Minutes of 58th FFIR/BDSIM meeting on 9/3/2003

The meeting was held in a room of 425 at KEK, 10:00-, 9/3/2003. We discussed on the dump line with beam dump, GM model in SLEPT and the permanent FF-Q magnet, etc. .

(1) Dump line with beam dumps (T. Tauchi)

(transparencies, 8 pages, pdf,1.4MB) The dump-line layout was briefly reviewed for the Roadmap design; 7 m rad crossing, superconducting final quadrupole magnet of QD1. The second focal point (2nd FP) is located at 140m from the IP, where the beam spot size and polarization would be measured. The beam dump of 1.6m diameter, 10m long is located at 300m from the IP. In the present design, extracted beam is horizontally bent towards a single dump where beamstrahlung photons are absorbed at the same time. Since the beam dump is only 2m from the opposite beam line, it must be difficult to shield against radiations from the dump.

There may be two options to prevent the difficulty. First is a large crossing angle of 20mrad as the NLC. Second is to use two beam dumps for beamstrahlung photons(dump-1) and extracted beam (dump-2) . The second option was discussed. The extracted beam is horizontally bent in direct opposition of the previous design as shown in transparencies. So, the dump-2 can be separated by about 6m from the opposite beam, while the dump-1 remains at the same position. Major issue must be whether the dump-1 of 1MW can be installed. Power of the dump-2 is 11.5MW at Ecm=1TeV.

Following issues were summarized for further investigation;

Finally, SLC/SLD energy spectrometer and NLC extraction line chicane were introduced. Please see the transparencies in details.

(2) GM model in SLEPT (K. Kubo)

Kubo briefly showed GM modeling in SLEPT. The SLEPT has larger power spectrum than that of the original one ( based on measurement), both of which must be consistent. So, he will investigate the modeling ( algorithm of program code etc. ) .

(3) Permanent FF-Q magnet(T.Mihara, Y. Iwashita, Kyoto univ.)

(Japanese proceedings paper, LINAC engineering workshop, 2003, 3 pages, pdf,1MB) One of major issues is changeability of field strength in developments of permanent final quadrupole magnet. A prototype magnet of 100(14)mm outer (inner) diameter, 20cm length has been designed with 4 longitudinal segmentations of 8, 1, 2 and 4cm length (1cm gaps), each of which has a binary switch of focus(F) and de-focus(D) by rotating 90 degrees. Actually the prototype has a double layer structure; r=0.7~3cm and 3.3~5cm for 1st and 2nd layer, respectively. The outer layer can be rotated, while the inner layer is fixed in order to produce a stable magnetic field. Field gradient can be changed from 3T/cm to 0.08T/cm with the 90 degree rotation. Apparently, it fulfills a requirement of 1% strength adjustment. Skew component should be OK. The prototype will be constructed in this fiscal year.

Since repulsive forces may become large in a case of large variation of field strength, there may be practical limit of the field changeability. So, we discussed on magnitude of energy variations at LC experiments. Generally, there are following example cases;

So, the changes would be a few % ~ 72%.

The next meeting will be on 17th September, 2003,10:00 - noon at 3 gokan, 425 .