acceleration

Paper	Title	Other Keywords	Page
ROAA05	An Approach to Stabilizing Large Telescopes for Stellar Interferometry	controls, feedback, site	497
	J. Sahlmann, A. Wallander, N. Di Lieto ESO, Garching bei Muenchen G. Vasisht Jet Propulsion Laboratory, Pasadena, California
	In stellar interferometry fringe-tracking is a method of stabilizing the Optical Pathlength Difference (OPD) from the observed astronomical source to the instrument detector via different telescopes in an interferometric array. At the ESO VLT Interferometer, which includes four 8.2 m class Unit Telescopes (UTs), stabilization to better than a tenth of the observing wavelength is required in order to improve the quality and sensitivity of fringe measurements on the interferometer's scientific instruments. Unfortunately, fast mechanical vibrations due to myriad sources in the observatory infrastructure couple to UT support structure and propagate to the large telescope mirrors. The mirror motions are fast and large (typically about a wavelength) and must be compensated for in real time. We have implemented a scheme to measure the accelerations imparted to the primary, secondary, and tertiary mirrors of the UTs via a grid of suitably placed accelerometers. The measured accelerations, coupled with a simple geometric model, are converted to optical pathlengths and canceled by a wideband feed-forward compensation to a downstream optical delay line.
	Slides
FOAA02	Timing and LLRF System of Japanese XFEL to Realize Femto-Second Stability	controls, laser, klystron, linac	706
	T. Fukui, N. Hosoda, H. Maesaka, T. Ohshima, T. Shintake RIKEN, Hyogo K. Imai, M. Kourogi OPtical Comb, Inc., Yokohama M. K. Kitamura, K. Tamasaku, Y. Otake RIKEN Spring-8 Harima, Hyogo M. Musya University of electro-communications, Tokyo T. Ohata JASRI/SPring-8, Hyogo-ken
	At SPring-8, the construction of a 5712-MHz linac and undulators as a light source for XFEL is in progress. There are two parts of the linac in accordance with requirements of phase accuracy to realize a stable SASE generation. One is a crest acceleration part using a sinusoidal wave. The other is an off-crest part that corresponds to a bunch compressor giving an energy chirp to a beam bunch. To generate the stable SASE, the beam energy stability of 10-4 is required. To obtain this stability, the accuracy of sub-picoseconds is required in the crest part, and several ten femto-seconds are necessary in the off-crest part. The requirement in the crest part was achieved by rf control instruments based on an electronic circuit in the SCSS prototype accelerator. However, realizing the several ten femto-seconds accuracy is almost impossible by the present electronic circuit technology. Therefore, for overcoming this fact, we employed laser technology. In this paper, we describe a system based on IQ control technology to obtain sub-picoseconds accuracy and an optical signal distribution system using an optical comb generator that could realize several ten femto-seconds accuracy.
	Slides