Soft end dipole magnet design for the MAX-IV storage rings

The future 3 GeV MAX-IV storage ring at MAX-Lab will be a low emittance storage ring for the production of synchrotron radiation. The vertical aperture in the straight sections, as well as in the bends, of the storage rings will be small. It is foreseen to use, among other insertion devices, superconducting cold bore short period undulators as insertion devices in order to obtain undulator radiation with short wavelengths. The cold bore insertion devices are sensitive to the deposited heat from the stored beam in the storage ring. An important contribution to the heat load to the cold core insertion devices comes from the synchrotron radiation from the upstream dipole adjacent to the insertion device. The synchrotron radiation from the upstream dipole adjacent to a superconducting insertion device can be minimized by the introduction of a soft end to the dipole. This note describes the proposed design of the dipoles with soft ends adjacent to the insertion devices in the 3 GeV MAX-IV storage ring. The soft ends of the dipole magnets have reduced the impinging heat load from synchrotron radiation on the superconducting undulators by a factor of 5.8 and they have also reduced the overall circumference of the storage ring.