A radio frequency system with a fourth-harmonic "Landau" cavity suppresses coupled-bunch instabilities and increases the beam lifetime of the Aladdin electron storage ring. When the storage ring is operated with a small momentum compaction, instabilities limit the utility of the Landau cavity. Analytical modeling of instability frequencies and growth rates, simulations, and experiments suggest that the observed instabilities result from coupling between dipole and quadrupole Robinson modes.

In a two-stage compression and acceleration system, where each stage compresses a chirped bunch in a magnetic chicane, wakefields affect high-current bunches. The longitudinal wakes affect the macroscopic energy and current profiles of the compressed bunch and cause microbunching at short wavelengths. For macroscopic wavelengths, impedance formulas and tracking simulations show that the wakefields can be dominated by the resistive impedance of coherent edge radiation. For this case, we calculate the minimum initial bunch length that can be compressed without producing an upright tail in phase space and associated current spike. Formulas are also obtained for the jitter in the bunch arrival time downstream of the compressors that results from the bunch-to-bunch variation of current, energy, and chirp. Microbunching may occur at short wavelengths where the longitudinal space-charge wakes dominate or at longer wavelengths dominated by edge radiation. We model this range of wavelengths with frequency-dependent impedance before and after each stage of compression. The growth of current and energy modulations is described by analytic gain formulas that agree with simulations.

A new 50.58 MHz RF system has been installed in the Aladdin synchrotron light source at the University of Wisconsin -Madison. A more compact aluminum RF cavity was constructed to make the original RF straight section available for a future insertion device. The original grounded cathode 4CW100000E power amplifier was also modified to improve its stability and control system. The new system delivers enough power to run the cavity at maximum gradient while supporting large beam currents. New low level RF electronics were constructed, including low level RF feedback. Feedback allows the use of a smaller RF bucket at injection to improve beam capture and eliminates operational difficulties with the Robinson instability. Operational results with the new system are presented.

The University of Wisconsin-Madison and its partners are developing a design for a free electron laser (FEL) facility operating in the VUV to soft x-ray range that will be proposed as a new multidisciplinary user facility. Key features of this facility include seeded, fully coherent output with tunable photon energy and polarization over the range 5-900 eV, and simultaneous, independent operation of multiple beamlines. The different beamlines will support a wide range of science from femtochemistry requiring ultrashort pulses with kHz repetition rates to photoemission spectroscopy requiring high average flux and narrow bandwidth at MHz rates. The facility will take advantage of the flexibility, stability, and high average pulse rates available from a CW superconducting linac fed by a photoinjector. This unique facility is expected to enable new science through ultrahigh resolution in the time and frequency domains, as well as coherent imaging and nano-fabrication. This project is being developed through collaboration between the UW Synchrotron Radiation Center and MIT. We present an overview of the facility, including the motivating science, and its laser, accelerator, and experimental systems.

A new high-resolution soft x-ray beamline utilizing a variable line density grating has been constructed and tested at SRC. In addition to normal grating rotation, the grating housing mechanism allows a translation of the grating. This additional motion of the grating can be used in such a way that grating aberration effects such as defocus, coma, and spherical aberrations are minimized over the entire scan range. In order to achieve the theoretical resolving power of 105–5000 over the photon energy range of 280–1150 eV, extreme care had to be exercised in positioning and controlling the grating scan angle (<0.12 arcsec) and focus drive position (<10 μm). Using a spherical grating with a figure error of <0.2 arcsec and 10 μm slits, we were able to experimentally reproduce our theoretical predicted energy resolution over a wide energy range. We present photoabsorption data of the K-shell edges and associated Rydberg states of Ne, O2, and CO. The high-resolution monochromator unveils structures which were previously not seen or only poorly resolved. A quantitative data analysis of the Ne absorption peak shows the intrinsic lifetime broadening of the Ne 1s state agrees well with theoretical estimates.