Letter to the Editor Further studies on the performance of large area planar drift chamber "lled with a He-based mixture

We tested the performance of large-area planar drift chambers "lled with a He}iC 4 H 10 mixture in a 1.1 T magnetic "eld. Even with a coarse compensation of the Lorentz angle with the equipotentials in the drift cell the behaviour of the chamber is satisfactory. ( 2000 Elsevier Science B.V. All rights reserved.