94th ATF2 weekly meeting

International phone/webex meeting

Report on the mechanical measurements of ATF2 "Final Doublet" magnets and how they relate to their measured multipoles and the predicted IP beam spot size, Cherrill Spencer (SLAC)

SLAC technician achieved accuracy of 1/2 mil for relative gaps between adjacent pole tips, which is needed for reduce the 6, 10 and 12 pole components below the latest tolerances set by the beam dynamics experts. Also, the procedure for re-assembling the magnets so that their previously attained mechanical symmetry is maintained has been "established", as explained at this meeting in Spencer's presentation. The manual describing the re-assembly procedures is available.

In the QF1 re-assembling procedure, there is one difficult issue. The relative diameters between opposite pole tips can not be measured with gauge blocks because the BPMs are installed. Spencer wanted to use the BPM beampipe as a measuring tool to guide the quadfs top half into the correct position relative to the bottom half. Also, the BPM beam pipe is not perfectly cylinder within 1 mil for it is extruded one (reported Terenuma) and so is not suitable to be used as a tool.

The various poletip distances have never changed in transportation between SLAC, LAPP and KEK over several months. So, the magnets are very rigid.

On Spencer's slide # 12, the beam size effects of multipole components are shown as a function of their overall magnitude up to 2 times their present values as measured at SLAC.

Q to Spencer: How rough are the gap distances after just mounting the top half on the bottom half without doing any of the special instructions ?

A : We did not deliberately do such a test, so I do not know. But the range in values will probably be like the ones we measured on 28th September 2007, shown on slide 7, as back then we were not doing these special procedures. That would be 1 mil range in the diameters and 2 mil in the gaps, as shownon slide 7 . The resulting sextupole/quad would be about 0.038%, compared to the 0.0255% achieved with the special re-assembly procedures.

Q to Spencer: We would like to know just raw effect of assembling without any specific procedure.

A: If the sext/quad is 0.038% that is 1.5 times what we could achieve and so use Whitefs graph on slide 12 to see the beamspot size will grow by about 40 microns.

Q to Glen White: The results of slide 12 are re-tuned ones ?

A : They are Lucretiafs results without re-tuning as shown at last meeting, There are still residuals of 40 -45 nm .

Q : The multipole multiplication factor of 1.5 will get worse beam size ?

A : It will be re-matched for the nominal size.

C : The error (factor) must be within the range ( re-match ).

Q : How to rematch ?

A : We have to find the best re-match.

Q : If the multipole components are known, we can re-match ?

A : Tuning knobs are very complicated for sextupole components especially. So it is not simple.

Q : Even if the factor is zero in the graph on slide 12, the beam size is 40nm ?

A : It is due to multipoles of the 3 dipoles and sextupoles.

Q : Again the 40nm effect at zero comp. , is it consistent with those shown at the last task meeting ?

A : It is a result by using entire tuning knob, but the multipole components are the same as previous one.

Q : The multipole effect of QD0/QF1 is from 37 to 41nm. How do bend and sexupoles effect the spot size?

A : It is 39nm from 35nm with only FD-system.

Q : Can we have signs of multipole components ?

A : As shown in slide 10, angles are available.

Q : The table of multipole comp. is available?

A : there is the data on the SLAC wiki-site.

A : The multipole in bends measured (IHEP) is smaller than tolerance. The data will be sent to Glen. Glen will post on the wiki.

Q : Are there 18 poles in the FD sextupoles?

A : FD sextupoles came from SLAC and were last measured at SLAC, in 1993/94 .

A : The effect has been estimated to b e a few nm by Glen.

Q : Have the 3 sextupoles arrived at KEK (were air-shipped on Sept 28)?

A : They will be installed in next week? Actually, they were installed on 10 October.

Q: Returning to issue of re-assembling the quads: Is CMM measurement of pipe of s-band BPM possible at KEK?

A : We are sure that it is not circular even it looks so .

Q : Can you measure it ?

A : ...

: What can we do if the beampipe cannot be used as a measuring tool? We can measure gaps between the adjacent poletips at the gopenh end of the quad and we know what values they should have. You can also measure the gap between the pipe and the 4 pole tips at one end after the BPM installation, but if the pipe is not really centered in the aperture these measurements do not help so much. Or we try a different approach for example : we may do a trial assembly without the BPM and get the top half in the correct position and then measure "position of top-half iron yoke" with tooling balls by laser tracker- then use these values when put together with the BPM in place .

A : With installation of s-band BPMs, the gaps will not be measured precisely. In early next year, we will look at this prblem some more and there may be find a solution ? After the installation of BPMs, we can find a method of the precise alignment at KEK.

Options for Matching the Extraction line, Mauro Pivi (SLAC)

Beta must be matched between kicker-1 and -2 with zero dispersion, where QM7R is close to the kicker-1. We evaluated a "real" gradient of QM7R, where extracted beam goes through 22.4mm off-axis.

Field map of QM7R is provided by Cherrill. The bending angle is correct, while the gradient can be varied by 20%. Actually, we could get a perfect matching with reducing QM7R to 50% if the twiss parameters (betas and alphas) are flexible and can be varied in a range ±30%. Flexible twiss parameters at the entrance of the extraction line let the matching of the extraction line possible and easier. When it is 30% of reduction, -I matrix is destroyed for too weak QM7R. We may install an extra Q in phase for the 30% case. Beta function varies from 100m to 120m ( 200m) when QM7R reduces to 80% ( 50%).

We would like to propose 2 shifts for these studies in December.

Q : Do you need H-bump orbit at QM7R ?

A : Yes, it helps, e.g. scanning of bumps.

C : The bump varies strength and K2L also i,e, sexupole comp .

C : Beta matching will not be effected.

Rematch DR & EXT Optics for QM7R Gradient Error, Mark Woodley (SLAC)

As mentioned by Mauro, optics can be found in DR at least 50% reduction of QM7R. The 6 matching parameters of beta, alpha and dispersion in x, y coordinates can be optimized by 6 quadrupoles of QM1R to QM6R.

MAD calculations show that QM7R with 50 to 100% strength seems OK, while beta in the straight section becomes bigger. So the matching is also OK. There may be a finite difference of dispersion between MAD and SAD calculations.

In these optimizations, the QM2R varies from QD to QF as shown in tables. The injection optics should not be changed and neither the LW optics at the north straight section.

C : Poisson and 2D (PRIAM) field calculations of QM7R have agreed.

Q : Can we measure the field map of QM7R ? It is difficult to estimate them by beam studies since trajectory changes in H and V directions at the same time.

A : If we remove the magnet, we can measure them with a hall probe.

Q : It is question to KEK colleagues.

A : ....

C : It may be easy to measure a dispersion generated at QM7R at new extraction line. The dispersion should be zero without residual one at QM7R.

KEK site meeting

Since QM2R power supply was broken, It has been set to be 0. The power supplies are repaired now. So, we can use it in next run.

We will operate the DR with the nominal optics which was specified with "0" in Mark's presentation. K.Kubo will announce the nominal DR optics. Of-cource, the optics can be changed in a machine time for studies as SLAC team proposed.