Minutes of 35th FFIR meeting on 2/21/2002

The meeting was held in a room of 3-425 at KEK, 13:30-15:00, 2/21/2002. We discussed on the present status of support tube R&D and an organization of subgroup of Beam Delivery System (JLC-BDS group).

(1) Support tube R&D (H.Yamaoka)

(transparencies, 14 pages, pdf ,1.1MB ) Since we purchased a multiple (8ch) FFT analyzers with 8-accelerometers, the system has been calibrated. First, FFT result was obtained with no input, i.e. no signal but noise. The FFT spectrum has rapidly increased towards f=1Hz, where the amplitude ( defined by square-root of sum of real and imaginary parts of FFT-result ) reaches to -10dB(0.32 m/s^2) at f=1.25Hz and it drops to -69dB (0.00035 m/s^2) at f=100Hz. It was found that this funny behavior was caused by a DC-offset of inputs. So, eliminating the DC-offset by a function of the FFT analyzer, the amplitude decreased to -50dB(0.003 m/s^2) event at f=1.25Hz. Another check was done by a sine-wave with frequency of 5Hz and peak amplitude of 0.2m/s^2. The FFT result shows a peak of -17dB at f=5Hz. These are in a perfect agreement; i.e. -17 = 10 log (V/sqrt(2))^2.

Then, a specimen, which is a cantilever arm, was vibrated by sweeping sine-waves(1-1kHz), where 8 accelerometers were attached along the arm and they were measured at the same time. These measured results were analyzed by a program of ME'scope ( visual engineering software ). This program can execute a mode-shape analysis calculating natural frequencies and it can calculate damping factors by curve fits around resonant frequencies. It can also visualize vibration at each natural frequency. With these new devices and softwares, a working efficiency was very increased.

Therefore, various patterns of input-oscillations will be tested and also various configurations of arms will be tested. Detailed comparisons between measurements and ANSYS analyses are expected soon.

(2) BDS group

We discussed on an organization of group which studies a Beam Delivery System. A major task of this group is to establish a software-tool for uniformly transferring beams from a dumping ring to interaction point, then into a beam dump, where all the issues such as beam dynamics, scattering, collimation, feedback, ground motions can be handled. It must be based on SAD. From a view point of experiment, machine-background (beam halo) and stability of luminosity are the most interesting. We could have a consensus to organize such a group. K. Kubo will lead the group. An organization meeting will be opened soon, in this March.

Background must be studied by simulation based on GEANT(4) which can take account of detectors. One doctrant (Niigata university) will investigate it in order to optimize a masking system including various option of final doublets. His original interest is a background at CCD-VTX. For this purpose, a configuration of beam-line magnets shall be identified. N.Yamamoto and K.Kubo will provide lists of final doublet and dump line, respectively. Then, K. Tsuchiya will design these magnets for the GEANT-simulation.

The next meeting will be on 28 March (Thu.), 2001 13:30 - 15:00 at 3 gokan, 425.