• E.C.M. Rial, J.C. Schouten
  Diamond, Oxfordshire

Diamond Light Source is currently operating with two multipole superconducting wigglers, one with 49 poles at 3.5 T and another with 49 poles at 4.2 T. The cryogenic arrangement is similar in both cases; each cryostat contains a liquid helium bath cooled by four cryocoolers. The design goal was to allow up to six months continuous operation in the storage ring between refilling the liquid helium bath. However, the helium boil-off is much higher than expected, necessitating much more frequent refills. As well as having a cost implication, this also currently poses a restriction on the operating beam current. In this report we present the results of measurements carried out under various beam conditions to try to understand the reason for the higher boil-off in terms of heat load seen by the cryostat and effective cryocooler performance. We also present our plans for dealing with the problem in the near and longer term.

• S. Gerstl, T. Baumbach, S. Casalbuoni, A.W. Grau, M. Hagelstein, D. Saez de Jauregui
  Karlsruhe Institute of Technology (KIT), Karlsruhe
• V. Baglin
  CERN, Geneva
• C. Boffo, G. Sikler
  BNG, Würzburg
• T.W. Bradshaw
  STFC/RAL, Chilton, Didcot, Oxon
• R. Cimino, M. Commisso, B. Spataro
  INFN/LNF, Frascati (Roma)
• J.A. Clarke, D.J. Scott
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• M.P. Cox, J.C. Schouten
  Diamond, Oxfordshire
• R.M. Jones, I.R.R. Shinton
  UMAN, Manchester
• A. Mostacci
  Rome University La Sapienza, Roma
• E.J. Wallén
  MAX-lab, Lund
• R. Weigel
  Max-Planck Institute for Metal Research, Stuttgart

One of the still open issues for the development of superconducting insertion devices is the understanding of the beam heat load. With the aim of measuring the beam heat load to a cold bore and the hope to gain a deeper understanding in the beam heat load mechanisms, a cold vacuum chamber for diagnostics is under construction. The following diagnostics will be implemented: i) retarding field analyzers to measure the electron flux, ii) temperature sensors to measure the total heat load, iii) pressure gauges, iv) and mass spectrometers to measure the gas content. The inner vacuum chamber will be removable in order to test different geometries and materials. This will allow the installation of the cryostat in different synchrotron light sources. COLDDIAG will be built to fit in a short straight section at ANKA. A first installation at the synchrotron light source DIAMOND is under discussion. Here we describe the technical design report of this device and the planned measurements with beam.