Minutes of 70th FFIR/BDSIM meeting on 3/17/2004

The meeting was held in a room of 425 at KEK, 10:00-12:00, 3/17/2004. We discussed on final focus system, FEATHER and dark current at the LINAC.

(1) Final focus system (S. Kuroda)

(transparencies, 1 pages, pdf, 55KB)

Kuroda showed three figures of chromaticity as a function of magnets for cases of "ATF-FF original", "(a) &xiy correction" and "(b) &xix", which have been discussed at previous meetings. The three cases have the same optical configuration, while dispersion functions near the IP can be varied by adjusting a matching section in the upstream. As mentioned in the previous meeting, the (a) and (b) clearly show local chromaticity corrections. One of distinct features is a pair of final doublet system with the same optics in them for geometric aberration corrections. Therefore, the local corrections can be seen at the two final doublet systems, i.e. SF1F~QB1F and SF2F~QC3F, where beta functions become large. Next, vibrational tolerances of quadrupole magnets and tolerances of their strength will be investigated.

(2) Dark current in LINAC (T.Yamamura)

(transparencies, 6 pages, pdf, 1.8MB)

Yamamura has investigated initial conditions of electrons at the cell surface which can go through the structure (100 cells). There are two major parameters for the generation of electrons, which are initial position (zi along a longitudinal axis of the structure) and initial timing (relative phases to RF pulse; &phir,i and &phiz,i). The electrons were tracked by using Runge-Kutta method with a time bin of 1psec. The survived electrons were concentrated in a very small region of |zi|<1.5mm and 5.6< &phir < 6.2 radian, where the initial position is zi=0 at the upstream edge of first cell. There is a "linear" correlation in them. He also plotted relative phases (&phir and &phiz) as a function of z for a short lived electron with &phir,i=&phiz,i=2.95. The two phases walk away from each other and quickly get in out of phase (-&pi difference). For further investigation, positron cases may be interested.

(3) FEATHER (N.Delerue)

(transparencies, FEATHER, 7 pages, pdf, 347KB)

Nicolas briefly reported recent beam test on the BPM with movable electrodes. To be able to calibrate the BPM, we need to know the BPM as a function of the beam position measured by other BPMs. Four informations were extracted from the BPM signals; each electrode signal, sum and difference of the electrodes' signals. To ensure synchronization, a first ATF_CONTROL was issued, the the digital oscilloscope was set into single Acquisition mode, then a second ATF_CONTROL command was issued for the second data taking. He showed measurements of the BPM signals with wide, 1mm, 2mm and 4mm gaps as a function of beam vertical position at the BPM. Signals of each electrodes varied as the beam position, while the differences distributed rather widely. For cases of the 2mm and 4mm gaps, correlation plots of sum-signal and beam intensity were made. No sharp correlation was seen. There may be wrong synchronization. Since these measurements were the first, he has mostly concentrated on the data acquisition. He will continue the BPM calibration. Also, he will try to fully simulate signals in the feedback system.

The next meeting will be on 8 April, 2004,13:30 - at 3 gokan, 325 .