On the mechanics of MQXF – the low-beta quadrupole for the HL-LHC

Submitted by ogomezal on Fri, 02/26/2021 - 20:09


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The High Luminosity LHC Project target is to reach an integrated luminosity of the LHC of 3000 fb−1, corresponding to a factor 10 increase in collisions with respect to the current accelerator. One of the main components is the superconducting quadrupole called MQXF. It is based on Nb3Sn technology and has a 150 mm single aperture with a field gradient of 132.6 T/m. The MQXF magnets are heading towards production in a joint collaboration between CERN and the US-LHC Accelerator Upgrade (AUP). The first prototype magnet based on 7-m-long coils (MQXFBP1) was assembled and preloaded in 2019. The testing and disassembly was done in 2020. The coils were equipped with optical Fiber Bragg Grating (FBG) sensors. The magnet did not reach the nominal current, quenching at 15.15 kA.

Meanwhile, the short model series has been continued with MQXFS6a/b/c/d magnets, assembled with PIT (Powder In Tube) coils. The MQXFS6b/d did not have any training quenches at 1.9 K and reached a record high, 19.57 kA quench current (95.4% of the short sample limit) with 13.4 T peak field. These magnets, together with MQXF6c that is unloaded to a low azimuthal preload, have given new insight on the effect of azimuthal preload to the magnet performance. MQXFS4 is the former record holder with only 6 training quenches to ultimate. At the same time it has the largest mechanical pole imbalance. The experiments of this magnet holds interesting facts enabling new insights in comparison with the MQXS6b/c/d.

In this seminar the main characteristics of MQXF are presented. The origins and efforts behind the development of MQXF are briefly introduced. Long and short model examples are explained in the light of a new preload characterization and a method for stress homogenization over length, after magnet preload, is presented. This is followed by the introduction and results of an FE model taking into account coil shape and size. The mechanical behaviour and performance of short model magnets, MQXFS4 and MQXFS6b/c/d in particular, are discussed and compared. After conclusions, comments are given regarding some of the curious events regarding MQXFBP1.

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