Abstract
The monolithic primary mirror of an 8m telescope, JNLT (Subaru), under construction will be made by fusion-bonding a number of hexagonal blank segments. These segments, made of zero expansion glass material, have very small coefficients of thermal expansion (CTE's) with averages in the range of -10 to +10ppb/°C; however, there are differences in CTE between individual segments, which result in the nonnegligible thermal deformation of the monolithic mirror. The deformation of the mirror can be evaluated from the measured CTE's of individual segments, once the arrangement of segments is specified. One can, therefore, pose a combinatorial optimization problem of finding the optimum solution for the arrangement of segments, that gives the minimum thermal deformation of the fused primary mirror.
In this paper, we show that this combinatorial optimization problem can be solved by a method using the simulated annealing approach. We demonstrate that the estimated deformation of the mirror can be reduced to a negligibly small level by applying the method to finding the optimum arrangement of segments in a fused mirror blank.
