Minutes of 24th FFIR meeting on 3/14/2001

The meeting was held in a room of 3-425 at KEK, 13:30-14:30, 3/14/2001. We discussed on the present status of support tube R&D, neutron background estimations for the dump line, and the ACFA report.

(1) Support tube R&D (transparencies, 7 pages, pdf ,751KB ) H.Yamaoka talked on the present status of the support tube R&D. Oscillating amplitudes and accelerations have been measured in vertical direction at both ends of a cantilever prototype, i.e. fixed and free ends, by laser-interferometers and accelerometers, respectively, where it was vibrated with forces of 0.3 - 0.5G for detectable amplitudes. The frequencies were manually varied from 1 to 300Hz. In the laser-measurement, two resonant structures have been seen at f=10 and 30Hz, where the 10Hz resonance was found to be caused by horizontal movements of this whole system. In the acceleration measurement, there were two resonance structures at f=30Hz and 200Hz. The 10Hz-signal was only visible at the fixed end with a very small magnitude. Overflows in the accelerations were due to floating the accelerometer(G-sensor), which have been observed at the free end. These results, i.e. observed signals at 30 and 200Hz, were in good agreement with ANSYS estimations which show the 1st and 2nd oscillation mode at 33 and 207 Hz, respectively. Next he changed a number of bolts(M10), which connect the prototype on the oscillator, from 3 to 9 in order to see an effect of rigidness of the connection. The results were very similar except for a slight increase of the first natural frequency from 30 to 31Hz. He will measure the same oscillations also for another configuration in a "both end" fixed case.

(2) Neutron background estimations Y.Sugimoto estimated a rate of neutron-backscattering from magnets by JIM(GEANT3). In this estimation, 10 electrons of 100GeV were injected into an iron-absorber, where a cross section of neutron creations was artificially magnified 100 times. Among the total created number of 17,480, 10,949 neutrons were backscattered, therefore the backscattering probability was 63%. It shows no self-shielding effect which is very large in a case of a water-dump. This indicates a strong need of "neutron-mask" in front of magnets such as polyethylene. During these estimations, he found a bug in a routine of neutron-generation which has been imported from Maruyama-san's program (SLAC) to JIM. The bug was a double-counting in secondary particles except for neutrons, which are gammas and electrons/positrons in this case. An effect in the neutron creation was calculated to be about 10% over-estimation.

(3) New FF optics N.Yamamoto compared two Pantaleo's optics. He found that the "unsuccessful" one has smaller dispersion at sextupoles than the "successful" one. Therefore, the strength of sextupoles become too strong to cancel a chromaticity of the final doublets. Now, he abandoned the "unsuccessful" one. He will work on the "successful" one hereafter.

(4) ACFA report Since the previous meeting, a chapter of the detector magnet, i.e. superconducting coil, 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 11 April (Wed.), 2001 13:30 - 15:00 at 3 gokan, 425.