The beam halo was measured by 5 wire scanners (MW0-4X) during this April beam time at ATF extraction line. Also, the halo was estimated by fitting the scanned data. Nominal wire scanner data can be well fitted with a Gaussian function, where the signals are detected by air-cherenkov counter with PMTs. In order to measure the halo, the high voltage was increased from 600V to 1500V, while the signals were saturated in cores. The saturated ones were not used in the fit.
First, fitting functions were adjusted by analyzing the data of vertical (y) MW1X. Subtracting the Gaussian core part, the tail part was fitted by a modified Gaussian function (spike, Gaussian and flat top) plus a linear function. Next, the fitted parameters were used as inputs for a combined function fit on the full data. The best modified Gaussian function was turned out to be Gaussian. Therefore, all the data were fitted by two Gaussian functions and linear function, where the second Gaussian function can have asymmetric distribution as shown in the presentation.
In this analysis, the halo is estimated by the second Gaussian function while the linear function seems to be considered as "pedestal". Finally, correlation of sigma between core and halo and ratio of amplitudes were plotted . The halo sigma has linear correlation with the core one, whose coefficient is about 3. Amount of halo was estimated to be 0.6 ± 0.4%.
There were following questions and comments.
Q : Did you confirm that the linear function is pedestal ? A: No, no measurement. (Comment: Previous experiments show that it is also "signals", i,e, which could be a halo. )
Comment : Simulations in DR show that a beam halo, which is generated by intra-bunch scattering, has a tail of polynomial shape. Therefore, you might have to increase the high voltages more for higher sensitivity in a long tail as previous measurements by Shintake monitor group, whose results have been presented in June 2005 as uploaded file.
Updates and news of FD support from LAPP were briefly presented during the FJPPL workshop, 9-11 May 2007, where comprehensive presentation on the ATF2 collaboration was given.
The honeycomb table has been simulated with the same dimension of CLIC table, where the density is 700kg weight divided by the volume (240x90x60cm) and the Young modulus has been chosen to obtain the first eigenfrequency of the table in free-free configuration (230Hz) . In order to compare the measurement of table on the floor at LAPP, the first eigenfrequency of table has been simulated to be 56.2Hz with 4 rigid supports at corners. This result is good agreement with the measured one at about 50Hz. Next, eigenfrequency of the table with weight of 1400kg was simulated to be 26Hz, while the measured one was 47Hz. We do not understand this difference. A student from Romania working on understanding and developing combination of passive and active damping, but stay too short to go very far in study.
The compliance curve was also measured to estimate the amplification factor. It was 8 at the first eigenfrequency of 65Hz. This result is consistent with the transfer function measurement.
In terms of FFTB movers, T-plate and blocs material have been received. Also, the machine shop time has been reserved for the fablication, but not yet started. There is still need to exchange information with Cherrill to see if the drawings and T-plate modifications correspond to what is needed. Student from Canada (until June 1st) is putting the drawings in electronic form for modification due to larger QC3=> QD0. He is already very well advanced! He could access to all the detail drawings initially drawn by hand!
In order to estimate non-linearity in the extraction line, the beam orbits were measured with 16 BPMs as a function of currents applied to kickers, last septum (BS3X) and a vertical steering magnet (ZV1X) at the extraction line as shown in a figure. The kickers and BS3X should have horizontal bend, while ZV1X should have vertical one. Results give the impression generally of performance being up to our expectations within the measurement errors. On the other hand, the orbit may have non-linearity at some BPM positions, and the kickers may cause a coupling to vertical orbit. The second kicker was suspected to have rotation. At present, it is very difficult to check the alignment since they are surrounded by lead bricks. He will continue this study. Your suggestions. especially on appropriate experiments/beam tests, must be very desired.
There was question on the calibration of these BPMs. He replied that all the BPMs use the same calibration constant. The linear dynamic range is within ±3mm near the center of BPM.
The next ATF2 meeting will be held on 16th May 2007, 2:30pm -, 3-gokan, 725, KEK, TV-ID#=31110 with the KEK Gatekeeper and ILC Webex.