Metal-core pad-plane development for ACTAR TPC

With the recent development of active targets and time projection chambers (ACTAR TPC) as detectors for fundamental nuclear physics experiments, the need arose for charge collection planes with a high density of readout channels. In order to fulfill the mechanical constraints for the ACTAR TPC device, we designed a pad-plane based on a metal-core circuit with an conceptually simple design and routing for signal readout, named FAKIR (in reference to a fakir bed of nails). A test circuit has been equipped with a micro mesh gaseous structure (micromegas ) for signal amplification and a dedicated readout electronics. Test measurements have been performed with an $^{55}$FeX-ray source giving an intrinsic energy resolution (FWHM) of $22 \pm 1\%$ at 5.9 keV, and with a 3-alpha source for which a resolution of about $130 \pm 20$ keV at 4.8 MeV has been estimated. The pad-plane has been mounted into a reduced size demonstrator version of the ACTAR TPC detector, in order to illustrate charged particle track reconstruction. The tests preformed with the X-ray and the 3-alpha sources shows that results obtained from pads signals are comparable to the intrinsic result from the micro-mesh signal. In addition, a simple alpha particle tracks analysis is performed to demonstrate that the pad plane allows a precise reconstruction of the direction and length of the trajectories.