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Message ID: 6458     Entry time: Tue Mar 27 21:37:51 2012
Author: keiko 
Type: Configuration 
Category: IOO 
Subject: Beam Profile measurement: IPPOS beam 

 From the mode measurement I and Suresh have done yesterday, I calculated what beam size we expect at ETM ((1) upper Fig.1)  and at ETM after one bounce ((2) lower Fig.1).

expsche.png

Fig.1 (Yarm)

In case of (1), we expect approximately w=6300 um (radius), and w=4800 um for one-bounce spot (2) from the measured mode, see Fig.2.

drawing.png

Fig.2

This roughly agree with what we observed on CCD camera. See, pic1 for (1) and pic2 for (2). The spot at the ETMY (1) is larger than the one-bounced spot (2). From the monitor it is difficult to assume the radius ratio. The observed spot of (2) is a bit smaller than the prediction. It could happnen when (A) the ETMY (as a lens) is slightly back of the ideal position (= the distance between the ITM and ETM is longer than 40m) (B) the real waist is farer than ITM position toward MC (I assumed roughly 5 m from Jenne's plot, but could be longer than that).

P3270007-s.jpg  P3270008-s.jpg

pic1 (left): beam spot hitting on the suspension frame. pic 2 (right): the one-bounced beam spot hitting on the suspension frame.

 

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