LBNL is pursuing design studies and the scientific program for a facility dedicated to the production of xray pulses with ultra-short time duration, for application in dynamical studies of processes in physics, biology, and chemistry. The proposed x-ray facility has the short x-ray pulse length (~60 fs FWHM) necessary to study very fast dynamics, high flux (up to approximately 10 11 photons/sec/0.1%BW) to study weakly scattering systems, and tuneability over 1-12 keV photon energy. The hard x-ray photon production section of the machine accomodates seven 2-m long undulators. Design studies for longer wavelength sources, using high-gain harmonic generation, are in progress. The x-ray pulse repetition rate of 10 kHz is matched to studies of dynamical processes (initiated by ultra-short laser pulses) that typically have a long recovery time or are not generally cyclic or reversible and need time to allow relaxation, replacement, or flow of the sample. The technique for producing ultra-short x-ray pulses uses relatively long electron bunches to minimise high-peak-current collective effects, and the ultimate x-ray duration is achieved by a combination of bunch manipulation and optical compression. Synchronization of x-ray pulses to sample excitation signals is expected to be of order 50 -100 fs. Techniques for making use of the recirculating geometry to provide beam-based signals from early passes through the machine are being studied.

We present an updated design for a proposed source of ultra-fast synchrotron radiation pulses based on a recirculating superconducting linac [1,2], in particular the incorporation of EUV and soft x-ray production. The project has been named LUX -Linac-based Ultrafast X-ray facility. The source produces intense x-ray pulses with duration of 10-100 fs at a 10 kHz repetition rate, with synchronization of 10's fs, optimized for the study of ultra-fast dynamics. The photon range covers the EUV to hard x-ray spectrum by use of seeded harmonic generation in undulators, and a specialized technique for ultra-shortpulse photon production in the 1-10 keV range. Highbrightness rf photocathodes produce electron bunches which are optimized either for coherent emission in freeelectron lasers, or to provide a large x/y emittance ration and small vertical emittance which allows for manipulation to produce short-pulse hard x-rays. An injector linac accelerates the beam to 120 MeV, and is followed by four passes through a 600-720 MeV recirculating linac. We outline the major technical components of the proposed facility.

The Spallation Neutron Source Low Level RF Team includes members from Lawrence Berkeley, Los Alamos, and Oak Ridge national laboratories. The Team is responsible for the development, fabrication and commissioning of 98 Low Level RF (LLRF) control systems for maintaining RF amplitude and phase control in the Front End (FE), Linac and High Energy Beam Transport (HEBT) sections of the SNS accelerator, a 1 GeV, 1.4 MW proton source. The RF structures include a radio frequency quadrupole (RFQ), rebuncher cavities, and a drift tube linac (DTL), all operatingat 402.5 MHz, and a coupled-cavity linac (CCL), superconducting linac (SCL), energy spreader, and energy corrector, all operating at 805 MHz. The RF power sources vary from 20 kW tetrode amplifiers to 5 MW klystrons. A single control system design that can be used throughout the accelerator is under development and will begin deployment in February 2004. This design expands on the initial control systems that are currently deployed on the RFQ, rebuncher and DTL cavities. An overview of the SNS LLRF Control System is presented along with recent test results and new developments.

We report on impedance calculations and single-bunch and multi-bunch instabilities in the NLC damping rings. Preliminary designs of vacuum chambers and major components have addressed beam impedance issues, with the desire to increase instability current thresholds and reducing growth rates. MAFIA calculations of short-range and long-range wakefields have allowed computations of growth rates and thresholds, which are presented here. Resistive wall instability dominates long-range effects, and requires a broadband feedback system to control coupled-bunch motion. Growth rates are within the range addressable by current feedback system technologies. Single-bunch instability thresholds are safely above nominal operating current. The purpose of the damping rings is to provide low emittance electron and positron bunch trains to the NLC linacs, at a rate of 120 Hz. The main damping rings operate at 1.98 GeV and may store up to 0.8 amp in 3 trains of 95 bunches each, have bunch lengths of less than 4 mm, and normalized extracted beam emittances γεx ≤ 3 µm-rad and γεy ≤ 0.03 µm-rad. The number of particles per bunch is 0.75x10 10 for 1.4 ns spacing, and 1.5x10 10 for 2.8 ns spacing. The optical designs are based on a theoretical minimum emittance (TME) lattice, and major parameters are shown in Vacuum chambers are made of aluminum, with antechambers through the arcs to allow adsorption of synchrotron radiation on discrete photon stops electromagnetically isolated from the beam. Beam-pipe apertures are 32 mm diameter in the arcs and injection/extraction straights, and 16 mm diameter through the damping wiggler straight. The RF cavities are higher-order-mode damped, with apertures of 64 mm, and the beampipe diameter is increased to 64 mm through the RF section [3]. Blends are used to mate sections of different cross-section, using tapers of at least 10:1 aspect ratio. All components are designed with minimizing impedance as a design constraint. Stability of the extracted beam is critical to ensure effective bunch compression and luminosity at the interaction point. DAMPING RINGS DESIGN SHORT-RANGE WAKEFIELDS3-D MAFIA time-domain models have been used to compute the short-range wakefield for main damping rings beamline components. Major components modeled are• RF cavitiesThe resistive wall impedance has been calculated analytically.Wakefields were calculated at the nominal bunch length to determine the impedance budget. A shorter bunch length was used to obtain a Green's function wakefield for beam instability studies. Both longitudinal and transverse wakes have been calculated for the components listed.While detailed designs are not yet developed for many components, the models used here are based on experience with other rings (such as the ALS at Berkeley, and the PEP-II B-factory), and are believed to represent a realistic set of components. RF cavitiesIn order to reduce transverse mode impedance, the cavities have a larger bore than the straight section beampipe. Tapers are located at the ends of the RF section,...

We describe a proposed femtosecond synchrotron radiation x-ray source based on a flat-beam RF gun and a recirculating superconducting linac that provides beam to an array of undulators and bend magnets. X-ray pulse durations of <100 fs at a 10 kHz repetition rate are obtained by a combination of electron pulse compression, transverse temporal correlation of the electrons, and x-ray pulse compression.