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Stripline Transversal Filter Techniques for Sub-picosecond Bunch Timing Measurements

Description: Measurement of time of arrival of a particle bunch is a fundamental beam diagnostic. The PEP-II/ALS/BESSY/PLS longitudinal feedback systems use a planar stripline circuit to convert a 30 ps beam BPM impulse signal into a 4 cycle tone burst at the 6th harmonic of the accelerator RF frequency (2.856 GHz). A phase-detection technique is used to measure the arrival time of these BPM impulses with 200 fs rms single-shot resolution (out of a 330 ps dynamic range). Scaled in frequency, this approach is directly applicable to FEL and other sub-ps regime pulse and timing measurements. The transversal circuit structure is applicable to measurement of microbunches or closely spaced bunches (the PEP-II/ALS/BESSY/PLS examples make independent measurements at 2 ns bunch spacing) and opens up some new diagnostic and control possibilities. This paper reviews the principles of the technique, and uses data from PEP-II operations to predict the limits of performance of this measurement scheme for arrival phase measurement. These predictions are compared with results in the literature from electro-optic sub-picosecond beam timing and phasing diagnostics.
Date: July 6, 2007
Creator: Fox, John D.; Mastorides, Themis; Rivetta, Claudio Hector & Winkle, Daniel Van
Partner: UNT Libraries Government Documents Department

Selecting RF Amplifiers for Impedance Controlled LLRF Systems - Nonlinear Effects and System Implications

Description: Several high-current accelerators use feedback techniques in the accelerating RF systems to control the impedances seen by the circulating beam. These Direct and Comb Loop architectures put the high power klystron and LLRF signal processing components inside feedback loops, and the ultimate behavior of the systems depends on the individual sub-component properties. Imperfections and non-idealities in the signal processing leads to reduced effectiveness in the impedance control loops. In the PEP-II LLRF systems non-linear effects have been shown to reduce the achievable beam currents, increase low-mode longitudinal growth rates and reduce the margins and stability of the LLRF control loops. We present measurements of the driver amplifiers used in the PEP-II systems, and present measurement techniques needed to quantify the small-signal gain, linearity, transient response and image frequency generation of these amplifiers.
Date: July 6, 2007
Creator: Fox, John D.; Mastorides, Themis; Rivetta, Claudio Hector; Van Winkle, Daniel & /SLAC
Partner: UNT Libraries Government Documents Department

Longitudinal Bunch Position Control for the Super-B Accelerator

Description: The use of normal conducting cavities and an ion-clearing gap will cause a significant RF accelerating voltage gap transient and longitudinal phase shift of the individual bunches along the bunch train in both rings of the SuperB accelerator. Small relative centroid position shifts between bunches of the colliding beams will have a large adverse impact on the luminosity due to the small {beta}*{sub y} at the interaction point (IP). We investigate the possibility of minimizing the relative longitudinal position shift between bunches by reducing the gap transient in each ring and matching the longitudinal bunch positions of the two rings at the IP using feedback/feedforward techniques in the LLRF. The analysis is conducted assuming maximum use of the klystron power installed in the system.
Date: May 15, 2009
Creator: Bertsche, Kirk; Rivetta, Claudio; Sullivam, Michael K.; /SLAC; Drago, Alessandro & /Frascati
Partner: UNT Libraries Government Documents Department

Friction model of the 2.5mts SDSS telescope

Description: The 2.5mts telescope designed for the Sloan Digital Sky Survey (SDSS) is a mechanical structure that presents five degree-of-freedom. Azimuth, altitude and the instrument rotator axis are fitted with servo controls. The low frequency dynamic are dominated by the bearing friction. Several mathematical models have been presented in the literature to include its effect into the dynamic model of mechanical structures. The model employed in this paper includes consideration of the Striebeck effect, dynamic behavior at very low velocities and the pre-sliding at near zero-velocity. Results of the parameter estimation of the friction model of the three principal axes are presented as well as the behavior of the structure when different torque stimuli are applied. The mathematical model used to include the friction phenomena into the telescope dynamic model is simple. It does a good job of describing the friction over a wide range of velocities but particularly at or below siderial rate. It is a straight forward process to determine the parameters and, in simulations, does not require large amounts of computer time. 10 refs. , 8 figs.
Date: February 1, 1998
Creator: Rivetta, Claudio H. & Hansen, Sten
Partner: UNT Libraries Government Documents Department

Modeling and Simulation of Longitudinal Dynamics for LER-HER PEP II Rings

Description: A time domain modeling and simulation tool for beam-cavity interactions in LER and HER rings at PEP II are presented. The motivation for this tool is to explore the stability margins and performance limits of PEP II RF systems at higher currents and upgraded RF configurations. It also serves as test bed for new control algorithms and can define the ultimate limits of the architecture. The time domain program captures the dynamical behavior of the beam-cavity interaction based on a reduced model. The ring current is represented by macro-bunches. Multiple RF station in the ring are represented via one or two macro-cavities. Each macro-cavity captures the overall behavior of all the 2 or 4 cavity RF station. Station models include nonlinear elements in the klystron and signal processing. This allows modeling the principal longitudinal impedance control loops interacting with the longitudinal beam model. Validation of simulation tool is in progress by comparing the measured growth rates for both LER and HER rings with simulation results. The simulated behavior of both machines at high currents are presented comparing different control strategies and the effect of non-linear klystrons in the growth rates.
Date: March 6, 2007
Creator: Rivetta, Claudio; Mastorides, T.; Fox, J.D.; Teytelman, D.; Van Winkle, D. & /SLAC
Partner: UNT Libraries Government Documents Department

Modeling and Simulation of Longitudinal Dynamics for Low Energy Ring_High Energy Ring at the Positron-Electron Project

Description: A time domain dynamic modeling and simulation tool for beam-cavity interactions in the Low Energy Ring (LER) and High Energy Ring (HER) at the Positron-Electron Project (PEP-II) is presented. Dynamic simulation results for PEP-II are compared to measurements of the actual machine. The motivation for this tool is to explore the stability margins and performance limits of PEP-II radio-frequency (RF) systems at future higher currents and upgraded RF configurations. It also serves as a test bed for new control algorithms and can define the ultimate limits of the low-level RF (LLRF) architecture. The time domain program captures the dynamic behavior of the beam-cavity-LLRF interaction based on a reduced model. The ring current is represented by macrobunches. Multiple RF stations in the ring are represented via one or two macrocavities. Each macrocavity captures the overall behavior of all the 2 or 4 cavity RF stations. Station models include nonlinear elements in the klystron and signal processing. This enables modeling the principal longitudinal impedance control loops interacting via the longitudinal beam model. The dynamics of the simulation model are validated by comparing the measured growth rates for the LER with simulation results. The simulated behavior of the LER at increased operation currents is presented via low-mode instability growth rates. Different control strategies are compared and the effects of both the imperfections in the LLRF signal processing and the nonlinear drivers and klystrons are explored.
Date: March 6, 2007
Creator: Rivetta, Claudio; Mastorides, T.; Fox, J.D.; Teytelman, D.; Van Winkle, D. & /SLAC
Partner: UNT Libraries Government Documents Department

Commissioning of the LHC Low Level RF System Remote Configuration Tools

Description: The LHC Low Level RF system (LLRF) is a complex multi-loop system used to regulate the superconductive cavity gap voltage as well as to reduce the impedance presented by RF stations to the beam. The RF system can have a profound impact on the stability of the beam; a mis-configured RF system has the potential of causing longitudinal instabilities, beam diffusion and beam loss. To configure the RF station for operation, a set of parameters in the LLRF multi-loop system have to be defined. Initial system commissioning as well as ongoing operation requires a consistent method of computer based remote measurement and model-based design of each RF station feedback system. This paper describes the suite of Matlab tools used for configuring the LHC RF system during the start up in Nov2009-Feb2010. We present a brief overview of the tool, examples of commissioning results, and basics of the model-based design algorithms. This work complements our previous presentation, where the algorithms and methodology followed in the tools were described.
Date: August 26, 2010
Creator: Van Winkle, Daniel; /SLAC; Fox, John; /SLAC; Mastorides, Themis; /SLAC et al.
Partner: UNT Libraries Government Documents Department

Simulation of E-Cloud Driven Instability And Its Attenuation Using a Feedback System in the CERN SPS

Description: Electron clouds have been shown to trigger fast growing instabilities on proton beams circulating in the SPS, and a feedback system to control the instabilities is under active development. We present the latest improvements to the Warp-Posinst simulation framework and feedback model, and its application to the self-consistent simulations of two consecutive bunches interacting with an electron cloud in the SPS.
Date: July 6, 2012
Creator: Vay, Jean-Luc; /LBL, Berkeley; Byrd, John; /LBL, Berkeley; Furman, Miguel; /LBL, Berkeley et al.
Partner: UNT Libraries Government Documents Department

A Design Report of the Baseline for PEP-X: an Ultra-Low Emittance Storage Ring

Description: Over the past year, we have worked out a baseline design for PEP-X, as an ultra-low emittance storage ring that could reside in the existing 2.2-km PEPII tunnel. The design features a hybrid lattice with double bend achromat (DBA) cells in two arcs and theoretical minimum emittance (TME) cells in the remaining four arcs. Damping wigglers are used to reduce the horizontal emittance to 86 pm-rad at zero current for a 4.5 GeV electron beam. At a design current of 1.5 A, the horizontal emittance increases, due to intrabeam scattering, to 164 pm-rad when the vertical emittance is maintained at a diffraction limited 8 pm-rad. The baseline design will produce photon beams achieving a brightness of 10{sup 22} (ph/s/mm{sup 2}/mrad{sup 2}/0.1% BW) at 10 keV in a 3.5-m conventional planar undulator. Our study shows that an optimized lattice has adequate dynamic aperture, while accommodating a conventional off-axis injection system. In this report, we present the results of study, including the lattice properties, nonlinear dynamics, intra-beam scattering and Touschek lifetime, RF system, and collective instabilities. Finally, we discuss the possibility of partial lasing at soft X-ray wavelengths using a long undulator in a straight section.
Date: June 2, 2010
Creator: Bane, Karl; Bertsche, Kirk; Cai, Yunhai; Chao, Alex; Corbett, Willian; Fox, John et al.
Partner: UNT Libraries Government Documents Department

Concepts for the PEP-X Light Source

Description: SSRL and SLAC groups are developing a long-range plan to transfer its evolving scientific programs from the SPEAR3 light source to a much higher performing photon source that would be housed in the 2.2-km PEP-II tunnel. While various concepts for the PEP-X light source are under consideration, including ultimate storage ring and ERL configurations, the present baseline design is a very low-emittance storage ring. A hybrid lattice has double bend achromat (DBA) cells in two of the six arcs that provide a total 30 straight sections for insertion device (ID) beam lines extending into two new experimental halls. The remaining arcs contain TME cells. Using 90 m of damping wigglers the horizontal emittance at 4.5 GeV would be 100 pm-rad with 1.5-A stored beam. PEP-X will produce photon beams having brightnesses near 10{sup 22} (ph/s/mm{sup 2}/mrad{sup 2}/0.1% BW) at 10 keV. Studies indicate that a 90-m undulator could have FEL gain and brightness enhancement at soft x-ray wavelengths with the stored beam. Crab cavities or other beam manipulation systems could be used to reduce bunch length or otherwise enhance photon emission properties. The present status of the design of PEP-X as a storage ring is presented.
Date: August 26, 2010
Creator: Hettel, Robert; Bane, Karl; Bertsche, Kirk; Cai, Yunhai; Chao, Alex; Dolgashev, Valery et al.
Partner: UNT Libraries Government Documents Department