LBNL, Berkeley, California, USA
Electron clouds impose limitations on current accelerators that may be more severe for future machines, unless adequate measures of mitigation are taken. The simulation package WARP-POSINST was recently upgraded for handling multiple bunches and modeling concurrently the electron cloud buildup and its effect on the beam, allowing for direct self-consistent simulation of bunch trains generating, and interacting with, electron clouds. We have used the WARP-POSINST package on massively parallel supercomputers to study the buildup and interaction of electron clouds with a proton bunch train in the CERN SPS accelerator. Results suggest that a positive feedback mechanism exists between the electron buildup and the e-cloud driven transverse instability, leading to a net increase in predicted electron density.
Used resources of NERSC.
LBNL, Berkeley, California, USA
Start-to-end simulation plays an important role in designing next generation light sources. In this paper, we present recent progress in further development and application of the parallel beam dynamics code, IMPACT, towards the fully start-to-end, multi-physics simulation of a next generation X-ray FEL light source. We will discuss numerical methods and physical models used in the simulation. We will also present some preliminary simulation results of a beam transporting through photoinjector, beam delivery system, and FEL beamlines.
LBNL, Berkeley, California, USA
UCB, Berkeley, California, USA
LBNL, Berkeley, California, USA
* F. Sannibale et al., this conference.
LBNL, Berkeley, California, USA
The operation at high current of the SPS at CERN is limited by transverse Single-Bunch instabilities generated by the effect of electron clouds. A model of a high bandwidth feedback control system has been implemented in the macro-particle code WARP to study bunch dynamics and identify system requirements for the efficient damping of single-bunch transverse instability. We analyze the effect of numerical noise and choice of simulation parameters on the modeling of beam dynamics, focusing in particular on the investigation of the feedback system requirements of minimum power to damp the instability and frequency bandwidth given a fixed gain. We report on simulation results and discuss the plans for the future improvements of the feedback model.
LBNL, Berkeley, California, USA
We report on the beam dynamics studies and optimization methods for a high-repetition (1 MHz) photoinjector based on a VHF normal conducting electron source. The simultaneous goals of beam compression and preservation of 6-dimensional beam brightness have to be achieved in the injector, in order to accommodate a linac driven FEL light source. For this, a parallel, multiobjective optimization algorithm is used. We discuss the relative merits of different injector design points, as well as the constraints imposed on the beam dynamics by technical considerations such as the high repetition rate.
LBNL, Berkeley, California, USA
LBNL is developing design concepts for a multi-beamline soft x-ray FEL array powered by a superconducting linear accelerator, operating with a high bunch repetition rate of approximately one MHz. The cw superconducting linear accelerator is supplied by an injector based on a high-brightness, high-repetition-rate photocathode electron gun. Electron bunches are distributed from the linac to the array of independently configurable FEL beamlines with nominal bunch rates up to 100 kHz in each FEL, and with even pulse spacing. Individual FELs may be configured for different modes of operation, and each may produce high peak and average brightness x-rays with a flexible pulse format, and with pulse durations ranging from sub-femtoseconds to hundreds of femtoseconds. In this paper we describe conceptual design studies and optimizations. We describe recent developments in the design and performance parameters, and progress in R&D activities.
CLASSE, Ithaca, New York, USA
CalPoly, San Luis Obispo, California, USA
CMU, Pittsburgh, Pennsylvania, USA
KEK, Ibaraki, Japan
LBNL, Berkeley, California, USA
SLAC, Menlo Park, California, USA
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 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. We also compare the measurements 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.
LBNL, Berkeley, California, USA
LLNL, Livermore, California, USA
NPS, Monterey, California, USA
The Advanced Photo-injector Experiment (APEX) at the Lawrence Berkeley National Laboratory is focused on the development of a high-brightness high-repetition rate (MHz-class) electron injector for X-ray FEL applications. The injector is based on a new concept gun, utilizing a normal conducting 186 MHz RF cavity operating in cw mode in conjunction with high quantum efficiency photocathodes capable of delivering the required repetition rates with available laser technology. The APEX activities are staged in 3 main phases. In Phases 0 and I, the gun will be tested at its nominal energy of 750 keV and several different photocathodes are tested at full repetition rate. In Phase II, a pulsed linac will be added for accelerating the beam at several tens of MeV to reduce space charge effects and measure the high-brightness performance of the gun when integrated in an injector scheme. At Phase II energies, the radiation shielding configuration of APEX limits the repetition rate to a maximum of several Hz. Phase 0 is under commissioning, Phase I under installation, and initial activities for Phase II are underway. This paper presents an update on the status of these activities.
CLASSE, Ithaca, New York, USA
LBNL, Berkeley, California, USA
Over the course of the CESRTA program at Cornell, Retarding Field Analyzers (RFAs) have been installed in drift, dipole, quadrupole, and wiggler field regions of the CESR storage ring. RFAs are used to measure the local electron cloud flux on the vacuum chamber wall. Through the use of a retarding grid and segmented collectors, they also provide information on the energy and transverse distribution of the cloud. Understanding these measurements on a quantitative level requires the use of cloud buildup simulation codes, adapted to include a detailed model of the structure of the RFA and its interaction with the cloud. The nature of this interaction depends strongly on the strength of the local magnetic field. We have developed models for RFAs in drift and dipole regions. The drift model has been cross-checked with bench measurements, and we have compared the RFA-adapted cloud buildup simulations with data. These comparisons have then been used to obtain best fit values for the photo-emission and secondary electron emission characteristics of some of the vacuum chamber materials and cloud mitigating coatings employed at CESRTA.