First, Kuroda showed beam size ratios (&sigma*x(y)/&sigma*x(y)0) with and without synchrotron radiations as a function of beam energy from Eb=250GeV to 500GeV for the L*=3.5m optics (Roadmap report). Without the radiations, the ratios are almost unity. With the radiations, only &sigma*y/&sigma*y0 start to grow at Eb=300~350GeV, and the ratio reaches to 2.35 at Eb=500GeV. This significant effect of the radiations may cause a change of optics at NLC since these two optics are very similar, which can be seen in Seryi's talk(pdf) at the ISG10, i.e. Δ&epsilon/&epsilon=30% at Eb=325GeV.
Secondly, he briefly reported chromaticity corrections at the ATF2, final focus test beam at ATF. The chromaticity (4πξ) of final doublet and IP is listed below at the nominal optics;
|solution||&sigma*x(μm)||&sigma*y(nm)||"local" &xix||"local" &xiy||IP &xix||IP &xiy|
In order to examine these performances in more details, he will calculate similar chromaticity at the Roadmap FF optics.
(2) Support tube R&D (H.Yamaoka)
(transparencies, 6 pages, pdf, 49.6MB)
Yamaoka reported vibrational properties of prototype support tube with heavy loads for simulating effects of mask and quadrupole magnets. Major issue was a comparison between measurements and ANSYS calculations for the validity. He has measured the 1st and 2nd resonance frequencies of cantilever and tube with and without loads. Weight of a load is 0.9kg, and two loads were applied at each cantilever. Results are listed below together with the ANSYS calculations;
|Structure||loads (kg)||1st res.(Hz)||2nd res.(Hz)||ANSYS:1st (Hz)||: 2nd (Hz)|
Then, he concluded that; (1) Since frequencies of the 1st, 2nd resonance modes are in good agreement with FEM (ANSYS calculations), natural frequency, mode shape and amplitude can be well predicted by the ANSYS; (2) Support tube structure is necessary for good correlation between two cantilevers, and thickness of the central CFRP tube (real support tube) can be reduced from 10mm to 3mm for relative stiffness of 1/64 still. However, we need to make more serious installation plan; (3) Improvements must be considered for support structure of tungsten masks for more rigid structure.
(3) FEATHER (N.Delerue)
(transparencies, 5 pages, pdf, 285KB)
Nicolas reported results of beam test in last week. Before the beam test, alignment of the kicker was checked on 2 February. Upward tilt of the kicker-gap was observed, whereas downstream tilt has been seen during the previous beam tests. The alignment results are shown in this figure(pdf) with explanation, where a new beam axis has been proposed. Also, it has been confirmed that the electrodes are bent as shown in this figure.
He scanned beam trajectories by adjusting steering magnets upstream of the kicker. The trajectories were measured by BPMs across the kicker. Top and bottom electrodes of the kicker can be set by micrometers, The previous micrometer scales of "1.2mm gap" are (top,bottom)=(12.85, 12.65) in mm, while the new scales are (13.045, 12.455), i.e. increasing scales for narrowing the gap. So, the center of gap was set downward by 0.2mm. He confirmed the downward tilt with the previous scales, and parallel trajectories with the new ones. Oppositely setting scales at (13.45,12.06), upward tilt was also observed as expected. The smallest gap has been found at (13.09,12.49), so corresponding to "1.12mm" gap, and scales of (13.10, 12.50) was not acceptable.
He started to observe multi-bunch beams by the movable BPM. Many bunches were observed on the BPM with wide aperture. However, strange BPM ringing was observed.
Future plans are that; (1) we will try to achieve the simple model with the
envelope of the signal, and (2) later we may move again to a faster feedback system
(BPM issue need to be addressed before)...
(4) Discussion on LCWS2004
We has a general discussions on the LCWS2004, 19-23 April, in Paris. There are two working groups related to our FFIR group as follows; ( K) Machine Detector Interface, conveners:T. Tauchi, M. Woods, P. Bambade, and (M) Accelerator Issues being studied by particle physicists, conveners : R. Patterson, G. Blair, T. Nakanishi. There will be discussions on crossing angle, energy spectrometer, Pair-LUMON detectors, background issues and stabilization of collisions at IP, ground motions, etc. . So, cavity BPM, polarimetry, aberration tunig and beam diagnostics to infer spotsizes, bunch lengths, etc. would be included. Of-course, subjects shall depend on participants.