Cryogenic dielectric properties of sapphire at 2.45 GHz

Abstract

An exceptionally sensitive calorimetric technique has been devised for measuring microwave absorption by small samples of ultra-low-loss dielectrics at cryogenic temperatures. The loss factor of sapphire at 2.45 GHz diminished progressively with decreasing temperature from 3.5*10-5 at 300 K down to 2*10-10 at 4.2 K. The rate of decrease showed no tendency to attenuate at temperatures down to 4.2 K.

Measurement of the dielectric properties of high-purity sapphire at 1.865 GHZ from 2-10 Kelvin

“…The results for the heat capacity look to be reasonable compared to other data [2]. The loss tangent data is much higher than previous work [3,4]. The 4.2 K measurement made in this set is slightly better than previous work using RF cavities, except for one measurement where Q was measured to be 10 -9 [3].…”

“…The 4.2 K measurement made in this set is slightly better than previous work using RF cavities, except for one measurement where Q was measured to be 10 -9 [3]. However it is much higher than 2*10 -10 measured using calorimetry at 4.2 K by Buckley [4].…”

“…The Buckley line [4] uses the best loss tangent data taken and extrapolates the performance of the test cavity. It reaches the BCS limit with 500 W, and the sapphire's temperature rises only to 19 K. These calculations include the heat being removed from the cavity through the sapphire stem into the helium bath.…”

Invited Article: Dielectric material characterization techniques and designs of high-Q resonators for applications from micro to millimeter-waves frequencies applicable at room and cryogenic temperatures

“…A one layer cylindrical sapphire Bragg resonator with Q-factor of 230 000 was achieved at 9.7 GHz 14 (Figures 16 and 17). This is higher than a Whispering Gallery mode resonator at room temperature at the same frequency (Q WGH ∼ 200 000, Q WGE ∼ 100 000) 83,84,[96][97][98][99][100] and equivalent to a single spherical Bragg resonator. 20 However, the machining and assembly are much easier in the spherical case.…”

Conceptual design of a sapphire loaded coupler for superconducting radio-frequency 1.3 GHz cavities

“…20. In HFSS simulation, we use that sapphire and alumina window materials have dielectric loss tangents of 1 × 10 −9 and 0.44 × 10 −4 respectively at 10 and 2 K temperature [22,23]. In this study, we use single crystalline sapphire rod thus presume the material is anisotropic [24,25].…”