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List of Abstracts
John Byrd - LBNL
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
Laser slicing for Terahertz Pulse Shaping
We present a new method to generate steady and tunable, coherent, broadband THz radiation from a relativistic electron beam modulated by a femtosecond laser (laser slicing) at a 1.5 GeV electron storage ring in the Advanced Light Source (ALS). Interaction of an electron beam with a femtosecond laser pulse co-propagating through a wiggler modulates the electron energies within a short slice of the electron bunch comparable with the duration of the laser pulse. The resulting hole in the electron distribution emits short pulses of temporally and spatially coherent THz pulses which are inherently synchronized to the femtosecond laser. Propagating around an electron storage ring, this bunch develops a longitudinal density perturbation due to the dispersion of electron trajectories, and therefore shifts the spectra of the radiation at different beamlines due to path length dispersion. We present measurements of the intensity and spectra of these pulses at different tunable conditions. Because the laser/beam interaction is not limited by any material properties, this technique allows the THz pulse to be arbitrarily shaped by appropriate modulation of the laser pulse.
John Byrd - LBNL
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
Seeding of the CSR microbunching instability
The CSR microbunching instability is a microwave instability driven by the radiation impedance of the dipole bends in a storage ring. It has been observed and characterized and several facilities. We describe observations of this instability during laser slicing which indicate that this instability can be triggered by slicing. We summarize our observations of this effect and our present understanding of it.
Caterina Biscari - INFN-LNF
Working Group: Lattice, Dynamic aperture, Lifetime, Beam-beam effects
Bunch length modulation in storage rings*
Bunch length modulation in an electron storage ring appears with the combination of a high rf voltage derivative and large dispersion in the dipoles, producing drifting of the longitudinal phase plane along the closed orbit. The modulation can be obtained in two different regimes: the one corresponding to high momentum compaction structures, in which the drifting in all dipoles has always the same direction, and the other one corresponding to low momentum compaction in which the drifting changes sign along the ring. The bunch length modulation is always connected to increase of longitudinal emittance and energy spread
Godehard Wüstefeld - BESSY
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
The Generation of Short Electron Bunches and Coherent Synchrotron Radiation in the BESSY Storage Ring
We report on the BESSY Low Alpha Optics for bunch length manipulation. Electron bunches of ps and sub-ps length are achieved and analysed with streak camera and Fourier transform spectroscopie. The scaling between bunch length/ current relation is discussed.
Michael Borland - Argonne National Laboratory
Working Group: Lattice, Dynamic aperture, Lifetime, Beam-beam effects
Single-Particle Beam Dynamics for X-ray Compression using Crab Cavities
We present results of simulations Zholents's concept for using crab cavities in a storage ring for the purpose of producing short x-ray pulses. In particular, we look at the optimization and performance of such a system for the Advanced Photon Source. We find the concept is practical and that x-ray pulse durations of about 1.5 ps FWHM should be achievable with more than 15% of the original intensity retained. Issues covered include lattice design, emittance degradation, lifetime, photon beam modeling, errors, and optimum choice of rf parameters.
Shaukat Khan - BESSY
Generation of Femtosecond Synchroton Radiation at BESSY via Femtoslicing
In April 2004, BESSY completed a facility to generate x-ray pulses with 100 fs (fwhm) duration. linear or circular polarization, a photon energy of 400-1400 eV, 1 kHz repetition rate and excellent signal-to-background ratio. These pulses are produced by "femtoslicing" (A. Zholents & M. Zoloterev, PRL 76, 1996, p.912). The talk reviews the principle of femtoslicing, its first undulator-based implementation at BESSY, commissioning results and present activities.
Kees Scheidt - ESRF
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
Sub-picosec Accumulating Streak-Camera for X-rays in Pump-Probe experiments
A jitter-free, laser-triggered streak camera was developped at the ESRF that yields time resolution below 500ps while operating in accumulation mode for over 50,000 shots. The jitter-free synchronisation between the laser light pulse and the streak camera is performed through a GaAs photo-switch in a simple HV circuit that connects directly to the streak-tube's deflection plates. With this technique high dynamic range data can be obtained in typical laser-pumped(100fs), Xray-probed (100ps) experiments. The main development work was performed in the optimization of the optical synchronisation which was carried-out on a detection 267nm wavelength from a 100fs Ti:Saph laser.
Tomonori Agoh - KEK
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
Bunch lengthening and instabilily due to CSR in SuperB factory
A short bunch can suffer from self-induced coherent synchrotron radiation (CSR). In storage rings one of the most important effect related to CSR is the shielding by the vacuum chamber which reduces the intensity of CSR. Therefore, vacuum chamber properties should be properly considered in the investigation of CSR. We present a method which calculate CSR with shielding by a beam pipe and discuss the impact of CSR causing bunch lengthening or collective instability. Future storage ring colliders such as SuperB factory require short length and high charge to increase the luminosity, however, CSR may limit their performance.
Samuel Heifets - SLAC
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
Study of the low momentum compaction B- factory
For a given rf frequency, the quasi-isochronous lattice allows, in principle, to double the number of bunches compared with the nominal lattice. We explore such a possibility considering the luminosity of the PEP-II B-factory, design of the lattice, rf stability, parasitic crossings, and the longitudinal head-tail instability.
Alireza Nassiri - ANL
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
RF System for the ANL-APS proposed SC crab cavity for short x-ray pulse generation
The Advanced Photon Source at Argonne National Laboratory is considering to implement a "crab cavity" system based on Zholent's concept, in the APS storage ring to produce short x-ray pulses. Various rf configurations have been studied including single-cell and multi-cells deflecting cavities operating in TM110 mode. Initial simulation and analysis have been done which including HOM and LOM damping. Our recent results on cavity and rf system design feasibily will be presented.
Anke-Susanne Mueller - Forschungszentrum Karlsruhe
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
Operation of the ANKA Storage Ring with Short Bunches
To generate coherent radiation in the far IR (THz) region, an operation mode with a significantly reduced momentum compaction factor has been established for the ANKA storage ring at a beam energy of 1.3 GeV. The spectral dependence of the emitted radiation is recorded at the ANKA-IR beam line, where the synchrotron light is produced in the fringe field of a bending magnet. The edge radiation has the advantage of being more collimated than constant field radiation. This allows the observation of frequencies down to 1 1/cm through a modest vertical aperture, which would not be possible with classical constant field emission due to the increasing beam divergence with decreasing frequency. In order to maintain reliable operating conditions for the production of stable coherent synchrotron radiation a series of accelerator studies has been performed. This presentation reviews the status and the ongoing studies of ANKA's low alpha operation.
Peter Kuske - BESSY
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
Longitudinal stability of short bunches at BESSY
The stability of short bunches circulating in the storage ring BESSY was investigated experimentally with a streak camera and by observing bursts of coherent synchrotron radiation. These results will be compared to numerical solutions of the Vlasow-Fokker-Planck equations with wake functions based on assumptions for the vacuum chamber impedance as well as the unshielded CSR impedance.
Yuelin Li - Argonne National Laboratory
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
Application, limitation, and distortion of single-shot EO sampling techniques
We have conducted a series of testing experiments on single-shot electro-optical sampling (EOS) techniques for applications in ultrafast beam diagnostics. The "phantom" electron beam in the experiment is THz radiation generated by optical rectification from a 3-mm ZnTe crystal. The THz radiation is crossed with a probe laser beam on a 1-mm ZnTe crystal and after a polarizer, imaged onto a CCD camera. We examined waveform distortion due to factors such as natural residual birefringence of the ZnTe crystal, azimuthal rotation of the sampling crystal, and the polarization of the THz radiation. All these effects are critical for obtaining a precise profile of the charged particle beams in accelerator-related applications.
We also discuss possible application of the EOS technique in storage ring as a beam profile and timing monitor for individual bunches. We also describe our effort and the obstacle faced in demonstrating a single-shot FROG-EO that will take advantage of the full bandwidth of the sampling crystal.
Sergei Nikitin - BINP
Working Group: Lattice, Dynamic aperture, Lifetime, Beam-beam effects
Simulation of Touschek Effect for DAFNE with Strong RF Focusing
The general feature of the DAFNE II proposal is the use of the strong RF focusing to reduce significantly the bunch length at the IP. In this paper we calculate the Touschek effects in DAFNE taking into variation of all beam parameters including the bunch length along the machine azimuth. To calculate particles loss rate, beam emittance and energy spread we apply the method accounting two-dimension character of particle collisions inside the beam. The aperture limitation affecting the beam lifetime is determined by influence of the synchro-betatron resonances and depends on azimuth. Simulation results demonstrate increasing of the loss rate, beam emittance and energy spread for the strong RF focusing case.
P. Piminov - BINP
Working Group: Lattice, Dynamic aperture, Lifetime, Beam-beam effects
Dynamic Aperture of the Strong RF Focusing Storage Ring
Recently the strong RF focusing regime has been considered as a basic principle for the design of a super factory at the Phi energy. To prove this regime the bunch modulation experiment was proposed at the DAFNE storage ring. In the paper we present the results of the 6D nonlinear beam dynamics simulation for this experiment. Different lattices and machine parameters are considered.
Katherine Harkay - Argonne National Laboratory
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
Effects of impedance in short pulse generation using crab cavities
At the Advanced Photon Source, a feasibility study has been carried out for the generation of ultrashort x-ray pulses, on the order of 1 ps, using Zholents' rf deflection method. This scheme requires installation of two rf cavities operating in the TM110 deflecting mode (also known as "crab" cavities). Although crab cavities have long been used in beam transport lines, to date there are no crab cavities installed in a storage ring. One of the key issues is sufficiently damping the parasitic modes to avoid collective effects, and preserve the beam stability and emittance that are the hallmark of light sources. The APS crab cavities are based on S-band superconducting technology and follow the KEK-B/Cornell design (installation in KEK-B planned in 2006). In this talk, we present studies of the effects of the ring impedance as well as the parasitic modes on the chirped beam.
Katherine Harkay - Argonne National Laboratory
Working Group: Lattice, Dynamic aperture, Lifetime, Beam-beam effects
Short pulse generation through beam manipulation
The length of the X-ray pulse generated at a synchrotron light source is typically determined by the electron bunch length. The value is ~40 ps rms at the Advanced Photon Source. The vertical beam size, however, is three orders of magnitude less, therefore, shorter pulses can be obtained by vertically tilting the bunch. A. Zholents proposed tilting the bunch using rf deflection. We found that tilted bunches can also be generated by beam manipulation. A vertical tilt ("chirp") develops after a vertical kick in the presence of non-zero chromaticity because the betatron phase varies along the longitudinal position. We carried out an experiment and obtained a 6 ps pulse from a 31 ps electron bunch. The next step is to carry out a demonstration x-ray experiment on an APS beamline using the synchrobetatron technique. Synchrobetatron and decoherence beam dynamics, simulation, and experimental approaches will be presented.
Kazuhito Ohmi - KEK
Working Group: Lattice, Dynamic aperture, Lifetime, Beam-beam effects
Beam-beam effect and longitudinal degree of freedom
Longitudinal motion of particles plays an important role for the beam-beam effect. The longitudinal degree of freedom enhances emittance growth due to nonlinear diffusion, while coherent motion is suppressed by the tune spread of particles along the bunch length. We discuss the beam-beam effect related to the bunch length.
Vadim Sajaev - Argonne National Laboratory
Working Group: Lattice, Dynamic aperture, Lifetime, Beam-beam effects
Containing a blow-up of the vertical emittance in the RF deflection scheme for a generation of subpicosecond x-ray pulses
RF deflection scheme is a promising technique to generate high intensity short x-ray pulses [1]. As recent simulation studies at APS have shown [2], the overall vertical emittance may increase drastically even when the kick is contained between two cavities. We have found that the main cause of the emittance blow-up is a combination of first- and second-order effects in sextupoles: linear coupling due to vertical trajectories in sextupoles and residual vertical and horizontal trajectories due to sextupole nonlinearities. Maintaining zero chromaticity between cavities is also important; therefore the sextupoles between cavities cannot be turned off. We show an example of sextupole optimization that allows us to contain the emittance blow-up within acceptable limits. [1] A. Zholents, P. Heimann, M. Zolotorev, J. Byrd, Generation of subpicosecond X-ray pulses using RF orbit deflection, NIMA (425)1-2 (1999) pp. 385-389. [2] M. Borland, Simulation and analysis of using deflecting cavities to produce short x-ray pulses with the Advanced Photon Source, Phys. Rev. ST Accel. Beams, 74001.
Riccardo Bartolini - Rutherford Appleton Laboratory
Working Group: Lattice, Dynamic aperture, Lifetime, Beam-beam effectsAccelerator
Physics studies for generating short radiation pulses at the Diamond Light Source
Diamond is a third generation light source under construction in Oxfordshire UK. In view of the increasing interest in the production of short radiation pulses, we have investigated both the possiblity to operate with a low-alpha optics and also the implementation of a crab cavity scheme in the Diamond storage ring. The results of the initial accelerator studies will be described, including the modification of the beam optics, non linear beam dynamics optimisation, choice of RF parameters for the crab cavity operation. The expected performance of these two schemes will be summarised.
Alessandro Gallo - INFN-LNF
The DAFNE Strong RF Focusing Experiment
No storage ring has been so far operated in the strong RF focusing regime, where the combination of large RF voltages and R56 peaks result in a modulation of the bunch length along the machine together with an increase of the momentum spread. In this paper we present the proposal of creating the experimental conditions to study the strong RF focusing in DAFNE. The machine lattice providing the proper R56 shaping, the upgrade of the RF system based on a new multi-cell superconducting cavity, the upgrade of the cryogenic plant, the proposed methods to measure bunch lengths in the mm scale, and a list of the possible beam experiments are illustrated and discussed.
Alessio Bocci - Università di Firenze, INFN-LNF
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
Applications of fast mid-IR detectors as beam monitor in the subnanosecond time domain
Technological improvements of the IR detectors manufacturing makes available devices capable to detect fast pulsed long wavelength radiation sources with resolution time in the subnanosecond domain. An example are uncooled HgCdTe photodetectors optimized at wavelength around 10 µm. The performance of such devices is less by two order of magnitude compared to the fundamental BLIP limit that is readily achievable with typical liquid nitrogen cooled IR detectors. The detectivity of the uncooled devices in sufficient, however, to monitor the emission of brilliant sources like sinchrotron radiation storage rings.
At DAFNE a set of emission measurements of the electron bunches at mid-IR wavelengths has been performed with an uncooled fast infrared detector with response time of a few ns. Due to the limitation of the voltage amplifier working at 500 MHz of bandwidth with a specific bunch filling a minimum bunch separation of only 8 ns, equivalent to a frequency of RF/3(125 MHz) has been observed. Improvement in the resolution time may be achieved with a fast transimpedence preamplifier with wider bandwidth. Moreover, single IR uncooled detectors with response time <100 ps are available and should be used also as elements of a linear array for future high speed diagnostics.
Dmitry Shatilov - BINP
Beam-beam simulations with large synchrotron tune for strong RF focusing scheme
One of the main features of strong RF focusing scheme is the abnormally high synchrotron tune. As a result, the synchrotron satellites of betatron resonances cross the standard "good" working areas of the betatron tunes, reducing them essentially. We present results of beam-beam simulations with large synchrotron tune: Qs=0.4. We made a 2D betatron tune scan in order to find good working points, and compare this scan with the one made for small Qs. We discuss also some peculiarities of tracking technique which allow to obtain the correct values of emittances, bunch length and energy spread, and cross-check the analytical formulae.
Alexander Temnykh - Cornell Univ.
Working Group: Lattice, Dynamic aperture, Lifetime, Beam-beam effectsAccelerator
Effect of high synchrotron tune on Beam-Beam interaction: simulation and experiment
To reduce bunch length and increase luminosity Cornell Electron Storage Ring (CESR) operates with high RF voltage which results in high synchrotron tune. Experimental observations and results of a simple simulation indicating strong impact of high synchrotron tune on beam-beam interaction performance will be presented.
Fabio Marcellini - INFN-LNF
Working Group: Diagnostics, RF design, Impedance, Coherent radiation, Bunch lengthening
Design of a Multi-Cell, HOM Damped Superconducting Cavity for the Strong RF Focusing Experiment at DAFNE
A strong RF focusing experiment to be performed at the DAFNE has been proposed to create and observe a bunch length modulation along the ring. The very large RF gradient required to reach the strong focusing regime can only be obtained by using a multi-cell superconducting cavity. Moreover, in order to demonstrate the feasibility of a high luminosity collider based on this principle, a total multibunch current of the order of 1A has to be stored under stable conditions in this regime. A 1.3 GHz 7-cells cavity has been designed for this purpose, based on the TESLA geometry with small modifications of the basic cell to comply with the DAFNE revolution frequency. The number of cells has been changed from 9 to 7 to reduce the number of the cavity HOMs, while the beam tubes have been enlarged to let most of the HOMs propagate and be damped by room-temperature ferrite rings. The modes of the first longitudinal band, which include the accelerating TM010-pi, do not propagate in the beam tubes and have been studied with special care to prevent the overlap with the bunch revolution harmonics and to cure the effects of coupling to the synchrotron tune sidebands. A strong RF focusing experiment to be performed at the DAFNE has been proposed to create and observe a bunch length modulation along the ring. The very large RF gradient required to reach the strong focusing regime can only be obtained by using a multi-cell superconducting cavity. Moreover, in order to demonstrate the feasibility of a high luminosity collider based on this principle, a total multibunch current of the order of 1A has to be stored under stable conditions in this regime. A 1.3 GHz 7-cells cavity has been designed for this purpose, based on the TESLA geometry with small modifications of the basic cell to comply with the DAFNE revolution frequency. The number of cells has been changed from 9 to 7 to reduce the number of the cavity HOMs, while the beam tubes have been enlarged to let most of the HOMs propagate and be damped by room-temperature ferrite rings. The modes of the first longitudinal band, which include the accelerating TM010-pi, do not propagate in the beam tubes and have been studied with special care to prevent the overlap with the bunch revolution harmonics and to cure the effects of coupling to the synchrotron tune sidebands.
MG - 2 November 2005