(1) How much is a tolerance for common movement of final focus doublets (QC1&QC2's for e+ and e- beams) relative to other magnets (QC3, QC4...) in the final focus system ? For example, the support tube may move commonly 6nm at 15Hz(resonant frequency) while relative movement between two e+, e- QC1s is negligily small.
(2) Nominal field gradient of QC1 is 225T/m in the JLC Design Study (1997). Can the field gradient decrease to 160-183T/m ? At the same time, can the QC1 distance from IP (L*) increase from 2m to 2.5m ?
His answers are as follows;
(1) The tolerance is about 100nm, since such movement must make a dispersion at IP as ( the relative displacement between QC1&QC2 and the other magnets ) x ( momentum spread ) = 100nm x 1% = 1nm << 3nm ( typical sigma_y ).
(2) It is possible. However, L* becomes longer, the chromatic aberration increases more. So we must lose something. An optimization shalle done on a balance between the gain and lose.