• A. Xiao, M. Borland
  ANL, Argonne

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
We present a Monte-Carlo method implemented in the code elegant for simulating Touschek scattering effects in a linac beam. The local scattering rate and the distribution of scattered particles can be obtained from the code. In addition, scattered particles can be tracked to the end of the beam line and the local beam loss rate and beam halo information recorded. This information can be used for beam collimation system design.

• M. Borland, V. Sajaev
  ANL, Argonne

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
An Energy Recovery Linac (ERL) is one possibility for an upgrade to the Advanced Photon Source (APS). In addition to the linac itself, our concept involves a large turn-around arc (TAA) at 7 GeV that would eventually accommodate many new beamlines. Previously, we based the TAA design on isochronous triple-bend archromat (TBA) cells, since these are expected to provide some immunity to the effects of coherent synchrotron radiation. In the present work, we compare the previous TBA-based design to a new design based on double-bend achromat cells, in terms of emittance growth, energy spread growth, and energy recovery. We also explore the trade-off between optimization of the beta functions in the straight sections and minimization of emittance growth.

• M. Borland
  ANL, Argonne

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
An Energy Recovery Linac (ERL) is one possibility for an upgrade to the Advanced Photon Source (APS). Such a system involves not only a long linac, but also long transport lines with many dipole magnets. Since the bunches are short, we may expect that coherent synchrotron radiation and longitudial space charge will have an affect on the beam dynamics. Although previous studies have shown minimal effects for an initially quiet beam distribution, the possibility of a microbunching instability seeded by initial density modulation must be evaluated. We present and discuss simulation results showing the growth of density modulations in two possible lattices for an ERL upgrade of the APS.

• V. Sajaev, M. Borland
  ANL, Argonne

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
One of the possible options for the Advanced Photon Source (APS) upgrade is an energy-recovery linac (ERL). In its main operating mode, the ERL bunch length would be two picoseconds. Even though this bunch length is already a factor of 20 shorter than the present APS bunch length, some experiments might require shorter X-ray pulses. For the APS storage ring, we plan to use an rf deflection technique* to generate one-picosecond X-ray pulses. In this approach, an rf cavity is used to deliver longitudinally dependent vertical kick to the electron beam and then a pair of slits is used to slice vertically streaked X-ray beam. We investigate the possibility and benefits of utilizing this technique to generate shorter X-ray pulses at the ERL.

*A. Zholents, et al., Nucl. Instr. and Meth. A 425 (1999) 385.

• A.H. Lumpkin
  Fermilab, Batavia
• W. Berg, M. Borland, Y.L. Li, S.J. Pasky, N. Sereno
  ANL, Argonne

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357
Strong enhancements of the optical transition radiation (OTR) signal sampled after bunch compression in the Advanced Photon Source (APS) linac chicane have been observed as has been reported in LCLS injector commissioning. A FIR CTR detector and interferometer were used to monitor the bunch compression process of the PC gun beam down to sub-0.5 ps (FWHM) and correlate the appearance of spatially localized spikes of OTR signal (5 to 10 times brighter than adjacent areas) within the beam image footprint. We also observed that a beam from a thermionic cathode gun with much lower charge per micropulse (but a similar total macropulse charge to the PC gun) showed no enhancement of the OTR signal after compression. Reconstructions of the temporal profiles from the autocorrelations of both beams were performed and will be presented. Spectral-dependence measurements of the enhanced OTR were done initially at the 375-MeV station using a series of bandpass filters inserted before the CCD camera. Tests with an Oriel spectrometer with ICCD readout are now being planned to extend those studies. Discussions of the possible mechanisms for the OTR enhancements will be presented.

• Y.-E. Sun, M. Borland, K.C. Harkay, Y.L. Li, H. Shang
  ANL, Argonne

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
An energy recovery linac based light source is a potential revolutionary upgrade to the Advanced Photon Source (APS) at Argonne National Laboratory. The concept relies on several key research areas, one of which is the generation of ultra-low emittance, high-average-current electron beams. In this paper, we present our investigation of a dc-gun-based system for ultra-low emittance bunches in the 20 pC range. A parallel multi-objective numerical optimization is performed in multi-parameter space. Parameters varied include experimentally feasible drive-laser shapes, the dc gun voltage, and the thermal energy of the emitted photo-electrons. Our goal is to deliver a 10 MeV, 20 pC bunch at the entrance of the linac with an emittance of 0.1 μm or lower, rms bunch length of 2 to 3 ps, and energy spread no larger than 140 keV. We present the machine parameters needed to generate such an injector beam, albeit without a merger.