Zlobin, A.V. Novitski, I. JACoW Geneva, Switzerland 978-3-95450-180-9 10.18429/JACoW-NAPAC2016-MOPOB30 English 137-139 MOPOB30 ion dipole operation collider controls Contribution to a conference proceedings 2017 2017-01 http://dx.doi.org/10.18429/JACoW-NAPAC2016-MOPOB30 https://jacow.org/napac2016/papers/mopob30.pdf Main design challenges for 15 T accelerator magnets are large Lorentz forces at this field level. The large Lorentz forces generate high stresses in the coil and mechanical structure and, thus, need stress control to maintain them at the acceptable level for brittle Nb3Sn coils and other elements of magnet mechanical structure. To provide these conditions and achieve the design field in the FNAL 15 T dipole demonstrator, several mechanical structures have been developed and analysed. The possibilities and limitations of these designs are discussed in this paper.