Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft

Status of theANKA Short Bunch OperationAnke-Susanne Müller
Institut für Synchrotronstrahlung (ISS), Forschungszentrum Karlsruhe
Laboratorium für Applikationen der Synchrotronstrahlung (LAS), Uni Karlsruhe

UVSOR, 24/9/2007

Short Bunches at ANKA

page 1

Das “ANKA-THz-Team”
The Team:
I. Birkel, T. Bückle❖ , S. Casalbuoni, M. Fitterer,
B. Gasharova, E. Huttel, Y.-L. Mathis, D.A. Moss,
A.-S. Müller, M. Süpfle, P. Wesolowski

Institut für Synchrotronstrahlung, Forschungszentrum Karlsruhe❖

Lab. f. Appl. d. Synchrotronstrahlung, Universität Karlsruhe (TH)UVSOR, 24/9/2007

Short Bunches at ANKA

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Outline
Operation with short bunchesÜ Beam energies
Ü SCU14Beam studies
Ü Systematics of bunch length measurements with aMichelson interferometer
Radiation characteristics
Ü Polarisation
Ü Development of bursts
Summary & Perspectives
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Short Bunches at ANKA

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Research Centre Karlsruhe
Research & development in various fields:
environmental analysis
medicine/bio technology
material science
microsystem technology(astro) particle physics
IT sciencenano technology...

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Short Bunches at ANKA

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The ANKA Storage Ring
4 C = 110.4 m
4 0.5 ≤ E0 ≤ 2.5 GeV
4 εx = 40 nm·rad
4 DBA lattice

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Short Bunches at ANKA

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Low-αc Operation
Per year 12 days are dedicated short bunch operation for users as“special user operation”.
Typical beam energy in this mode is 1.3 GeV
Ü longitudinal instability due to one higher order cavity mode forE0 < 1 GeV
Low-α mode also operational at 1 GeV and 1.6 GeV on demand.

F. Pérez et al., PAC03

In May 2007 a Helmholtz University Young Investigators Group dedicated to the study of the short bunch dynamics in storage rings has beenfounded.

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Short Bunches at ANKA – Operation

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SCU14 and Short Bunches
Short bunch operation for X-ray users at E0 = 1.3 GeV
Ü boost the photon energy with the SCU14
Ü potential for time resolved experiments (∼ 106 integral photons/pulse)

A. Bernhard et al., “Performance of the First Superconducting Cold-BoreUndulator in an Electron Storage Ring, PRSTAB 2006UVSOR, 24/9/2007

Short Bunches at ANKA – Operation

page 7fs / kHz

Bunch Length and Beam Energy
The synchrotron tune is given byq
αc h2 − U2Q2s =e2 VRF
02πE
A global fit yields an effective αc :αc = (6.6 ± 0.1) · 10−3
RDP at 2.5 GeV: (7.39 ± 0.01) · 10−3

VRF = 1.2 MV

60

VRF = 0.6 MV
Global Fit

2010002000

Ebeam / MeV

The bunch length scales ∝ (E0 )3/2σs / mm401510Calculate σs from fs with global αc“Low-αc squeeze” achieved for different beam energies

αc scan at 0.8 GeV
αc scan at 1.0 GeV
αc scan at 1.3 GeV
αc scan at 1.6 GeV
αc scan at 1.8 GeVfrom fit with VRF=0.6 MV
from fit with VRF=1.2 MV

50UVSOR, 24/9/2007

Short Bunches at ANKA – Operation

1000

2000

Ebeam / MeV
page 8

FIR-Spectrum & Beam Energy

Amplitude [a.u.]

FIR spectrum for different beam energies (measured with a Michelsoninterferometer)
Observations

E0 = 0.802 GeV, 0.21 mA80

Ü shift towards lower
frequencies (longerbunches) withincreasing E0E0 = 0.998 GeV, 0.47 mA

70

E0 = 1.300 GeV, 0.43 mA
E = 1.613 GeV, 0.27 mA

60050

Ü suppression of low
frequency content for
shorter bunchesþ non-linearities ofthe detector?

4030
20
1000UVSOR, 24/9/2007

0.5

11.5Frequency [THz]

Short Bunches at ANKA – Operation

Observation of stable
CSER also at 1.0 and
1.6 GeV.
page 9Bunch Length from Interferograms
1

Simplified view: wave train of frequency ωemitted by charge distribution of RMS length σ:−“1 t22 σ2 +iωt−

1 t22 σ2 +iωt”−120.50.25”

A(t) = eThe pulse overlayed with itself shifted by a time
∆ due to the Michelson interferometeris„“0.75(t+∆)2σ2+iω(t+∆)

0-0.25-0.5-0.75-1-5-4-3-2-1

0

12

345

«

A(t, ∆) = e+e
The time integrated intensity observed by the detector is thereforeZZ2− ∆22Ĩ(∆) = I(∆)dt = |A(∆)| dt ∝ cos (ω∆) e 4σ
Assumption: Since the shortest wave length emitted coherently is equalto full bunch length λmin = 2σw , the max. frequency isωmax = 2πc/λmin = πc/σw . It follows thatπ 22− ∆2− ∆2Ĩ(∆) ∝ cos (ωmax ∆) e 4σ = cos∆ e 4σσÜ Exponential doesn’t change peak width: FWHM yields σ

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Short Bunches at ANKA – Bunch Length Systematics

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Background Subtraction
The coherent signal in the interferogram is superimposed by theincoherent and the thermal contributions
Ü The width of the central peak (i.e. the cos term) must be
determined only after background subtraction

Amplitude / A.U.

Ü FWHM is very sensitive to noise þ determine zero-crossings
raw data

E0 = 1.3 GeV

backgroundsignal

0.2

010UVSOR, 24/9/2007

1112131415

1617181920

Mirror Sweep Time / ps

Short Bunches at ANKA – Bunch Length Systematics

page 110.25

fs = 12.4 kHz

0.2

E0 = 0.998 GeV

Amplitude / A.U.

Amplitude / A.U.

Interferograms and Energy
fs = 11.7 kHz

0.15

fs = 10.2 kHz

0.1

fs = 7.2 kHz

0.05
0fs = 9.30 kHz

E0 = 1.3 GeV

fs = 8.00 kHz

0.15

fs = 6.25 kHz

0.1

fs = 3.60 kHz

0.05
0-0.05

-0.05

-0.1

-0.1

-0.15
101112

13

1415

16

171819Mirror Sweep Time / ps

Background subtracted data fordifferent beam energies and“squeeze states”:
Ü the higher the energy, thelower the noiseÜ cavity mode?

-0.15

20

Amplitude / A.U.

-0.2

0.2

0.2

1112

13

14

15

16

17

18

1920

Mirror Sweep Time / ps

fs = 9.60 kHz

E0 = 1.6 GeV

fs = 8.60 kHz

0.15

fs = 7.60 kHz

0.1

fs = 6.40 kHz

0.05
0-0.05-0.1-0.15UVSOR, 24/9/2007

1010111213

Short Bunches at ANKA – Bunch Length Systematics

14151617181920

Mirror Sweep Time / pspage 12

Bolo 4.2K, 2, 6 µm Si/Myl

Hg lamp

12Amplitude / A.U.

Amplitude / A.U.

Beam Splitter Comparison
Bolo 4.2K, 2, 50 µm Myl
Bolo 4.2K, 2, 125 µm Myl

1086

Bolo 4.2K, 2, 125 µm Myl

0.60.4-0.2
01020305060

Wave Number / cm

Bolo 4.2K, 2, 50 µm Myl

6010-1

Bolo 4.2K, 2, 6 µm Si/Myl

E0 = 1.3 GeV7040Amplitude / A.U.

Amplitude / A.U.

Bolo 4.2K, 2, 50 µm Myl

0.802

Bolo 4.2K, 2, 125 µm Myl

5040110-0.2

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30405060-1

Wave Number / cm

14151617181920Mirror Sweep Time / ps

Bolo 4.2K, 2, 6 µm Si/Myl

E0 = 1.3 GeVBolo 4.2K, 2, 50 µm Myl

0.4020130.6

201012

Bolo 4.2K, 2, 125 µm Myl

0.20110.8

300

Bolo 4.2K, 2, 6 µm Si/MylHg lamp

0.24011011121314

Short Bunches at ANKA – Bunch Length Systematics

151617181920

Mirror Sweep Time / pspage 13

Bunch Length and Current I
Conclusion from beam splitter comparison: thin splitters are moresensitive in the critical region of the spectrum

σs / psÜ 6 µm Si/Mylar splitter expected to be more sensitive to small bunch
length changes (e.g. due to beam current change) than 125 µm
Mylar splitter
Bolo 4.2K, 2, 6 µm Si/Myl

E0 = 1.3 GeV

1.5

Bolo 4.2K, 2, 125 µm Myl

10.505< σs >= (0.538 ± 0.008) psUVSOR, 24/9/2007

10Ibeam / mA

Short Bunches at ANKA – Bunch Length Systematics

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Bunch Length and Current II
Observation of coherent emission for2 π σs,real√. λobservedorln Nσs,real .

√ln N

πσs,observed

σcorr / psCorrect the σ derived from interferogram accordingly
Ü if the beam splitter is sensitive, the N dependence must vanish
E0 = 1.3 GeV

2Bolo 4.2K, 2, 6 µm Si/Myl
Bolo 4.2K, 2, 125 µm Myl

1.5

insensitive
1sensitive0510< σs >= (0.787 ± 0.008) ps
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1520Ibeam / mA

Short Bunches at ANKA – Bunch Length Systematics

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Determination of σ fromnormalised spectrum
Ideally normalisation byincoherent spectrum(Pcoh / PHg) / a.u.

Bunch Length from Spectrum
E0 = 1.3 GeV

10 410 3

Ü Problem: low intensity

10 2

Ü Alternative: Normalise byspectrum of Hg lamp10

fs = 6.25 kHz
Gaussian with σk=10cm-1

1
10Wave Number / cm-1

The bunch length is related to the spectral bandwidth σkby (G. Wüstefeld, SBSR05):1√σs =2 π 2 σkThe bunch length determined thus is 0.375 ps.
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80Polarizer at 0oPolarizer at 30oo
Polarizer at 60
Polarizer at 90o

70
60
50

2

Amplitude [a.u.]

Amplitude [a.u.]

Polarisation

1.5

14030
200.5

10(Pmax−Pmin) / (Pmax+Pmin)

00

0.2

0.4

0.6

0.8

11.2

Frequency [THz]

0030

60

90120

150

180

Polarizer Orientation in Deg

1Edge radiation in mid-IR shows radialpolarisation

0.95

0.9For very low frequencies only a slice ofthe radiation in the orbit plane is visible

0.85

0.8

E = 1.3 GeV0f = 6.0 kHzÜ measure mostly linear polarisation

s0.75
0UVSOR, 24/9/2007

0.2

0.4

0.6

0.8

11.2

Frequency [THz]

Short Bunches at ANKA – Radiation Characteristics

4
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amplitude / mV

Bursting Emission
0.05
0-0.05
-0.1
-0.15
-0.2
-0.25
-0.3
-0.04

-0.02

00.02

0.04

time / sInvestigate the frequency content time slice by time slice
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Zooming into a BurstÜ signal around a burst is cut
in slices that are analysed
separately

Ibunch = 0.47 mA
10.8
LNP

Study of the change of thebolometer signal frequency
contents during the build-up of aburst

0.6
0.4
0.2

00.05
6000

03.5

Time (sec)

34000
−0.05

2000
0Frequency (Hz)

LNP

2.5
2

High current: double peak structurearound fs (σs oscillations?)

1.5
10.5

00.05
6000
04000
2000

Time (sec)

Ibunch = 0.16 mA
UVSOR, 24/9/2007−0.050Low current: fs structure gone andmax. of burst more pronounced

Frequency (Hz)Short Bunches at ANKA – Radiation Characteristics

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Perspectives
Accelerator :Ü A dual sweep streak camera will be added to the ANKA
diagnostics for direct bunch length measurements
Ü A single bunch gun will replace the present diode gun
for systematic studies of single bunch / multi-bunch
differencesÜ HEB to resolve revolution
Experiments:
Ü Time resolved measurements making use of the short
X-ray pulses generated in the SCU14UVSOR, 24/9/2007

Short Bunches at ANKA – Radiation Characteristics

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SummaryRegular low-αc mode for special user operation at 1.3 GeV
Potential for X-ray experiments using the SCU 14
Beam studies:Ü Extensive and ongoing study of bunch length
measurements systematics
Ü Investigation of radiation properties
Ü Further instrumentation will allow a closer look

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(Pcoh / Pincoh)

Bunch Length from Spectrum
E0 = 1.3 GeV

10 410 310 210

fs = 6.25 kHz-1Gaussian with σk=10cm110UVSOR, 24/9/2007-1

Wave Number / cm

Short Bunches at ANKA – Radiation Characteristics

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