Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Status of the ANKA Short Bunch Operation Anke-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 page 2
Outline Operation with short bunches ➜ Beam energies ➜ SCU14 Beam studies ➜ Systematics of bunch length measurements with a Michelson interferometer Radiation characteristics ➜ Polarisation ➜ Development of bursts Summary & Perspectives UVSOR, 24/9/2007 Short Bunches at ANKA page 3
Research Centre Karlsruhe Research & development in various fields: environmental analysis medicine/bio technology material science microsystem technology (astro) particle physics IT science nano technology ... UVSOR, 24/9/2007 Short Bunches at ANKA page 4
The ANKA Storage Ring ✔ C = 110.4 m ✔ 0.5 ≤ E 0 ≤ 2.5 GeV ✔ ε x = 40 nm · rad ✔ DBA lattice UVSOR, 24/9/2007 Short Bunches at ANKA page 5
Low- α c 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 ➜ longitudinal instability due to one higher order cavity mode for E 0 < 1 GeV Low- α mode also operational at 1 GeV and 1.6 GeV on demand. In May 2007 a Helmholtz University Young Investigators Group dedica- ted to the study of the short bunch dynamics in storage rings has been founded. . Pérez et al., PAC03 F UVSOR, 24/9/2007 Short Bunches at ANKA – Operation page 6
SCU14 and Short Bunches Short bunch operation for X-ray users at E 0 = 1.3 GeV ➜ boost the photon energy with the SCU14 ➜ potential for time resolved experiments ( ∼ 10 6 integral photons/pulse) A. Bernhard et al., “Performance of the First Superconducting Cold-Bore Undulator in an Electron Storage Ring, PRSTAB 2006 UVSOR, 24/9/2007 Short Bunches at ANKA – Operation page 7
Bunch Length and Beam Energy f s / kHz The synchrotron tune is given by V RF = 1.2 MV 60 V RF = 0.6 MV � α c h � � Global Fit e 2 V 2 Q 2 RF − U 2 s = 0 2πE A global fit yields an effective α c : 40 α c = ( 6.6 ± 0.1 ) · 10 − 3 RDP at 2.5 GeV: ( 7.39 ± 0.01 ) · 10 − 3 σ s / mm α c scan at 0.8 GeV 20 α c scan at 1.0 GeV 1000 2000 15 α c scan at 1.3 GeV E beam / MeV α c scan at 1.6 GeV α c scan at 1.8 GeV The bunch length scales ∝ ( E 0 ) 3/2 from fit with V RF =0.6 MV 10 from fit with V RF =1.2 MV Calculate σ s from f s with global α c 5 “Low- α c squeeze” achieved for dif- ferent beam energies 0 1000 2000 E beam / MeV UVSOR, 24/9/2007 Short Bunches at ANKA – Operation page 8
FIR-Spectrum & Beam Energy FIR spectrum for different beam energies (measured with a Michelson interferometer) Observations Amplitude [a.u.] E 0 = 0.802 GeV, 0.21 mA 80 ➜ shift towards lower E 0 = 0.998 GeV, 0.47 mA frequencies (longer 70 E 0 = 1.300 GeV, 0.43 mA bunches) with E 0 = 1.613 GeV, 0.27 mA 60 increasing E 0 50 ➜ suppression of low frequency content for 40 shorter bunches 30 ➾ non-linearities of 20 the detector? 10 Observation of stable CSER also at 1.0 and 0 0 0.5 1 1.5 Frequency [THz] 1.6 GeV. UVSOR, 24/9/2007 Short Bunches at ANKA – Operation page 9
Bunch Length from Interferograms 1 Simplified view: wave train of frequency ω 0.75 0.5 emitted by charge distribution of RMS length σ : 0.25 t2 “ ” 1 − σ2 + iωt 0 A ( t ) = e 2 -0.25 -0.5 The pulse overlayed with itself shifted by a time -0.75 ∆ due to the Michelson interferometer is -1 -5 -4 -3 -2 -1 0 1 2 3 4 5 „ « ( t + ∆ ) 2 t2 1 “ ” − + iω ( t + ∆ ) 1 − σ2 + iωt σ2 2 A ( t, ∆ ) = e + e 2 The time integrated intensity observed by the detector is therefore � � ∆2 cos ( ω∆ ) e − | A ( ∆ ) | 2 dt ∝ ˜ I ( ∆ ) = I ( ∆ ) dt = 4σ2 Assumption: Since the shortest wave length emitted coherently is equal to full bunch length λ min = 2σ w , the max. frequency is ω max = 2πc/λ min = πc/σ w . It follows that � π ∆2 ∆2 � cos ( ω max ∆ ) e − 4σ2 = e − ˜ I ( ∆ ) ∝ σ∆ cos 4σ2 ➜ Exponential doesn’t change peak width: FWHM yields σ UVSOR, 24/9/2007 Short Bunches at ANKA – Bunch Length Systematics page 10
Background Subtraction The coherent signal in the interferogram is superimposed by the incoherent and the thermal contributions ➜ The width of the central peak (i.e. the cos term) must be determined only after background subtraction ➜ FWHM is very sensitive to noise ➾ determine zero-crossings Amplitude / A.U. raw data E 0 = 1.3 GeV background signal 0.2 0 10 11 12 13 14 15 16 17 18 19 20 Mirror Sweep Time / ps UVSOR, 24/9/2007 Short Bunches at ANKA – Bunch Length Systematics page 11
Interferograms and Energy 0.25 0.2 Amplitude / A.U. Amplitude / A.U. f s = 12.4 kHz E 0 = 0.998 GeV f s = 9.30 kHz E 0 = 1.3 GeV 0.2 f s = 11.7 kHz 0.15 f s = 8.00 kHz 0.15 f s = 10.2 kHz f s = 6.25 kHz 0.1 f s = 7.2 kHz f s = 3.60 kHz 0.1 0.05 0.05 0 0 -0.05 -0.05 -0.1 -0.1 -0.15 -0.2 -0.15 10 11 12 13 14 15 16 17 18 19 20 10 11 12 13 14 15 16 17 18 19 20 Mirror Sweep Time / ps Mirror Sweep Time / ps 0.2 Amplitude / A.U. f s = 9.60 kHz E 0 = 1.6 GeV Background subtracted data for f s = 8.60 kHz 0.15 f s = 7.60 kHz different beam energies and 0.1 f s = 6.40 kHz “squeeze states”: 0.05 ➜ the higher the energy, the 0 lower the noise -0.05 ➜ cavity mode? -0.1 -0.15 10 11 12 13 14 15 16 17 18 19 20 Mirror Sweep Time / ps UVSOR, 24/9/2007 Short Bunches at ANKA – Bunch Length Systematics page 12
Beam Splitter Comparison 1 Amplitude / A.U. Amplitude / A.U. Hg lamp Bolo 4.2K, 2, 6 µ m Si/Myl Hg lamp Bolo 4.2K, 2, 6 µ m Si/Myl 12 Bolo 4.2K, 2, 50 µ m Myl Bolo 4.2K, 2, 50 µ m Myl 0.8 Bolo 4.2K, 2, 125 µ m Myl Bolo 4.2K, 2, 125 µ m Myl 10 0.6 8 0.4 6 0.2 4 0 2 -0.2 0 0 10 20 30 40 50 60 10 11 12 13 14 15 16 17 18 19 20 Wave Number / cm -1 Mirror Sweep Time / ps 1 Amplitude / A.U. Amplitude / A.U. E 0 = 1.3 GeV Bolo 4.2K, 2, 6 µ m Si/Myl E 0 = 1.3 GeV Bolo 4.2K, 2, 6 µ m Si/Myl 70 Bolo 4.2K, 2, 50 µ m Myl Bolo 4.2K, 2, 50 µ m Myl 0.8 60 Bolo 4.2K, 2, 125 µ m Myl Bolo 4.2K, 2, 125 µ m Myl 0.6 50 0.4 40 0.2 30 20 0 10 -0.2 0 0 10 20 30 40 50 60 10 11 12 13 14 15 16 17 18 19 20 Wave Number / cm -1 Mirror Sweep Time / ps UVSOR, 24/9/2007 Short Bunches at ANKA – Bunch Length Systematics page 13
Bunch Length and Current I Conclusion from beam splitter comparison: thin splitters are more sensitive in the critical region of the spectrum ➜ 6 µ m Si/Mylar splitter expected to be more sensitive to small bunch length changes (e.g. due to beam current change) than 125 µ m Mylar splitter σ s / ps E 0 = 1.3 GeV Bolo 4.2K, 2, 6 µ m Si/Myl 1.5 Bolo 4.2K, 2, 125 µ m Myl 1 0.5 0 5 10 I beam / mA < σ s > = ( 0.538 ± 0.008 ) ps UVSOR, 24/9/2007 Short Bunches at ANKA – Bunch Length Systematics page 14
Bunch Length and Current II Observation of coherent emission for √ 2 π σ s , real ln N � λ observed or σ s , real � σ s , observed √ π ln N Correct the σ derived from interferogram accordingly ➜ if the beam splitter is sensitive, the N dependence must vanish σ corr / ps E 0 = 1.3 GeV Bolo 4.2K, 2, 6 µ m Si/Myl 2 Bolo 4.2K, 2, 125 µ m Myl 1.5 insensitive 1 sensitive 0 5 10 15 20 I beam / mA < σ s > = ( 0.787 ± 0.008 ) ps UVSOR, 24/9/2007 Short Bunches at ANKA – Bunch Length Systematics page 15
Bunch Length from Spectrum (P coh / P Hg ) / a.u. E 0 = 1.3 GeV Determination of σ from 10 4 normalised spectrum Ideally normalisation by 10 3 incoherent spectrum 10 2 ➜ Problem: low intensity ➜ Alternative: Normalise by f s = 6.25 kHz 10 spectrum of Hg lamp Gaussian with σ k =10cm -1 1 10 Wave Number / cm -1 The bunch length is related to the spectral bandwidth σ k by (G. Wüstefeld, SBSR05): 1 σ s = √ 2 π 2 σ k The bunch length determined thus is 0.375 ps. UVSOR, 24/9/2007 Short Bunches at ANKA – Bunch Length Systematics page 16
Polarisation 80 2 Amplitude [a.u.] Polarizer at 0 o Amplitude [a.u.] Polarizer at 30 o 70 Polarizer at 60 o Polarizer at 90 o 60 1.5 50 40 1 30 20 0.5 10 0 0 0 0.2 0.4 0.6 0.8 1 1.2 0 30 60 90 120 150 180 Frequency [THz] Polarizer Orientation in Deg 1 (P max −P min ) / (P max +P min ) Edge radiation in mid-IR shows radial 0.95 polarisation 0.9 For very low frequencies only a slice of 0.85 the radiation in the orbit plane is visible 0.8 E 0 = 1.3 GeV ➜ measure mostly linear polarisation f s = 6.0 kHz 0.75 ✔ 0 0.2 0.4 0.6 0.8 1 1.2 Frequency [THz] UVSOR, 24/9/2007 Short Bunches at ANKA – Radiation Characteristics page 17
Bursting Emission amplitude / mV 0.05 0 -0.05 -0.1 -0.15 -0.2 -0.25 -0.3 -0.04 -0.02 0 0.02 0.04 time / s Investigate the frequency content time slice by time slice UVSOR, 24/9/2007 Short Bunches at ANKA – Radiation Characteristics page 18
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