  We have developed and constructed the field cage of a prototype Time
Projection Chamber for research and development studies for a detector at the
International Linear Collider. This prototype has an inner diameter of 72 cm
and a length of 61 cm. The design of the field cage wall was optimized for a
low material budget of 1.21 % of a radiation length and a drift field
homogeneity of Delta(E)/(E) less or equal 10^-4. Since November 2008 the
prototype has been part of a comprehensive test beam setup at DESY and used as
a test chamber for the development of Micro Pattern Gas Detector based readout
devices.
