## 3 Mechanical Design of BPL  
In the vacuum vessel of BPL, there is no separated fixed support in the vertical direction; the only fixed supports are the magnet flanges. The vacuum vessel is elastically supported in the vertical direction by long-stroke spring supports. After adjustment of the spring forces, the supports carry the full weight of the BPL in the desired vertical position. The vacuum vessel is attached to the magnet flanges by corrugated compensators (Figure 5). These compensators are used only to compensate for the misalignment of the flanges of BPL with flanges of the magnet during the assembly process. After adjustment and flange mounting, the compensators are fixed by four rods, making the connection of BPL modules with the magnets rigid. As in standard transfer line designs, two additional axial compensators per module are used to increase BPL flexibility and compensate for a thermal contraction in the case of helium leakage. Axial supports are located at the ends of each BPL to carry the full axial pressure forces acting on the vacuum vessel. The axial supports are separated from magnet axial compensators in order to avoid transferring pressure forces onto the magnet flange. Liquid helium, distributed along the BPL, has a temperature of 4.5 K. In order to avoid significant heat loads from the vacuum vessel, liquid helium process pipes are thermally separated by high-insulation vacuum and multilayer insulation (MLI). The MLI covers process pipe surfaces and all other cold components in vacuum space. In addition, the 4.5 K process pipes are surrounded by a thermal shield (TS) that is kept at a 60-80 K temperature level. This allows the interception of a large amount of heat that would be transferred from the vacuum vessel directly to the liquid helium process \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Pipe**} & \multirow{2}{*}{**Headers \& Shells**} & **O. Diameter \&** & **Operating** & **Operating** & **Design** & **Test** \\  & & **Thickness\({}^{\circ}\)** & **Temperature** & **Pressure** & **Pressure** & **Pressure** \\  & & **[mm]** & **[K]** & **[bar(a)]** & **[bar(a)]** & **[bar(a)]** \\ \hline A1 & He supply magnets & \(54\times 2\) & 4.5 & 3 & 20 & 28.6 \\ \hline \multirow{2}{*}{A2} & He supply vacuum chamber (VC) & \multirow{2}{*}{\(32\times 2\)} & \multirow{2}{*}{4.5} & \multirow{2}{*}{3} & \multirow{2}{*}{20} & \multirow{2}{*}{28.6} \\  & He return magnets + VC & & & & & \\ \hline C & He supply shield & \(42.4\times 2\) & 50 & 18 & 20 & 28.6 \\ \hline D & He return shield & \(42.4\times 2\) & 80 & 17 & 20 & 28.6 \\ \hline \end{tabular}
\end{table} 
Table 1: The specification of the design and operating parameters of the process pipes. Figure 4: General cross-sectional layout of the SIS100 bypass line: without supports (**left**); with supports (**right**). A1, A2, B, C, D—helium process pipes, BB—superconducting busbars. pipes. The thermal shield is also cooled with the use of cold, high-pressure helium that circulates in the supply and return lines of the TS circuit. As the thermal shield is made of aluminum, which, by high thermal conductivity, ensures homogenous temperature distribution along the shield, it is thermally coupled with the shield's return process pipe by flexible braids made of copper. Such design decouples the stresses due to the difference in the stainless steel and aluminum thermal contraction, especially during cool-down and warm-up. The design of the bypass line uses an innovative concept of the floating cold mass (Figure 6). Its principle is to remove the internal supports of the BPL cold mass and suspend the entire interior on swinging links. Free movement of the BPL cold mass significantly reduces the forces exerted on the magnets and makes it easier to maintain their stable position relative to the beam axis. Simultaneously, in case of displacement of the cold mass, gravity provides a small centering reaction.