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An Advanced Tuning Algorithm for Suppressing Josephson Currents in Band 9 ALMA Receivers

Vos, Tobias (2019) An Advanced Tuning Algorithm for Suppressing Josephson Currents in Band 9 ALMA Receivers. Master's Thesis / Essay, Astronomy.

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The NOVA instrumentation group at the University of Groningen, the Netherlands, has played an important role in the development of Band 9 and Band 5 ALMA receivers. Both bands make use of superconductor-insulator-superconductor (SIS) tunnel junction technology. Both normal electrons and superconducting electron pairs can tunnel through the insulating barrier. The latter is undesired in SIS mixers and can be suppressed by applying a magnetic field in the plane of the junction. This suppression is especially critical in Band 9 receivers. I have used my own Novasoft measurement software to automate the old magnet tuning algorithm. I have also worked on improving said algorithm. New insights include a linear relationship between the noise temperature and the current that generates the magnetic field, with a slope of ~ 8 K/mA. This suggests that we should not focus on suppressing pair tunneling, but on keeping the magnetic field strength as low as possible. For polarization 0 (1) of our test receiver, this approach has reduced the average noise temperature by 6% (15%). On the downside, the algorithm has become more complicated. For example, the magnetic field and bias voltage can no longer be tuned independently. Several recommendations are made for the advanced tuning project which, as of now, is still ongoing.

Item Type: Thesis (Master's Thesis / Essay)
Supervisor nameSupervisor E mail
Degree programme: Astronomy
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 14 Jan 2019
Last Modified: 18 Jan 2019 15:07

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