Abstract
Microwave SQUID (Superconducting QUantum Interference Device) multiplexing is a suitable technique for reading a large number of detector channels, using only a few connecting lines. In the HOLMESexperiment, this is based on inductively coupled rf-SQUIDs fed by TES (Transition Edge Sensors). Operation of the whole rf-SQUID chain is achieved with a single transmission line, by means of the recently introduced flux-ramp modulation technique—a sawtooth signal which allows signal reconstruction while operating the rf-SQUIDs in an open loop condition. Due to the crucial role of the sawtooth signal, it is very important that it does not suffer from ground-loop disturbances and electromagnetic interference (EMI). Introducing a transformer between the sawtooth source and the SQUID is very effective in suppressing disturbances. The sawtooth signal has both slow and fast components, and the frequency can vary between a few kHz up to a MHz, depending on the TES signal and SQUID characteristics. A transformer able to handle such a broad range of conditions must have very stringent characteristics and needs to be custom designed. Our solution exploits standard commercial and inexpensive transformers for LAN networks, stacked in a user-selectable number, to better fit the bandwidth requirements. A model that allows handling of the low- and high-frequency operating range has been developed.
Highlights
IntroductionThe use of SQUIDs (Superconducting QUantum Interference Devices) in cryogenic particle detectors allows implementation of the readout of large arrays using different configurations
The use of SQUIDs (Superconducting QUantum Interference Devices) in cryogenic particle detectors allows implementation of the readout of large arrays using different configurations.A promising approach for reading out a large number of detectors with a SQUID array using a common transmission line is microwave rf-SQUID multiplexing
A multiplexed microwave readout will be used in the HOLMES detectors [1], an array of 1000 micro-calorimeters based on TES (Transition Edge Sensors) [2], each coupled to a rf-SQUID
Summary
The use of SQUIDs (Superconducting QUantum Interference Devices) in cryogenic particle detectors allows implementation of the readout of large arrays using different configurations. The classical set-up of Figure 1 is not convenient when one wants to minimize the number of connecting lines to the array, since every channel needs its own feedback link To overcome this limitation, flux-ramp modulation was recently successfully implemented. By evaluating the phase shift as a function of time, the signals due to particle interactions are properly reconstructed This is depicted, where feedback is not needed anymore, and the ST signal can be common to all of the rf-SQUIDs in the array. For the final configuration of HOLMES, the detector signal-rise time is expected to be close to 10 μs, and the ramp frequency will be set to 500 kHz. In the current R&D studies, it is required to work down to small frequencies, as several TES optimized for different ranges are foreseen. To confirm the validity of the developed system, we characterize and model the transformers
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