Minutes of 25th FFIR meeting on 4/11/2001

The meeting was held in a room of 3-425 at KEK, 13:30-14:00, 4/11/2001. We discussed on the present status of support tube R&D, new FF optics, the ACFA report and budget in FY2001.

(1) Support tube R&D (transparencies, 7 pages, pdf ,3.31MB ) H.Yamaoka talked on the present status of the support tube R&D. So far the cantilever system has been studied. Results showed a good agreement with an ANSYS analysis. Here, two cantilevers (Al plates of 100mm wide, 20mm thick and 725mm long, each) are connected by thin Al sheets of 1mm thickness to simulate a "both-ends support tube". The support tube was shaken on the both ends with 0.3-0.4G and frequencies (sine waves) were manually varied from 0 to 900Hz. Accelerations and variations were measured by two sets of accelometers and three sets of laser-systems, respectively. In the accelerations, many resonances were clearly observed at 30Hz,70-100Hz, 130Hz, 190Hz, 210Hz and 230Hz, while in the variations only one resonance was visible at 30Hz. The ANSYS calculations shows three resonances at 34Hz (1st), 42Hz(2nd) and 200Hz(3rd). Apparently there are discrepancies between measurements and calculations. So, he speculated that the connection was not rigid as what the ANSYS-calculation assumed, where the ANSYS assumed a box of 1mm-thick for the connection. For soft connection, the thickness of the box was changed to 0.1mm. As expected, more resonances appears at 24, 35.3, 35.4, 67 and 130Hz. Therefore, calculations could qualitatively explain the measurements. He will re-design the connection for more rigid one.

In this FY2001, further spectrum analysis and investigation must be done with "random" waves instead of "sine" ones. Since the "real" support tube is divided into 4 pieces, the rigidness must be recovered by proposed structures, which shall be tested by this prototype-system. Also, a vibration-proof table will be constructed. The laser system will be updated for increasing sensitivity by an order of magnitude, i.e. 1 micron-m.

(2) New FF optics (transparencies, 1 page, pdf ,21kB ) Although Yamamoto san could not attend the meeting, he sent us informations of final doublets at new FF optics as follows;

--------------------------------------------
   distance from IP  field gradient  length 
         m               T/m           m
QC1      4.3            64.3         3.35
sext.    7.65                        0.61
QC2     12.53           22.4         4.0
--------------------------------------------
where the optics is optimized at Ebeam=500GeV and the field gradients are assumed to be scaled linearly as beam energies. As expected, the field gradients are significantly reduced at the new optics from the JLC-nominal one. These parameters would be inputs for designs of superconducting Q magnets and dump line.

(3) ACFA report Since the previous meeting, a section of neutron backgrounds has been updated. We are still waiting for a section of the pair monitor. Our draft is posted on the web site of http://acfahep.kek.jp/subg/ir/group.only/acfarep/ .

The next meeting will be on 25 April (Wed.), 2001 13:30 - 15:00 at 3 gokan, 425.