Lutz Bornschein

To study thermodynamic properties and dynamic phase space behavior of hydrogen isotopologues (Q2) at cryogenic temperatures and at high density, the Tritium Absorption InfraRed Spectroscopy 2 (T2ApIR) experiment has been set up and commissioned at Tritium Laboratory Karlsruhe (TLK). In the frame of the experiment, Q2 behavior in different phases, ortho/para states, temperatures (10 K - 300 K) and pressures (up to 2.5 bar a) will be investigated with optical methods, infrared and Raman spectroscopy. The facility consists of a fully tritium compatible cryostat, which includes an optical cell, ortho/para converter and windows for optical and spectroscopic studies. The cryostat can be cooled below the H2 triple point by a two-stage cryocooler and contains openings in the cryogenic shielding for the optical access. The challenge of combining these scientific requirements in a design with high amounts of tritium (14 g), in a limited space, all while maintaining the TLK safety philosophy was solved by the presented design. The experiment is ready to be fully integrated into the TLK closed loop tritium infrastructure. This contribution reports a comprehensive overview of the commissioning phase of the experimental facility and the results of the firstcommissioning experiments, including cryogenic performance tests, commissioning experiments with non-radioactive gases, and tests of the analytical instruments.

The KATRIN experiment aims for the determination of the effective electron anti-neutrino mass from the tritium beta-decay with an unprecedented sub-eV sensitivity. The strong magnetic fields, designed for up to 6 T, adiabatically guide β-electrons from the source to the detector within a magnetic flux of 191 Tcm². A chain of ten single solenoid magnets and two larger superconducting magnet systems have been designed, constructed, and installed in the 70-m-long KATRIN beam line. The beam diameter for the magnetic flux varies from 0.064 m to 9 m, depending on the magnetic flux density along the beam line. Two transport and tritium pumping sections are assembled with chicane beam tubes to avoid direct "line-of-sight" molecular beaming effect of gaseous tritium molecules into the next beam sections. The sophisticated beam alignment has been successfully cross-checked by electron sources. In addition, magnet safety systems were developed to protect the complex magnet systems against coil quenches or other system failures. The main functionality of the magnet safety systems has been successfully tested with the two large magnet systems. The complete chain of the magnets was operated for several weeks at 70% of the design fields for the first test measurements with radioactive krypton gas. The stability of the magnetic fields of the source magnets has been shown to be better than 0.01% per month at 70% of the design fields. This paper gives an overview of the KATRIN superconducting magnets and reports on the first performance results of the magnets.

The introduction of a dielectric rear side passivation with local contacts (PERC) opens a path for improvements in the cost of crystalline silicon photovoltaics. First, the cell efficiency is increased by higher internal rear side reflectance and better passivation. Second, the elimination of the cell bow allows the use of thinner wafers to reduce the silicon consumption. While the PERC cell concept is well known, there is still no favorable industrial solution for the rear side metallization. Currently, there are two candidates for industrially relevant processes: The i-PERC process, where the dielectric is opened before the application of the rear-side metallization, and laser-fired contacts (LFC), where the contacts are laser-fused after metallization. LFC promises good process robustness. However, so far, state-of-the-art efficiencies were only reported with evaporated Al rear-side metallization (PVD). Nevertheless, near-term introduction of the PERC concept would favor a fully screen-printed (SP) metallization to maintain compatibility with established process equipment. We report on the development of a fully screen-printed PERC cell with LFC. The optimization of the cell performance requires a co-optimization of both the passivation stack and the rear-side metallization.