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 report on the design and development of a strongly HOM damped copper RF cavity for the NLC damping rings. The cavity is based on the successful PEP-II RF cavity but incorporates many simplifications and improvements. The cavity is designed for a frequency of 714 MHz, gap voltage of 500 kV and beam current of 800 mA. We present the RF design and HOM impedance calculations done in MAFIA, the RF, thermal and stress analyses performed in ANSYS and the simplified mechanical design and assembly process. Designs for the RF window, HOM loads and tuners are described. Options for increasing the stored energy or further lowering the HOM impedance are discussed. This design could easily be scaled up or down in frequency and could be useful for other projects such as new light sources.
We report on techniques developed for producing electromagnetic, thermal, and structural solutions to RF cavity design problems in ANSYS, using one model [1]. Methods for preparing imported geometry from solid modeling programs are discussed, and meshing techniques are suggested. A study of mesh density is presented, comparing mesh size with heat flux and Q factor convergence. The general analysis protocol is presented in a stepwise fashion, describing the macros that are used for conducting RF calculations. Finally, these techniques are applied to a proposed RF cavity for the NLC damping rings, which is shown as an example.
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