Design Studies for the Pixelized Readout of a TPC for the ILD

Abstract

A large Time Projection Chamber (TPC) is foreseen as central tracking device of the International Large Detector (ILD), as it provides a large number of measured track points simultaneously with a minimum of material budget. Many modern TPCs rely on micro-pattern gaseous detectors (MPGDs) as amplification stage and a readout based on pads or strips. The performance can be further improved with a pixelized readout structure, as the size of the amplification stage is matched by the granularity of the readout.<br /> A pixelized readout can be realized with pixel chips with an integrated Micromegas structure which is added to the chips by techniques of industrial post-processing. The holes of the grid are perfectly aligned to the pixels, i.e. there is only one hole above each pixel. Due to the alignment, the gas amplification takes place directly above a single pixel and the created charge is mostly collected by this pixel. This way, even single electrons of the primary ionization can be separated.<br /> To apply this kind of readout in large experiments, such as the TPC of the ILD, the technology has to be available in large quantities, as several square meters of readout area have to be covered. To this end, the original production process is transferred to the production on 8 00-wafers. Post-processed chips from this new production process are tested in terms of energy resolution, occupancy, detection efficiency and discharge stability. The results are compared with those obtained with devices of the original method of fabrication.<br /> For the application in a TPC for the ILD it has to be ensured that pixelized readouts are capable of dealing with backgrounds present in the detector. Hence, the two main backgrounds, γγ → hadrons and e⁺ e^--pairs are simulated with the required precision and the performance of an integrated pixel readout is examined, especially with the respect to the momentum resolution required at the ILD.