In order to maintain beam quality during transport through a storage ring, sextupole magnets are used to make chromatic corrections, but necessarily introduce deleterious effects such as nonlinear resonances and reduced dynamic aperture. Implementing intricate sextupole distributions to mitigate these effects will rely on precision beam-based measurement of the applied sextupole distribution. In this work, we generalize previous sextupole mapping techniques by using resonant phase-locked excitation of the beam at the Cornell Electron Storage Ring (CESR) [1], which accounts for variations in the normal mode tunes on a turn by turn basis. The methods presented here are applied to simulation and actual turn by turn (TbT) data in CESR for both simplified and realistic sextupole distributions.

After operating as a High Energy Physics electron-positron collider, the Cornell Electron-positron Storage Ring (CESR) has been converted to become a dedicated synchrotron light source for the Cornell High Energy Synchrotron Source (CHESS). Over the course of several years CESR was adapted for accelerator physics research as a test accelerator, capable of studying topics relevant to future damping rings, colliders and light sources. Initially some specific topics were targeted for accelerator physic research with the storage ring in this mode, labeled CesrTA. These topics included 1) tuning techniques to produce low emittance beams, 2) the study of electron cloud (EC) development in a storage ring and 3) intra-beam scattering effects. The complete conversion of CESR to CesrTA occurred over a several year period, described elsewhere [1–3]. A number of specific instruments were developed for CesrTA. Much of the pre-existing instrumentation was modified to accommodate the scope of these studies and these are described in a companion paper [4]. To complete this research, a number of procedures were developed or modified, often requiring coordinated measurements among different instruments [5]. This paper provides an overview of types of measurements employed for the study of beam dynamics during the operation of CesrTA.

The Cornell Electron-positron Storage Ring (CESR) has been converted from a High Energy Physics electron-positron collider to operate as a dedicated synchrotron light source for the Cornell High Energy Synchrotron Source (CHESS) and to conduct accelerator physics research as a test accelerator, capable of studying topics relevant to future damping rings, colliders and light sources. Some of the specific topics that were targeted for the initial phase of operation of the storage ring in this mode, labeled CesrTA (CESR as a Test Accelerator), included 1) tuning techniques to produce low emittance beams, 2) the study of electron cloud development in a storage ring and 3) intra-beam scattering effects. The complete conversion of CESR to CesrTA occurred over a several year period, described elsewhere. As a part of this conversion the CESR beam position monitoring (CBPM) system was completely upgraded to provide the needed instrumental capabilities for these studies. This paper describes the new CBPM system hardware, its function and representative measurements performed by the upgraded system.

The Cornell Electron-positron Storage Ring (CESR) has been converted from a High Energy Physics electron-positron collider to operate as a dedicated synchrotron light source for the Cornell High Energy Synchrotron Source (CHESS) and to conduct accelerator physics research as a test accelerator, capable of studying topics relevant to future damping rings, colliders and light sources. Some of the specific topics that were targeted for the initial phase of operation of the storage ring in this mode for CESR as a Test Accelerator (CesrTA) included 1) tuning techniques to produce low emittance beams, 2) the study of electron cloud development in a storage ring and 3) intra-beam scattering effects. The complete conversion of CESR to CesrTA occurred over a several year period, described elsewhere [1–3]. In addition to instrumentation for the storage ring, which was created for CesrTA, existing instrumentation was modified to facilitate the entire range of investigations to support these studies. Procedures were developed, often requiring coordinated measurements among different instruments [4]. This paper describes the instruments utilized for the study of beam dynamics during the operation of CesrTA. The treatment of these instruments will remain fairly general in this paper as it focusses on an overview of the instruments themselves. Their interaction and inter-relationships during sequences of observations is found in a companion paper describing the associated measurement techniques. More detailed descriptions and detailed operational performance for some of the instrumentation may be found elsewhere and these will be referenced in the related sections of this paper.

Cornell's electron/positron storage ring (CESR) was modified over a series of accelerator shutdowns beginning in May 2008, which substantially improves its capability for research and development for particle accelerators. CESR's energy span from 1.8 to 5.6 GeV with both electrons and positrons makes it ideal for the study of a wide spectrum of accelerator physics issues and instrumentation related to present light sources and future lepton damping rings. Additionally a number of these are also relevant for the beam physics of proton accelerators. This paper is the third in a series of four describing the conversion of CESR to the test accelerator, CESRTA. The first two papers discuss the overall plan for the conversion of the storage ring to an instrument capable of studying advanced accelerator physics issues [1] and the details of the vacuum system upgrades [2]. This paper focusses on the necessary development of new instrumentation, situated in four dedicated experimental regions, capable of studying such phenomena as electron clouds (ECs) and methods to mitigate EC effects. The fourth paper in this series describes the vacuum system modifications of the superconducting wigglers to accommodate the diagnostic instrumentation for the study of EC behavior within wigglers. While the initial studies of CESRTA focussed on questions related to the International Linear Collider damping ring design, CESRTA is a very versatile storage ring, capable of studying a wide range of accelerator physics and instrumentation questions.

Experiments have been performed at the Cornell Electron-Positron Storage Ring Test Accelerator (CESRTA) to probe the interaction of the electron cloud with a 2.1 GeV stored positron beam. The purpose of these experiments was to characterize the dependence of beam–electron cloud interactions on the bunch spacing and the vertical chromaticity. These experiments were performed on a 30-bunch positron train, at a fixed current of 0.75mA/bunch. The bunch spacing was varied between 4 and 56 ns at three different vertical chromaticity settings. The beam dynamics of the stored beam, in the presence of the electron cloud, was quantified using: 1) a gated beam position monitor (BPM) and spectrum analyzer to measure the bunch-by-bunch frequency spectrum of the bunch trains; 2) an x-ray beam size monitor to record the bunch-by-bunch, turn-by-turn vertical size of each bunch within the trains. In this paper we report on the observations from these experiments and analyze the effects of the electron cloud (EC) on the stability of bunches within these different trains. ELECTRON CLOUD INTERACTIONS CESRTA has been studying the effects of ECs on stored beams to understand their impact on future low emittance storage ring and linear-collider damping ring designs. It is important to understand the way that the electron cloud alters the dynamics of bunches within the train. Measurements of the shift in the coherent betatron tunes from bunch to bunch along the train provide evidence for the change in EC density within the train. Another question is how does the damping of the coherent motion of bunches change in the presence of the EC. One technique is to observe the BPM signal from a single bunch and to drive this bunch in one of its coherent modes, then turn off the excitation and measure the damping of the motion.[1] A second method is to observe the change in the spectral amplitude of the coherent modes as the damping is changed. In our case we chose to alter the damping by changing the chromaticity of CESR.

In this paper, we will describe some of the recent experimental measurements [1, 2, 3] performed at CESRTA [4], and the supporting simulations, which probe the interaction of the electron cloud with the stored beam. These experiments have been done over a wide range of beam energies, emittances, bunch currents, and fill patterns, to gather sufficient information to be able to fully characterize the beam-electron-cloud interaction and validate the simulation programs. The range of beam conditions is chosen to be as close as possible to those of the ILC damping ring, so that the validated simulation programs can be used to predict the performance of these rings with regard to electroncloud- related phenomena. Using the new simulation code Synrad3D to simulate the synchrotron radiation environment, a vacuum chamber design has been developed for the ILC damping ring which achieves the required level of photoelectron suppression. To determine the expected electron cloud density in the ring, EC buildup simulations have been done based on the simulated radiation environment and on the expected performance of the ILC damping ring chamber mitigation prescriptions. The expected density has been compared with analytical estimates of the instability threshold, to verify that the ILC damping ring vacuum chamber design is adequate to suppress the electron cloud single-bunch head-tail instability.

Electron clouds can adversely affect the performance of accelerators, and are of particular concern for the design of future low emittance damping rings. Studies of the impact of electron clouds on the dynamics of bunch trains in Cesr have been a major focus of the Cesr Test Accelerator (CesrTA) program. In this paper, we report measurements of coherent tune shifts, emittance growth, and coherent instabilities carried out using a variety of bunch currents, train configurations, beam energies and transverse emittances, similar to the design values for the ILC damping rings. The measurements will be compared with simulations which model the effects of electron clouds on beam dynamics, to extract simulation model parameters and to quantify the validity of the simulation codes.

Over the course of the past four years, the Cornell Electron Storage Ring (CESR) has been reconfigured to serve as a test accelerator (CESRTA) for next generation machines, in particular for the ILC damping ring. A significant part of this program has been the installation of diagnostic devices to measure and quantify the electron cloud effect, a potential limiting factor in these machines. In particular, several Retarding Field Analyzers (RFAs) have been installed in CESR. These devices provide information on the local electron cloud density and energy distribution, and have been used to evaluate the efficacy of different cloud mitigation techniques. This paper will provide an overview of RFA results obtained in wigglers. Understanding these results provides a great deal of insight into the behavior of the electron cloud.

The study of electron cloud-related instabilities for the CESR-TA project has required developing new automatic and semi-automatic measurement techniques. The dynamics of the interaction of electron clouds with trains of bunches has been studied via three basic observations. Measurements of tune shifts of bunches along a train has been used extensively with the most recent observations permitting the excitation of single bunches within the train to avoid collective train motion from driving the ensemble of bunches. Another technique was developed to detect the coherent self-excited spectrum for each bunch within a train. This method is particularly useful when beam conditions are near the onset of an instability. The third method was designed to study bunches within the train in conditions before there is unstable motion. This is accomplished by separately driving each bunch within the train for several hundred turns and then observing the damping of its coherent motion. These last two techniques have been applied to study both transverse dipole (centroid) and head-tail motion. We report on the observation methods and give examples of typical results.

beam dynamics in the presence of electron cloud effects. These new instruments are also required to develop low emittance beam conditions which are key to the success of Differential Position Accuracy Channel-to-Channel Sampling Time Accuracy BPM Tilt Errors (after correction) 10 μm 10 ps 10 mrad the damping ring design for the International Linear Collider. This poster will detail some of the architecture and tools which have been developed to support these efforts. Experiment Specific Instruments •Server/client code •Multi Language Functions •Lab wide networking •Hardware interface designs

Over the course of the CesrTA program, the Cornell Electron Storage Ring (CESR) has been instrumented with several retarding field analyzers (RFAs), which measure the local density and energy distribution of the electron cloud. These RFAs have been installed in drifts, dipoles, quadrupoles, and wigglers; and data have been taken in a variety of beam conditions and bunch configurations. This paper will provide an overview of these results, and give a preliminary evaluation of the efficacy of cloud mitigation techniques implemented in the instrumented chambers.

The baseline configuration for the International Linear Collider (ILC) damping rings specifies a single 6.6 km damping ring for electrons and two 6.6 km rings for positrons. Kicker requirements are determined by the damping ring circumference and the train structure in the main linac. The nominal bunch train parameters in the ILC main linac are trains of 2820 bunches with 308 ns spacing and a train repetition rate of 5 Hz. The pulsers for the damping ring kickers must have rise and fall times suitable for bunch spacings of ns, must be able to operate with 3.25 MHz bursts, and must support an average pulse rate of 14.1 kHz. We describe bench and beam tests of a pulser from FID Technology whose specifications roughly meet these requirements. We then discuss the implications of our results for the ILC damping ring kickers.

Measurement of the betatron phase in the vertical and horizontal planes as well as the transverse horizontal-vertical coupling is a standard procedure now used at the Cornell Electron/Positron Storage Ring. The measurement is made by shaking the beam and observing the phase of oscillation at detectors located around the ring. The measurements allow quadrupolar errors to be corrected.

Total stored electron and positron beam currents at the Cornell Electron Storage Ring (CESR) have been limited by the presence of a dipole multibunch longitudinal instability having a threshold at approximately 250 mA of total current. A longitudinal feedback system has been under constant development, test, operation and upgrade over the past several years. The result has been an increase in the High Energy Physics operating current to over 500 mA total. This paper describes the overall design of the present system, using a horizontal stripline kicker to produce combined horizontal and longitudinal bunch by bunch beam stabilization. Some details on specific subsystems, including: receiver design, individual bunch phase DC offset correction, digital signal filtering, and the RF modulator will be given, as well as an outline of plans for further development.

Using the silicon strip detector of the CLEO experiment operating at the Cornell Electron-Positron Storage Ring (CESR), we have observed that the horizontal size of the luminous region decreases in the presence of the beam-beam interaction from what is expected without the beam-beam interaction. The dependence on the bunch current agrees with the prediction of the dynamic beta effect. This is the first direct observation of the effect.