Honda presented details about the straightness monitor (Laser BPMs) the KEK group is developing. There are 2 monitors planned, one on top of the KEK reference bar to monitor its straightness and one of a 2m length on the floor. First installations will be this summer. The straightness monitor has a resolution of vertical displacements in the order of several nanometers but is also sensitive to tilts of the laser beam.
David Urner presented an updated version of a monitor which can monitor the vertical displacement of the KEK nano-BPM with respect to the SLAC nano-BPM. A triangle placed between the two nano-BPMs is referenced by distance measurements to its corners from 3 points of each nano-BPM. The interferometers are placed into the corners of the triangle, (the triangle itself is determined by 3 distancemeters). Two of the corners could be mounted on the bar on the ceiling; the third should be anchored in the floor. The resolution can be greatly improved if the floor is stable against at least one of the nano-BPMfs. Tauchi agreed to go back and look what kind of motion of the ground against the KEK-BPM we can expect. Installation of some parts of this system will begin at earliest Jan 2006.
After the meeting, Tauchi updated the GM information on the home page of http://acfahep.kek.jp/subg/ir/nanoBPM/index.html#GM , where all the GM measurements of ATF and the assembly area are linked as well as some useful links.
The use of a LiCAS survey train for ATF2 was also discussed. A three car prototype train is being built currently and will be tested sometime end of 2005. A full 6 car train is the next round of development, which needs a slimmer design than the current prototype. Besides that funding for this stage still has to be found, the development time is clearly too long for it to be available at the start of ATF2. The straight section of ATF2 is only 13 m. A train which would be able to survey all of ATF2, would need considerable modification, so that it could do measurements along a bend section too. There is also the question of wall markers. The wall at ATF2 is not sufficiently vibration free to mount the wall markers on. Unless one could put permanent mounts along the wall for the markers, one would have to develop a system which is able to look down onto some markers on the floor. That would be quite some work. The reason why it would be useful to have a LiCAS survey train is that one should be able to get a better resolution. We agreed, that one will have to make a good case, that a LiCAS survey can improve the resolution considerably over the usual alignment techniques. David Urner will inquire what the tolerances for ATF2 are on the alignment and if LiCAS can provide them. LiCAS presently only determines the position of wall markers (or monuments).
written by M.Ross, D.Urner and T.Tauchi