CLASSE, Ithaca, New York, USA
LBNL, Berkeley, California, USA
ANL, Argonne, USA
Over the course of the CesrTA program at Cornell, over 30 Retarding Field Analyzers (RFAs) have been installed in the CESR storage ring, and a great deal of data has been taken with them. These devices measure the local electron cloud density and energy distribution, and can be used to evaluate the efficacy of different cloud mitigation techniques. Obtaining a quantitative understanding of RFA data requires use of cloud simulation programs, as well as a detailed model of the detector itself. In a drift region, the RFA can be modeled by postprocessing the output of a simulation code, and one can obtain best fit values for important simulation parameters with a chi-square minimization method.
CLASSE, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
Energy Recovery Linacs (ERLs) are proposed as drivers for hard X-ray sources because of their ability to produce electron bunches with small, flexible cross sections and short lengths at high repetition rates. The advantages of ERL lightsources will be explained, and the status of plans for such facilities will be described. In particular, Cornell University plans to build an ERL light source, and the preparatory research for its construction will be discussed. This will include the prototype injector for high current CW ultra-low emittance beams, superconducting CW technology, the transport of low emittance beams, halo formation from intrabeam scattering, the mitigation of ion effects, the suppression of instabilities, and front to end simulations. Several of these topics could become important for other modern light source projects, such as SASE FELs, HGHG FELs, and XFELOs.
CLASSE, Ithaca, New York, USA
LBNL, Berkeley, California, USA
CalPoly, San Luis Obispo, California, USA
Measurements of coherent tune shifts at the Cornell Electron Storage Ring Test Accelerator (CesrTA) have been made for electron and positron beams under a wide variety of beam energies, bunch charge, and bunch train configurations. Comparing the observed tunes with the predictions of several electron cloud simulation programs allows the evaluation of important parameters in these models. These simulations will be used to predict the behavior of the electron cloud in damping rings for future linear colliders. We outline recent improvements to the analysis techniques that should improve the fidelity of the modeling.
CLASSE, Ithaca, New York, USA
Cornell University, Ithaca, New York, USA
Electron cloud buildup is a primary concern for the performance of the damping rings under development for the International Linear Collider. We have performed synchrotron radiation profile calculations for the 6.4-km DC04 and 3.2-km DSB3 lattice designs using the SYNRAD utility in the Bmad accelerator software library. These results are then used to supply input parameters to the electron cloud modeling package ECLOUD. Contributions to coherent tune shifts from the field-free sections and from the dipole and quadrupole magnets have been calculated, as well as the effect of installing solenoid windings in the field-free regions. For each element type, SYNRAD provides ring occupancy, average beam sizes, beta function values, and beta-weighted photon rates for the coherent tune shift calculation. An approximation to the antechamber design has been implemented in ECLOUD as well, moving the photoelectron source point to the edges of the antechamber entrance and removing cloud particles which enter the antechamber.
CLASSE, Ithaca, New York, USA
CERN, Geneva, Switzerland
The Cornell Electron Storage Ring Test Accelerator (CesrTA) program includes investigations into electron cloud buildup, applying various mitigation techniques in custom vacuum chambers. Among these are two 1.1 meter long sections located symmetrically in the east and west arc regions. These chambers are equipped with pickup detectors shielded against the direct beam-induced signal. Here we report on results from the ECLOUD modeling code which highlight the sensitivity of these measurements to model parameters such as the photoelectron energy distributions, and the secondary elastic yield value.
CLASSE, Ithaca, New York, USA
LBNL, Berkeley, California, USA
The Cornell Electron Storage Ring has been reconfigured as a Test Accelerator (CesrTA). Shielded pickups have been installed at three locations in CesrTA for the purpose of studying time resolved electron cloud build-up and decay. The pickup design provides electromagnetic shielding from the beam wakefield while allowing cloud electrons in the vacuum space to enter the detector. This paper describes the hardware configuration and capabilities of these detectors at CesrTA, presents examples of measurements, and outlines the interpretation of detector signals with regard to electron clouds. Useful features include time-of-flight measurement of cloud electrons and the use of a solenoidal field for energy measurement of photoelectrons. Measurement techniques include the use of two bunches spaced in multiples of 4ns, where the second bunch samples the decay of the cloud produced by the first bunch.