Superconducting Multipole Wigglers: Magnetic and Cryogenic Systems

Superconducting Multipole Wigglers (SCMWs) represent a sign-alternating sequence of magnets with a lateral magnetic field. Relativistic electrons, passing through such set of magnetic elements, create radiation with properties of synchrotron radiations depending on product of maximum field and its period. SCMWs are installed on Synchrotron Radiation (SR) sources to increase the brightness and the rigidity of the radiation. Without being the main magnetic elements of SR sources nevertheless to them high demands on reliability are made. SCMWs should be independent and reliable devices working in the conditions of limited access which follows from the continuous work of SR sources. The work presents a review of superconducting wiggler designed and fabricated in Budker Institute of Nuclear Physics (BINP) for the last ten years, which are successfully working in various centers of synchrotron radiation. A typical bath cryostat with liquid helium for superconducting wiggler magnets provides long a continuous independent work of the SCMWs with a year-averaged liquid helium consumption less than 0.03 litre/hour. The cryostat concept is based on interception of all possible heat-in-leak into liquid helium vessel by means of thermal screens and heat sinks connected to cryocoolers which are built-in into the cryostat. Two types of two-stage cryocoolers with temperatures 50 kappa/10K and 50 kappa/4 kappa are used. The 4K cryocooler stage is used for the liquefaction of evaporated helium and the temperature reduction down to 3.1-3.5 kappa. The cryocooler stage with temperature 10 kappa is used for interception of heat induced by the electron beam of a SR source in a copper liner which is inside of the SR source vacuum chamber. Several superconducting wigglers with this kind of the cryostat are successfully working in the various synchrotron radiations centres (CLS (Canada), DLS (England), LNLS (Brazil), ELETTRA (Italy), BESSY (Germany), CAMD (USA), Siberia (Russia), ASHo (Australia), ALBA-CELLS (Spain). The zero liquid helium consumption in the cryostats is provided by cryocoolers made by the companies SUMITIMO HI or Leybold.