Publications of the Astronomical Society of the Pacific, 119: PP.583, 2007 May
K.Enya, N.Yamada, T.Onaka, T.Nakagawa, H.Kaneda, M.Hirabayashi, Y.Toulemont, D.Caste, Y.Kanai, AND N.Fujishiro
Abstract:
We present the results of high-precision measurements of the thermal expansion
of sintered SiC, SiC-100, intended for use in cryogenic space telescopes,
in which minimization of thermal deformation of the mirror is critical,
and precise information of the thermal expansion is needed for the telescope
design. The temperature range of the measurements extends from room temperature
down to 10 K. Three samples, Nos. 1, 2, and 3, were manufactured from blocks of
SiC produced in different lots. The thermal expansion of the samples was
measured with a cryogenic dilatometer, consisting of a laser interferometer,
a cryostat, and a mechanical cooler. The typical thermal expansion curve is
presented using an eighth-order polynomial of the temperature. For the three
samples, the coefficients of thermal expansion (CTE), 1, 2, and 3, were
derived for temperatures between 293 and 10 K. The average and the dispersion
(1σrms) of these three CTEs are 0.816 × 10-6 and 0.002 × 10-6 K-1,
respectively. No significant difference was detected in the CTE of the three
samples from the different lots. Neither inhomogeneity nor anisotropy of the
CTE was observed. Based on the CTE dispersion obtained, we performed a
finite-element method (FEM) analysis of the thermal deformation of a 3.5 m
diameter cryogenic mirror made of six SiC-100 segments. It was shown that
the present CTE measurement has an accuracy that is sufficient for the design of
the 3.5 m cryogenic infrared telescope mission SPICA (Space Infrared Telescope
for Cosmology and Astrophysics).
