Minutes of the MAS/MA geometry meeting

 08/04 2005

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Present:

Marta Bajko, Jerome Beauquis, Gilles Berard, Marco Buzio; Rocio Chamizo, Zhengwei Gao, Juan Garcia;, Jean-Pierre Koutchouk, Dominique Missiaen, Frederic Savary, Elena Wildner

Pen:  ElenaWildner

Update of situation for the SSS measurements:

Marco showed the latest status of the SSS measurements (“update of data base list”).

Spool piece position measurements at CERN:

The estimated spool piece position in the database is base on the fact that there is coherent movement of the ends of the cold mass. No measurements are made at CERN and for the control of the adjustment procedure at CERN and for discussions on field quality related to spool piece positioning we have only this information to base our decisions.

Comparison of measured spool piece positions fro the pre-series magnets measured at WP01 with these calculated data showed large discrepancies. Therefore it was decided to re-measure 5 magnets at CERN after checking and calibration of measurement devices and measurement procedures. The result is going to be documented in a report (Juan, Rocio and Dominique). The results so far, presented by Rocio (attachement “sext”), show that the measurements confirm the idea of assuming a coherent movement of the end of the cold mass on which fact the calculations are based, and the conclusion is that the way we calculate the spool piece position at CERN is a reasonable approach. However, for one case, it was shown that the spool piece position in industry was not based on the itp20 measurement but rather on the previous measurement (itp15), in which case the spool piece position at itp20 is wrong (the calculation of the spool piece position at CERN is base on the spool piece position in industry at itp20, this is the only value we have).

Elena showed statistics from the three firms showing that the difference between the itp15 and the itp20 measurements is rather large, especially in the beginning of the production and more pronounced for Alstom (attachment “sagitta-itp15-itp20”). Reshaped magnets have to be taken out from the statistics and the fact that for the spool piece position the itp15 is not the most relevant reference but rather the last itp15 measurement before the assembly of the spool piece. Whether this measurement can be used for a correction of the spool piece position in industry has to be examined.

Use of the positioning triangle to estimate the itp20 position :

To improve the spool piece position at CERN without extra fiducializations, Jerome studied the correlation of the evolution of the triangle formed by the three cold feet pads from itp20 to WP01 and the evolution of the sagitta between the same work packages. The sagitta at WP01 was estimated from the values at WP08 and the statistical shift was subtracted from this value to get the value at reception. The sagitta is the parameter used for the adjustment of the central support. In industry the cold feet pad position is measured by Leica and at CERN, at reception, a mechanical jig is used. The jig has recently been adjusted and Jerome used data only from after this adjustment.

There seems to be no correlation between the triangle evolution and the sagitta evolution (“SagHTR”). Possible explanations are the not enough reliable measurements of the pads or local deformations at the pads or elsewhere. This method cannot be used to estimate the adjustment of the magnet at WP08.

The beam screen measurements:

Zhengwei showed the measurements of the beam screen ends (“Beam Screen”). There is an additional positive bias of the ends towards the centre of the machine (0.28 mm average V1 and 0.15 mm average V2). This may be due to the prolongation of the already bent cold bore in the end or from the increase of the sagitta still going on. Study to be continued.