M. Borland

Start-to-end simulation of self-amplified spontaneous emission free-electron lasers from the gun through the undulator.

Abstract It is widely appreciated that the performance of self-amplified spontaneous emission free-electron lasers (FELs) depends critically on the properties of the drive beam. In view of this, a multi-laboratory collaboration has explored methods and software tools for integrated simulation of the photoinjector, linear accelerator, bunch compressor, and FEL. Rather than create a single code to handle such a system, our goal has been a robust, generic solution wherein pre-existing simulation codes are used sequentially. We have standardized on the use of Argonne National Laboratorys Self-Describing Data Sets file protocol for transfer of data among codes. The simulation codes used are PARMELA, elegant , and GENESIS. We describe the software methodology and its advantages, then provide examples involving Argonnes Low-Energy Undulator Test Line and Stanford Linear Accelerator Centers Linac Coherent Light Source. We also indicate possible future direction of this work.

A self-describing file protocol for simulation integration and shared postprocessors

A typical accelerator physics code uses a combination of text output, unformatted output, and special-purpose graphics to present results to the user. Most users must learn multiple graphics and postprocessing systems; many resort to manual extraction of data from text output, creation of customized postprocessing programs, and even modification of the simulation code. This situation slows down research, results in duplication of effort, hampers unforeseen use of simulation output, and makes program upgrades potentially traumatic. This paper discusses the design and use of a self-describing file protocol that addresses these problems. An extensive toolkit of generic postprocessing programs, including sophisticated graphics, is available. This system has been used for most of the data collection for advanced photon source (APS) commissioning, and is incorporated into a number of simulation codes.

Measurements of nonlinear harmonic generation at the Advanced Photon Source's SASE FEL

SASE saturation was recently achieved at the Advanced Photon Sources SASE FEL in the low-energy undulator test line (LEUTL) at 530 nm and 385 nm. The electron beam microbunching becomes more and more prominent until saturation is achieved. This bunching causes nonlinear harmonic emission that extends the usefulness of a SASE system in achieving shorter FEL wavelengths for the same electron beam energy. They have investigated the intensity of the fundamental and second-harmonic undulator radiation as a function of distance along the undulator line and present the experimental results and compare them to numerical simulations. In addition, they have measured the single-shot second harmonic spectra as well as the simultaneous fundamental and second harmonic spectra and present the experimental results.

An improved thermionic microwave gun and emittance-preserving transport line

The positron/electron linac for the Advanced Photon Source (APS) at Argonne National Laboratory can be used to accelerate electrons to 650 MeV. As part of a project, to use this linac to test the quality of insertion devices, work has been done to develop a higher-brightness thermionic microwave gun of the SSRL type. The new gun design has smaller emittance by a factor of 3 to 4. The ratio of cathode field to maximum surface field is more than doubled. The new alpha-magnet-based transport line design produces negligible emittance degradation due to chromatic aberrations, in spite of the /spl plusmn/5% momentum spread.<<ETX>>

Lattice design challenges for fourth-generation storage-ring light sources.

Third-generation low-emittance storage-ring light sources based on double- and triple-bend cells and undulator magnets have been in operation around the world for more than two decades. On the horizon is a new generation based on the multi-bend achromat (MBA) lattice concept promising two to three orders of magnitude higher brightness than is available in todays sources. In this paper, the challenges inherent in designing MBA lattices, as well as potential solutions, are described. Topics covered include lattice concepts, scaling of storage-ring performance, brightness optimization, nonlinear dynamics, beam lifetime and injection schemes.

Planned use of pulsed crab cavities for short X-ray pulsed generation at the Advanced Photon Source

Recently, we have explored application to the Advanced Photon Source (APS) of Zholents[1] crab cavity scheme for production of short x-ray pulses. We assumed use of superconducting (SC) cavities in order to have a continuous stream of crabbed bunches and flexibility of operating modes. The challenges of the SC approach are related to the size, cost, and development time of the cavities and associated systems. A good case can be made [2] for a pulsed system using room-temperature cavities. APS has elected to pursue such a system in the near term, with the SC-based system planned for a later date. This paper describes the motivation for the pulsed system and gives an overview of the planned implementation and issues. Among these are overall configuration options and constraints, cavity design options, frequency choice, cavity design challenges, tolerances, instabilities, and diagnostics plans.

Start-to-end jitter simulations of the linac coherent light source

The Linac Coherent Light Source (LCLS) is a fourth-generation light source demonstration project based on the self-amplified spontaneous emission (SASE) free-electron laser (FEL) concept. It will combine a new photoinjector, the Stanford Linear Accelerator Center (SLAC) linac, with two stages of bunch compression and a long undulator to create intense radiation pulses at 1.5 A. Successful operation of the LCLS will require consistent delivery of a high-brightness electron beam to the undulator, in the face of effects such as wakefields and coherent synchrotron radiation (CSR). Because of the sensitivity to beam quality and subtle effects, it is necessary to perform integrated tracking from the cathode through the undulator. We report on the combined use of PARMELA, elegant, and GENESIS to perform these simulations, and in particular the simulation of pulse-to-pulse variation in FEL performance due to rf- and laser-related variation in the electron beam.

New features in the SDDS-compliant epics toolkit

This paper introduces new features and programs developed to enhance various aspects of the SDDS-compliant EPICS toolkit. A new optimization program, sddsoptimize, was added to the toolkit; it employs the Simplex and 1-D scan methods and can be used for both EPICS and non-EPICS optimizations. Several new data logging programs were also developed, including a new, more flexible glitch logger that logs data before and after a glitch occurs. Another new data logger logs data every time the value of a process variable changes. With the data generated from this program, it is now possible to restore settings from any arbitrary time without the need for a snapshot of the system. Another new addition is the capability of saving and restoring waveform process variables. In addition to these new features, performance improvements have been realized in all the toolkit programs by replacing EZCA calls with low-level channel-access calls. Some of the toolkit programs have been upgraded to run on vxWorks to achieve higher performance

Implementation and performance of parallelized elegant

The program elegant is widely used for design and modeling of linacs for free-electron lasers and energy recovery linacs, as well as storage rings and other applications. As part of a multi-year effort, we have parallelized many aspects of the code, including single-particle dynamics, wakefields, and coherent synchrotron radiation. We report on the approach used for gradual parallelization, which proved very beneficial in getting parallel features into the hands of users quickly. We also report details of parallelization of collective effects. Finally, we discuss performance of the parallelized code in various applications.

SDDS-based software tools for accelerntor design

The self-describing data set (SDDS) file protocol is a standardized way to store and access data and is the basis of an extensive toolkit. It is also the file protocol used for many accelerator design tools. Over the years, several of these SDDS-compliant accelerator programs (e.g., clinchor, elegant, estat, shower, and spiffe) have been developed at the Advanced Photon Source. Also, existing accelerator design tools for which the source code is available (e.g., ABCI, GENESIS, GINGER, MAFIA, and URMEL) have been converted to read and write SDDS files. As a result, we now have a capable set of accelerator codes that make use of the same data format and the same pre- and postprocessing suite. Further, the SDDS toolkit program sddsoptimize can be used around any of these tools or around a script that runs one or more of these tools. This provides the capability of very general, multicode optimization. In this paper, we discuss the capabilities of the existing SDDS-compliant accelerator codes, then provide examples of applications of these tools