Summer 1998
May
The experiments on dual recycling at the Garching prototype worked very well.
The dual recycling lock was extremely stable. The trickiest part of the
experiment was manual alignment of signal recycling even when aided by
auto-alignment. The signal enhancement was improved by optimising the
demodulation phases and the modulation frequency. The signal recycling led
to a significantly larger contrast of the interferometer. The agreement
between our model and the measured signal sizes and modulation frequency is
good. These experiments show that dual recycling can be used to improve the
performance of GEO 600.
July
Both tubes have been resuspended using stainless steel wires. The pressure
in the eastern tube is already in a region that is low enough. At the ends of
the tube it is in the mid 10-9 mbar region with a clear air
signature.
The mode-cleaner vacuum system is ready for a bake-out (70 to 80 °C
for four days).
No fairy tale: A mouse built a nest in the glass-fibre cable tray and the
inmates munched through the whole bundle. We try to repair it by installing
plugs at the free ends. (We are in search of a pest controller...)
September
The northern tube has been wrapped with rockwool. Even when wrapped possible leaks can be detected "easily" enough by means of a helium leak test.
