Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 99–102 The SLS storage ring support and alignment systems S. Zelenika a, *, R. Kramert a , L. Rivkin a , M. Rohrer a , D. Rossetti a , R. Ruland b , V. Schlott a , A. Streun a , P. Wiegand a a Paul Scherrer Institut - Swiss Light Source, CH-5232 Villigen PSI, Switzerland b Stanford Linear Accelerator Centre, 2575 Sand Hill Rd., Menlo Park, CA 94025, USA Abstract Storage rings of third generation synchrotron radiation facilities pose severe challenges for lowering the beam emittances and increasing the lifetimes, requiring thus increasing positioning and alignment precisions that must be preserved over long time spans. This work describes the SLS storage ring mechanical support, alignment and disturbances compensation systems that allow to meet these requirements. In particular, their design, the tests done on the respective prototypes and the applicability of the developed arrangement to beam-based alignment are addressed. # 2001 Elsevier Science B.V. All rights reserved. PACS: 29.20.Lq; 29.20.Dh; 07.85.Qe; 07.10.h Keywords: Storage ring; Support; Positioning; Alignment 1. Introduction The main goal at SLS is to achieve a high quality source (brightness), which is mainly determined by electron beam quality (low emit- tance). This poses severe challenges for the stability and reproducibility of the stored beam. However, the room left for lattices optimisation is limited; precise magnets adjustment becomes therefore increasingly important to reach small emittances and reduce orbit distortions before switching on correctors [1]. To meet these require- ments, provisions for accurate positioning and dynamic minimisation of ground motion and thermal effects have been foreseen during the storage ring design. 2. Configuration of the SLS storage ring support and alignment systems A girder structure was designed as the basic support unit of the storage ring elements (Fig. 1). In total 48 girders are used, four in each of the 12 triple bend achromats (TBA). The upper part of the girders provides ground reference surfaces with a precision of  15 mm, onto which the magnets are laid and fixed; in this way a single pre- assembled object is obtained, not necessitating fiducialization of individual items. *Corresponding author. Tel.: +41-56-3104586; fax: +41-56- 3103151. E-mail address: sasa.zelenika@psi.ch (S. Zelenika). 0168-9002/01/$-see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0168-9002(01)00246-7