Minutes of nanoBPM meeting on 19 February, 2004

"Performance of prototype mover", Y.Honda

(transparencies, 13 page, pdf, 411KB )

X, X', Y and Y' movers were assembled, and the active mover, which will be placed on the assembled one, has been ordered for fabrication. Their dynamic ranges and correlations were measured, where the angular and position resolutions were 0.4urad by auto collimator and 1um by laser displacement sensor, respectively. The X and Y positions can be adjusted by the stacked Piezo devices. The both dynamic ranges were 60um at 140V applied voltage, while the design values were 60um at 90V. Hysteresis of movements were observed at about 10% level. The difference may come from more rigid structure than the assumed one. The X' and Y' can be also adjusted by the stacked Piezo devices. The dynamic ranges and correlations (or cross talks) are summarized in following table.
mover at 140V/measurementXX'YY'
Since the rotational center in the Y' mover moves upward more than expected, diameter of supporting rod will be reduced to 15mm so that the center movement shall be less than 3mm.

Vertical motion was measured by the laser interferometer in the same way as the final setup. The preliminary result shows less than 10nm at f>20Hz.

A nano-laser-BPM was demonstrated by using a method of balance receiver. The BPM consists of laser beam, triangular mirror (prism) for the beam split and photo diodes. The prism has a role similar to cavity-BPM. The laser has wavelength(&lambda) of 532nm, spot size(w0 = 2&sigma) of 900um and power of 20mW, where the Rayleigh length (πw02/&lambda) is 4.8m enough for "long" distance flight. The differential signals of photodiodes have been calibrated by a micrometer stage, where 4um displacement generated 4V signal corresponding to 1nm/1mV. There are two systems of the nano-laser-BPM which are put on the same table. Direct laser produced 10nm oscillation at 100Hz and 10Hz slow vibration in the two systems, which were completely correlated because of the laser stability. Transporting lasers in a few meter long fibers, the oscillation and vibration disappear so that the 1nm resolution was confirmed. The nano-laser-BPM system can simulate the nanoBPM phase-2 for stabilization and monitoring the relative displacement of two system.

"Thermal Distortion and Optical Anchor System", Y. Higashi

(transparencies, 6 pages, pdf,1.6MB )

Higashi proposed a strategy against thermal distortion in the reference system. He introduce a Japanese paper of "Development of Simple Shelter Styrol Foam for Supporting High Precision Machining" by I.Tanabe et.al., Journal of Japan Society for Precision Engineering, Vol.67, No.7(2001),1154. Conclusion of this paper is that the thermal stability can be obtained to be 1/20 of ambient temperature inside a thermal shelter of styrol foam walls 270mm thick with two layers of normal(150mmt) and high density(120mmt) ones, i.e. within 0.1oC at room temperature of 20±1oC.

Two possible systems(A and B) of optical anchor with the shelter were briefly explained. The concept of the optical anchor is a stabilization of the reference system(bar) relative to the floor. Lasers are transported outside of the nano BPMs in the A, while lasers go through the girder from the floor to the reference bar in the B. Inside the shelters of both system the temperature can be controlled with 23±0.025oC for ambient temperature of 23±0.5oC measured at the ATF.

He would like to test the shelter soon, after the granite table (girder) and reference system are completed.

"GM measurement at ATF", H. Yamaoka

(transparencies, 13 page, pdf, 1.1MB )

From 16:00, 10th to 9:00am,12th February, the ground motions have been measured for 10 minutes in every 1 hour at the ATF floor where the NanoBPM system will be installed. The measurements were done by collaboration with R.Sugahara's group and J-Power company. We used our sensors of accelerometer and the J-Power used velocity type sensors. In this time, results by our sensors are only presented except for calibration results of the J-Power ones.

For 9 and 10th February before the measurements, the sensors have been calibrated on the granite table at the ATF. A sharp resonance peak was observed at 15 Hz on the granite table, which may be caused by water cooling pipes nearby. Vibrations were also measured on the water pipe, which show large amplitude at higher frequencies of greater than 20Hz. On the granite table, the J-Power sensors clearly show several resonance peaks at 0.4Hz, 3Hz, 15Hz and ~20Hz. Our sensors have good coherence at f>2Hz, while the J-Power ones do at f>0.2Hz.

Measurement points were on the floor(P1) and on the girder(P2) where the LLNL support tube will be installed. A clear difference between them was observed at ~10Hz only on the girder. Results on the floor are consistent with the previous measurements in last summer. On the girder, the NS components have larger motions since the girder is not fixed in the NS direction along the beam line. The girder has 50% and 100% more amplitudes in vertical direction at frequencies of greater than 5 and 10Hz, respectively. Coherence between the girder and floor motions was observed for 2Hz < f < 10Hz in all three directions. A strange vibration of 14 Hz was observed in NS at the floor. This 14Hz vibration suddenly appeared in middle of 10 minutes data taking.

The "famous" 78 sec periodic noize has been identified as a software bug.

"C-band and X-band cavity BPM and LLNL sysytem", H.Hayano

Design of the C-band cavity (KEK nano-BPM) has been completed. Total length is 180mm including a reference cavity and flanges with bellows. The cavity will be mounted on the active mover with a V-block. One cavity will be fabricated until end of this April, and it will be tested at the ATF in May. Other two cavities will be fabricated until end of August, 2004. First electronics circuit will be tested with the Russian cavity BPM without reference cavity soon.

The X-band cavity has problems in the fabrication. Brazing was failed to leak up into the cavity for asymmetric response in position dependence due to XY coupling. The resonant frequency was shifted by several 10MHz. However, it will be tested at end of the ATF-LINAC for shorter bunch length. Hereafter, Naito-san has a responsibility of the X-band BPM fabrication.

The LLNL support tube will be installed on 1st March.

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