Minutes of video meeting on 17 February, 2005

"BPM for FF test (ATF2)", V.Vogel

(transparencies, 10 pages, pdf, 1.5MB )
First, Vladimir showed the dipole-mode electric field calculations as a function of z along the beam axis in three cases of beam pipes with 4mm, 6mm and 8mm diameter. Apparently, the field with smaller beam pipe is more contained in the 2mm gap of cavity-BPM.

He updated the configuration with three cavity-BPMs at the focal point. The three BPM are connected with bellows which are also advantage of damping higher order modes in the beam pipe instead of the damped cavities in the previous configuration. Each BPM has 62.1mm length including a bellow with small VLEPP type flanges. So the total length is 186.5mm. He asked us that the three BPM shall measure only vertical beam positions or the horizontal positions shall also be measured such as three pairs of x and y BPMs doubling the total length. Since the beam profile is very asymmetric, i.e. flat with aspect ratio of about 100, the horizontal coupling slot could be made in the same cavity. So, he will investigate this possibility.

For the BPM calibration, the BPMs must be mounted on precision movers with <10nm step and steering magnets shall be installed for scanning the beam at the focal point which is necessary for the Shintake monitor,too.

"Optics designs for a bunch compressor in ATF2" by E.S.Kim (PAL)

(transparencies, 9 pages, pdf, 100KB )
Kim-san presented the optics designs for a bunch compressor in ATF2. The bunch compressor utilizes the chicane which has been proposed for beam diagnosis at the previous meeting. A RF section is added in front of the chicane in his scheme. Two cases of different RF frequencies have been studied. First, he considered a L-band system with 3m length and 30MV/m. The bunch can be compressed from &sigmaz=8mm to 1.2mm while the energy spread changes from &sigma&delta=0.09% to 1.22%. The second case is S-band system with 3m length and 16MV/m instead of the L-band. The compressed bunch length and energy spread are &sigmaz=0.66mm and &sigma&delta=1.67%, respectively. He concluded that (1) one rf system with ~3 m long may be used for a bunch compressor, (2) compression factor of 5~10 may be obtained, (3)we need estimation of tolerances and more optimization for the bunch compressor, (4) matching with Final Focus optics remains and hope to work together tuning of Final Focus optics, if is available.

The similar study has been done at SLAC. see a homepage of http://www-project.slac.stanford.edu/lc/bdir/Meetings/beamdelivery/2005-02-15/index.htm . Also, Okugi-san sent us a file of "proposal of ATF2 bunch compressor" after this meeting. His scheme also utilize the chicane while two S-band RF systems are introduced at upstream and downstream of the chicane. About half compression can be obtained.

"ATF2 organization" by T.Tauchi

(transparencies, 13 pages, pdf, 2.4MB )
Tauchi briefly reported the ATF2 organization. There must be an international steering group, e.g. consisting of 3 representatives from each region, for responsibility of planning and operation of the ATF2. There are 6 major working groups; (a) Optics, tuning and commissioning, (b) Magnets and vacuum, (c) Alignment and supports, (d) Instrumentation , (e) Conventional facility , and (f) Optional facility. Individual working group would be a body for budget plan, request and execution. Each WG consists of a few sub WG's. "Daily/realtime" international discussions should be encouraged within working groups.

We will have a next video meeting in this March, i.e. between 3 and 16 March, for the draft design.