Minutes of nanoBPM meeting on 25 July, 2003

"Design of support system for the 3 BPMs", Y.Honda

Honda explained a design of support system of a BPM collaborating with Higashi. A cavity BPM of 110mm diameter is set on a V-block. The V-block is put on movers, which are six of y,x,Y',Y,X',X-movers from top to bottom, where y and x are active ones with dynamic range of +/- 3um ( Piezo), Y' and X' are rotational ones with +/- 100urad, and Y and X are coarse adjustment ones with +/- 80um (stacked Piezo). All movers except for Y' mover take advantage of hinges whose structure has been used at the laser wire system. The Y' mover employs torsion of round bar, whose axis goes through the center of the BPM, i.e. it is a swing mechanism. There is no brand-new component necessary for specific R&D.

During discussions, major concern was its height of 449 mm. It looks too tall to control positions at nanometer level. The height may be reduced if fine and coarse adjustments can be located at same position. Although there was no clear idea for such modification, Honda and Higashi will re-design a shorter system within 2 weeks,

"Design of reference block system", H.Yamaoka

(transparencies, 14 pages, pdf , or power point file) Yamaoka designed a reference block system based on informations from Honda. The 3 BPMs are assumed to be aligned in a space of 200(width) x 600(length) x 450(height) mm3. The block is L-shaped one of 50mm thick Aluminum, whose overall size is 320(width) x 900(length) x 130(height). The block is supported by 4 square bars (legs) of SUS 50 x 50 mm2x 500 (420)mm length. Materials were chosen for enough rigidness for deformation.

Vibrational properties of this system were estimated in two configurations with and without isolators in the legs by ANSYS. The isolator has three different spring constants which are 98N/mm, 125N/mm and 37N/mm in X, Y and Z directions of mover convention, respectively ( in Yamaoka's transparency, X=Y, Y=Z, Z=X ).

The system without isolators has the third resonance frequency at 103Hz which is the lowest one with deformation of the reference block, while the first resonance frequency is 62Hz in X-direction. Frequency responses were also calculated with inputs of measured power spectrum at typical noisy site. Responding power spectra were calculated at both ends (L,R) and a center (C) of the reference block. All the three points follows the ground motion up to the first resonance frequency. At the resonances (62, 69 and 103Hz), the block would vibrate about 25 times more than the ground in the amplitudes.

The isolators produce resonances at lower frequencies (4.8, 5.5 and 13Hz of 1st, 2nd and 3rd resonances, respectively). However, they shift resonances accompanied by deformations to higher frequencies of more than 203Hz. Responses of the power spectrum show that the isolators reduce the ground motion by 2-order magnitude at f > 20Hz. The X and Y vibrations shall be largely enhanced at f < 10Hz, while the Z vibration is suppressed at all frequency region. ( The large enhancements are parallel displacement of the reference block. ) This asymmetric behavior must be due to differences of the spring constants.

We discussed on effectiveness of isolators. Because of the large enhancement, they may not be effective for our purpose. If we can suppress the enhancement by adding active feedback or reducing spring constants, the isolator system may become the most stable one. Such possibilities will be looked for.

Video conference and Nano-BPM meetings

Marc Ross made proposals in his recent e-mail. He would like to have a video conference in this August. He informed that the Livermore structure schedule was delayed and installation date would be January, so it is three month delay. However, he would like to present a laser based stabilization (to Higashi-san) and discuss how it might fit in the extraction line system. Also he would like to hold a meeting in October at KEK to review nanoBPM plans and results.

After discussions, the video conference will be held at 9 - 10am, 21 August. The nanoBPM meeting can be in 6th ~ 17th, October. After a communication to him, the date was fixed to be 6-7, October.

Next meeting will be on 8th August, 2003, 13:30-15:30 at 3 gokan, 425.