Two amazingly low-material medium sized trackers are at the heart of the magnetic spectrometers for MAGIX. They are implemented as GEM based short drift Time Projection Chambers (TPC) with a novel open field cage concept and state-of-the-art VMM3 ASICs for readout.
A TPC enables a complete three-dimensional reconstruction of the track. When a charged particle enters the active volume filled with an Argon based counting gas, it ionizes the atoms in its path. Through an external electric field, the free electrons drift to the amplification stage, which makes use of the GEM technology, where they are multiplied and read out by the VMMs. To homogenize the drift field and minimize material in the particle track, field-shaping extensions are used instead of the commonly used field cage on the inlet side of the TPC. The detector also offers a new approach to online calibration through the use of a UV LED system that triggers test probes from fixed positions on the cathode and produces a snapshot of dynamic field distortions.