Experience with the Time Projection Chambers for the T2K Near Detectors

The Near Detector at 280m (ND280) has been operating for over a year in the Tokai to Kamioka (T2K) neutrino beam. The detector is designed to provide a good knowledge of the neutrino beam before the neutrinos oscillate, including measuring the backgrounds and their energy dependence. An important feature of ND280 is the tracker which consists of two active scintillator-bar target systems sandwiched between three large time projection chambers (TPCs), and surrounded by calorimeters and a large dipole magnet for charged particle tracking. Novel features of the TPCs are the rectangular construction from composite panels, the bulk micromegas detectors for gas amplification, electronics readout based on a new ASIC, and the photoelectron calibration system. This article will review the design, operation and performance of the TPCs as deduced from measurements with particle beams, cosmic rays, and the photoelectron calibration system.