Within SRON a first Development Model (DM 1.0) of the X ray Integral Field Unit Focal Plane Assembly (X-IFU FPA) has been designed, realized and tested over the past years. Since the start of the FPA DM 1.0, the X-IFU instrument design has significantly evolved. Moreover, the recent Athena redefinition activities have resulted in a new overall planning in which the Mission Adoption Review (MAR) and X IFU instrument PDR are now foreseen for 2027. To ensure the required experimental feedback for FPA EM conceptual design is available by the time of the PDR an update of the existing FPA DM 1.0, called DM 1.1, is planned which better reflects the evolved instrument design. In the DM 1.1 the existing 4 channel Frequency Domain Multiplexing (FDM) readout is replaced by an 8 channel Time Domain Multiplexing (TDM) differential readout. A small sized TES array is replaced by a flight-sized kpixel array including full on-chip wiring, of which a limited subset is read-out. The interconnections between the main TES array and the SQUID Multiplexer (MUX) chips are realized in a manner which is flight scalable. Superconducting multilayer Niobium flex cables are used to route the TDM signals from the T0 detector stage at nominally 50 mK to the amplifier (AMP) SQUID stages and external interfaces at 2 K.
This work describes the redesign performed on the X ray Integral Field Unit Focal Plane Assembly (X-IFU FPA) Development Model (DM) with a focus on the mechanical modifications of the T0 detector stage. In addition the development progress of several critical interconnection technologies used within the DM 1.1 is described. These include fixation of the main TES array to the metal support, a dedicated wire bonding process of the main TES array to the side panel MUX carrier chips and interconnection of the super-conducting Nb flex cables to the connecting Printed Circuit Boards (PCB).
The X-ray Integral Field Unit (X-IFU) instrument is the high-resolution X-ray spectrometer of the ESA Athena X-ray Observatory. X-IFU will deliver spectra from 0.2 to 12 keV with a spectral resolution requirement of 4 eV (3 eV design goal) up to 7 keV from 5" pixels, with a hexagonal field of view of 4' equivalent diameter. The main sensor array and its associated detection chain is one of the major functional chains of the X-IFU instrument, and is the main contributor to XIFU performance. CNES (Centre National d’Études Spatiales) is the prime contractor for the X-IFU and leads the project development and procurement aspects within the X-IFU Consortium; additional major partners of the main detection chain are NASA-GFSC, SRON, VTT, APC, NIST, IRAP, and IAP. The detection chain design for X-IFU has evolved in the past few years in order to secure the performances and development costs, in the frame of the New Athena mission. New TES pixels are implemented with slower time constant and a reduced sensitivity to magnetic field. The slower time constant directly allows an increase of the MUX factor and a reduction of the number of channels, together with the decrease of the number of proximity electronics boxes, or warm front end electronics (WFEE). The cryostat outer vessel temperature is now a 50 K thermal interface, cooled passively thanks to L-shaped thermal shield (L-grooves). This has a direct impact of the cryo-harness between the 4 K core interface and the WFEE interface. In the past years, we have performed early demonstration on the critical components in order to secure the detection chain design and performances. This paper presents the progress done on early demonstrations (warm electronics, cryo-harness breadboarding,...), while providing an update to the detection-chain design description.
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