Giles, Travis, Betsy
After discussion with SYS and SUS it was decided that we should continue using the ETM03 PUM with the fracture behind one prism, monitoring for further damage. This afternoon we proceeded with welding on the remaining fibers with no further damage observed. Mid evening saw a successful hang of the ETMx mass from the fibers. A late note from Giles describing the day:
We have just returned from the end station where we hung the ETM. The differential pitch was 0.66mrad and the CoM separation 601.3mm. After 5 mins we supported the optic back on the jack and set to the starting height to relieve tension on the fibres. We then lifted the UIM springs to place 40kg onto the prism (i.e. the PUM hanging). This will be left overnight to check for crack propagation. Applying load to the PUM does not seem to close the crack, although only half the load is being applied. A total of 5 fibres were used.
We also made a series of measurements of temperature of the weld mirror and prism during welding. The maximum value observed for the mirror and prism was 75 degrees centigrade. Interestingly, the prism got to this temperature before the laser beam was directed onto the mirror, suggesting radiation as being the dominant heating mechanism. During heating the crack disappeared, presumably due to thermal expansion. There was no crack line visible suggesting that the crack surfaces are intact. On cooling the crack re-appeared.
Tomorrow we plan to lower the optic and measure the modal frequencies and violin modes, before installing fibre guards.