Minutes of the 4th FFIR meeting on 2/17/2000

The meeting was held in a room of 3-425 at KEK for 13:30-16:00. We discussed on (1) support system of QC1 and mask (2) background estimations with various configurations at IP, (3) dump line and (4) tail development in linac.

(1) H.Yamaoka presented the support system for QC1 and tungsten mask. (Transparencies, pdf, 29 pages,6.85MB). As discussed in the previous meeting, he analyzed the support system without the support tube. It consists of conical and cylindrical tungsten masks, inside of which there are QC1 and QC2 magnets. There are two fixed points at 7 and 8 m from IP in each. The total weight is estimated to be 81 ton for both two systems. The gravitational sag is 1.6mm at the front and the maximum stress is 23MPa. He executed three kinds of analyses, that is, Modal analysis, harmonic oscillation (resonance response) and spectrum analysis, for two cases of rigid and "soft"(15Hz spring constant) fixed points with ANSYS program. The case of "soft" fixed points resembles might be realistic. From the Modal analysis, the first, second and third eigen frequencies were calculated to be 17, 81 and 173Hz, respectively, for the rigid case. They become 15, 38 and 105Hz for the "soft" case. Responses were estimated at resonances by the harmonic oscillation analysis. Inputs of oscillations are measured values at Tsukuba-hall as previous analysis. With a typical damping ratio of 2%, the maximum displacement was calculated to be 8.2nm on 15 Hz resonance at 2m from IP. Relative displacement between two QC1's can be estimated by the spectrum analysis for any kinds of ground motions. He is learning how to estimate it for "un-correlated" ground motions (with any phase differences). Since the gravitational sag seems to be large, he added one more fixed point at 3.85m from IP, where the tungsten mask can be supported on pole tip (iron structure). The sag becomes much smaller value of 0.09mm with the maximum stress of 5MPa. The first and second eigen frequencies increase 71 and 189 Hz, respectively.

He also presented a method of assembling the tungsten mask which must be divided into 4 pieces. Basically the same talk will be given at the ISG5 meeting, SLAC, in next week.

(2) Y.Sugimoto presented "Beam background hits in the JLC detector with different mask configurations". (Transparencies, pdf, 6 pages, 154KB ) At B=3 Tesla, the size of the CDC shall be reduced to 2/3 for the same geometrical acceptance as that at B=2 Tesla although the momentum resolution gets slighter worse for the shorter lever arm. Therefore, the front face of the endcap calorimeter can move at 1.9m from IP. Since the conical mask covers up to 2m from IP, thickness of the cylindrical mask which surrounds QC1 may get thinner. He first calculated energy deposits due to photons and neutrons in the calorimeter as a function of the thickness. He found a steep and shallow deceases for photons and neutrons, respectively. Without the mask, the energy deposits were 7.5GeV(photons) and 4.4GeV(neutrons) per bunch crossing. With 2cm thickness, they becomes about 1/5 and 70%. The CDC hit rates were also calculated. The results are more impressive, that is, all the hit rates were "negligibly" small. This tells us that the calorimeter works well even for no mask case. Then, he presented an aggressive mask configuration. The major change is the conical part. The angular coverage is from 60 to 100mrad and the top is located at 1m from IP. Even with this configuration, backgrounds was estimated to be small.

(3) K.Kubo updated the "JLC dump line design" to reduce beam loss. (Transparencies, pdf, 4 pages, 530KB or tif, 4 pages,523KB ) The major change was to move the vertical bend further near the second IP. He showed the energy distributions of loss particles for various apertures. He also showed neutron yields ,which can be directly seen from IP, as a function of aperture. The realistic aperture produced neutrons with a flux of 10^{15}/cm^2/year. It exceeds the tolerable flux by 10^5 times.

(4) K.Kubo presented "Beam tail study in main linac tracking", since the most difficult one in the pre-linac collimation is a longitudinal collimation of beam tail. (Transparencies, pdf, 4 pages, 447KB or tif, 4 pages,441KB ) He found that 5 sigma_z collimation is necessary for momentum range of +/- 2% after the main linac acceleration.

Next FFIR meeting will be held on 3/8 (Wed.) at 13:30-, 3-425, KEK, Japan. We will discuss on 3 tesla solenoid magnet , support tube/tungsten mask, super-QC1 and extraction line and others.