Drift Distortions in Alice TPC Field Cage

Calculations of drift distortions for the TPC field cage with two coaxial cylinders with closed ends are presented. The calculation method is based on the solutions of Laplace's equation in cylindrical coordinates. It is applied to the Alice TPC to study a variety of possible defects in design and construction of the field cage. Distortions are calculated due to finite width of the equipotential strips, errors in resistor chain values, ordering of the resistors, shorted strips, mismatch of the field cage cylinder ground end voltage with the pad plane, deformations of the pad plane, etc. The results show that the precision in mechanical construction has to be better than 0.5 mm. The finite width of the equipotential strips is not a problem and a proper ordering of resistors in the resistor chain can significantly reduce errors due to the tolerance of the resistance. A shorted strip pair has large distortion and it would be necessary to be repaired in order to avoid large correction.