Synchrotron light source insertion device vacuum systems now in operation and systems proposed for die future are reviewed. An overview of insertion devices is given and four generic vacuum chamber designs, transition section design and pumping considerations are discussed. Examples of vacuum chamber systems are presented. INTRODUCTION During the past 10 years increased flux and brightness of synchrotron radiation has been achieved from electron storage rings with the development and

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... n of insertion devices (wigglers, undulators and wave-length shifters) at these facilities 1 . Successful vacuum system design of these devices has contributed to this development. With the advent, in the near future, of the 3rd generation synchrotron light facilities, those designed as low emittance electron storage rings expressly for wiggler/undulator sources, vacuum system design for these insertion devices will be challenging. The importance of vacuum system design for insertion devices can be appreciated when reviewing the development of insertion devices. Most insertion devices built to date can be grouped according to the technology used in the magnetic field structure construction. These include conventional electromagnet, superconducting magnet and permanent magnet technologies. Figure 1 summarizes peak field performance for period length of various devices built and operated to date 2 -3 -4 -5 -*-7 ' 8 "' 10 ' 11 . Dashed curves show approximately the present range of performance of insertion devices for the various construction technologies. Insertion devices built with conventional electromagnet technology are generally longer period length devices. At long period lengths these devices have peak fields near the saturation induction of iron and at shorter period lengths the peak field decreased due to limitations in coil cooling. Superconducting magnet technology construction generally is limited in peak field by critical current density in the superconductor. Systems of this type generally tend to be complex and expensive. Wave length shifters use this technology because very high fields are possible. Peak fields obtained in insertion devices built with permanent magnet technology are dependent on the permanent magnet materials used and geometry. Devices using rareearth-Cobalt and Neodymium-Iron magnetic materials have demonstrated high peak fields with short period length. Generally, peak field performance of conventional and superconducting magnets is inverse to the magnet gap if iron saturation, coil cooling or critical current density are not limiting whereas with permanent magnet insertion devices the field is approximately proportional to the inverse exponential of the