# Minutes of 29th FFIR meeting on 9/27/2001

The meeting was held in a room of 3-425 at KEK, 13:30-15:20, 9/27/2001.
We discussed on new final focus system (longer L*) , presentations at the
ACFA-LC workshop and present status of support tube R&D.
## (1) New final focus system (discussion)

A design of L*=4 - 5m is very preferable since we may not need a compensation
superconducting magnet around the final quadrupole magnets. Fring field of
the detector-solenoid(Bz=3Tesla) has been calculated as a function of distance(L)
from IP, where an endcap iron yoke is located at L=3.9m . The strength of
field is rapidly changing at L>4m, for examples, Bz=1.6T, 0.6T and 0.16T at
L=4, 5 and 6m, respectively . So, longer L* is highly desired, where
L*=4.3m is a critical value of saturating the magnetic poles.
Noboru Yamamoto will investigate the final focus optics with L*=4.5 - 5m,
or even longer value.
The strength of fring field also strongly depends on the structure of iron yokes.
The present design has 4 slits between them, which produces relatively large
field. H.Yamaoka will calculate the field for a case that the slits are filled
in for angular region of theta<200mrad.

We discussed on possible presentations from our group the ACFA-LC workshop
(10/31 - 11/2, at Tsinghua University). Hitoshi Yamamoto already expressed a
desire for a talk on the pair monitor. Progress report should be expected at
the workshop since the Taipei workshop. Therefore, at least two more
presentations can be proposed, which are on "new masking system optimized for
B=3Tesla and L*=4.5 - 5m" and "R&D status of support tube for final
quadrupole doublets" by Y.Sugimoto and H.Yamaoka, respectively. We will
communicate to the local organizers at the workshop with these proposals.
## (3) Support tube R&D

(transparencies, 12 pages, pdf
,2.1MB ) Yamaoka reviewed the previuos studies.
The ANSYS calculation could not reproduce the measurements on frequency
spectrum. Meanwhile, he participated in a seminar on experimental technique
at Chu-o university, which was sponsored by JMAC ( Japanese Modal Analysis
Conference). He learned a lot on experimental techniques and analysis of
vibration tests. One of limitations in his previous test is a small number of
sensors or measurement points along the support tube whereas more measurements
shall be necessary to resolve different oscillation modes. The sensors may not
be well attached to the specimen. He also must study correlations among
various eigen modes in his analysis. So, he has to carefully orthogonalize
the spectrum analysis taking account of mesurement directions, positions and
frequencies. If succeed, ANSYS must reproduce measurements.
For the first trial, he tested the support tube by hammaring, where a sensor
(accelerometer) on the open edge to measure oscillation in up-and-down direction.
He observed two peaks in the acceleration-frequncy spectrum. The first observed
peak is 35Hz consistent with the first eigen mode. From the spread, the
damping factor was estimated to be 1.2%. A simple bolted structure is
expected to have 0.2%. The second observed peak is also prominent, however
the frequency of 193Hz is different from expected value of 217Hz.
More improvement is necessary in measurement technique and analysis.

The next meeting will be on 11 October (Thu.), 2001 13:30 - 15:00 at 3 gokan,
425.