Introduction to the Compensation Systems

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Large scale cryogenic systems applied in modern fusion reactors (Claudet and Aymar 1990), superconducting particle accelerators (Lebrun 1999b; Van-Sciver 1998) or coolant transfer lines (Lebrun 1999a) as well as small scale refrigerators and cryo-coolers generate significant progress in multiple domains related either to material sciences or to structural behaviour. When designing large scale cryogenic systems the engineers quickly realise that it is impossible to build a continuous “cold mass” since the material — by its physical nature — exhibits the thermal contraction and the thermo-mechanical strain fields, developed locally in the constraint structure might damage the object. Thus, any large cryogenic system has to be subdivided into the “cold segments”, each of them constructed separately and all of them assembled together in the destination place. A typical example can be found in the domain of particle accelerators where a continuity of the magnetic field is strongly postulated by the accelerator physics. On the other hand, the real structure has to be discontinuous, since the magnets are limited in length (for technological reasons) and separated by the so-called interconnections (Fig. 1.1). A similar problem appears in the cryogenic transfer lines, that convey liquid nitrogen or helium, where the maximum length of segments is often a function of the technological process of their manufacture and assembly. A typical liquid and gaseous helium transfer line containing several headers, located next to a superconducting accelerator, is shown in Fig. 1.2.