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 test 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 Gallery 1. 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).
-
-
Gallery 1 (from left to right):
a) CAD drawing of the chamber
b) Picture of the chamber with unmounted GEM tower
c) Picture of the voltage supply connectors
d) Schematic of the measurement setup
(click on a picture to see larger version)
The chamber was reassembled for GEM performance studies. Comparative studies of different GEM types from four manufactueres are ongoing and described in Jeannine Beck's diploma thesis. Therefore gains were determined with the help of an iron-55 source (see Figure 1).
Another topic is the development of a new way to mount GEMs in a TPC. For the large prototype and mainly the TPC in the ILD detector larger GEM structures - than the standard 10 x 10 sqcm - are needed. A grid made of ceramics - aluminium oxide - was developed and tested in the Small TPC. Figure 2 shows the grid inbetween two GEMs.
