Impulse responses of Shintake monitor was presented in order to show the rigidity of optical table where the laser optical elements and vacuum chambers are mounted. The table of 1.6x1.5x0.11m3 has a honeycomb structure consisting of 100mm thick aluminum core sandwiched with 5mm thick stainless steel plates. The table has a square hole (0.42x0.42m2) for the chambers. The weight of the table is 220kg, while the total weight of Shintake monitor is 740kg. Measurement and analysis have been done by Herz company at university of Tokyo. Hitting at a point, compliance and eigen modes of vibrations have been calculated, where the 1st through 6th eigenfrequencies are 42.4, 53.7, 73.7, 91.9, 98.1 and 125Hz, respectively. Peak compliance was calculated to be 1.5μm/N at the 1st eigen-mode (42.4Hz).
Typical integrated ground motion is 1nm at 40Hz on the ATF floor. So, Shintake monitor may need more rigid table for higher 1st eigenfrequency. For examples, tables of alminum-250mm thickness, steel-200mm thickness and steel 250mm thickness have eigenfrequencies at 74, 82 and 112 Hz, respectively.
A rigid mount structure was also shown for support of Shintake monitor. However, it is very difficult to simulate the mount structure in order to maximize the rigidity. The company could make the best support based on knowledge of experienced engineers in anti-vibration area.
Primary goal is to achieve relative motion between the Shintake monitor and the final magnets less than 6nm where they are separately supported as in the ILC configuration. Since the ATF2 floor will have good coherent ground motion up to a distance of 4-5m, where the distance between the Shintake monitor and the last magnet is 4m. Therefore, their support should be rigid for the coherent motion.
TMC company specifies the CLIC (very stiff honeycomb, 2.4x0.9x0.6m3, 700kg) table with the first eigenfrequency at 230Hz in free-free configuration. Also the company provides the compliance as a function of frequency; it is 57nm/N at 230Hz by reading the figure.
Nicolas Geffroy (LAPP) simulated the table with a simple block approximation where Young modulus has been chosen to obtain the first eigenfrequency in free-free configuration at 230Hz. The first eigenfrequency was calculated to be 56.2Hz in fixed-fixed configuration of fixing to the floor at its 4 corners. The others were 58.1, 58.6, 76.0, 85.4, 95.4 and 248.1Hz .
LAVISTA team measured vibration transmissibility between table and floor at LAPP. Up to 20Hz the table transfer function magnitude is around 1, while it increases above 20Hz where the amplification is peaked to 11 at 68Hz. The data show eigenfrequecies at 25.1, 37.1, 48.3, 50.9, 62.1, 67.9, 73.0, 82.0 and 97.5Hz. The first two must not be really eigenfrequencies for the table was not well put on supports and the supports were not well put on the floor. Also, coherency was measured between the table and the floor. The coherency was around 1 up to 20Hz, and it falls down above 20Hz. It was pointed out that slightly decrease of coherency around a few Hz may be caused by coupling between horizontal and vertical motions.
In order to estimate relative motion between the table and floor at ATF ring, two GM measurements were combined for the GM spectrum from 0.1 to 100Hz. The power spectrum density (PSD) of relative motion was calculated by using the PSD of GM and the table transfer function. The integrated relative motions were calculated to be 5.95nm and 0.78nm above 0.1 and 50Hz, respectively, between the floor and table at ATF ring. They are below the ATF tolerance. In near future, LAVISTA team will improve the fixation of the table to the ground in fixed-fixed configuration. Lower relative motion should be expected.
After the meeting, a report of "Honeycomb table simulation with different boundary conditions" is written, where there are new simulations of the table fixed to the floor on one entire side with and without weight of 1,400kg .
We discussed on the budget which the LC office suggested. We agreed on necessity of budget reallocation and schedule readjustment. We will continue the discussion at next meetings.
The next ATF2 meeting will be held on 25th April 2007, 2:30pm -, 3-gokan, 725, KEK, TV-ID#=31110 with the KEK Gatekeeper and ILC Webex.