## 3 Mechanical Design of BPL
Due to the floating support, the cold structure of the bypass line is able to contract toward the thermal contraction centers of the magnets without compensation elements between the magnet and the BPL. The suspension of the thermal shield was designed in two versions. The first was based on aramid fiber cords (Kevlar 49) with a diameter of 3 mm (Figures 7 and 8). The single cord, in the form of a closed-loop, supports the thermal shield tube by four thermally insulating spacers made of G11 glass fiber laminate to avoid direct thermal contact of the cord and the multilayer insulation (MLI) of the thermal shield. The spacers simultaneously provide 10 mm space for the MLI to avoid its compression. The weight of the thermal shield and all the cold mass inside the thermal shield is  
Figure 5: Suspension and compensation of the BPL vacuum vessel. Figure 6: The floating support system of the thermal shield: displaced thermal shield (**left**); centered thermal shield (**right**). The lateral displacement is exaggerated for clarity. distributed among all four spacers and reaction forces are applied to the thermal shield only in the radial direction. The vertical adjustment, shown in Figure 7a, can be used to balance the forces in all the aramid cords along the BPL module during the manufacturing stage. Figure 8: Suspension of the thermal shield (aramid fiber cable version) with interior details. Figure 7: Suspension of the thermal shield on aramid (Kevlar 49) cords: (**a**) vertical adjustment of the single loop; (**b**) location of G11 spacers on the circumference of the thermal shield with multilayer insulation (MLI); (**c**) G11 axial support of the thermal shield segment. Both upper ends of the loop pass through the holes in the vacuum vessel and are supported on rollers with an adjustment range in a vertical direction. The rollers provide the ability of self-balance of the forces in all lines of the aramid cord. Loops are located along the pipe, with a 2.7 m average distance between them. The thermal shield is divided into approximately 6-m-long segments; the axial position of each segment is fixed with the use of a G11 axial support arm (shown in Figure 7c). The second concept of the thermal shield suspension is based on the stainless-steel rods instead of aramid cords (Figure 9). A pair of steel rods are attached to the thermal shield by hinges. Because of the significant force and bending moment acting on the TS, the area of connection to TS is strengthened. Upper ends of the rods are supported by the vacuum vessels with the possibility of vertical adjustment. In Figure 10, the cold mass suspension system in the area of magnet connection is shown. Aramid cord suspension has several advantages compared to steel rod suspension. The ratio of strength to thermal conductivity of Kevlar is much higher than for stainless steel (Figure 11). The thermal conductivity of Kevlar 49 [15; 16] at the 50-300 K temperature range is approximately 80%  
Figure 10: Connection of the BPL cold mass to the magnet in a lateral direction by elastic hoses on process pipes. Figure 9: Suspension of the thermal shield (stainless steel rod version). lower than the thermal conductivity of stainless steel. The summary cross-section of the pair of aramid strings is twice smaller than the cross-section of the steel rod because of the higher strength of Kevlar. In the case of aramid cords, the mechanical load is applied to the TS as a force in the radial direction, distributed among four G11 spacers. No bending moment is applied, and forces can be carried directly by the TS pipe. The loop suspension is also a simpler and cheaper solution. The only disadvantage of Kevlar cord suspension is the risk of creeping during long-term operation. Even if the load of the aramid cord is well below the yield strength, the plastic material can suffer mechanical creep, a slow increase of plastic deformation that depends on the load, temperature, and time. As a result, the deformation can exceed mechanical tolerances or even cause the loss of mechanical stability.