To obtain 100 micron transverse accuracy in the large trackers the following considerations are important:
The plastic blocks as well as the pocalon foils have a large thermal
expansion coefficient of m m
K
, which
will effect the location accuracy under experimental conditions.
Therefore, even with a rigid honeycomb structure,
optical monitoring of alignment references on the chamber is
important to obtain 100
m location accuracy.
Figure:
Geometry with 4 identical modules around the beam hole.
Figure:
Chamber module consisting of 12 layers honeycomb cells.
Independent of the overall thermal expansion of a single chamber, with all planes glued together, the relative positions around a local track stay fixed and this is important for the drift time calibration.