Minutes of nanoBPM meeting on 22 January, 2004

"Performance of prototype mover", Y.Honda

(transparencies, 22 page, pdf, 411KB )

Performances of X-X' and Y' movers have been studied on the mechanical resonance frequency, the rotational axes and the angular ranges. The resonance frequency of X-mover was clearly measured by a capacitive sensor just after the mover was pushed for about 10μm by a piezo device with 10V-input pulse. Resultant frequency was 150Hz, while the expected one was 40Hz for the hinge strength of K=2 x 106N/m (design value) and the moving weight of about 20kg. In much the same way, the X' and Y' resonances were measured to be 286 and 400Hz, respectively.

In order to determine the rotational axes of X' and Y' movers, laser intensities were measured by shading half a laser-profile as a function of two dimensional displacement, where the profile is assumed to be perfect circle and put on the geometrical center. The laser profile was reflected at a mirror placed on the movers. If the geometrical center is same as the rotational one, the laser intensity should not change for the half shade. These two centers were coincident within a few mm at the X' mover. The rotational center of the Y' mover was shifted up 7mm from the geometrical one.@ The Y' rotational center was also calculated to be shifted upward 5mm by using ANSYS program. Therefore, the result seems to be reasonable.

The X-mover may displace a moving plate in orthogonal direction to X, which is actually direction of beam. Such coupled displacements were measured as 2% for 50μm. The X' mover has 7% coupling of Y'/X' for 100μrad with 10% hysteresis. The Y' mover has 3.3% coupling of X'/Y' for 120μrad also with 10% hysteresis.

"Optical Anchor", Y. Higashi

Higashi reported a position measurement by detection of two divided laser beam at a prism. The laser beam of 1mm-diameter is emitted to the prism by an optical fiber, where the prism is placed at 20cm from the fiber. Modulation of the fiber with amplitude of 20nm was able to be measured at frequency of less than 200Hz. Smaller diameter laser beam could provide better position resolution, i.e. 1nm resolution with 0.1~0.05mm diameter laser beam in which case the system must be set in vacuum (~10-2Pa). This method is alternative to laser interferometer for measurement of lateral displacement at floor.

"Laser seismometer", T. Kume

Kume raised a question on the differential amplification of interference in the laser seismometer since two signals seem to be in same phase. There were explanations by conservation of laser intensity or opposite phase due to different number of reflections etc. . However, these were no satisfactory for him. He will look into the question in more details.


The nanoBPM schedule was reminded. Especially, the KEK system must be completed without cavity-BPMs within this fiscal year. This system is consisted of three movers, reference frame, girder(granite table) and dummy-BPMs. The schedule will be updated on the web site.

Next meeting will be held in 19 February, 2004, at 1:30pm-, 3-gokan 425.