[Hugo Jeff Arnaud]

Now that one of the satellite box of ITMY (see 7780) has been changed, and following Jeff's and Vincent's investigation on the 6.18Hz noise injected from sus to sei (see 7720 7709 and 7609 for details), a spectra of GS13 on stage 2 of ISI has been taken (using Vincent's scripts), as well as a spectra of the left and right osems before and after changing the sat amp, with the ISI isolated level 3, and the suspension with all the damping loops closed. The pdf attached are described below :

(1) Light blue is GS13 from Sept 10th before the sat amp was changed, and the 6.18Hz peak is present. Dark blue from Sept 30th, and we don't see the peak anymore. Pink and Violet are showing ground motion.

(2) Dashed curves are left and right osems from September 10th before the sat amp was changed, the 6.18Hz peak is present. Plain blue and red are from September 27th, after the sat amp was changer, the peak is a lot reduced.

From those plots, it looks that changing the satellite box reduced the peak by a large amount.

We would need to get the ISI to the requirements, as shown on dark blue of first pdf, and do the same measurement, in order to conclude that it entirely fixed the problem.