Pressure test of the bushing at liquid Nitrogen temperature

Pressure test of a coil support bushing for the CBM superconducting dipole

On 6^th of June 2025 the CBM Magnet team visited the company BNET in Würzburg which is constructing the superconducting dipole for the CBM experiment. The team attended a pressure test of a coil support bushing, one of the most critical components of the magnet. Each coil of the magnet is supported by 12 bushings, which have to compensate for a Lorentz force corresponding to 309 t, while thermally isolating the cold coil (T = 5 K) from the yoke (at room temperature). Each bushing consists of three rings made of composite material G11 and two stainless steel rings, with different diameters and heights and alternatively nested. The total diameter of the bushing is 226,85 mm, the total height is 180 mm. In the first test the bushing was exposed to a force of 313 kN over 10 minutes, which is about 10% above the maximum load expected for one bushing. The bushing was elastically deformed by 2.42 mm, which is 1.2% of the height. For the second test, the lower part of the bushing was cooled by liquid Nitrogen to simulate the real situation during operation of the magnet. After cooling down, the bushing shrank by 1.15 mm, and after applying again 313 kN over 10 minutes, the bushing was elastically deformed by 1.63 mm. While the lower part of the bushing was cooled down to -190°C, the upper part was still at +20°C. Therefore, both the tests of pressure and of the heat loss were successful. According to the mechanical calculation based on the material properties of the bushing, the upper limit for the force is 600 kN.

Coil support bushing with three G11 rings (yellow) and two stainless steel rings (grey)

The magnet support plate, a component of the alignment system

Winding of the coil for the CBM magnet

Moreover, the coil winding machine has been set up in the clean room, and the preparations for winding have started. Also, parts of the magnet support have been produced.