The focal plane development of SPT-SLIM, an on-chip superconducting filter-bank spectrometer pathfinder for millimetre line intensity mapping

Robson, Gethin 2024. The focal plane development of SPT-SLIM, an on-chip superconducting filter-bank spectrometer pathfinder for millimetre line intensity mapping. PhD Thesis, Cardiff University.

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Abstract

Millimetre wave line intensity mapping (LIM) of carbon monoxide (CO) rotational transitions and the carbon fine structure (CII) spectral lines is a new, complimentary and efficient approach to map the large scale structure of the Universe between red-shifts of 0 < z < 10, which could provide further constraints on our cosmological model of the Universe. To utilise the full potential of LIM, a new kilo-pixel scalable, photon noise limited detecting technology is required with moderate spectral resolving powers (R~1000) and minimal integration times for fast mapping. This thesis presents the focal plane development for a superconducting on-chip filter-bank spectrometer (FBS) technology pathfinder for LIM at millimetre wavelengths called SPT-SLIM as it prepares for the first deployment on the South Pole Telescope in November 2024. The motivations which lead to a focal plane of 9 pixels and 18 x R=100 spectrometers are presented, most notably are the efficiency concerns due to mm-wave dielectric losses and microwave detector multiplexing constraints due to high cross-coupling between neighbouring lumped element kinetic inductance detectors (LEKIDs). The LEKID design is shown to be on the cusp of the expected photon noise limit, limited in responsivity by the aluminium inductor thickness and the geometric inductance of the large interdigital capacitors (IDC) required for frequency scheduling in a suitable range for the readout bandwidth. The parallel plate capacitor (PPC) is presented as an alternative to remove many of the IDC limitations, however, currently the PPC suffers significantly from two level systems in the dielectric resulting in excess noise. FBS devices that were tested have successfully demonstrated optical measurements of spectra at millimetre wave (~100 - 200 GHz), however, the spectral resolution of the spectrometers are shown to be limited (R=100 -> 67) which we attribute to the dielectric loss tangent. Despite this, SPT-SLIM will provide cutting edge LIM measurements and pave the way for future experiments.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	Kinetic inductance detectors, MKID, Resonators, Millimeter/Submillimeter Spectroscopy, Filterbank spectrometer, Line intensity mapping, LIM
Funders:	STFC
Date of First Compliant Deposit:	20 January 2025
Last Modified:	20 Jan 2025 15:45
URI:	https://orca.cardiff.ac.uk/id/eprint/175383

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