Minutes of 64th FFIR/BDSIM meeting on 12/10/2003

The meeting was held in a room of 425 at KEK, 10:00-11:50, 12/10/2003. We discussed on LINAC simulation and requirements for active mover of the FF-Q.

(1) LINAC simulation (T. Yamamura)

(transparencies, 12 pages, pdf, 21.3MB)

Yamamura estimated the elastic scattering effect on the beam emittance a the LINAC. The cross section was calculated to be 1.25 x 10-23 m2 with the minimum angle of h/p a , a=2 x 10-13m. The probability is 8.05 x 10-5 at the mail LINAC, assuming the vacuum pressure=10 n Torr and the temperature = 300K. At exit of the LINAC, the scattering can add errors of 1um position and 0.1urad direction at average to electrons equally with Gaussian distributions (< 6 sigmas). Taking account of the probability, the scattering generates a tail up to nx = 30 sigma and ny = 400 sigma on the gaussian beam profile. ( Note added by Tauchi: nominal collimation depths are 12 and 53 sigma in x and y-directions, respectively, in the roadmap report. So, the probabilities over these depths are about 10-8 and 10-7 in x and y, respectively. ) The emittance does not be affected by the scattering for the very low probability. He also calculated emittance growth as a function of vacuum pressure(P) due to the scattering. At P=10-7 Torr, 1% increase of the vertical emittance was calculated. However, it was pointed out that usual definition of the emittance can not be relevant for such non-Gaussian beam. Also, it was suggested that other sources of the tail such as dark current and particles at several sigmas behind the bunch etc. should be investigated.

(2) Discussion on requirements for active mover of the FF-Q

(transparencies on spectrum analysis of the support tube, 2 pages, pdf, 1.7MB)

First, Yamaoka briefly explained the vibrational property of the support tube inside of which the FF-Q is set with active movers, which has been calculated by ANSYS. The ground motion model has been constructed from the measurement at the ATF extraction floor and input to the ANSYS analysis. Since the support tube is rigid, internal vibration mode would be excited only at f > 70Hz with three points support at each side. Approximating the fixed points with 20Hz springs for realistic support of the tube, a common mode is excited at f=20Hz, whose peak amplitude is 20nm in standard deviation.

Although a relative displacement must be very small at f=20Hz, the common one should be stabilized against the other final focus system. Tolerance of the common mode amplitude must be estimated.

In order to measure the position of final focus magnet, inertial sensors must be rigidly attached to the magnet. Variations against the ground would be measured by the optical anchor based on laser interferometer. Signals from these sensors can be used in feedback control for the active mover of the magnet.

We could estimate a dynamic range of the active mover by the above spectrum analysis (ANSYS), that is, typically +/- 1um with O(nm) resolution. However, more investigation must be needed. Also, tolerance of initial alignment should be estimated.

We discussed on how to install such long support tube too. It could be installed while assembling. Engineering investigation must be necessary.

(3) Others: FEATHER and background simulation

The next meeting will be on 24th December, 2003,10:00 -noon at 3 gokan, 425 .