Small TPC

The Small TPC

The Small TPC prototype was built to test and study the properties of GEMs. It consists of a small fieldcage, that fits into the 5 T magnet and has a built in holder for an iron 55 source. Some pictures and a schematic of the measurement setup can be seen in Figure1a-d. More information about its construction and first measurements taken with it can be found in the diploma thesis of Bernhard Voigt (DESY-THESIS-2004-049, 2004-04).

Figure 1a: CAD drawing of the chamber

Figure 1b: Picture of the chamber with unmounted GEM tower

Figure 1c: Picture of the voltage supply connectors

Figure 1d: Schematic of the measurement setup

The chamber was reassembled for GEM performance studies. Comparative studies of different GEM types from four manufacturers are ongoing and described in Jeannine Beck's diploma thesis. Therefore, gains were determined with the help of an iron-55 source (see Figure 2).

Figure 2: Gain of the different GEM types in dependency of the applied voltage.

Another topic is the development of a new way to mount GEMs in a TPC. For the Large Prototype TPC and mainly the final ILD TPC larger GEM structures - larger than the standard 10 x 10 cm² - are needed. In the new mounting technique the GEM foils are glued to a thin ceramic grid made out of aluminium oxide. First test of such a grid mounted GEM stack were performed in the Small TPC. At a later stage, resolution performance measurements were done using the MediTPC in a 5T magnet. Figure 3 shows the grid in between two GEMs.

Figure 3: Photo of two GEMs mounted with grid structure.