Minutes of 10th FFIR meeting on 5/24/2000

The meeting was held in a room of 3-425 at KEK, 13:30-15:30, 5/24/2000. We discussed on (1) prototype of the support tube, (3) magnetic field calculation of conventional QC1 for the dump line, (4) status of tail re-population and so on.

(1) prototype the support tube: (transparencies, 6 pages of pdf, 880kB) or tiff, 880kB Yamaoka explained a study plan by constructing miniatures of support tubes. The prototype system consists of two support tubes which are connected by CFRP or its equivalent. The overall scaling factor is about 1/10, so the total length is 1.6m and the diameter is 50-100mm. The tube is actually solid rod of Aluminum. Properties relevant to spectrum analysis, such as natural frequencies, should be very similar to the real system. He also introduced an oscillator and seismometer whose typical output is 1V/13 micro-m at 1Hz ( 13 nanometer / 1 mV ). One possible problem of this seismometer is too big for the prototype support tube. As another monitor, Sanuki showed an laser interferometer which his group (Tokyo univ.) has and whose sensitivity is 10 nanometer. pdf,85kB) or tiff, 132kB We discussed on how the prototype test can simulate the real one since two scales are very different. The primary purpose is to verify our ANSYS calculation for oscillation problems. The plan will be re-examined especially on the size of prototype.

(3) Dump line: (transparencies, 7 pages of pdf,930kB) or tiff, 930kB Miyamoto showed the magnetic field of the conventional QC magnets (QC1 and QC2) along extracted beam line. Calculated results were passed to Kubo who expanded them into multipoles for SAD analysis. We will see new calculation of dump line with the magnetic field in next meeting.

(4) Tail re-population: Sanuki explained an idea for implementation of gas scattering in SAD calculation, which has been developed in discussions with Oide-san. The major issue is that a probability of tails is extremely small (<<10^{-7} ). Since SAD can provide transfer matrix at arbitrary points in main linac, we must set beam-profiles corresponding to tail generated by Coulomb scattering in the phase space (sigma_x(y), sigma_x(y)', p ) at each point. Multiplying them by the matrix, one can get tail-distributions at the exit of linac. In this calculation, the tail distributions are assumed to be Gaussian too. The other method was also discussed. The tails can be simulated by particles, that is, by using SAD-tracking method. The latter method does not assume Gaussian distribution in tails and it is more relevant for high energy physicists. It may be worth to compare these two methods. Anyway, he got KEK-computer account for interactive SAD.

(5) Discussions We had a general discussion on the beam delivery system including pre-linac collimation, although the details depend on our further studies. The major issue is to minimize the total length (BDS) for site- and cost-optimizations. In the second bunch compressor after the pre-linac (8GeV), there is a (pre-linac) colimation section where beams are collimated in < +/- 5 sigma_z , <+/- 6 sigma_x, , <;/- 40 sigma_y. The (second) collimation system down-stream of the main linac shall be dedicated to a machine protection (MP), so only momentum collimation. Following final focus section shall be optimized at 250GeV of beam energy by Oide/Yamamoto's or Pantaleo's optics. Roughly we expect the pre-linac collimation of <50m, the MP collimation of ~200m and the FF of ~300m, which are compared to the present JLC design of 1200m collimation and 1600m FF. For energy upgrade, FF should be optimized at Pantaleo's optics whose length is expected to be "independent" on beam energy, and the collimation section could expand into the main linac, assuming the energy upgrade is done by higher acceleration-gradient. There were many discussions and they will continue.

The next meeting will be on 7 June, 2000 10:00 - 12:00 at 3 gokan, 425.