20180327
Today's activities
Workers: K. Nagano, Yokogawa, Ko. Yamamoto, Sugimoto, Akutsu
- After Uchiyama-san allowed us to turn on the green laser source, we did it, and went to EYT.
- Tried to check the situation, but the green beam got crazy many times and it was so tough to check. The actual cause was still unclear but probably due to the BS suspension's something (no idea!).
Brought several optical parts and the holders to EYT; see here
- Preparations for aligning the BRT.
Attached a diaphragm (or iris) along the optical axis after the 2nd BRT lens; call iris-1.
Attached another iris (iris-2) as well between the 2nd mirror and the 2nd BRT lens.
Then we can use the beam positions on the two irises along with the beam position on the 2nd mirror as references; see here
- Loosened the foots of the BRT base plate, and hooked up the BRT very slightly.
- (Pitch and) height alignment
- Found the beam position was relatively down along with the hooking up of the BRT... actually down to the height of the goal!
- So it seems, in addition to the pitch alignment on March 22, needed to do the height adjustment of the legs.
- To do so, we rotated halfly (180-deg rotation) every leg of the BRT; each leg part (misumi SGKS10-50) has M10 screw, the pitch of which is 1.5 mm, so the half screwing down each would lead 0.75-mm up of the base plate when the base plate sits on the fixed stage.
- Even though the beam position is higher than the irises, we stopped the pitch and height alignment. The reason is written below.
- Yaw and X-shift (translational) alignment
- Note that the BRT was still hooked up by the chain block (or just a crane), so the three foots of the BRT base plate were still loosened.
- First I tried to rotate the base plate to align the green beam to the iris-1's center hole.
But the required direction of the rotation was opposite against what we expected... speaking about it, it would be impossible to definitely say whether the initial position and alignment of the BRT (on 15 March 2018?) was actually nominal or not.
- Note that the center pin and the alignment pin are fixed to the fixed stage, while combination plates (a set of two plates to accept a pin; two plates for one pin) on the BRT base plate accept the pins.
- The only reference we were able to use to determine the combination plates is a groove on the BRT base plate (showing the nominal optical axis line); a groove on the combination plates were aligned to the groove on the base plate only in the human-eyeball-accuracy at that time.
- The grooves are 1mm widths, while the precisions we need to tune are 0.xxx mrad and 0.xxx mm, respectively (see the short summary memo below); it is impossible to align the stuffs only refering the groove by human being.
- Moreover note that in average in KAGRA, the accuracy of the location of the vaccum chamber would be a few mm!
- Finally used the green-beam-itself-today as the reference.
- First we loosened only a combination plates for the alignment pins, and rotated the BRT base plate. The BRT itself was able to be rotated, but the result is not so better in terms of the position adjustment of the beam spots. This somehow moved the beam position on iris-1, but the reflection point on the 2nd mirror was not improved (shifted too much in -X direction).
- So we also loosened another combination plates, which accepted the center pin to do X-shift as well at the same time!
Then I pushed and pulled somehow... so that the green beam positions on iris-1, -2, and on the mirror2 were improved. The results are shown here
Considering the reference beam we used today is not be the actual one, we don't think we need to do much more extreme alignment today, so stopped.
Note that even after the alignment here, it seems the grooves of the combination plates and the base plate keep in the "center-to-center" relations, as the shift or tilt amount was too small to be resolved by human eyeballs.
Short memo
- According to "図3_EXT，EYTの位置.pptx", (1) EYT chamber center: [ -0.013, 3023.297+8.3], and (2) ETMY AR: [ -7.590557e-03 3.023372e+03] (all units are in meters).
- So the yaw tilt to EYT would be (x1-x2)/(y1-y2)= -6.5768e-04 rad, here y1-y2= 8.2250 and x1-x2= -0.0054.
- More precisely speaking, the primary lens of the BRT is located about 450mm "upper" （20181003追記、たぶんこれ、光学的に上流って意味だと思う。自分で書いててもわからん。 by 阿久津）from the center of EYT; so 450mm x -6.6rad = -0.296 mm shift; considering a few mm accuracy of the vacuum chamber location, it is too small.
- To avoid just a qualitative discussion, let us consider with more quantitative ways.
- The rough ABCD matrix of the BRT: [ [A,B],[C,D] ]=[ [0.1,2000],[about 0,10] ].
- The input beam matrix is [x, theta]=[-0.296mm, -6.5768e-04 rad]
- Then -0.296*0.1+2000*-6.5768e-4=-1.34mm; actually the first term is negligible; only tilt should have the dominant effect, but still difficult to be sensed by humans without micrometers or something...
- So in the end, I think only the actual light beams traveling 3km can be used for the alignment reference.
Next plan
- Measure the height with a laser leveler?
- Locate the BRT on the stage base on XXX as references.
- Make GPT on the optical table
- Make a model to drive signals from the TMS
- Check the response of the TMS by swinging BS, PR2, PR3... etc... with commissioning people
- Endのend用のフランジとりつけ。たぶん最後のほうで。
- そこのフランジにとりつける透過光用ビューポート。まだ柏にあるはず。
- 外側の光学定盤の上の取り回しを考えよ。
Wanted!
Four M10 eye bolts
M8 SDC bolts? to tighten the top plate to the stage body are shortened!
- Markers (black and white)
From VIS
- Four clean slings (from Hirata-san)