Minutes of 7th FFIR meeting on 4/12/2000

The meeting was held in a room of 3-425 at KEK , 13:30-15:30, 4/12/2000. We discussed on (1) ANSYS analysis on the support tube with ground motions, (2) tail repopulation in the main linac and (3) superconducting QC etc. .

(1) Yamaoka briefly reported a present status of ANSYS(finite element) analysis on the tungsten support tube consisting of 4 segments for ground motions. The mesh sizes are optimized with respect to accuracies as well as an available disk space and CPU time. He examined ground motion measurements which Nagoya university has made at all public elementary schools in Nagoya-city for earthquake proof. For examples, Denba elementary school has a peak of "63 micron m" at 3Hz while Morinaka elementary school has" 1 micron-m" at the peak. He observed large variations in the ground motions which must depend on so-called "N-value" as a function of ground-depth at each place. He also looked at data gathered at FREESIA stations by BOSAI-lab with an accuracy of 1nm, which can be obtained by e-mails. Data are very interesting at f < 50Hz. For spectrum analysis, we can use models of ground motions which have been reviewed at previous meeting by Tauchi (ref. minutes of 5th JLC structure meeting written in Japanese, 8/25,1999).

(2) Yokoya explained the NLC estimations(1 page of pdf) of tail repopulation. Assuming a vacuum pressure of 10-8 torr, the probability has been calculated to be 10-8 by beam-gas scattering. If beams have vertical-betatron oscillations of 20 &sigmay at their injections, the probability becomes significantly worse to 10-5. Even in this case, luminosity would be 20% of the nominal one. He mentioned that it was hardly believed and 10 &sigmay could be possible because of strong attractive force between two beams during collisions. The question is " Do we need to consider 20 &sigmay betatron oscillation for experimental runs ?" We think that we must tune up beams whenever the luminosity gets worse in such amount. He will contact to Tor for details in the NLC motivation.

(3) Tsuchiya showed an asymmetric "slit" design for superconducting quadrupole. So, the aperture can be decreased with the slits and the magnetic field can decrease to ~50%. Major concern must be the field quality along beam line. He will calculate the field map and estimate the multipole components.

Next meeting will be on 4/21 (Friday), 13:30-15:30, at 3 gokan, 525.