Speaker
Ms
Isabel Catarino
(Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa)
Description
The cold head on mechanical Pulse Tube Cryocoolers (PTCs) are subject to substantially less mechanical vibration and electromagnetic interference compared to that typically found in Gifford MacMahon coolers. However, thermal fluctuations at the PTC frequency are still present at the cold-head, typically at a level of 200 mK peak-to-peak at 1.4 Hz for a Cryomech Model PT405 cooler running at 4 K. It is highly desirable to damp out these fluctuations if PTCs are to be used successfully for running systems sensitive to such thermal fluctuations, for example, bolometeric detectors.
We report here the characterization over the temperature range 2.5 K to 9 K of two materials, GOS and GAP, for use as low-pass thermal filters. These materials have antiferromagnetic transitions at around 4 K giving rise to an enhanced heat capacity and have a high thermal conductance when fired as ceramic discs. These are two highly desirable properties for thermal dampers in this application. Thermal filter assemblies with discs of diameter 75 mm and thickness 2.5 mm and 1.5 mm (GOS and GAP, respectively) mounted in a Cryomech Model PT405 cooler show thermal attenuation levels of x0.12 (GOS) and x0.11 (GAP) at 0.01Hz with a clean-side temperature of 4 K; the PTC induced fluctuations at 1.48 Hz are damped completely to within the noise limits (0.2 mK) of the thermometers. Experimentally determined thermal conductance and heat capacity data is reported. For this system, with a PTC cold-head (dirty-side) temperature of 2.5 K, a clean-side power dissipation of up to 30 mW before its temperature rises above 4.2 K.
Author
Ms
Isabel Catarino
(Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa)
Co-authors
Mr
Daniel Martins
(Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa)
Mr
Rashmi Sudiwala
(School of Physics and Astronomy, Cardiff University)
Ms
Samantha Stever
(School of Physics and Astronomy, Cardiff University)
