The INFN-LNF Astrophysics and Cosmology Integrated Test Facility Startup

Abstract

Starting from January 2023, Permanent Staff Personnel and Associated Personnel of INFN-LNF (Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali di Frascati) have founded, and are setting up, the local Astrophysics and Cosmology Team (ACT). The INFN-LNF ACT joined the initial development phases of one of the forthcoming (early 2030) next-generation cosmology space-borne probes, with particular emphasis on (1) thermal balance tests (and correlation to models) of the electronics of interest; (2) (non)destructive irradiation tests of the electronics of interest and X-ray circuitry diagnostics on a specifically dedicated and instrumented optical bench; and (3) joining the simulation-related, and data analysis-related, activities, at both the cosmological and instrumental levels. The INFN-LNF ACT has constituted an Integrated Test Facility (ITF), which is being instrumented in a dedicated space and will also make use of the pre-existing INFN-LNF infrastructures. In the following, as a first contribution, mainly related to what was completed in late 2023 and early 2024, the activities of the commissioning and setup of the so-called ‘pocket’ cryostat are described, linking them to the envisaged thermal balance tests (and correlation to the models) of the electronics of interest. While mainly devoted to cosmology-oriented tasks, the INFN-LNF ACT ‘pocket’ cryostat will, in principle, be available to the wider community for other dedicated activities.

1. Introduction

The INFN [1] is the Italian National Institute for Nuclear Physics, founded in 1951, a public research institution that is government-run and devoted to the study of nuclear and subnuclear physics. Its original mission was to conduct fundamental research in the field of particle physics; however, over the decades, the INFN has widened its range of action, encompassing many fields of theoretical and applied physics, engineering, and technology transfer.

Thanks to the Commissione Scientifica Nazionale 2—National Scientific Commission 2 (CSN2) [2]—the INFN evaluates, funds, and oversees research activities in astroparticle physics, in the broadest possible sense, including (but not limited to) the study of cosmology, cosmic rays, dark matter, gravitation, neutrinos, and other astrophysical phenomena.

The Frascati National Laboratory (LNF) [3] of the INFN is a multidisciplinary research center, primarily focused on particle physics, accelerator physics, and related fields. However, over the decades, the LNF has also widened and increased its range of internal facilities and infrastructures, including (but not limited to) the Double Annular Factory for Nice Experiments (DAFNE), the Stored Particles Atomic Research Collaboration (SPARC) electron–positron accelerator, the Satellite/lunar/GNSS laser ranging/altimetry and cube/microsat Characterization Facilities Laboratory (SCF_Lab) [4], and the XLab Frascati (XlabF) [5].

Within such a framework, starting from January 2023, INFN-LNF personnel have founded, and are setting up, the local Astrophysics and Cosmology Team (ACT), which is joining the initial development phases of one of the forthcoming (early 2030) next-generation cosmology space-borne probes [6,7].

Based on previous positive work of the same kind [8,9,10,11,12,13], the Integrated Test Facility (ITF) will build upon the established experiences of the participants regarding the thermal balance tests (and correlation to models) of the electronics of interest [14,15,16,17,18,19] and the X-ray irradiation and diagnostics of the same [20,21]; meanwhile, the ‘higher’-level involvement of the participants in the simulation and data analysis activities is ongoing.

This first INFN-LNF ACT contribution focuses on the commissioning and setup of the so-called ‘pocket’ cryostat, an infrastructure belonging to the INFN-LNF, currently assigned to cosmology-oriented tasks, yet in principle available to the wider community for thermal tests.

2. The INFN-LNF ACT ITF

2.1. Commissioning and Setup of the ‘Pocket’ Cryostat

The so-called ‘pocket’ cryostat, a portable infrastructure belonging to the INFN-LNF, was designed, engineered, and manufactured for conducting thermal balance tests and validating thermal models with utmost accuracy, and it is shown in Figure 1a. The test volume is shielded from the external shell (which is built with AISI 316 L grade stainless steel) by a copper inner shroud, coated with a high-emissivity and low-outgassing black paint. The copper inner shroud is also equipped with a series of Kapton heaters, and a brazed coil, in which liquid nitrogen (LN₂) can be fluxed, producing a controllable simulated space environment essential for the tests of the flight electronics of interest.

Its operational design incorporates multiple layers of insulation and programmable temperature control electronics in order to achieve temperatures ranging from about 80 K to about 380 K (Figure 1b). The ‘pocket’ cryostat expandable architecture enables seamless integration with various vacuum heads, thermal sensors, and active instrumentation, facilitating data acquisition and analysis. That would be crucial when, over the next 5 to 10 years, the engineering and flight models of the electronics of interest are tested: while exposed to the simulated, yet realistic, space conditions, the circuitry, possibly assembled into a rack, will be activated, operated, heated up, and cooled down in order to validate its behavior and make sure it will be able to operate according to requirements.

The key features of the ‘pocket’ cryostat are the following:

• it was specifically designed for thermo-vacuum tests and thermal balance tests;
• operational pressure, p < 10⁻⁶ mbar, and operational temperature, (80 < T < 380) K (both expandable);
• controllable through remotely operated electronics;
• accessible internal test volume ≈ 8 × 10⁴ cm³ = 80 L (roughly a cylindrical inner copper shroud with diameter = 40 cm and height(cylinder) = 60 cm); overall maximum volume of the whole apparatus < 2 m³ (roughly, length × width × height = 1 m × 1 m × 2 m); overall maximum volume of the whole apparatus including LN₂ cooling tank < 3 m³ (roughly, length × width × height = 1 m × 1.5 m × 2 m);
• portability, meaning transportability: while being instrumented in a dedicated space, the hardware was equipped with a wheeled custom-made stand, and, given the aforementioned volumes, it may (and it will) be moved to customer site when in operation.

The portability is not a peregrine feature because, as will be for the cases of interest, it may be compelling to perform tests at the customer site for security reasons (i.e., electronics may be subjected to confidentiality or other NDA (Non-Disclosure Agreement)-governed clauses).

2.2. Description of Execution of Thermal Balance Tests [22]

The ‘pocket’ cryostat is a Ground Support Equipment (GSE) conceived to characterize, in a simulated spatial environment, the thermal behavior of the hardware of interest. Operationally, in the cryostat, it is possible to pull a vacuum lower than 10⁻⁶ mbar, and to cool down the environmental temperature to T_shroud ≈ 80 K (through LN₂ fluxing the inner shroud). The GSE has several service portholes and windows and other service connectors, and it is equipped with a rotating shaft for sample suspension and rotation. The service pressure and temperature are reached thanks to the inner shroud, a copper cylinder encased by the main steel cylindrical shell. It has several characteristics:

• it embeds the LN₂ cooling coil;
• it is painted black with Aeroglaze Z306 flat black (or similar), enhancing the black body characteristics of the environment;
• it is blanketed by multiple layers of Coolcat 2 NW insulator, increasing the thermal isolation regarding the outer environment, and decreasing LN₂ consumption;
• it is seeded with ≈50 independent PT100 probes for temperature monitoring, together with resistive heater tapes for quick-response return to Standard Temperature and Pressure (STP).

The Vacuum, Cryogenics, and Electronics Subsystems are devoted to command, reach, control, maintain, and read the operational environment parameters, including data acquisition, movement system, and payload temperature controls.

The vacuum subsystem makes use of two pumps:

• scroll pump, used to achieve the prevacuum condition of ≈10⁻¹ mbar;
• turbo molecular pump, used to reach the service pressure lower than 10⁻⁶ mbar.

Once the GSE reaches the pressure of ≈10⁻⁶ mbar, the LN₂ can be fluxed through the inner shroud to reach a service temperature lower than 90 K:

• LN₂ flux, from the service tank, is remotely controlled by a fluxmeter, which is in turn telecommanded by in-house developed scripts (Figure 2a);
• once the shroud is cooled down, the LN₂ is diverted towards the exterior and freed in atmosphere.

The electronics subsystem collects all the custom-developed and dedicated scripts, together with the commanded hardware and boards, used to monitor and control the GSE and all the test phases (Figure 2b):

• ≈50 independent PT100 probes for temperature monitoring are installed on the cryostat, together with the other necessary payload-dependent probes, and are monitored and fed back to custom developed scripts. Based on temperature reads, the Proportional, Integral, Derivative (PID) can open or close the LN₂ flux, thus governing the test;
• resistive heater tapes for quick-response return to STP through the power supplied by external power unit.

2.3. Rationale of Envisaged Irradiation and Diagnostics Tests

The main activity of XLab Frascati is focused on X-ray analysis by means of desktop techniques, mostly based on polycapillary optical elements, and on theoretical studies on charged and neutral particles’ interactions in different fields, especially concerning channeling, a field of physics that studies the path of charged particle or electromagnetic radiation inside regular structures such as crystals.

The laboratory equipment serves a number of purposes: analysis of micro/macro X fluorescence (traditional, confocal, or total internal reflection) applied on cultural heritage and geological samples; X-ray diffraction applied to the examination of materials; temporary experimental setups and testing systems for the design of new detectors; and study of imaging techniques and X-ray tomography projects.

XLab Frascati centers its research activity on the study and characterization of peculiar X-ray optics: polycapillary lenses. Invented in 1984, these lenses are based on the phenomenon of total internal reflection of X-rays. The lens is composed of millions of glass channels, in which the impinging radiation is efficiently transmitted by multiple reflections.

This way, it is possible to collect the divergent radiation, focusing it or converting it into a parallel beam, hence enabling the beam to be modelled as needed, for instance, directing another flux of X-rays on research samples. This behavior opens up the possibility of building a brilliant X-ray source with performance comparable to that of the synchrotron light by combining a conventional X-ray tube and polycapillary optics. XLab Frascati is one of the few facilities in the world that is able to manufacture polycapillary optics.

Thanks to such unique capabilities and peculiarities, over the next 5 to 10 years, the engineering and flight models of the electronics of interest will be tested through X-ray irradiation.

3. Discussion

Non-destructive testing (NDT), and destructive testing alike, are indispensable tools for aerospace, science, and engineering, particularly in the demanding arena of space exploration. The reliability and safety of space hardware are crucial given the duration of space projects (from ideation to data analysis) and their non-negligible costs.

NDT techniques enable the meticulous examination of designs, materials, and structures without causing disruptions. NDT also couples with destructive testing, needed to test for the ultimate survival performance of the hardware.

Given the unforgiving environment of space, where even the slightest flaw can escalate into a deadly failure, especially when the spacecraft is sent away from the ‘comfort’ zone surrounding Earth and beyond the reach of eventual rescue missions (e.g., the first servicing mission to Hubble Space Telescope in December 1993), NDT acts as both a preventative measure and a quality assurance tool.

Within such a framework, the INFN-LNF ACT joined, in 2023, the initial development phases of one of the forthcoming next-generation cosmology space-borne probes, aiming at contributing to (1) the thermal balance tests (and correlation to models) of the electronics of interest and (2) (non)destructive irradiation tests of the electronics of interest and X-ray circuitry diagnostics on a specifically dedicated and instrumented optical bench. That would be crucial when, over the next 5 to 10 years, the engineering and flight models of the electronics of interest are tested: while exposed to the simulated, yet realistic, space conditions, the circuitry, eventually assembled into a rack, will be activated, operated, heated up, and cooled down in order to validate its behavior and ensure that it will be able to operate according to the requirements before its delivery for integration onboard the spacecraft.

The INFN-LNF ACT ‘pocket’ cryostat, as an infrastructure belonging to the INFN-LNF, together with the rest of the ITF, will be available to the wider community for other analogous activities.