Jennie W, Camilla C

A while ago we heated up then cooled down the SR3 heater (alog #84749).

As part of measurements using this data I calculated the curvature change, following the approach at LLO by Aidan given iin alog #27262. Matlab code is below.

%calculate SR3 spherical lens

Pin = 2;%W

double_pass = 2;

SR3_t = (3*3600) + (11*60); % Time for cooldown in s.

delta_ITMY = -2.67e-5;% decrease in defocus of ITMY according to Hartmann sensor.

D_ITMY = delta_ITMY./double_pass;% defocus change in Dioptres

D_ITMY_error = 5e-6;% error on defocus in Dioptres.

R_SR3 = 36.013;% cold radius of curvature in m

delta_R = (2./((2/R_SR3)+D_ITMY))-R_SR3; % change in curvature during cooldown in m/

delta_delta_R = D_ITMY_error.*(2./((2./R_SR3)+D_ITMY)); % error on curvature change.

This means the rate of defocus change is 6.6750uD per Watt.

The final curvature change is + 0.0087 m +/- 0.0002 m as the mirror becomes less curved due to cooldown.