  We have developed a position-sensitive Parallel Plate Avalanche Counter
(PPAC), which has been used as a focal plane detector in the BigRIPS fragment
separator and the subsequent RI-beam delivery lines at the RIKEN Nishina Center
RI Beam Factory. The PPAC detector plays an important role not only in the
tuning of the separator and delivery lines but also in the particle
identification of rare isotope (RI) beams. The PPAC detector has a sensitive
area of 240 mm x 150 mm, and the position information is obtained by a
delay-line readout method. Being called double PPAC, it is composed of two full
PPACs, each measuring the particle locus in two dimensions. High detection
efficiency has been made possible by the twofold measurement using the double
PPAC detector. The sensitivity uniformity is also found to be excellent. The
root-mean-square position resolution is measured to be 0.25 mm using an alpha
source, while the position linearity is as good as +/-0.1 mm for the detector
size of 240 mm. Characteristics, operating principles, specifications,
performance and issues of the PPAC detector are presented, including its signal
transmission system using optical fiber cables.
