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The Field Quality Crisis Unit of the LHC main dipoles production

Feedback on magnetic length using laminations

June 2002, Manufacturer 2. Azimuthal coil size of both inner and outer layer of 2012 and 2014 are larger than nominal, requiring for the use of 0.1 mm less thick inner and outer layer pole shims. This has an impact of about 10 negative units on the main field, which is observed in the collared coils measurements. Even though the effect is not very large, it is decided to profit of this case to try for the first time the use of additional laminations to recover a longer magnetic length, thus compensating the integrated main field. In the specification Annex B.? it is stated that up to 100 mm of additional iron laminations, replacing the nested ones, can be added (50 on each side). Since the difference in the main field between iron laminations and nested laminations is around 10%, 100 mm more should give a 10 mm increase in the magnetic length, i.e. 7 units.

April 2003, Manufacturer 2. Data of cold masses 2012 and 2014 are available. Analysis shows (see file) that in average cold masses with nominal laminations have a magnetic length that is 55 mm less than the collared coil, with a sigma of 4 mm. In the case of 2012 and 2014, with 100 mm more of iron laminations, the difference of magnetic length between cold mass and collared coil is -45 mm, with a sigma of 2 mm.

April 2003, CERN. On the basis of the measurements, it is asked to add 100 mm more of lamination also in 2013, 2016, 2017 and 2018 that has lower main field due to non-nominal shims. Moreover, it is asked to add 100 mm more laminations in 2022 and 2026 that, even though with nominal shims, featured a lower main field.

(... to be continued ...)