Minutes of 68th FFIR/BDSIM meeting on 2/12/2004

The meeting was held in a room of 525 at KEK, 10:00-11:00, 2/12/2004. We discussed on final focus system, support tube R&D, FEATHER and other.

(1) Final focus system (S. Kuroda)

(transparencies, 5 pages, pdf, 139KB)

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;
IP (total) 49.893166.022
.where Δp/p=±10-3 (uniform), &sigma*x=3.39μm, &sigma*y=34.2 nm, and the dispersion accidentally becomes zero downstream of QB3F. Usually, &sigma*x(y)=&xix(y)&delta&sigma*x(y)0, where &delta=Δp/p. In order to demonstrate local chromaticity correction, strengths of QA1F~QA7F, SF2F and SD2F have been adjusted by minimizing "local" chromaticity (&xix,&xiy) downstream of QB3F. There seems to be two solutions at least, which are (a) minimum &xiy with moderate &xix (FitFunction:={LocalChroX,LocalChroY}/3000) and (b) minimum &xix with moderate &xiy (FitFunction:={LocalChroX,LocalChroY/20}/1000). Their performances are listed below;
solution&sigma*x(μm)&sigma*y(nm)"local" &xix"local" &xiyIP &xixIP &xiy
The above results show that &xix and &xiy are partially corrected by upstream sextupoles in (a) and (b) cases, respectively.

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;
Structureloads (kg)1st res.(Hz)2nd res.(Hz)ANSYS:1st (Hz) : 2nd (Hz)
tube (a)0.094289146389
tube (a)0.9+0.978168101186
tube (a)1.8+0.97716896181
tube (b)0.088126107116
, where tube (a) has a central tube of 3mm thickness and 200mm length with relative stiffness of 1/2.6, and two cantilevers in the tube (b) are connected with two thin plate of 1mm thickness, 20mm width and 200mm length with relative stiffness of 1/1000. The measured results have varied delicately with supporting mechanism of the tube (see previous minutes on 30 July,2003 and 15 October,2003 ) .

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.

The next meeting will be on 25 February, 2004,10:00 -noon at 3 gokan, 425 .