ATF2 meeting FD Stabilised support
Thursday March 15 2007 (23h00 SLAC, 15h00 KEK, 7h00 France)
Present: T.Tauchi (KEK), R.Sugahara (KEK), J.Urakawa (KEK), S.Kuroda (KEK), T.Okugi (KEK), K.Kubo (KEK), N.Terunuma (KEK), T,Sanuki (University of Tokyo), P.Bambade (LAL), B.Bolzon (LAPP), A.Jeremie (LAPP), Ch.Spencer (SLAC), A.Seryi (SLAC).
Agenda: http://ilcagenda.linearcollider.org/conferenceDisplay.py?confId=1453
Introduction: P.Bambade
New measurements of CLIC honeycomb structure: B.Bolzon
Further studies and possible scenario: A.Jeremie
Enlarging QC3: Ch.Spencer
General discussion: all
Summary:
P.Bambade made a short introduction welcoming everyone and introduced the agenda.
B.Bolzon presented his latest results on measurements done on the CLIC honeycomb structure. He presented the transfer function of the honeycomb block including metal supports between the floor and the top of the table. It is equal to 1 between 0.1 and 35Hz. The table starts to resonate above this frequency and consequently coherence between the floor and the honeycomb block falls above this same frequency. TMC, the manufacturer of the table, gives the first resonance frequency to be at 230Hz. This difference comes probably from the supports used for the measurements which are not well fixed to the floor nor to the table. Annecy group is studying the possibility of buying special TMC rigid supports.
In addition, B.Bolzon has done the exercise of calculating what would be the displacement on the table using ground motion measurements done by R.Sugahara at KEK and the above described transfer function. The difference of integrated displacement RMS between the honeycomb block and the floor is 3.3nm between 0.1Hz and 50Hz! ATF2 requirements need only 6nm stability. Although this simple calculation doesn’t take into account phase differences which exist above 35Hz between the floor and the honeycomb block (fall of coherence), this result is very encouraging because integrated RMS of ATF2 ground motion and of the expected honeycomb block displacement at ATF2 are only 1.1nm and 2.8nm respectively between 35Hz and 50Hz.
A.Jeremie presented the latest news on movers. The movers are at Annecy: 3 short movers and one long mover. We are having difficulties in finding CAMAC material in Annecy (electronic clean-up recently). The mechanics is ongoing to fix the movers on the table and fix the equivalent masses on the movers. For the moment, we will only use mock-masses. More precise measurements will be done when the QC3 magnet has been modified. We are not considering putting BSM (Shintake monitor) on the same rigid support as the FD.
Ch.Spencer presented the new scenario for modifying the old FFTB QC3 style quads to become ATF2 final doublet quads. Sextupole component is very sensitive to pole tip being at wrong radius or the pole tip being offset “azimuthally”; appears that errors of size 0.001” (=25 microns) are significant for producing unwanted sextupoles. There will not be machining of these old quads (too expensive) but there will be shims added to change the size of the aperture, adding some buttons to correct some unwanted 12-pole content. If this does not work, then there still is the possibility of machining. There is experience at Orsay in this area (head of mechanical department previously worked for a magnet manufacturer and knows companies able to do precision machining) which can be made available if and when needed.
Questions and suggestions during discussion:
- what are the honeycomb characteristics: max weight, 230Hz with load, minimum load?
- procedure to bolt table to the floor
- bolt table on floor
- choice of TMC or home-made supports
- what is the height, price, vibration properties and maximum weight of TMC support
- since two QC3 type magnets: need to build a large T-plate in Annecy
- include Imaginary part to improve calculations folding the transfer function and KEK ground vibration measurements.
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