Yesterday we made excitations of the HAM1 HPI loops and saw coupling to DARM.
We saw that the horizontal motion is coupling to DARM more than the horizontal vertical motion. The first attached plot shows projections based on the HPI L4C of the HAM1 motion to PRCL, MICH, SRCL and DARM. Both X + Y directions contribute to the noise of our length degrees of freedom, the L4C motions in X and Y are partially coherent.
The coupling isn't through the CHARD loops, their control signals are not increased increased by the HPI injection (next two screenshots). A few weeks ago Hang made the CHARD blends more aggressive than they were in O2, 44352. That probably explains the difference from what Marie found 38184.
Did you mean to write that horizontal motion couples more than vertical ? Was the elevated DARM noise always coherent with the elevated HAM1 motion? If not (or even if yes), it might be worth repeating these tests, but bandlimiting the HAM1 HEPI excitations to be below 20 Hz, to see if there is any upconversion of HAM1 motion into higher frequencies in DARM. That's of interest because if we replace the HAM1 seismic with a HAM-ISI, it will give much lower platform motion below about 20 Hz, but higher motion above that (less passive filtering at higher frequencies).
Yes, I meant to say horizontal couples more than vertical.
Attached is a plot of coherences between the X L4C during the excitation and different signals. The L4C isn't very coherent with DARM, MICH, PRCL or SRCL, but it is coherent with PR2 ASC signals which are from the REFL WFS now.
