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The BESSY (and MLS) Low Alpha Optics and the Generation of Coherent Synchrotron Radiation J. Feikes, K. Holldack, H.-W. Hbers*, P. Kuske, G. Wstefeld BESSY and * DLR, BERLIN see contribution in ICFA Beam Dynamics Newsletter No. 35, December

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SLIDE 1

The BESSY (and MLS) Low Alpha Optics and the Generation of Coherent Synchrotron Radiation

  • J. Feikes, K. Holldack, H.-W. Hübers*, P. Kuske, G. Wüstefeld

BESSY and * DLR, BERLIN

see contribution in ICFA Beam Dynamics Newsletter No. 35, December 2004

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007
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SLIDE 2

abstract & content

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007

Content

  • 1. Low alpha optics
  • 2. Coherent radiation
  • 3. Bunch-length current relation
  • 4. Limits of short bunches
  • 5. Upgrading idea: short bunches at BESSY II

Abstract The BESSY II optics is tuned to a low alpha mode for bunch length shortening. About 1mm short bunches emit coherent synchrotron radiation in the THz range. Details of the machine optics and measured THz signals are discussed. Plans for the presently commissioned MLS ring * for short bunch generation are presented.

* thanks to the PTB and BESSY commissioning team

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SLIDE 3

BESSY II and MLS storage rings Berlin-Adlershof (south east of Berlin) Europe's most modern Technology Park BESSY II foot print

76 m Scientific employes: 6500 (+ 6500 students) New media: 1500 employes

  • thers: 4300 empoyes

MLS

new : Metrology light source MLS

The BESSY II ring: energy 1.7 GeV circumference 240 m number of cells 16 / DBA rf frequency 500 MHz the MLS ring: energy 0.2 – 0.6 GeV circumference 48 m number of cells 4/ DBA rf frequency 500 MHz

16 m

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007
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SLIDE 4

the machine optics

  • ptics parameter

reg.user

  • ptics

low alpha

  • ptics

tunes Qx / Qy 17.8 / 6.7 14.7 / 6.2

  • nat. chrom ξx

/ ξy

  • 53 / -27
  • 35 / -27

tune parameters

  • very stable machine operation,

good life time 20 mA and 20 hours

the BESSY Low Alpha Optics

  • single & multi bunch 1.25 MHz to 500 MHz rep. rate

current per bunch 10 μA < I< 0.1 mA

  • 4 sextuple families for beam dynamics corrections

S D Q Q D S

Low alpha optics for bunch length manipulation

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007
slide-5
SLIDE 5

α=-3·10

  • 6

fs=350Hz

synchrotron frequency and alpha synchrotron frequency fs as a function of rf frequency

  • fs

increases strongly with deviating rf frequency

  • optics tuned by sextupoles (long. chromaticity)

extracted momentum compaction factor α

  • fit to measured data

2 2 1

δ α δ α α α + + = 03 . , , 10 3

2 1 6

− = = ⋅ − =

−

α α α

δrms

longitudinal chromaticity

=0.1%

condition for stable beam operation: α ≠

See also: Control of the bunch length on an electron storage ring

  • H. Hama, S. Takano and G. Isoyama, NIM A329 (1993)
  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007
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SLIDE 6

low alpha tuning for the MLS

Metrology Light Source (MLS) of the Physikalisch-Technische Bundesanstalt (PTB), next to the BESSY II site, expected values: scheme of MLS ring

dipole quadrupole sextupole

  • ctupole

circumference / m 48 energy / MeV 200 - 600 momentum deviation / % 2 chromatic sextupoles 3 chromatic sextupoles (slope of α)

  • non. lin. low alpha tuning

User optics α=0.02 , bunch length σ= 4.5 mm at 600 MeV THz optics α=0.001, bunch length σ= 1.0 mm at 600 MeV applied rf: 500 kV, 500 MHz low alpha tuning (simulation) for the presently commissioned MLS ring

100 MeV microtron 3 sextupole, one octupole (curvature of α)

see also R. Müller et al., Infrared Phys. Technol. 49 (2006) 161

α-value / 0.01

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007
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SLIDE 7

temporal resolved THz pulse of pulse length of few 100 ps: multiple reflections in THz beam line

H.-W. Hübers et al. Applied Phys. Lett. 87,184103 (2005)

InSb-bolometer

resolution of single turns, detector τ=1μs

1 turn 1 turn bursting CSR stable CSR CSR intensity CSR intensity time

THz detectors at BESSY

Typical values Si-Bol. InSb HEB NEP (W/Hz1/2) ~10-13 ~10-12 ~10-10 Rise time τ (ns) ~106 ~1000 ~0.03 Frequency (THz) 0.1 - 15 0.1 -1.5 0.3 - 6

Detector parameters H.-W. Hübers et al., ICFA Newsletter No. 35

hot-electron bolometer HEB

resolution of single bunches, detector τ=30ps

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007

CSR signals & fast THz detectors

first strong CSR signals

  • T. Nakazato et al.,Phys. Rev. Lett. 63, 1245 (1989)

bunch revolution 800 ns

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SLIDE 8

spectral range of BESSY CSR

power spectrum analysis by Fourier transform spectrometer brilliance of the BESSY THz spectrum in cooperation with Dr. U. Schade, BESSY 10 gain

7

10 gain

7

1 10 100 1000 10000

10

  • 14

10

  • 9

10

  • 4

10

1

low alpha stable CSR, 18 mA user optics burstig CSR, SB 15 mA 0.1THz 1THz

black body, 1200 K, 10 mm^2 incoherent radiation 250 mA, user optics

BRILLIANCE [W/mm

2/sr/(0.1% bdw)]

WAVENUMBER [cm

  • 1]

raw data power spectrum interferogram source comparison user optics, single bunch 15 mA

from Fourier spectra to power spectra BESSY offers 4 low alpha shifts of 3 days / year application: coherent THz radiation, ICFA No. 35, article by U. Schade et al. short x-ray pulses at BESSY, PRL 95, A. Krasyuk et al., 2005

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007
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SLIDE 9

single bunch current / mA bursting frequency / kHz at spectrumsanalyzer temporal emission spectrum

  • f CSR bursts (user optics)

single bunch current in mA

  • rel. THz power signal

parabolic fit measured CSR signal

CSR from deformed, but stable bunch, fs=7.2 kHz

1.6 1.7 1.8

start of bursting

transition from stable to bursting CSR, user optics

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007

single bunch CSR-intensity I

back ground level

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SLIDE 10

bunch current / mA bunch current / mA bunch current / mA bunch current / mA frequency / MHz frequency / MHz

Current and temporal emission dependencies

  • f CSR radiation at

different settings of the low alpha parameter fs

fs=7.2 kHz fs=5 kHz fs=3 kHz fs=2.1 kHz

single bunch CSR-intensity II

spectrums analyzer records, centered around 1.25 MHz rev. frequency

1.20 MHz 1.25 MHz 1.30 MHz

frequency / MHz

1.20 MHz 1.25 MHz 1.30 MHz

frequency / MHz

1.20 MHz 1.25 MHz 1.30 MHz 1.20 MHz 1.25 MHz 1.30 MHz

frequency / MHz

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007
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SLIDE 11

THz optics 3 ps user optics 13 ps sub-ps

  • ptics

700 fs

bursting instability Stupakov & Heifets

streak camera data THz data bursting data

2 / 3 4 4

) / ( ) / ( ) / ( I I f f + = σ σ empirical scaling relation between bunch length σ, synchrotron frequency f and current I: bunch length - current relation

bunch length and current relation

bursting data

σ~I

0.384

σ~I

3/7

σ~I

3/8

single bunch current / mA bunch length / ps

results at bursting threshold:

  • eff. / naturale

bunch length σ/σ = 1.5

  • eff. bunch length ·

unstable mode σk =2πσ/λ =5

  • bunch length ~ current relation σ~I ª

a=3/8 from experiments, a=3/7 from theory

i i

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007
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SLIDE 12

0.45 MV 45.0 MV rf-voltage: Emax=600 MeV circumference = 48 m longitudinale bunch length is chromatic H dependent.

x-x’ x-x’ z-z’ z-z’

H=1.2 rad·m H=0.035 rad·m

bunch length / mm bunch length / mm

limits of short bunches I

σ= 1.0 mm σ= 0.1 mm σ= 1.0 mm σ= 0.5 mm

t

MAD tracking simulation, 8·10 turns = 10 damping times & quantum excitation

5

scheme of MLS ring longitudinal-horizontal couplings effect in the MLS ring ultra short bunches are only possible at small H locations

see also : Y. Shoji in

  • Phys. Rev. ST Accel. Beams 8 094001 (2005)
  • Phys. Rev. ST Accel. Beams 7 090703 (2004)
  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007
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SLIDE 13

BESSY II, user optics: MAD-simulation of electron diffusion due to radiation damping

↓

↓

longitudinal delay / ps

r e l a t i v e m

  • m

e n t u m d e v i a t i

  • n

‰

bunch rotation 90 degree

↓

longitudinal delay / ps

n u m b e r

  • f

e l e c t r

  • n

s / a . u .

bunch rotation 180° quantum excitation

↓

2 3 4 5 6 7 8 9 1 1.6 3.3 5.0

  • 5
  • 3.3
  • 1.6

σ-rms=0.4 mm=1.2 ps

conclusion: radiation damping limits the multiple usage of

  • ‘laser sliced’ electrons for short x-rays
  • ‘laser sliced’

dip as a THz-source

limits of short bunches II

180° in phase long. space 80 turns around machine initial value: no spread in phase space, only natural spread in momentum distribution

  • long. bunch length

spread of σ=0.4 mm

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007
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SLIDE 14

upgrading of the rf-gradient idea of enhanced THz radiation and short X-ray pulses at BESSY II

rf-upgrading: 1.5 GHz & 50 MV sub-ps bunches!

single bunch current / mA rms-bunch length / ps user optics user optics THz optics THz optics 0.5 GHz & 1.5 MV 1.5 GHz & 50 MV bursting threshold bursting threshold

present rf upgraded rf

13 ps 3 ps 1.3 ps 0.3 ps

applying the scaling law for bursting threshold:

dz dV I

rf z

/

3 / 8

σ ∝

for upgrading the rf-gradient by a 1.5 GHz, cw superconducting rf-structure placed into one straight ID-section

  • G. Wüstefeld et al., BESSY Low

Alpha & CSR, UVSOR, Japan, 2007

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SLIDE 15

conclusion Conclusion: the low alpha optics is a scheme to extends the photon spectrum of storage rings to intense THz and short X-ray pulses coherent THz radiation as a diagnostics tool delivers sensitive and new information on beam dynamics

  • G. Wüstefeld et al., BESSY Low Alpha & CSR, UVSOR, Japan, 2007