY II 

e 

laser beam 


U-139 

UE-56 

0 1 2 3 m 


dispersive 

section 


diagnostic 

station 


aperture 


femtoslicing 

X-ray beam 

e 

11

X-ray beamline 

& Experiment 

pump pulse 

0 10 m 

pump / probe experiments are important 

for dynamic studies on the fsec scale 

Femtoslicing cont. 

THz 

beamline 

Laser hutch 

UE-56 / U-139 


12

Motivation: 

Provide high photon flux up to 60 keV for 

♦ X-ray residual stress analysis of 

technical samples 

♦ X-ray magnetic scattering 

7T Multipole Wiggler 

Specific design goal: 

10 10 photons/sec at 60 keV in an aperture of 

0.5 x 0.5 mm in 30 m distance from the source 

→ necessary flux ≈ 5. 1012 photon/s/mrad/0.1% 

bw @ 300mA 

♦ NbTi technology, iron poles 

♦ Stacked race track coils, 7T 

♦ Cold magnet bore 5. 1012 600 A/mm 

344 A/mm 

40 poles 

permanent magnet 

13 poles 

NbTi technology 


/ mrad 

Nb 3 Sn 

technology 

13

7T Multipole Wiggler cont. 

Wiggler development in collaboration with 

BINP in Novosibirsk 

Technical challenge: 

Power incident on cold chamber 

SR backscattered from 1. absorber 0.25 W 

Vertical orbit errors 1mm, 1mrad 4.3 W 

Ohmic losses of mirror currents: SS 2.8 W 

Cu 0.04 W 

Available cooling power only 1 W @ 4.2 k 

→ 

Radiation shield (Cu liner) at 20K inside 

the beam chamber at 4.2K is required 

Field measurements: 

♦ Hall probe: i) field on axis 

ii) horizontal field distribution 

♦ Stretched wire: integral multipoles 


20K radiation 

shield 

(Cu liner) 

14

♦ Wiggler is strongest lin. 

perturbation in BESSY II 

edge focusing ~ ∫ B2 ds 

♦ 

♦ 

♦ 

Installation in straight 

section with low β z 

helps 

Compensation of linear 

perturbations is essential 

small β x is necessary to 

avoid emittance increase 

due to wiggler dispersion 

7T Multipole Wiggler cont. 


15

vertical tune shift 

0,07 

0,06 

0,05 

0,04 

0,03 

0,02 

0,01 

0,00 

Wiggler Implementation in BESSY II 

♦ e-beam can be injected at max. field 

but: strong lifetime degradation 

♦ Nonlinear field components are small 

♦ However: tune shift and β-beat disturb 

nonlinear tuning and reduce dynamic 

aperture, → must be compensated 

♦ Compensation method: tune the Q-pole 

pairs individually in all straight sections 

such that 

► 

- nominal tune is restored, 

- β-beat is minimized, 

- β function phase error is kept 

localized at the wiggler straight sec. 

Residual degradation of lifetime 

only ~ 15% 

HMI-Multipole-Wiggler 

tune shift 

~ B**2 

0 1 2 3 4 5 6 7 

wiggler field [T] 

87,5 

75,0 

62,5 

50,0 

37,5 

25,0 

12,5 

0,0 

betatron frequency shift [kHz] 

E:user:berger:einfahren042003:tuneshift.op 

β-funtion phase difference with 

- global correction only (red) 

- local tune compensation (black) 


16

Cryo-coolers 

high T c current 

feedthroughs 

7T Wiggler cont. 


17

Higher Order Mode Damped Cavity Development 

Figure of Merrit: Photon Beam Brilliance 

3rd Generation SR Sources: use undulators 

implemented in a low emittance lattice 

Minimize ε ~ γ2 θ3 

♦ small θ → many lattice cells 

♦ complex lattices → many magnets per cell 

► 

Low emittance / high brilliance 

is an expensive ingredient ! 

Avoid emittance / brilliance degradation 

Potential source for brilliance degradation: 

RF cavities ! 

Narrow band HOM impedances of the cavities 

excite coupled bunch oscillations if Fourier 

components of I b coincide with HOMs 

♦ Emittance increase due to transverse 

multi bunch oscillations 

♦ Large eff. energy spread ΔE/E due to 

longitudinal oscillations 


18

� 

� 

� 

� 

� 

Design Goals 

Frequency 

f rf = 500 MHz 

Insertion length 

L � 1 m 

Shunt impedance 

R > 3 M� 

Max. thermal power 

P = 100 kW 

V ≈ 800 kV 

Design to fit into 

existing ring tunnels 

BESSY HOM Damped Cavity 

Most existing SR sources use 500 MHz rf systems 

Project collaboration: - BESSY / Germany 

(EC funded) - Daresbury Lab / England 

- DELTA / Dortmund University, Germany 

- National Tsing Hua University / Taiwan 

0.5 m 

HOM waveguide 

Double ridged HOM waveguide 

f cutoff = 625 MHz 


Tuner 

vertical cut 

Coaxial rf 

coupler 

f rf < f cutoff < f HOM 

Broadband ferrite 

rf absorber 

19

3.4 MOhm 

Z 

thresh. 

|| 

1 

� 

N 

C 

� 

f 

1 

||, HOM 

HOM Impedance 

Longitudinal Impedance Transverse Impedance 

Instability threshold: instability rise time = radiation damping time 

2� 

E0 

�Q 

� 

I � � 

b 

s 

s 

thresh. 

x, 

y 

All existing SR sources in the 1- 3 GeV range can be operated 

below the thresholds of longitudinal multibunch instabilities 


Z 

1 

� 

N 

C 

� 

f 

rev 

2� 

E 

I � 

b 

0 

x, 

y 

� 

x, 

y 

20

Beam test of prototype cavity 

in the DELTA ring at Dortmund 

University in 2006 

E = 1.3 GeV 

no cavity driven multibunch 

oscillations 

observed 

HOM Damped Cavity 

Metrology Light Source 

Cavity in operation since 2007 

with P = 35kW cw 

6 cavities installed in the ALBA ring at 

CELLS/Spain in 2010 

Cavities tested up to P th = 80 kW 

Beam test will start in Nov. 2010 

At ESRF a 352 MHz cavity based on the 

same concept is under development, a 

first prototype cavity is under fabrication 


21

BERLinPro: Berlin Energy Recovery Linac Project 

ERL: Potential to combine advantages of FELs and storge rings 

BerlinPro: Feasibility study and proof of principle 

experiment to study essential problems 

100 MeV 

Beam Manipulation 

5-10 MeV 

Main Linac SRF Module Merger Section 

Spent Beam 

Beam Dump 

Undulator tests 

Return Arc 

Challenges: 

1.5 MeV 

SRF Booster 

Collaboration with 

DESY, FZK, FZR, 

Cornell Univ., J-Lab 


SRF Gun 

• Emittance compensation and preservation 

• Pulse to pulse beam stability (position, 

size, intensity, time) 

• Beam breakup, handling of strong HOMs 

• Bunch compression 

22

Superconducting CW RF Photo-Gun 

First step: 1.5 cell 1.3 GHz photo gun with Pb cathode 

Cold gun and solenoid – warm diagnostics 

SRF cavity with Pb cathode 

Next step: SRF gun with NC cathode stock and semiconductor 

cathode (CsK2Sb) to achieve high average current. 

Challenges: 

Collaboration with 

DESY, FZR, J-Lab 


23

Test Facility for SC Cavities at HZB: HoBiCaT 

CW vs Pulsed Operation of TESLA Cavities 

♦ Increase coupler power 

capability 

♦ Minimise microphonic 

effects 

♦ Improve HOM damping 

feedthroughs 

♦ Piezo tuner tests 

Collaborations with 

DESY, FZR, J-Lab 

Microphonics: ♦ Feed forward to compensate 

mechanical resonances in the 

10-300Hz range 

♦ Dominant part below 1Hz due to 

He pressure fluctuations: 

compensation by feedback 


24

♦ 

♦ 

♦ 

♦ 

3rd generation SR sources at medium energies can provide photon beams in a 

very large spectral range from several meV to 100 keV with the help of 

→ 

Summary 

low alpha operation to generate coherent THz radiation 

superconducting wigglers to generate hard X-rays 

provided the lattice offers enough flexibility 

With the femtosecond slicing technique X-ray beams can be generated for time 

resolved experiments and pump-probe experiments in the fsec range 

With the BESSY HOM damped cavity existing SR facilities can be operated below 

threshold for multibunch oscillations 

With BERLinPro a prototype energy recovery linac (ERL) is under development to 

study the feasibility of a future multi-user facility based on ERL technology 


25

Additional Material 


26

BESSY I (1978) 

First dedicated SR source in Germany for 

♦ Radiation metrology 

♦ Fundamental research 

♦ X-ray lithography 

First Tripple Bend Achromat lattice 

2 3 

min k� 

Cq� 

� 

� x � 

J x 

TBA: 

DBA: 

k� 

� 

k� 

� 

1. 34 

�3 

36 

4 

� 9. 

62* 

10 

15 

1 �2 

� 6. 

4* 

10 

15 

E = 800 MeV 

ε = 20 nm*rad 

L = 64.8 m 

λc = 2 nm 

BESSY History 

BESSY I COSY 

Ring and booster synchrotron disassembled in 2000 

→ send to Jordan for SESAME 

COSY (1985) 

Compact Synchrotron for industrial use: 

X-ray lithography for chip production 

superconducting 180 ° bending magnets 

B = 5.4 T 

E = 600 MeV (EINJ = 50MeV) 

L = 9.6 m 

λc = 1,2 nm 

Based on COSY concept two machines 

have been built by Oxford Instruments 

♦ X-ray lithography source for IBM 

♦ Singapore Light Source 


27

IRIS - Infrared Beamline at BESSY II 

hxv 60x40 mrad 2 

dipole 

Useful IR spectral range at BESSY II: 

2-10000 cm-1 

Limitations by chamber cut-off 

below 2 cm-1 

• Bruker 66/v NIR, MIR, FIR 

• Ellipsometer (ISAS) MIR 

• Martin-Pupplet FIR (THz) 

• Near-field microscope FIR (THz) 

• Nicolet Nexus 870 NIR, MIR 

• Scanning Microscope MIR 

• Vacuum Microscope FIR (THz), MIR 


28

BESSY I Lattice Functions 


29

Frequency domain: 

power spectra by 

Fourier transform 

spectroscopy 

5 10 15 20 25 30 

wave number cm -1 

BESSY II: Coherent radiation 

detector signal / a.u. 

power spectrum analysis 

power spectra 

7 

7 

10 gain 

10 gain 

BESSY II user optics, single bunch 15 mA 


Pcoherent / Pincoherent 

N e 

N e� 

form factor 

Very versatile radiation source in the THz range 

30

InSb IR detector, BW ≈ 1MHz 


f s ~ σ 

31

Preinjector Linac for BESSY II 

Increase capability for more flexible 

bunch population patterns 

→ 

for femto sec slicing, and other 

time domain experiments 

Provide high single bunch current 

→ for top-up operation 


32

♦ LHe bath cryostat, p= 180 mbar 

♦ High Tc current leads 

♦ 2 Radiation shields: 60K and 20K 

♦ 

♦ 

2 Leybold recondensers (on top) 

0.5 W at 4.2K (per system) 

45 W at 50K 

2 Leybold cryo-coolers (bottom) 



Wiggler Cryostat 


33

Beam induced LHe consumption 

I=0, B=0 : Q= 0.5 l/h (0.36 W) 

I=0, B=7T: Q= 0.71 l/h (0.51 W) 

LHe Consumption 

Large beam induced consumption @ 100mA: 

Qb = 1.1 l/h (0.8 W) 

Current dependence: Qb � I2 20K-shield temperature: T = 10 K @ I = 0. 

T = 28 K @ I = 300 mA 

Potential causes: 

Wake fields induced by 

♦ cross section steps in the liner and rf-spring 

MAFIA estimate for 1 mm step / 300mA: P = 3.6 W 

♦ pumping slits in the liner 

MAFIA estimate for 30 slit pairs P = 12 µW 

Ernst Weihreter The BESSY II 7T Multipole Wiggler Workshop on SC Technology NSRRC June 5-6 2006 

4th Nat. Congress on Particle Accelerators and Applications / Bodrum / Turkey 30.8. – 1.9. 2010 Ernst Weihreter / HZB BESSY II 34

20K 

4K 4K 

Vacuum Chamber Design 

♦ Total radiation power of 56 kW @ 1.9 GeV, 500 mA 

♦ max. power line density: 4.1 kW/m 

♦ Peak power density: 200 kW/cm2 → 

Chamber material: CuAg(0.1%) 

High thermal conductivity: 393 W/m*K 

High tensile strength: 270 N/mm 2 

Superconducting 7T-multipolewiggler 

outwards 

inwards 

longitudinal 

x 

20K 

Steerer 

1. Absorber 

Valve 

NW 160 

Chamber 1 

Quadrupole 

Ernst Weihreter The BESSY II 7T Multipole Wiggler Workshop on SC Technology NSRRC June 5-6 2006 

4th Nat. Congress on Particle Accelerators and Applications / Bodrum / Turkey 30.8. – 1.9. 2010 Ernst Weihreter / HZB BESSY II 35 

Sextupole 

Quadrupole 

Chamber 2 Dipole chamber 

barriers 

0 1110 

2063 2305 3033 3995 4425 

Sextupole 

Quadrupole 

Dipole 

5182 

2. Absorber 

5850 

h� 

e -

1/ 

I 

threshold 

� Z 

tot 

Cures for Coupled Bunch Oscillations 

� 

� Nc 

� 

� 

� 

R 

Q 

0 

� 

� 

� 

� 

HOM 

♦ 

Detuning of the dominant HOM 

- by changing cavity temperature e.g. ELETTRA 

- by a second tuner 

♦ Higher harmonic rf system for Landau damping e.g. SLS 

♦ Use broad band feedback systems e.g. ALS, BESSY II 

However: All these methods have their specific limitations ! 

► 

Q 

♦ Minimize number of cavities Nc 

♦ Minimize (R/Q0 ) HOM 

♦ Minimize Qext Damp all HOMs in the cavities in a broadband 

way by 2 - 3 orders of magnitude 

ext 

Two Concepts for Broadband HOM Damping: 

Waveguides Beam Tubes 

nc cavities sc cavities 

f rf < f cutoff < f HOM 

→ Trade off between 

• effective coupling to HOMs 

• Minimum coupling to 

fundamental mode 


36

Importance high 

low 

Conditions for Radiation Sources at User Facilities 

Eckard Rühl, longterm User at BESSY II, Flash, SLS, ESRF, ALS 

Potential for new scientific achievements in important fields 

Uniqueness 

Accessability for Users 

Reliability 

Stability 

Support 

Infrastructure 


37

f generator 

TM 011 

TM 010 

≈ 

f rf rf frequency 

h = 4 

Coupled Bunch Oscillations 

4 bunches → 4 oscillation modes 

μ = 0,1,…h-1 coupled bunch mode number 

n = 1,2,3,… m = 1,2,3… 

transverse beam spectrum 

f rf � 

� 

� � nf � ( �f0 f� 

μ = 0 3 1 2 2 1 3 0 

f rf 

f � nf � � 

� 

�m 

( �f0 

mfs 


f 0 

effective emittance increase 

longitudinal beam spectrum 

rf 

effective increase in energy spread 

) 

f β 

) 

2f rf 

38

Dipole modes: 

2 polarisations 


39


40


41


42


43

Synchrotron Radiation Source R&D at BESSY II in Berlin

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