PXS Cryogenic Requirements

The haloscope axion experiment model requires superconducting magnet technology, as well as quantum-limited readout. We have had the fortunate ability to develop the sub-systems independently. Each system has unique demands to work cryogenically. The magnet requires hundreds of amps to be delivered at 4 Kelvin, all while being cooled exlcusively through conduction mechanisms. For the readout development, we have had to design and commision a custom cryostat with a base temperature of 270 milli-Kelvin, as well as integrate testing equipment into a Dilution Refrigerator for device testing that requires the 10 milli-Kelvin base temperature.

Each of these systems requires hardware and software design that ensures high-reliabilty, minimizes cost, and meets the research-grade performance.

Sub-system Research Components

High-Current Leads

To meet the design requirements of our superconducting magnet, we designed a system that enables us to connect our power supply to a standard vaccuum interface and creates a heatload within the capability of a mechanical pulse tube at each temperature exchange. The coldest temperature stage is able to leverage commercially available high-temperature superconducting current leads, but the link from room temperature to 40 Kelvin required innovation. We were able to design a system that balanced the joule-heating of the material against the thermal diffusivity to minimize the heat flux. By optimizing the interfaces we have been able to run over 500 Amps to 4 Kelvin for over 10 hours without raising the temperature above 5 Kelvin.

SolidWorks rendering of the high-temperature-superconducting current-lead assembly An early Solidworks render of the current lead design - which we call the ‘snake’

Rapid Prototype Cryostat

The development of the RF chain requires the ability to balance individual device tests with large-volume, short-turnaround, screening and full-chain debugging. By re-using Helium-4 and Helium-3 adsorption pots from a decommissioned cosmology experiment, we were able to create an inexpensive cryostat that can cycle from room temperature to 300 milli-Kelvin in 3 days. A major part of this rapid cooldown was our development of graphite heat switches - more detail is available under publications. By designing robust control software to safely automate parts of the experiment, see more in PXS Software Development, we are able to ensure that maximize our experimental uptime.

We have used this cryostat to refine our coaxial cable development process, develop our noise temperature measurement procedure, and screen numerous components for our full-scale system architecture. We have been able to achieve this testing scale by developing our own analog control circuits, see PXS Electronics, and complimentary software to integrate cryogenically-rated multi-pole switches without introducing and digital noise sources.

Sub-Kelvin Work

Precise noise temperature measurements are a critical output for our research group. We designed and commissioned a homemade variable temperature stage to be able to do Y-factor style noise measurements on both commercially available low-noise amplifiers, and the Kinetic Inductance Traveling Wave Parametric Amplifiers. By creating a solution in house, we were able substantially reduce the cost, and have greater control on trade-off between cooldown time and conductance to the reference stage.

This work supports the broader Princeton Axion Search (PXS) experiment, which searches for dark matter particle candidates in the axion mass range corresponding to the transitional region between lumped-element and cavity haloscope search techniques.

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