Development of Amplifier and Shaper for High-Rate MWPC

A multi-wired proportional chamber (MWPC) will be installed as an in-beam charged particle detector for J-PARC E14 (KOTO) experiment aiming at the discovery of CP-violating rare decay, KL->pi0 nu nu. The counting rate of the MWPC is expected to be 1 MHz per channel due to high neutron and gamma flux, 1 GHz for 30 x 30 cm^2 area, respectively. An amplifier and shaper to cope with such high counting rate are necessary. A prototype of such amplifier and shaper has been developed with enough S/N to achieve required chamber efficiency (99.5%). It reduces a characteristic signal tail of the MWPC, typically hundreds of microseconds, to several tens of nanoseconds. Figure 1 shows the schematic diagram of the prototype. The preamplifier part is a charge sensitive amplifier with a time constant of 50 ns, followed by a pole-zero cancellation part to shorten its time constant to 5 ns. It is directly connected to a double pole-zero cancellation network[1] to cancel the 1/t tail of the MWPC. Fast-FET operational amplifiers with a gain-bandwidth product 410 MHz are used for all the amplifying stages, which enables fast pulse shaping.