Minutes of 57th FFIR/BDSIM meeting on 7/30/2003

The meeting was held in a room of 425 at KEK, 10:00-, 7/30/2003. We discussed on support tube R&D status and beam scattering, dark current at LINAC.

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

(transparencies, 8 pages, pdf,305KB and ppt,4.7MB) Yamaoka reported recent results of 1/10 prototype in the case of "tube" structure with a thin central tube. The prototype tube was clamped at both ends on a H-shaped steel beam by vises. The tube was vibrated by hammering with load cell. Accelerations of the vibration were measured at 21 positions on the tube in order to measure vibrational patterns along the tube. Vibrational resonances can be well shown by frequency response function (FRF) which is defined by "output" acceleration/"input" force ( m/s2/N ) as a function of frequency based on FFT. The input force was measured by the load cell. There are 4 major resonances at 77.5, 90, 258 and 522Hz. From the measured patterns, the 77.5 and 90Hz resonances must be "hyper fine" split pair of one resonance due to imperfect clamping, since ANSYS calculations have major three resonances at 76, 256 and 489Hz. He also measured these resonances with different bolt-joining strength of 3-M6, 6-M6 and 12-M6 at taper flanges. Variation of resonant frequencies was very small. He will measure them in case of flat flange. Future plan is also summarized in minutes of previous meeting(2003.5.7).

There was a question that how the ANSYS calculation is reliable in the actual case. He replied that he could have reliable calculations up to third resonance, that is, about 500Hz in the case of the prototype. We must remind for the first resonance to appear at about 17Hz in the real size support tube. Major concern must be amplification factors (e.g. vibration/ground motion) at resonances. So, higher resonance frequency is more preferable for less ground motion at higher frequency.

(2) Beam scattering at LINAC(T. Yamamura, Univ. of Tokyo)

Yamamura briefly reported recent progress. In the SAD calculation, he put 1952 scattering points along the LINAC by introducing MAP at every Q-magnet. For background study, apertures of Q-magnets (radius~5mm) must be installed in the SAD calculations. Also he would like to estimate non-linear optics, while the effect can be negligibly small at LINAC. Other dynamics such as wake field effects may need to be implemented in the SAD. A useful reference of Perry Wilson was introduced by Yokoya.

Besides of the gas scattering, dark current may be a background source. Akasaka has estimated dark current in c-band LINAC by simulation, whose results were published in proceedings of EPAC96, KEK preprint 96-65. In this paper, he concluded that field-emitted electrons will not be a problem (at IP), However, surface electric field at x-band accelerating structure is much higher. So, the conclusion may not be applicable to the x-band LINAC. Yamamura will consider a possibility to estimate dark current by SAD.

The next meeting will be on 3rd September, 2003,10:00 - noon at 3 gokan, 425 .