(1)Prototype support tube R&D H.Yamaoka briefly reported the present status. The prototype and test bench have been constructed at KEK-machine shop. The oscillator system was finally arrived on this Monday at KEK. He checked out the system and confirmed that everything was working properly. The R&D place is B4-floor at Oho experimental hall.
(2) Superconducting QC (S-QC) (transparencies, 4pages, pdf ,470kB ) First, K.Tsuchiya briefly explained a motivation of superconducting QC. The major points are less background for larger aperture and no requirement of compensating magnet. However, with a finite crossing angle this option has drawbacks of synchrotron radiations from extracted beam and deflection of disrupted beam. To improve these drawbacks, it is preferable to have a design with smaller crossing angle and weaker field gradient of the S-QC. Since the nominal crossing angle of 8mrad has been chosen for the conventional QC and it must be larger than the diagonal angle (sigma*_x/sigma_z) of 3mrad, the angle can be 5mrad. The field gradient(G) becomes smaller at larger L*. Assuming the new FF optics of L*=4m, which is twice as the conventional one, the gradient can be a half, i.e. 100 T/m, with the same length (L=2.2m). There is also a possibility of G=50T/m and L=4.4m for L*=4m. So, he considered these two cases at Ebeam=250GeV; (a) G=100T/m,L=2.2m and (b) G=50T/m, L=4.4m both with L*=4m and the crossing angle=5mrad, assuming that the S-QC has no slit for extraction beam, which has been proposed in the previous design.
(a) The extraction beam must be bent by about 6mrad in addition to the 5 mrad crossing angle, and it passes horizontally about 4cm apart from the center of S-QC at the exit, since the S-QC acts as a horizontally de-focusing lens. Since half aperture of S-QC1 is 5cm, the beam can go through it with no scattering. The synchrotron radiation can also pass through. However, a large spread of the radiation may cause serious backgrounds at downstream magnets, although it must be masked somewhere in a dump line. In addition, a possible problem may come from disrupted beams which have long energy tails at low energies. In the case of (b),the situation is very similar except for requiring larger apertures at the down stream magnets, especially QC2.
(c) He considered another possibility to exchange optical properties of QC1 and QC2, i.e. QC1 and QC2 are horizontally focusing and de-focusing magnets, respectively. In this case, the extracted beam is bent inward and passes through almost in parallel to the incoming beam. This configuration can gather disrupted (low energy) particles in limited apertures, which means that it can solve one of two possible problems in the above cases. However, the synchrotron radiation may hit the magnets if there is no mask, which is still open question.
From a point view of superconducting technology of S-QC, The field gradient (G) and half aperture (r) must be related to be G x r < 5 Tesla at 4.2K, or G x r < 7 Tesla at 1.9K. Apparently, a further study needs a definite design of FF optics (L*=4m) under this technological constraint.
(3) ACFA report We will ask you to write the contents.
(4) Others At next meeting, we will discuss on a report of GM2000 and progress reports.
The next meeting will be on 13 December (Wednesday), 2000 13:30 - 15:30 at 3 gokan, 425.