16 - 21 June 2024
Yokohama, Japan
Conference 13093 > Paper 13093-160
Paper 13093-160

The X-IFU focal plane assembly development model: evaluation of the global magnetic shielding factor

On demand | Presented live 17 June 2024

Abstract

This work describes the evaluation of the global shielding factor of the Development Model (DM) of the X-ray Integral Field Unit Focal Plane Assembly (X-IFU FPA) for the Athena X-ray observatory. The main task of the FPA is to provide an environment for the X-ray transition-edge sensors (TESs) microcalorimeter in which they can reach optimal performance, with stringent requirements on the thermal, electro-magnetic, mechanical, and electronic aspects of the environment. Within the FPA a two-stage thermal suspension system will isolate the detectors, operating at nominally 50 mK (T0 stage) from the FPA mechanical interfaces at 2 K (T2 stage). An intermediate temperature stage (T1 stage) operated at nominally 300 mK is implemented as a heat intercept.

The required magnetic shielding attenuation is obtained combining a cryogenic mu-metal (CMM) shield and a superconducting Niobium (Nb) shield. From a finite element model (FEM), the CMM shield alone should suppress the static field (for example Earth magnetic field) at the detector location with a factor 50; while the combination of the two has the goal of suppressing variable fields with a shielding factor of ∼106, defined as the ratio of the magnitude of the external field relative to the maximum field perpendicular to the sensor array. These numbers are referring to the component normal to the plane of the sensor array. In plane with sensor array the shielding factor can be a 104 times larger.

We use the TES detectors as very sensitive magnetometers. The TES critical current Ic exhibits oscillatory Fraunhofer-like behaviour, when magnetic field perpendicular is applied to it. Whether the variable external magnetic field perpendicular to the detectors penetrates the shields, the operating current ITES through the TES, which is stabilised in temperature and biased in a sensitive point in transition, may change and this variation can be used as witness for the shielding factor evaluation.

In this work we discuss the difficulties in performing such a measurement, where a Helmholtz coil outside the cryostat were used to apply an external magnetic field (< 200 μH) in order to avoid any permanent magnetisation of the CMM shield. Both AC and DC external magnetic field have been applied with different orientation respect to the detector plane. This improves the statistic of a very sensitive measurement, but also serves to maximise the signal measured by a number of TESs spread over the south-quadrant (closer to the Nb shield) of the array, where the field lines show different intensity. Preliminary results set a lower limit in the evaluation of the global FPA shielding factor of ∼105. Improvement in the measurement setup and in the analysis will be discussed in view of the future models of the FPA.

Presenter

Emanuele Taralli
SRON Netherlands Institute for Space Research (Netherlands)
Emanuele Taralli is instrument scientist at Netherland Institute for Space Research (SRON) and his field of interest are single photon detectors, in particular transition-edge sensors TES microcalorimeters for X-ray detection. He is currently involved in the characterisation and development of the Focal plane assembly (FPA) of the X-ray Integral Field of Unit (X-IFU), one of the two instruments aboard of ATHENA space telescope.
Application tracks: Astrophotonics
Presenter/Author
Emanuele Taralli
SRON Netherlands Institute for Space Research (Netherlands)
Author
SRON Netherlands Institute for Space Research (Netherlands)
Author
Johannes Dercksen
SRON Netherlands Institute for Space Research (Netherlands)
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SRON Netherlands Institute for Space Research (Netherlands)
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SRON Netherlands Institute for Space Research (Netherlands)
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SRON Netherlands Institute for Space Research (Netherlands)
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Willen-Jan Vreeling
SRON Netherlands Institute for Space Research (Netherlands)
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SRON Netherlands Institute for Space Research (Netherlands)
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Geert Keizer
SRON Netherlands Institute for Space Research (Netherlands)
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SRON Netherlands Institute for Space Research (Netherlands)
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SRON Netherlands Institute for Space Research (Netherlands)
Author
SRON Netherlands Institute for Space Research (Netherlands)
Author
SRON Netherlands Institute for Space Research (Netherlands)