TUB, Beijing
PSI, Villigen
CIAE, Beijing
In high intensity cyclotrons with small turn separation, both the space charge effects of single bunch and the interaction of radially neighbouring bunches play important roles. A PIC-based three-dimensional parallel code, OPAL-CYCL, is newly developed under OPAL framework which self-consistently covers these two collective effects. In this paper we also present the simulation results from the compact cyclotron CYCIAE-100 in the context of the ongoing upgrade program of BRIF at CIAE, with the goal of 100 MeV, 200 μA CW proton beam on target.
FZK, Karlsruhe
Ruhr-Universität Bochum, Bochum
KIT, Karlsruhe
HZB, Berlin
DLR, Berlin
PTB, Berlin
BESSY GmbH, Berlin
Funding: This work has partly been supported by the Initiative and Networking Fund of the Helmholtz Association under contract number VH-NG-320.
In synchrotron radiation sources coherent radiation is emitted when the bunch length is comparable to or shorter than the wavelength of the emitted radiation. A detector system based on a superconducting NbN ultra-fast bolometer with an intrinsic response time of about 100 ps jointly developed by the University of Karlsruhe (Institute of micro- and nanoelectronic systems) and German Aerospace Center (Berlin) was used to resolve the radiation emitted from single bunches. This paper reports the observations made during measurements at the MLS and ANKA storage rings.
LBNL, Berkeley, California
BNL, Upton, Long Island, New York
Funding: Supported by DOE BES contract DE-AC03-76SF00098.
Several years ago experiments at the APS demonstrated the possibility of creating crabbed beam through vertically kicking the beam and letting it oscillate for a half of a synchrotron period. Such a crabbed beam would allow the possibility of creating a few ps xrays. At the ALS we have repeated these experiments. In this paper we will present the results obtained and compare them to theoretical predictions.
SLAC, Menlo Park, California
Funding: Work sponsored by U.S. Department of Energy Contract DE-AC03-76SF00515 and Office of Basic Energy Sciences, Division of Chemical Sciences.
Recent experimental results and advances in the theory of short-bunch dynamics have lead to an improved understanding of the parameters and limitations of short-bunch operation in storage rings. In this paper the measurement and analysis of short bunches under a variety of operational parameters is reported for SPEAR3.
QMUL, London
USC, Los Angeles, California
For 70 years particle acceleration schemes have been based on the same technology which places particles onto rf electric fields inside metallic cavities. However, since the accelerating gradients cannot be increased arbitrarily due to limiting effects such as wall breakdown, in order to reach higher energies today’s accelerators require km-long structures that have become very expensive to build, and therefore novel accelerating techniques are needed to push the energy frontier further. Plasmas do not suffer from those limitations since they are gases that are already broken down into electrons and ions. In addition, the collective behavior of the particles in plasmas allows for generated accelerating electric fields that are orders of magnitude larger than those available in conventional accelerators. As plasma acceleration technologies mature, one of the main future challenges is to monoenergetically accelerate a second trailing bunch by multiplying its energy in an efficient manner, so that it can potentially be used in a future particle collider. The work presented here analyzes the use of multiple electron bunches in order to enhance certain plasma acceleration schemes.
CEA, Gif-sur-Yvette
The probe beam linac of the CTF3 test facility, named CALIFES, is developed by the CEA Saclay, the LAL Orsay and CERN to deliver short bunches (0.75 ps) with a charge of 0.6 nC to the CLIC 12 GHz accelerating structures. To setup the machine and obtain a precise beam handling, six high resolution beam position monitors (BPMs), based on a radiofrequency reentrant cavity with an aperture of 18 mm, are installed along the linac. The associated electronics is composed of an analog signal processing electronics with a multiplexing to control the six monitors. Due to mechanical tolerances, dipole mode frequencies are different for each BPMs, 100 MHz IF frequency is, therefore, used so that monitors operate in single and multi-bunches. Digitalised signals from acquisition boards are made available to the operation crew thanks to the OASIS interfaces. In this paper, the BPMs acquisition and the signal post processing, to extract the beam position, will be discussed and first beam tests will be presented.
I-Tech, Solkan
ELETTRA, Basovizza
Libera Brilliance is a standard device for beam position monitoring on circular synchrotron light sources. Initially, the idea of optimizing its signal processing for the single bunch measurement came from the users community. This was afterwards followed by the idea of using it on transfer lines on the same 3rd generation light sources as well as on injector system for the FELs. The device can be used on pickup buttons and on striplines. The single pass functionality is contained in newest Libera Brilliance software Release 2.0, no hardware changes are needed. The measurement principles and first measurements with results are presented.
ASCo, Clayton, Victoria
Generating short bunches for time resolved studies or the generation of THz radiation has been done at many other light sources and is of increasing interest in the user community. Light sources not designed with ps bunchs can usually tune the lattice to reduce ps bunchs without much difficulty, sometimes referred to as a Low Alpha mode. At the Australian light source a low alpha configuration has been investigated. The results looking into the 'shaping' of the momentum compaction factor, beam stability and current limitations will be presented.
USTC/NSRL, Hefei, Anhui
In HLS streak camera system has been built. The system is used to measure some parameters of bunch like bunch length, longitudinal bunch profile and synchrotron frequency and so on, as it may report a direct derivation of fundamental machine characteristics. The system mainly consists of the synchrotron light extracting optics setup, the OPTOSCOPE streak camera and PC with a frame grabber interface card. The light extracting optics setup is used to extract synchrotron light at the bending magnet and the setup consists of the light extracting path and the optics imaging system. The streak camera realizes the functions of acquiring light and imaging. PC with a frame grabber interface card and ARP-Optoscope software package is used to monitor the light in real-time, acquire the image of light and analyze the data. The streak camera system operates with either synchroscan sweep mode or dual time base sweep mode. At present, some results are given, which include the bunch lengthening, the longitudinal bunch profile and the synchrotron frequency. These results are compared with the results acquired by using oscilloscope.
CLS, Saskatoon, Saskatchewan
I-Tech, Solkan
A high-purity single-bunch operating mode, required for time-resolved experiments, has been introduced into the CLS Storage Ring. The newly deployed Transverse Feedback System, which uses the Libera Bunch-by-Bunch system as the feedback processor, has added features that inherently enable bunch cleaning. The bunch purification mechanism is based on a frequency modulated signal that drives the unwanted bunches into betatron oscillations to remove them from the Storage Ring. Bunch purities of 10-6 are achieved, limited only by the leakage rate from adjacent bunches.
JAI, Oxford
ATOMKI, Debrecen
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
We present the design of prototype fast beam position monitor (BPM) signal processors for use in inter-bunch beam-based feedbacks for linear colliders and electron linacs. We describe the FONT4 intra-train beam-based digital position feedback system prototype deployed at the Accelerator test facility (ATF) extraction line at KEK, Japan. The system incorporates a fast analogue beam position monitor front-end signal processor, a digital feedback board, and a fast kicker-driver amplifier. The total feedback system latency is less than 150ns, of which less than 10ns is used for the BPM processor. We report preliminary results of beam tests using electron bunches separated by c. 150ns. Position resolution of order 1 micron is obtained.
SOLEIL, Gif-sur-Yvette
Ever since the first user operation, the digital transverse bunch by bunch feedback system developed at SOLEIL has successfully been operated, achieving a stable multibunch beam at the highest intensity in the two planes at zero chromaticity with a single chain working in a diagonal mode. Since then a vertical stripline, optimised to generate large deflections to combat the strong single bunch headtail instability, was installed to construct another chain. The combined use of the two chains allowed enhancing the feedback performance. In particular, by differentiating the feedback gain between high and low intensity bunches, the system is capable of working in hybrid filling modes. In parallel, online applications were integrated into the control system to allow measuring the tunes by selectively exciting a single bunch, damping and growth rates, and analysing the bunch by bunch data in frequency or time domain for post-mortem purposes. Future plans including installation of a horizontal stripline and a noise reduction by avoiding the baseband conversion of the beam signal are also discussed.
ANL, Argonne
Illinois Institute of Technology, Chicago, Illinois
Euclid TechLabs, LLC, Solon, Ohio
We report on the design of a dual-frequency higher-order-mode dielectric-loaded power extraction set. This power extraction set consists of a dual-frequency dielectric-loaded decelerating structure (decelerator) and two changeable output couplers. In the decelerator, the TM02 mode synchronizes with an ultra-relativistic electron beam at 20.8GHz, and the TM03 mode synchronizes with the beam at 35.1GHz. These frequencies are both harmonics of 1.3GHz, the operating frequency of the electron gun and linac at the Argonne Wakefield Accelerator. The power generated in the unwanted TM01 mode is effectively suppressed for bunch train operation with a novel mode suppression technique. To extract power from the decelerator to standard rectangular waveguides, a TM02-TE10 output coupler was designed with S21 = -0.26dB at 20.8GHz, and a TM03-TE10 output coupler with S21 = -0.66dB at 35.1GHz. 90.4MW and 8.68MW rf power are expected to be extracted from a drive beam with charge of 50nC per bunch, at 20.8GHz and 35.1GHz respectively.
SOLEIL, Gif-sur-Yvette
Diamond, Oxfordshire
Good understanding of instabilities is of great importance in light source rings that provide high current beams. The inherently large machine impedance, which often evolves with continuous changes of insertion devices, enhances collective effects that need to be well controlled to assure the machine performance. The problem is usually not straightforward, as one must quantify short and long range wakes that excite single and multi bunch instabilities, the coupling between instabilities and different planes, as well as Landau effects in arbitrary filling modes. The paper presents the study made on DIAMOND and SOLEIL using the multiparticle tracking codes sbtrack and mbtrack. While sbtrack performs a 6-dimensional single bunch tracking, mbtrack does its direct extension to multibunches. The most recent code development includes a MATLAB version and a high precision Fourier analysis of collective modes. The study emphasises the use of realistic impedance models, either empirically or numerically constructed, and aims to elucidate the relative importance of different physical effects by closely comparing with experimental observations.
CERN, Geneva
The HEADTAIL code has been used for many years to study the interaction of a single bunch with a localized or lumped source of electromagnetic perturbation, usually self-induced (impedance, electron cloud or space charge). It models the bunch as macroparticles and at each turn slices up the bunch into several adjacent charged disks, which are made to subsequently interact with the perturbing agent. A first step toward the extension of HEADTAIL to multi-bunch simulations is presented in this paper. In this case, the bunches themselves are modeled as charged disks and are not sliced, which makes us lose information on the intra-bunch motion but can describe a zero mode interaction between different bunches in a train. The interaction of an SPS bunch train of 72 bunches with the resistive wall or a narrow-band impedance is studied as an example.
CERN, Geneva
In the main linac of the compact linear collider (CLIC) , wakefield induced multi-bunch effects are important. They have a strong impact on the choice of accelerating structure design. The paper presents the limit for the wakefield that one bunch exerts on the next. It also gives estimates for the allowed level of persistent wake fields and on the resistive wall wakefield.
HZB, Berlin
Bursts of coherent synchrotron radiation (CSR) in the far IR and down to the μ-wave region have been observed in many synchrotron light sources. At BESSY II the temporal structure of these pulses in the THz-region was observed as a function of the bunch length which was varied by changing the momentum compaction factor and as a function of the number of electrons in the single bunch. It was found, that for a bunch length between 3 and 15 ps the first signs of time dependent CSR occur at a frequency which is a multiple of the zero current synchrotron frequency. This frequency increases with the bunch length and indicates that higher azimuthal modes become unstable first. Slower bursts, with repetition rates on the time scale of mill seconds and much slower than the synchrotron period, show up slightly above this threshold. These bursts possess the much faster initial temporal structure and are probably the result of longitudinal mode mixing. The experimental observations are presented and compared to calculations.
JAI, Oxford
Diamond, Oxfordshire
Diamond is a third generation synchrotron light source built to generate infra-red, ultraviolet and X-ray synchrotron radiation (SR) of exceptional brightness. The operation of the Diamond storage ring with short electron bunches for generation of Coherent THz radiation and short X-ray pulses for time-resolved experiments is limited by the onset of microbunch instabilities. We have started a project to investigate the longitudinal electron beam dynamics and microbunch instabilities in the Diamond storage ring. In the first experiment we used an ultra-fast (time response is about 250 ps) Schottky Barrier Diode sensitive to the radiation within the 3.33-5 mm wavelength range. When the single bunch current exceeded 1.9 mA we observed a set of sub-THz bursts appearing quasi-periodically while the beam was circulating in the ring. The fast response allowed us to detect the signal turn-by-turn, which gives us an opportunity to study the bursts’ structure and evolution. It also allows us to study the effect in a multi-bunch mode when bunches are only 2 ns apart. In this report we will present our first preliminary results and also discuss future plans.
LBNL, Berkeley, California
CERN, Geneva
Funding: Supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Single and multi-bunch instabilities on bunch trains driven by electron clouds have been observed in the CERN SPS for some years. In this paper, we present initial results to implement a damping system in a computer simulation of a single bunch vertical instability using the HEADTAIL code. The code simulates the interaction between a proton bunch and a uniform electron cloud that has built up inside of the beam pipe. In all simulations we use typical SPS parameter sets for three different values of the beam momentum : 26 GeV/c, 55 GeV/c and 120 GeV/c. The feedback is implemented as a corrective kick calculated from the vertical centroid of each slice of the electron bunch with a one turn delay. The bandwidth of the feedback is varied by filtering the slice information along the bunch. Initial results indicate that the instability can be damped with a minimum bandwidth of 300 MHz with a relatively high gain.
SLAC, Menlo Park, California
A proposed high-brightness synchrotron light source (PEP-X) is under design at SLAC. The 4.5-GeV PEP-X storage ring has four theoretical minimum emittance (TME) cells to achieve the very low emittance and two double-bend achromat (DBA) cells to provide spaces for IDs. Damping wigglers will be installed in zero-dispersion straights to reduce the emittance below 0.1nm. In this paper, we present a preliminary estimation of the threshold of the transverse mode coupling instability(TMCI). Three approaches have been used in the estimation and they agree well with each other.