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[acfa-ir 113] Minutes of 71st FFIR/BDSIM meeting on4/8/2004 and next in 5/12, 10am

Subject:   [acfa-ir 113] Minutes of 71st FFIR/BDSIM meeting on4/8/2004 and next in 5/12, 10am
From:   田内 利明 <toshiaki.tauchi@xxxxxx>
Date:   Wed, 14 Apr 2004 18:13:14 +0900

Dear Colleagues,

We will have a next meeting at 10:00- on 12 (Wed) May, 2004.  The place is
room#425 at the 4th floor of 3-gokan.  It will be TV(ch#31110) conference.

NOTE!  The date and time are different from usual ones.

Can you also find an appended minutes of 71st FFIR meeting?
Please also see a web site of http://acfahep.kek.jp/subg/ir/minutes.html .
It may take some time to update the web site. So if you do not see the
minute, please wait for about 30 min. .

Comments and questions are welcome.

Best regards,
T.Tauchi  (KEK)

**************************************************************

Minutes of 71st FFIR/BDSIM meeting on 4/8/2004
 The meeting was held in a room of 425 at KEK, 10:00-12:00, 4/8/2004. We
discussed on final focus system, FEATHER and dark current at the LINAC.

 (1) Support tube R&D (H. Yamaoka)
 (transparencies, 7 pages, pdf, 740KB)

 Yamaoka updated the support tube vibrational tests and their wvaluations by
the ANSYS.  Previous measurements  shows large discrepancies from the
calculations. Since they are considered to be due to weaker H-shaped support
than that used in the calculations, removing the support was changed to a
plate whose equivalent thickness and width were estimated to be 96mm and
170mm, respectively. As in the previous measurements, results are summarized
below;

Structure loads(kg) 1st(Hz) 2nd(Hz) 3rd(Hz) ANSYS:1st(Hz) 2nd(Hz) 3rd(Hz)
cantilever-1 0.0     93     611      1442         92        501    1650
cantilever-1 0.89    62     564      1415         62        472    1630
cantilever-1 1.78    56     452      1342         60        464    1637
tube (a)     0.0    123     343       674        104        278     517
tube (a) 0.89+0.89   86     277       630         94        238     498
tube (a) 1.78+0.89   81     246       572         76        233     487
tube (b)     0.0     93     122       609         96        123     483

 , where tube (a) has a central tube of 3mm thickness and 200mm length with
relative stiffness of 1/2.6, and two cantilevers in the tube (b) are
connected with two thin plate of 1mm thickness, 20mm width and 200mm length
with relative stiffness of 1/1000. Therefore, agreements became better.

 He also estimated vibrational properties of the real sized support tube (
80cm-diameter, 16m long ) by ANSYS as a function of thickness of central
CFRP tube. In order to increase the resonant frequencies, i.e. from 17.8 Hz
to 75.6 Hz at the 1st resonance, additional supports have been introduced at
3.85m from the center as in the ACFA report. The input GM power spectrum has
been fitted one from measured spectrum at ATF. Differences of the amplitude
in ±2m (nm/Hz1/2) were calculated at the 1st and 2nd resonances as follows;

              1st mode         2nd mode
CFRP(mm)   Hz   nm/Hz1/2   Hz    nm/Hz1/2
 10       75.6     0      81.1     0.16
  5       75.5     0      78.4     0.33
  3       75.4     0      77.2     0.49
  1       75.4     0      75.5     0.79
  0.5     75.4     0      75.8     0.77

 In the above calculations, the two "cantilevers" were assumed to be
identical. Next, he estimated for the non-identical case, where the two
cantilevers have 75 and 70Hz at the 1st mode with slightly different
thicknesses. Results are listed below;

             1st mode           2nd mode
CFRP(mm)  Hz    nm/Hz1/2      Hz   nm/Hz1/2
 50      74.6    0.22        81.1    0.026
 20      73.6    0.32        81.1    0.05
 10      72.9    0.41        81.1    0.17
  5      75.5    0.45        78.4    0.27
  3      72.0    0.46        77.2    0.33
  1      71.5    0.45        75.5    0.39

 During discussions, a serious question was raised. If the limit with null
thickness corresponds to the cantilever system, the central tube can only
suppress a little relative displacement at the 1st mode in this case.
Therefore, it must be very important to have the same vibrational property
even for the tube structure. We should know how must is practical error in
the resonant frequencies for the "same" cantilevers.

 (2) Final focus system (S. Kuroda)
 (transparencies, 7 pages, pdf, 436KB)

 Kuroda estimated alignment tolerances at quadrupole magnets (Q's) for the
L*=3.5m optics (the Roadmap report) at the first setout (link to the BDS
system). So, beam sizes (σ*x, σ*y ) and horizontal beam position (x*) were
calculated as a function of horizontal displacements of each quadrupole
magnet, whose dynamic range was within ± 10 μm. He found several sensitive
Q's to the beam sizes, which are QD8, QF7, QD6, QF5.{1,2}, QD2B, QF3, QD2A
and QF1. The horizontal displacements of Q's have linear relation to x*
except for QF7 and QD0. Finally, he listed the displacements corresponding
to 50% increase of the beam sizes and x*=1σ*x for all the Q's. The most
sensitive Q to the beam sizes was QF2 except for final doublets, which was 2
μm for 50% increase of vertical beam size, while QF9.{1,2},{3,4} and
QF5.{1,2},{3,4} are the most sensitive to x*; i.e. 0.5μm for displacement
of 1 σ*x. These results assumed no correction. Therefore, actual tolerances
shall be estimated with corrections. Also, the tolerance shall be given in
terms of emittance growth (e.g. Δε/ε=10%) . One major interest is
requirements (setting resolution and dynamic range etc.) for movers of final
doublets.

 (3) Dark current in LINAC (T.Yamamura)
 (transparencies, 23 pages, pdf, 14.1MB)

 Yamamura refined the dark current simulation by dividing the generation
area of dark current into 4 regions in a cell; A, B, C and D are top
surface, upstream side, downstream side of a iris and adjacent cavity
surface (upstream of the iris). In this simulation, the iris is not rounded;
unloaded gradient is 65MV/m; 5/6π /cell; mode. In A, electrons can survive
only in the half upstream region, where their final phases are clustered
around two values of -0.7 and -5.58 radian. In the similar way, dark
currents were simulated in B,C and D. The final phases were also clustered
as those in A. A and B are the most likely survived regions. He also showed
the final energies of dark currents as a function of generated position. The
higher energy dark currents are generated in A. In future, he simulate the
dark currents at least in two structures in order to use SAD-program for
further tracking. One goal is an estimation of dark current probability at
exit of the main LINAC.

 (4) FEATHER (N.Delerue)
 (transparencies, 7 pages, pdf, 510KB)

 First, Nicolas briefly reported results of test bench study on the
electronics before a beam test. Artificial BPM signals with multi-bunch
structure were generated by a BPM pulser. Splitting the signals for the two
electrodes, their differences were made by a HH107 hybrid circuit. Then,
they were amplified. The attenuated signals were observed by an oscilloscope
together with the input signals from the pulser. Fluctuations in the peaks
corresponding to multi-bunches were not understood. Diode properties were
also measured as expected. Bandpass filter of 357MHz ±10MHz was tested.
However, the filtered signals were too distorted to be used for feedback
signals. Lowpass filters shall be tested too.

 Second, the beam test results were reported on the BPM calibration. At this
time, he succeeded to get a linear correlation between the ATF intensity and
sum of the BPM signals. However, he failed to get the position signals with
1mm and 2mm gap. The reason is not known. One of basic observation is a
measurement of pulse height as a function of gap. Also, beam orbit must be
checked within aperture of the BPM button electrodes.

 The next meeting will be on 12 May, 2004,10:00 - at 3 gokan, 425 .