Minutes of 1st FFIR meeting / 9th JLC structure meeting on 12/17/1999

The meeting was held in a room of 3-425 at KEK for 13:30-15:30. We discussed on (1) study plan on the iron structure for JLC detector and (2) super conducting final focus magnet.

(1) H.Yamaoka presented his idea for study plan on the iron structure for JLC detector. (Transparencies, pdf, 1.82GB or tif, 12 pages,1.9GB ) First, a basic iron-structure must be determined by solenoid-magnetic field properties such as uniformity, saturation(B vs current), leakage field. Also boundaries to detectors and methods of installation and service for detectors have to be known primarily. Secondary, the mechanical stability and reliability must be carefully checked for deformation and stress due to weight itself, an electromagnetic force and an earthquake to be within tolerances. Finally, the detailed structure shall be determined for construction.

Apparently, we are at the first stage. So, he summarized the magnetic field properties which have been studied. For examples, a distance between coil and pole tip is sensitive to field uniformity, and iron-permeability is not important for high magnetic field of 2-3 tesla. As reported at the previous ACFA-LC workshop, the poletip would moved inward by 68mm at B=3 tesla while it is 4mm at B=2 tesla. Since the tolerable movement must be within several mm, the iron structure must be reinforced.

Recently, a new geometry of calorimeter was proposed for the case of B=3 tesla by Y.Fujii, where the size of central tracking chamber(CDC) is assumed to be shrink to 2/3 as K.Fujii considered at the ACFA-LC99. The maximum radius is 350cm and the maximum length is 380cm, which determine the scale of coil since the coil is located outside of the calorimeter. Radius of the previous coil is 450cm for JLC-1 at B=2 tesla. So, the basic iron-structure will be studied with this new geometries.

We also discussed on a possibility of coil inside the calorimeter, that is, outside the coil there is a tail catcher of hadron showers, to reduce the radius further. Y.Fujii mentioned that the tolerable thickness of coil would be 0.4 lambda from TESLA study, where the resolution of hadron calorimeter becomes worse from 40% to 50%. We will keep this option in mind.

H.Yamaoka also introduced various experiences in TOPAZ and BELLE structures, cabling and installation of detectors.

(2) We discussed on super-conducting final focus magnet with K.Tsuchiya (KEK) who is an expert of superconducting magnets. The basic parameters are B'=224.8 (69.0) T/m and length of 2.2 (4.0) m for QC1 (QC2) without iron return yokes. Because of 8 mradian crossing angle and 0.5mradian spread of disrupted beam, they must have large aperture. He introduced very interesting idea for shifting the magnetic center and a feedback against movements ( 1-10nm at < 10Hz) by correction coils. We expect several iteration-loops to optimize the QC designs and FF optics.

Next FFIR meeting will be held on 1/12 (Wed.) at 13:30-, 3-425, KEK, Japan. H.Yamaoka will present the basic structure for new geometry at B=3tesla and a detailed study of support tube if possible.