Minutes of nanoBPM meeting on 8 August, 2003
"Reference block system", H.Yamaoka
(transparencies, 12 pages, pdf, 6.5MB , or power point file, 13MB)
Yamaoka found a mistake in the previous calculations for the reference block supported with isolators. In the ANSYS, the leg and isolator were approximated by beam element and three spring elements, respectively. The leg consists of two beam elements connecting with a spring element. A spring element has one spring constant, and it carries motion only along the length of the spring element. Since an isolator consists of three spring elements, the other two elements have no connection. Therefore, X and Z directional vibrations can not be directly transfered in the previous calculations. (Y is vertical, X is horizontal and Z is longitudinal directions as the same as the movers.)
In this calculation, X and Z vibrations were input from the ends of the X-, Y-spring elements while the Z components was the same as before. The isolator suppresses vibrations at f >10Hz, while there are resonances at lower frequency. Variations between two positions were also calculated. The variations have typically 1/10 of vibrations themselves at f <10Hz. However, the Y variation may not be tolerable.
He also showed a damping factor when the block is impulsed. General expression is an exponential of exp(-2 pai f d t), where d is a damping ratio. Typical value of d is 2 (1) % for bolted (welded) structure.
Further analysis should need vibrational measurements at the extraction line during the ATF is operational. Major concern must be whether a vibration-free table is necessary to achieve nanometer level stability.
"Updated design of support system for the 3 BPMs", Y.Honda
(transparencies, 7 pages, pdf, 1.1MB )
Honda could reduce the height by about 100mm, so the height of the BPM center is 336mm. Major modification was an integration of X(Y) and X'(Y') as clearly seen in transparencies. Three types of Piezo device were used, which are movable in +/-2um, +/-35um and +/-70um for fine control X,Y, coarse@X'(Y') and X(Y), respectively. During discussions, it was pointed out that further reduction of the height was possible if the Y-Piezo could be sticked out the X-mover. In this case, we can use even larger Piezo with dynamic range of +/- 100um which is better for alignment.
In this design, there should be two structures to be experimentally manufactured, which are an integrated mover of (X, X') and Y' mover. So we will make these two prototypes as the first step to the final design.
"QPD performance", Y. Hagashi
Higashi showed a result of QPD (Quadrant Photo Diode) illuminated by 100um diameter laser beam. Signals of the QPD clearly track 5 nm-step movements of the laser spot, although X-Y couplings could be seen. Measurement period was about 10 minutes.
We will have a video conference with SLAC and LLNL at 9:00am-10:00am on 21 August, 2003.