Time projection chambers for tracking and identification of radioactive beams

Time projection chambers (TPQ with delay-line readout have been built as position sensitive detectors for high-resolution experiments at the magnetic spectrometer FRS at GSI. The main qualities of TPCs are a small amount of material in the active area, a high tracking efficiency ( ∼ 98 %), and a spatial resolution of σ ∼ 115 μm in x-direction, measured by a delay line, and σ 50 μm in y-direction, measured by drift time. The TPC works as a true two-dimensional detector. A multiple energy-loss measurement allows to identify light fragments (Z = 4-6) with a resolution better then σZ < 0.14. With the TPCs, several parameters of the spectrometer could be improved considerably and a higher momentum resolution of the FRS was obtained. The TPC construction, test results, and physical experiments are presented. (author)