FPA CryoAC Design Concept

Abstract

This document provides the Conceptual design of the TES-based cryogenic anticoincidence (CryoAC) detector for ATHENA X-IFU inside the FPA section. The baseline design is based on an absorber made of a thin single crystal (0.5 mm thick) of Si, where the energy deposited by particles is sensed by TES sensors. The CryoAC is placed below the TES-arrays, at a distance 􀁤1 mm (TBC). The active part covers a full area of 4.91 cm2, larger than the arrays (2.3 cm2). The baseline detector is divided into 4 independent pixels, each one with an area of 1.23 cm2. This configuration offers important advantages. Being the pixel technology similar to the TES array, integration, interface and SQUID readout issues can be substantially accommodated by using the same technology solutions. The compliance of the design with requirements has been verified through an analysis of the system, including background assessment by Geant4 [RD1], [RD2], and tests on detector prototypes [RD3], [RD4], [RD5] and [RD6]. As for the front end electronics, the CryoAC detector will be read out by standard FLL technique based on SQuID, one for each of the 4 pixels in which the detector is divided into. We plan to adopt the same SQuID technology selected for the TES array, but having requirements tailored to the CryoAC needs. In order to keep the system redundant we have adopted as baseline an independent FLL chain for each SQuID (4 independent FLL for 4 pixels). Each “pixel + SQuID” will be served by a so-called quadrant service electronic section inserted in the CryoAC WFEE [RD7]. The baseline foresees that the veto operation will be performed on ground, given the expected modest telemetry rate.