Pad TPC

A new kind of TPC is described, in which no sense wires exist but gas amplification is obtained from a single parallel gap. A mesh separates the drift volume from the amplifying gap. The anode is segmented into circular rows of narrow pads for rphi measurement by centroid finding and into wide circular pads for dE/dx sampling. The expected advantages of this technique are: better, track angle independent rphi resolution (no need for wire pulse height corrections); better two-track separation if more electronic channels can be afforded; less dead space from frame structures; reduced positive feedback and slower chamber deterioration by deposit formation on the anode. Very tight construction tolerances are the principle drawback. The properties of the Pad TPC are discussed in view of large scale construction and first test results are presented