Design of a fast global orbit feedback system for the Advanced Light Source

The fast stability of the closed orbit of the electron beam at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory fulfills user requirements so far without any fast active correction system. In the range between 0.1 and 500 Hz the integrated rms closed orbit motion is significantly below one tenth of one sigma beamsizes. For the future there is some user demand to improve this stability further. Moreover, the expansion of the capabilities of the ALS creates new sources of closed orbit noise. Therefore the design of a fast global orbit feedback system has been started in conjunction with a general upgrade of the ALS control system. It will initially operate with an update rate of 500 Hz - 1 kHz, will include 24 beam position monitors and corrector magnets in each plane and will use standard computer and networking architecture. The system design, measurements of transfer functions and tests with small prototype systems will be presented.