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[bds 291] Minutes of the 20th ATF2 meeting, KEK, 13th September 2006



Dear Colleagues;

Can you find the minutes of the 120th ATF2 meeting, KEK, 13th  September
2006 ?

The major contents are; QBPM status, Optics of ILC-BDS with 2mrad crossing
angle, Formulation of magnet stabilization and Report of the Bend meeting,
12th September.

The minutes can be seen at the ATF2 home page of
http://atf.kek.jp/collab/md/projects/project_atf2.php.

Your comments are welcome.

Best regards,
Toshiaki Tauchi

-----   Minutes -----20th ATF2 meeting

September 13 10:00- 11:30, Rm.425 bldg.3 at KEK.

1. QBPM status, Y.Honda
presentation , pdf (2MB, 3pages)

First, repeatability of mounting accuracy was reported for the no.08
Q-magnet with adapter. The RMS of 11 measurements are 34um and 20um in
horizontal (x) and vertical (y) directions, respectively.

Second, positioning offset was studied in the QBPM mount procedure on the 13
Q-magnets. The pole aperture were measured by inserting a rod of 31.95mm
diameter into the magnet with three configurations (A,B and C) as shown in a
figure. The measured apertures distribute widely from 31.90mm to 32.15mm,
where the mean is 32.059mm with RMS of 70.4um. During the measurements, he
could use only 2 or 3 bolts of 4 in total in order to attach the adapter on
the pole. So, the adapter bolt-positions must be customized for each
Q-magnets for accurate mounting. Actually, the pole position was directly
measured from the magnet reference plate on top of the no.8 magnet by a
height gauge, and it was found to be shifted down by 215um from the design
value.

Finally, relative positions of (dummy)QBPM from the reference plate were
measured at two Q-magnets (no.08 and no.03) by a laser tracker (SMART). The
results of the no.8 magnet were -532 (22)um and 303(6) um in x and y
directions, respectively, where values in parenthesis are RMS for 5
measurements. The QBPM-center was measured to be shifted downward by 115um
in respect to the pole center of the no.8 magnet. Together with the above
height gauge measured one of 215um, the relative QBPM position from the
reference plate can be estimated to be 115+215=330um, which is consistent
with the measured one (303um).

In conclusion, there are large errors in alignment between the reference
plate on top of magnets and the pole center as previously measured by the
magnet group. These systematic offset can be corrected by customizing the
adapter of QBPM for each magnets.

2. Optics of ILC-BDS with 2mrad crossing angle, S. Kuroda
presentation , pdf (92kB, 2pages)

MAD file of the baseline optics of 2mr crossing angle was translated to SAD
by S.Kuroda. Off-axis optics in the extraction line, especially in the large
bore superconducting final doublet, was calculated by coordinate
transformation in SAD. Results are consistent with the MAD one by consulting
to Y. Nosochkov (SLAC). He will improve/optimize the 2mr optics especially
in the extraction line for realistic magnet designs.

3. Formulation of magnet stabilization, M.Kumada
presentation (Japanese partially) , pdf (2.5MB, 20pages)

M.Kumada has been motivated to formulate the stability of magnetic field
with his observation of "FLUX DENSITY seems never settles even with PERFECT
power supply". There has been no satisfactory formulation, while there have
been papers which report a temperature dependence of magnetic field
especially the long term drift. The temperature dependence has been thought
to be caused by the gap variation (e.g. at AGOR cyclotron), while its
temperature coefficient is less by one order magnitude than observed one.
Precise control of magnetic field has been realized by fine-tuning of
cooling water as a symptomatic treatment so far (e.g. at Research Center for
Nuclear Physics, Osaka university). Kenji Sato has tried to formulate it by
magnetization, but he has not succeeded. Temperature dependence of
magnetization (M(T)) has been calculated to be T3/2 by Bloch.

Magnetization (M) is defined by a formula of B = o ( M + Hi ), where B and
Hi are magnetic flux density and magnetic field inside iron. Since Hi is
very small, temperature variation of B can be expressed by B/Bo = o Teff,
where o= (1/Mo)(M/T) and Teff is an effective change of temperature in
iron. Actually, he derived this temperature dependence by using Ampere's law
with more manipulation. Temperature rise can be estimated to be 0.034oC/hour
in iron of 1m3, that is; it takes 30 hours to heat an iron cube of 8 ton by
1 oC . The typical temperature coefficient is about 140ppm/oC which is
comparable to observed one.

In conclusions, dominant temperature coefficient of iron magnetic field is
Bloch's T^3/2 for the magnetization, which is larger by an order magnitude
than that of physical variation such as gap; i.e. 12ppm/oC . We must be very
careful about non-uniformity of temperature in iron due to temperature
gradient. Thus, temperature variation near poles can disturb magnetic field
in beam line. Especially the variation effects on beam focussing at final
doublet.

In addition to above mentioned temperature coefficients, there are one due
to iron density variation of about 45ppm/oC and an eddy current effect
dependent on magnet structure with additional heat.

4. Report of the Bend meeting, 12th September, R.Sugahara
presentation , pdf (480kB, 6pages)

R.Sugahara briefly reported the video meeting for design of bends between
KEK and SLAC, yesterday. SLAC will produce three bending magnets with same
structure. C.Spencer and an engineer participated in the meeting from SLAC,
and R.Sugahara participated from KEK. Major his suggestions are as follows;
(1) number of alignment wholes should be 2 instead of 4 on top of the
magnet, (2) current leads should be downward for easy connection, (3)
support should be triangle with single bolt adjustment for a leg and the
mechanical resonant frequencies should be greater than 10Hz. Since SLAC has
no experience to use flow switches in the magnet, KEK will install them at
KEK. There were more detailed discussion on the design.

There were comments on the design at this ATF2 weekly meeting. It seems that
thickness of yoke is small since in general the thickness is about 1/2 of
gap.

SLAC already improved the design with KEK comments as shown in this figure.
 ------
The next ATF2 meeting will be held on 20th September 2006, 10:00am -,
3-gokan, 425, KEK, TV-ID#=31110 with the KEK Gatekeeper.