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Dear all, Following the threads in this discussion prompts me to make the following comments: 1) The statement re. not being able to move coils independently applies just to coils that are housed in the same cryostat. That is to say within the "QD0 cryostat" the QD0, SD0, OD0 (octupole), anti-solenoid and the extraction line quad QDEX1 coils move together as a rigid body and the equivalent coils in the QF1 cryostat also move together; however, the QD0 and QF1 cryostats themselves may be independently moved. 2) In fact because of push-pull they must be independently adjustable since QF1 remains in place and the QD0 magnets get swapped during a detector change (with the new QD0 most likely settling in at a different position). 3) That being said, there are different considerations/constraints for moving the QD0 and QF1 magnets. QD0 is supported within each detector and the considerations implied by being able to open a given detector for access have some impact here. It is expected that QD0 can be translated in all three axes. The yaw and pitch degrees of angular freedom are also reasonably easy to provide but roll, e.g. rotation about the incoming beam axis, is much more difficult. Thus we provide skew multiple coils within each coil package in order to provide an equivalent degree of freedom. Here it is good to also point out that the incoming and extraction beam lines define a plane; so making a physical roll about the common QD0/SD0/OD0 axis changes the vertical center of QDEX1 altering the path down the extraction line. 4) Also since the first part of QD0 sees significant fringe field from the detector solenoids (which is then compensated by the anti-solenoid), it is best to minimize any relative movement between the detector and QD0. This is because with a fixed anti-solenoid setting, a shifted QD0 sees a slightly different fringe field distribution and the correction may not be accurate. Given that the detector and anti-solenoid coils are large compared to the expected shifts, this is probably a very small effect but it should be studied. As I am currently reworking the anti-solenoid design to match the developing specifications for SiD and ILD, I am also giving some thought to doing "anti-solenoid correction adjustments" should this prove necessary. 5) Because the cryostat QF1 stays in place during push-pull, its position should be much more stable. Also the support structure for QF1 is not constrained by opening the detectors, so QF1 should reasonably be able to be moved in all six degrees of freedom; however, please remember as with QD0 movement of QF1 also impacts the focusing elements in the extraction beam line. Again all QF1 coils include skew correction coils. (Note for this terminology a skew-dipole deflects in the vertical plane.) 6) Fortunately because the QF1 coils have magnetic yokes (that will shield the beam from external fields) and the detector fringe fields are anyway much smaller that for QD0, there is no anti-solenoid needed for QF1. I hope the above comments are helpful to clear up any communication misunderstandings that may have occurred. Respectfully submitted, - Brett Parker --------------------------------------------------------------------------------------- -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] On Behalf Of Okugi, Toshiyuki Sent: Sunday, April 12, 2015 3:50 AM To: White, Glen Cc: [log in to unmask]; Marin Lacoma, Eduardo; ilc-bds Subject: Re: Comment for IP beam size optimization with octupoles Dear Glen, I communicated with Brett Parker the following issues. The requirement for the correction coils for SD0 or QD0 are as follows. When we don't have a SD0 mover, we can consider two methods of IP tuning instead of sextupole mover. 1) [by using the qudrupole and skew quadrupole correction magnet around SD0] The requirement of the strength of the correction magnet are the maximum strength of the correction magnet is GL=+/-2.6T, and the precision is at least 5e-5 in order to compensate the SD0 position movement by +/-1mm for ECM=250-500GeV operation. 2) [by using the combination of the cryo-mover and dipole correction coil around QD0] The requirement of the strength of the correction magnet are the maximum strength of the correction magnet is BL=0.15Tm, and the precision is also 5e-5. The requirement of SF1 is a little bit different, but I expect to be same order to SD0. I think the required precision is very hard to other magnets ( > 5e-4 ) for both cases (but not impossible??). We should decide whether will we put the SD0, SF1 mover or compensate by using correction coil. Sincerely, Toshiyuki OKUGI, KEK From: [log in to unmask] [mailto:[log in to unmask]] On Behalf Of White, Glen Sent: Saturday, April 11, 2015 7:08 PM To: [log in to unmask] Cc: Marin Lacoma, Eduardo; ilc-bds Subject: Re: Comment for IP beam size optimization with octupoles Dear Toshiyuki, Edu and all, I notice your use of SD0 and SF1 in correction knobs- just a reminder that there is currently no provision for being able to independently change the offset of these two sextupole field positions in the baseline design as they are co-wound onto the QD0 tube in the 2 final doublet cryostats. Hopefully there are enough degrees of freedom just using the other 3 sextupoles for the required disp_x, disp_y, waist_x, waist_y and <x’y> linear knobs. If not, this will be important information for the FD design considerations. Regards, - Glen. On Apr 6, 2015, at 8:29 PM, [log in to unmask]<mailto:[log in to unmask]> wrote: Dear Edu, In order to understand this issue, I wonder if in your lattice design process you use the FD octupole magnets. Since the IP profile has almost no tail, and the core and rms beam size is consistent with the design (see the previous report), the octupole should be no effect to the beam size for ECM=500GeV. For ECM=250GeV, we have a possibility to recover the luminosity by 5% by using higher order correction. But, since the beam size growths for horizontal and vertical are quite different properties, it seems difficult to correct only with single knob. Furthermore, the higher order correction has the disadvantage to decrease the collimation depth as I already pointed out. Also regarding the errors, do you include errors from the movers (2um) in your simulation? I did not put the mover error. But, when the sextupole position is shifted by micron order, the IP beam size is increased too much for the ILC FFS (see the attached file). If the mover resolution was only 2um, we cannot see the IP beam size response by using the linear knob. I wonder why the effect to your simulation is so small. Furthermore, the effect of the mover resolution is linear optics deformation, and it should be no effect to the octupole correction. Anyway, I will evaluate the tolerance of the mover resolution by the point of view of IP beam size tuning. (I expect one order smaller than your evaluation.) regards, Toshiyuki OKUGI, KEK On 04/06/2015 02:05 AM, Okugi, Toshiyuki wrote: Dear all, Since I could not connect the BDS meeting (3/30) well by my network problem, I will make a comment for the IP beam size optimization with octupoles. When we use the higher order multipole fields to focus the beam core, the tail particles will be spray and it makes the collimation depth small in generally. Therefore, it is better to focus the beam with lower order correction, if possible, and we can focus the beam only with sextupoles for ILC FFS (see attached file). Furthermore, when we assumed the errors in the beamline, the beam size growth is not only for vertical direction, but also horizontal. Since the horizontal IP profile is asymmetric shape, the correction with octupoles is not effective. Therefore, I think we had better to optimize the IP beam size without octupoles, and the octupole should be used for the tail folding. 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