Abstract
In the frame of the R&D program of the HL-LHC, the upgrade of the Large Hadron Collider (LHC), CERN augmented its test facility with two new large-scale vertical test stations for superconducting magnet testing. The cryostats composing the core of these test stations share design features but are of different dimensions: one allows testing magnets up to 1.5 m diameter, 2.5 m long for a maximum weight of 15 t, while the other can accommodate magnets up to 0.9 m diameter, and 5.5 m long for a maximum weight of 18 t. These test stations are designed to operate at 1.3 bar and at controlled temperatures in the range 1.9 - 4.5 K. They can provide for safe dissipation of stored energy in the magnet coils of up to 10 MJ. After a brief description of the cryostats, this paper describes the qualification measurements of heat loads at 4.5 K and 1.9 K of both cryostats, some design enhancements that were made and the performance improvements obtained.
Highlights
The cryostats composing the core of these test stations share design features but are of different dimensions: one allows testing magnets up to 1.5 m diameter, 2.5 m long for a maximum weight of 15 t, while the other can accommodate magnets up to 0.9 m diameter, and 5.5 m long for a maximum weight of 18 t
Two new vertical test stations for prototype magnets testing known as HFM and Cluster D have been recently installed and commissioned into the Vertical Magnet Test Facility of the SM18 Hall at CERN [1]
The new test cryostats are based on the Claudet bath principle, presenting a 4.5 K saturated liquid helium bath above a 1.9 K superfluid helium bath, as showed in figure 1.The pressure in the helium vessel is controlled at 1.3 bar where the superfluid helium is subcooled to the required temperature using a liquid-liquid heat exchanger filled with saturated helium at 1.8 K
Summary
Two new vertical test stations for prototype magnets testing known as HFM and Cluster D have been recently installed and commissioned into the Vertical Magnet Test Facility of the SM18 Hall at CERN [1] Both cryostats share design features [2] but are of different dimensions, both are designed to be as versatile as possible to be able to test large size future cryo-magnets. The whole helium vessel being surrounded by an actively cooled thermal shield at an average temperature of 50 K, the remaining source of conduction heat loads to the 4.5 K bath is that through the magnet insert and the neck part of the cryostat making the transition between room temperature and liquid helium temperature. Throughout the commissioning tests presented in this paper, this solution was found to be insufficient to limit the superfluid conduction heat loads to values within budget and alternative solutions were found to improve the leak-tightness, as presented hereafter
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