Beta Beams for Neutrino Production: Heat Deposition from Decaying Ions in Superconducting Magnets

This report describes studies of energy deposition in superconducting magnets from secondary ions in the "beta beam" decay ring as described in the base-line scenario of the EURISOL Beta Beam Design Study. The lattice structure proposed in the Design Study has absorber elements inserted between the superconducting magnets to protect the magnet coils. We describe an efficient and small model made to carry out the study. The specially developed options in the beam code "ACCSIM" to track largely off-momentum particles has permitted to extract the necessary information to interface the transport and interaction code "FLUKA" with the aim to calculate the heat deposition in the magnets and the absorbers. The two beta emitters 18Ne10+ and 6He2+ used for neutrino and anti-neutrino production and their daughter ions have been tracked. The absorber system proposed in the Design Study is efficient to intercept the ions decayed in the arc straight sections as foreseen, however, the continuous decay in the dipoles induce a large power deposition in the magnet mid-plane. This suggests a different magnet design, like an open mid-plane magnet structure (such a magnet has been designed for this purpose) and/or protecting liners inside the magnets. The power deposited in the superconducting magnets is, with the layout proposed in the Design Study, below the recommended value of 10 W/m. The work described was done in collaboration between CERN an d TRIUMF, Canada's national laboratory for particle and nuclear physics, during a 2-month's visit of one person from CERN at TRIUMF. The work was supported by the European Isotope Separation On-Line Radioactive Ion Beam Facility, EURISOL, in which "beta beams" is one of the work packages.