Physics

Abstract Direct-current superconducting quantum interference devices (dc-SQUIDs) are one of the most sensitive magnetic detectors. These sensors are extensively used in the readout of superconducting transition edge sensors (TESs), which are used for the detection of weak signals. A cosmic microwave background (CMB) polarization telescope operating in 22-48 GHz is currently under developing. The TESs calorimeter of the telescope will be readout by a time-division multiplexer (TDM) SQUID readout system. We develop a two-stage dc-SQUID amplifier circuit, comprising an input-stage SQUID with 4 SQUID cells and a series SQUID array (SSA) with 100 SQUID cells. This configuration has been shown to achieve extremely high signal gain while effectively controlling system noise. We assess the system noise at 300 mK in an adiabatic demagnetisation refrigerator (ADR). The the measured magnetic flux noise of the two-stage SQUID circuit system is approximately 0.3 µΦ 0 / √ Hz at 10 kHz. The current noise equivalent to the input coil of input SQUID is about 2.4 pA/ √ Hz. This result meets the low-noise readout requirements of the CMB TES and other applications with TES detectors.

Producing Al powder feedstock containing high levels of Ti and B through gas atomization remains technologically challenging. In this study, a different route is proposed based on the functionalization of powder surfaces rather than pre-alloying. A Ti-bearing Al-Mg powder was modified by decorating its surface with 0.5 wt.% of boron nanoparticles via a fluidized-bed process. This approach enabled powder surface decoration with B, leading to in-situ TiB 2 formation during Powder Bed Fusion - Laser Beam (PBF-LB/M), without the need for ex-situ ceramic additions. The approach, demonstrated here on an AlTiMgSi alloy, can be easily extended to other systems to design in-situ reinforced feedstocks for additive manufacturing. The results showed that the AlTiMgSi alloy is characterized by a partial suppression of epitaxial growth in PBF-LB/M due to the presence of Al₃Ti. In contrast, when B was added to the powder surface, the refinement effect was significantly enhanced , due to the combined effect of formation of TiB 2 particles and the segregation of excess Ti at their surface promotes the formation of Al₃Ti. After solution treatment and aging, differences in Al₃Ti precipitation behaviour were observed in the two investigated systems: the B-free alloy showed a dense distribution of acicular precipitates, whereas the functionalized alloy exhibited coarser and fewer Al₃Ti particles due to Ti consumption during TiB 2 formation. The AlTiMgSi(B) alloy exhibited higher ultimate tensile strength (305.7 ± 0.2 MPa) and yield strength (273.9 ± 8.1 MPa) compared to the B-free alloy (264.6 ± 5.9 MPa and 214.1 ± 0.2 MPa, respectively). • Novel powder AlTiMg decorated with B nanoparticles was produced • B enables in-situ TiB₂ formation during PBF-LB/M processing • TiB₂ and Al₃Ti jointly promote equiaxed grain refinement • B addition alters alloy precipitation behavior after T6 heat treatment