Minutes of 31th FFIR meeting on 10/25/2001

The meeting was held in a room of 3-425 at KEK, 13:30-15:10, 10/25/2001. We discussed on the present status of support tube R&D and dump line with superconducting QC1.

(1) Support tube R&D

(transparencies, 13 pages, pdf ,1.2MB ) H. Yamaoka has been investigating a discrepancy between measured eigen frequencies and calculated ones. After the oscillator was bolted on the floor and heavy weights were also placed on it, he still observed the discrepancy. He finally found that a table, where the specimen was set as seen in pictures, has not been taken account of in the ANSYS analysis. After inclusion of the table, ANSYS calculations have good agreements with measurements.

First result was for a specimen of 20t x100w x 695L (mm) with a cantilever support. The ANSYS expects the 1st, 2nd, 3rd, 4th, 5th and 6th oscillation-modes at f=33, 68, 205, 255, 272 and 467 Hz, respectively, while modes at the open edge were observed at f=30, 60, 190, 250, 340 and 460 Hz. Among them, the 2nd and 5th modes were horizontal oscillations and the 4th mode was back-and-forth one. The 6th mode was twisting one.

The second comparison was done for a specimen of 10t x 50w x 1440L (mm) with both ends support. The ANSYS expects the 1st, 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th and 10th oscillation-modes at 33, 68, 96, 134, 220, 224, 282, 302, 325 and 328Hz, respectively. Among them, the 3rd,6th and 9th modes were horizontal oscillations and the 8th mode was axial oscillation, which should not be observed by vertical accelerometers in these measurements. The 2nd, 5th and 7th have a node at the center. The accelerometer, which was set at the center, observed modes at f=25, 130 and 320Hz, while the accelerometer at off-center observed modes at f= 25, 60, 130, 220, 235, 280 and 320Hz. We could identify them as follows; f=25 (1st), 60 (2nd), 130(4th), 220 (5th), 235(6th?), 280 (7th) and 320 (9th or 10th) Hz.

The third case was for a specimen of two boards (20t x 100w x 695L mm each) connected with a small one of 5t x 70w x 200L mm with both ends support too, which is a simple model of the support tube. The ANSYS calculation shows the 1st, 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th and 10th oscillation-modes at 30, 62, 62, 181, 188, 206, 223, 259, 314 and 450Hz, respectively. Among them, the 2nd, 5th, 8th and 10th are horizontal modes. The 7th and 10th modes are back-and-forth and twisting oscillations, respectively. The central accelerometer observed modes at f=25 (1st), 60 (2nd, small signal), 170 (4th), 320 (9th) and 440 (10th) Hz. The off-central one observed modes at f = 25 (1st), 60 (2nd), 170 (4th), 200 (6th), 320 (9th) and 360Hz( 10th?). Anyway, the results should be compared with those of the cantilever( the first case).

Therefore, the ANSYS can calculate oscillation modes fairly well.

He also estimated damping factors(D) of the above three cases from measured power spectra as follows; D=(f1-f2)/2/fn, where f1 and f2 are frequencies where powers decrease to 1/sqrt(2) of a peak(1st resonance) at fn . They were estimated to be 0.28%, 0.32% and 1.0%, respectively, although measurements were very difficult because of overlapping high-frequency noises. The result may show an effect of bolted connection of the central board in the third case, since additional bolts increase the damping factor in general.

(2) Dump line optics for SQ1

(transparencies, 2 pages, pdf ,20.1kB ) K. Kubo made a dump line optics for SQ1(superconducting QC1) where L*=4.3m and the field gradient is 64.5 T/m at Ebeam=250GeV. Major issue is a transformation of disrupted low-energy particles. He showed trajectories of E/Ebeam=0.1, 0.2, 0.3,...1 along the dump line, where there is a second focus point for a measurement of energy spectrum. He also compared it with those of the conventional QC1. The low-energy trajectories have offset twice from the central orbit than those of the conventional QC1. So, an aperture of SQ1 is very important. He will calculate beam loss as a function of the dump line. K.Tsuchiya will make a design of SQC1 with wide aperture, e.g. 10cm at least. In parallel,a configuration of optical elements shall be summarized at the final focus system and the dump line, which has locations, length, strength and apertures, in order to see if there is any physical interference between the final focus and dump line optics.

The next meeting will be on 15 November (Thu.), 2001 13:30 - 15:00 at 3 gokan, 216.