IN12 with 12T, 15T
We present below the magnetic forces measured on IN12 with the 12T asymmetric split-pair coil magnet of the CRG-CEA group. The measurements have been performed for several positions, sometimes very near the neutron guide.
This magnet can be used at nominal field and any angular position when the distance between the cryomagnet and the analyser shielding is of 360 mm (radial force below 50 daN).
From the measurements performed with the 12T, we concluded that it is possible to work at nominal field when the distance between the cryomagnet and the analyser shielding is greater than 360 mm. The forces at 12T estimated from the measurements are 36 daN vertically and 48 daN horizontally. The limiting factor is the 50 daN radial force allowed for this magnet (due to historical reasons to our knowledge).
The maximum forces allowed with ILL magnets are larger as described here. These values were determined with OINS experts, Mechthild and the SANE team some years ago. From the measurements performed with the 12T, we can estimate that the expected radial force at 15T will remain less than 75 daN with the same configuration i.e. 360 mm between magnet and analyser shielding (the vertical force is not a limiting factor). This is within the limits established at ILL but can we apply those measurements to the 15T magnet ?
The forces measured on IN14 with the 12T in the geometrical conditions defined for the 15T show that the estimated forces at 15T are 80 daN radially and 120 daN vertically. With the 15T, at roughly the same A2 position (54.3° instead of 53°), we measured 90 daN radially and 160 daN vertically. So we can assume that the forces will be those measured with the 12T increased by 15% radially and 35% vertically.
From the above conclusions, we can reasonably estimate that the maximum forces at 15T will be less than 90 daN radially and 70 daN vertically when the distance between the magnet and the analyser shielding is 360 mm. With Fh = 90 daN, Fv = 70 daN and Fv+13Fh=1240 daN, we are at the limits agreed at ILL. Because it is extremely difficult to measure the forces for checking these assumptions, it was agreed to increase the distance between the magnet and the analyser shielding by 50 mm so that you work with a safer distance of 410 mm when using the 15T.