Minutes of the special geo meeting on the SSS axes,

25/05 2005

_______________________________________________________________________

Present:

Marta Bajko, Jerome Beauquis, Luca Bottura, Zhengwei Gao, Juan Garcia, Bernard Jeanneret, Jean-Pierre Koutchouk, Emanuele Laface, Michele Modena, Walter Scandale, Karl Schirm, Theo Tortschanoff, Elena Wildner

Pen:  ElenaWildner

Background:

The AC mole magnetic axis measurements of the correctors in the SSS assembly are out of tolerance values given by AB/ABP. An investigation was initiated and a study made by J. Beauquis was presented (Study of SSSaxes). The study is based on a comparison between the magnetic and mechanic axes measurements of the correctors and of the quadrupole. The mechanic axis is calculated by taking the mean of CBT data over the extension of the magnets. The magnetic axis data is calculated as a mean of the measurement points for the different magnets.

Results from statistical study:

1. The rms values of magnetic axes w.r.t. nominal axis are out of tolerance (0.4 mm; the tolerance is 0.2 mm), mean values are close to nominal.

2. The mean values of the mechanic axis positions of all magnets are close to nominal. See overview table below. A small deviation can be seen on the MO/MQT/MQS (0.1 mm deviation from nominal). The spread for MSCB and other correctors are similar (around 0.2 mm), on the quadrupole we see a smaller spread.  

The smaller spread on the quadrupole part was explained by Theo as being due to the insulation around the pole fingers slightly bulging into the magnet aperture thus limiting the CBT movements in the magnet aperture, see slides 1 and 2 in (SSS overview.ppt). The aperture diameter is 54 mm the outer tube diameter is 53 ±0.15 mm and the insulation is 0.1 mm thick.

3. There is a factor two in the correlation between magnetic and mechanic data.

4. The mechanical axis of the MS part and the MCB part of the MSCB corrector are very well correlated: there is no significant difference between the MS and the MCB parts.

The importance to see also the vertical plane was pointed out: action Jerome.

M. Coccoli explained the reason for the factor two in correlation between magnetic and mechanic data as a problem of sign in the reference used for the magnetic measurements. Instead of subtracting the difference between magnetic and mechanic data found by the mole, it was added and since the values of the magnetic axis are very close to zero, the effect appears as a factor two. In the vertical plane there should be no problem for the AC-mole, neither for the optical measurements of the mechanic axis. Actions to refill the data base will be started after reception of a document describing the problem and actions for correction of the AC mole software.

Aperture, according to specifications by ABP are in tolerance for MSCB part. Some small problems may be seen elsewhere in the SSS. Data from database shown by Elena (SSS aperture). MAS/MA will look at the aperture and the deviation of the axis from nominal along the SSS axis. Bernard showed magnets 66 and 128 where there were problems with aperture due to a need to rotate the assembly for alignment (mags 66 and 128).

Rob explained to us the assembly of the MSCB. The two possible reasons of a correlation between CBT center and magnetic axis center measurements (eddy currents and magnetic tube) were excluded by Rob ( MS alignment). Rob also showed that the cold bore tube itself is not straight: see the measurement where the cold bore tube has been rotated in the assembly (special SSS).

Discussions about a possible inter-axis problems for the CBT in the MSCB did not come to any conclusion. Further studies will be made and the results will be discussed in other meetings. In any case, since the production is almost finished, no remedy-actions in industry would be possible at this stage of production.

AOB:

Service lines out of tolerance are now treated after creation of NCs at CERN. The question is: do we insist on actions at ACCEL since so many non conform lines have been found? The study of the movements at CERN of the SSS (cold tests etc) by welding reference points at reception (Elena, Michele, Patrick Winkes) is progressing. Partick is working on measurements at ACCEL. When Patrick has found a way to be able to compare measurements at ACCEL and at CERN, Karl will be informed and take actions if necessary. The welding procedure of the end-covers may have to be revised (action Marta and Karl).