Even with no sextupoles, non-linear dependences were observed at |xi| > 0.1mm (|x'i| > 80 urad) while particles with |xi|< 8 mm (|x'i| < 3 mrad) were accelerated up to the LINAC end. For origin of the non-linearities, particle distributions in phase space have been studied. Phases were observed to depend on the initial positions. Final energies with large initial positions were less than those at central orbit, i.e. -5.5% at |xi|=8mm in a parabolic function. He speculated that particles would develop additional phases with large amplitudes since their orbit became longer.
Pure non-linear effect of sextupoles were estimated to be as follow; dxf=15nm at xi=0.1mm and dxf=50nm at xi'= 80urad in parabolic functions, where dxf is difference in final positions with and without sextupoles. For B3/B2 > 0.1, non-linearity became visible even in |xi|=0.1mm.
In future, he would like to try random seeds for the direction of sextupoles.
(2)GM effects at LINAC by SLEPT (K. Kubo)
(transparencies, 2 pages, pdf, 233KB)
Kubo updated a validation of the GM model in the SLEPT. He compared input GM spectrum with results of FFT. The agreement looks good while statistics of SLEPT simulation is poor around f = 0.1Hz .
He also summarized difference of feedback schemes between SLC and NLC in Linda's (SLAC) simulation. The SLC scheme has always pairs of correctors and BPMs, while the NLC scheme has additional BPMs between the pairs. He will investigate these schemes by the SLEPT.
(3) FEATHER status and Beamstrahlung (N. Delerue )
(transparencies, Status, 3 pages, pdf,135KB, and Beamstrahlung, 6 pages, pdf,339KB)
Nicolas briefly reported present status of FEATHER beam test at ATF. Kicker and BPM were installed with a help of Takano-san (ATF alignment group). In advance of the installation, electrode positions were calibrated with an accuracy of 0.1mm, where the positions can be precisely set by micro-meters (variable for 0 and 25mm) .
Beanstrahlung photon spectra have been investigated with various vertical offsets between two beams (0~100 sigma). He verified very similar distributions over wide energy regions. Possible backgrond of synchrotron radiations was pointed out by Yokoya. The synchrotron radiation can be studied by SAD and BDSIM (GEANT4).