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H1 ISC

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kiwamu.izumi@LIGO.ORG - posted 19:52, Friday 31 October 2014 - last comment - 11:10, Wednesday 20 June 2018(14788)

unclipping on PR2 baffle

Alexa, Kiwamu,

We spent most of the daytime today for

Measuring the spot position on various optics
Moving the spot on PR2 by 12 mm to minimize the risk of clipping on the PR2 scraper baffle

There were a few noticable effects after the PR2 spot was moved:

the right side of the BS elliptic baffle as seen by the analog camera became brighter.
POPAIR_RF18 increased to 260 uW from 220 uW in the PRMI sb lock.
However, the optical gain did not change either in PRCL of MICH, indicating that the recycling gain did not change.

Summary of the spot measurements before and after the unclipping.

		before [mm]	after [mm]
PRM	Pitch	-2.82	NA
	Yaw	0.402 toward West	NA
PR2	Pitch	-6.04	-5.44
	Yaw	2.26 toward West	14.1 toward West
PR3	Pitch	-24.5	NA
	Yaw	0	NA

(Some more notes)

We aimed for a displacement of 16 mm on PR2 in order to bring the beam to the ideal point according to Keita's measurement (see alog 14640). However, later, I realized that I had picked a wrong number from his entry -- I must have chosen eitehr 14 or 10 mm. Anyway, the resultant dither measurement suggested that we moved it by 11.5 mm to the right direction on PR2. So it happened to fall into a OK displacement. I think that we anyhow improved the clipping situation on the PR2 baffle.

The POP extraction path was then corrected by using the pico-motorized mirror in HAM3. This was not a difficult task as the beam was hitting the swiss cheese baffle and therore it was visible. We then went out and did fine tunings. The pico motor was adjusted to recover the highest green TRX. We steered a steering mirror for each POP diode.

In order to compute the off-centering on HLTS, I used the mirror sizes described in D1101381.

R = 132.5 mm
L = 101.4 mm
D = 206 mm for vertical
D = 120 mm for horizontal
conversion factor for vertical = 52.5 mm per alpha
conversion factor for horizontal = 94.9 mm per alpha

For computing the HSTS spot position, I used 42.2 mm per alpha (see alog 13765).

Comments related to this report

kiwamu.izumi@LIGO.ORG - 21:19, Friday 31 October 2014 (14789)

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Alexa measured another set of the beam spots. Here are the summary:

		spot positions [mm]
SRM	Pitch	+ 3.42
	Yaw	2.42 toward South
SR2	Pitch	+ 2.42
	Yaw	6.44 toward South
SR3	Pitch	-13.1
	Yaw	19.9 toward North

The measurement was done after the unclipping effort and we measured them in the DRMI sb lock configuration. The excitation was set at 131.7 Hz in order to reduce interference from the length loops.

craig.cahillane@LIGO.ORG - 11:10, Wednesday 20 June 2018 (42600)

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In 2017, Koji corrected his coil balancing calculations from 40m elog 2863

Now,  instead of , where  is the ratio of moment of inertia and optic mass,  is the coil force imbalance factor, and   is the distance between coils.

Corrected alpha to mm for HLTS optics: 
Vertical: 50.93 mm / alpha
Horizontal: 87.43 mm / alpha

For HSTS optics, see alog 42601