Minutes of ATF2 weekly meeting, 11 May, 2011

May 11 15:00 - 16:00 (JST time), Webex and ATF LC meeting room, KEK

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Recovery Status of ATF, N.Terunuma

So far, the recover is on the schedule.

Checkout of the cooling system was started from this Monday. There was no water leak at the LINAC and the final focus system (ATF2). Tomorrow, the DR-cooling system will be checked. In this inspection, we checked water leaks at pumps and valves etc., while the temperature control system will be checked in next week. We asked KEK administration for continuous operation of cooling system for checkout of powering magnets.

The re-positioning of shielding concretes was started yesterday, and will continue until end of this month. The roof concretes were removed at the ATF2 beamline, and all the cables have been removed in the IP area. We could see the 10cm wide gap at the side concretes which have been displaced by the earthquake.

Half of LINAC was re-aligned both in vertical and horizontal directions , and the remained LINAC will be done in this month. The DR and ATF2 will be re-aligned in June. These works will be done in day and a beam operation will be commissioned in evening.

Next work plan is to re-assemble the concrete shields, to commission the LINAC RF after the permission of continuous operation, to re-align beamlines and to prepare the safety inspection for beam operation in June.

Q : Who are the alignment people ?
A : KEK/ATF group is working.
Q : Is there floor movement/damage ?
A : No, only the concrete shields have been displaced.

ATF2 Lattices (Updated calculation of multipole effects and mitigation w/ and w/o a skew sextupole for nominal and ultralow beta configurations), E.Marin

Performances of the nominal (β^*_x,y=3.9, 0.1mm), and the ultra low beta (β^*_x,y=4.2, 0.025mm) optics have been studied with taking account of multipole components in sextupole and quadrupole magnets at the FF and EXT beamline. In this analysis, he used the multipole components of the QEA magnets which have measured by M.Masuzawa et al. at KEK according to the agreement at the 11th ATF2 project meeting, January 2011. Also, a new skew sextupole was used in this analysis, which corrects partially the skew quadrupole components.

Both IP beam sizes were calculated as a function of horizontal invariant emittance (γε_x) from 2.7 to 6μm. The resultant beam sizes are σ_y,RMS=72nm, σ_y,Shintake=49nm, σ_x,RMS=4.3μm and σ_y,RMS=79nm, σ_y,Shintake=52nm, σ_x,RMS=5.5μm at the nominal and ultra low beta optics, respectively. Major increase of vertical beam size is due to the dodecapole (5th order) component in QF1FF.

Q : Is the β^*_x 4mm, since the horizontal beam sizes are too large ?
A : Yes, but I will check it.

Possible solutions to cure the beam size growth are listed below;

decrease β_x in the QF1FF, i.e. larger β^*_x
decrease horizontal emittance, γε_x
replace the QF1FF with a superconducting Q
swap the magnets

First and last solutions are studied in this analysis. All matching quadrupole magnets are used to decrease β_x in the QF1FF, i.e. the optics was re-matched with β^*_x=10mm which 2.5 times of the designed one. The resultant beam sizes are σ_y,RMS=37.6nm, σ_x,RMS=4.5μm and σ_y,RMS=36.4nm, σ_x,RMS=4.6μm at the nominal and ultra low beta optics, respectively. Therefore, we obtained a good solution for the nominal optics, while the beam size of the ultra low beta optics can not decrease due to the geometrical aberration.

Tolerances of new skew sextupole magnets corresponding to 5% vertical beam size increase are calculated to -525μm of X offset, 3mm of Y offset and 400mrad of tilt for the nominal optics re-matched.

For the ultra low beta optics, he looked for intermediate β^*_y to correct the aberrations. He found that 42 μm of β^*_y was the optimum or minimum one, where the chromaticity is about 47,000 while the CLIC one is 63,000. From now on the ATF2 ultra-low beta refers to β^*_y a value of 42 μm at the IP.

He investigated the multi-knobs with displacements of sextupole magnets for the ultra-low beta optics too, i.e. the horizontal knobs of β_x,&alpha_x,β_y,&alpha_y and η_x, and the vertical knobs of <x,y>, <x',y>, <x',y'>, <y,η> and <y',η> .

He simulated the IP beam size tuning with the multi-knobs and following errors; Quads and Sext. misalignment of 30μm, Quads and Sext. tilt of 300μrad and the relative strength of 10^-4. The tuning order is <x',y>, &alpha_y, η_y, &alpha_x, η_x, <x,y>, η_y', <x',y'> ... Results are compared with experimental ones in December 2010. A similar tendency is observed. The tuning study for the new ATF2 nominal lattice shows that 63% of the seeds reach a finalσ_y<43 nm. Also, he simulated at the ultra-low beta optics, where 60% of the seeds/machines reach a final σ_y<34nm.

Finally, the swapping performance was shown, where the previous set of swapping magnets were used with the KEK multipole components. The vertical beam size, σ_{y, Shintake} was obtained to be 38nm, where 70% of less than 47nm.

Work ongoing to decrease β^*_x within 8-10mm, in order to obtain a more suitable ratio β^*_y /β^*_x and get closer to ILC and CLIC designs. ALso, I will propose an efficient quadrupole sorting.

Q : Where is the skew sextupole magnet ?
A : It is located at just upstream of QF5BFF.
Q : How did you tune the IP beam size with the skew sextupole magnet ?
A : First, β^*_x was varied from 4mm to 10mm with matching qudrupole magnets. Then, a skew sextupole magnet was used.
Q : How do the matching quadrupole magnets ?
A : They just matched the optics with β^*_x=10mm, i.e. no optimization.
Q : After correction with the the skew sextupole magnet, what remains the main component?
A : Sextupole component still remains .
Q : What is the beam size without the skew sextupole magnet ?
A : The beam size is 43nm , so the skew sextupole has a 5nm improvement. So, major reduction of beam size comes from the smaller β^*_x .
Q Edu : Can we swap magnets actually ?
A : In principle, yes. We need the verification for this work.

Re-matched optics with the new multipoles, S. Bai

She recently resumed the beam tuning study. Major motivation of this study is a cross check to Edu's result.

She used the M.Woodley's MAD decks ( mad_v4.3b and mad_v4.4) with both KEK and IHEP multipole components. For examples, the sextupole and octupole components (i.e. up to 3 order) and the multipoles up to 9 order of QM16FF (QEA-9) were shown for the KEK and IHEP values, respectively.

Beam sizes were calculated with the nominal optics (β^*_x,y=4, 0.1mm) and the KEK and IHEP multipole components for the comparison. Although the decks include the new skew sextupole magnet (SK1FF), it is turned off in this analysis. The resultant beam sizes are σ_y=61.5nm, σ_x=2.89μm and σ_y=266nm, σ_x=3.44μm with the KEK and IHEP multipoles, respectively. She found no effect by multipoles higher than octupole with the IHEP values.

She listed future study plans as;

Use the IHEP measurements with the new definition for the tilt angle in SAD.
Computing a correction for the effect of the multipoles: skew sextupole , swapping magnets, and seeing if this correction remains the same for both definitions of the TILT angles.
Check possibilities Edu found to correct the multipoles using the skew sextupole, especially in the ultra-low beta optics.
try to optimize beta_x to make it decrease to our goal beta_x, and also for the beta_y.
check the lattice, if the fitted optics gives symmetrical functions.

Q : We do not see any effect by multipoles higher than octupole. Is it true?
A : The higher poles have small/little effect.
Q : I suspect it, since we have to see the difference.
A Edu : I observed it, but the most contribution from the sextupole. The 5 FF sextupole magnets can correct it.
Q : Do you change the sext strength ?
A : I did not re-tune them.
Q : Could you check again ? If the sextupole magnets are tuned, the higher effect can be seen.
A : yes, I will.
A Edu : I observed σ_y= 72nm with tuning the sextupole components.
Q : Could you have a cross check by both of you ?
A : Yes.
C Glen : Replying the question on the higher components, I saw similar effects with minimal effect of >oct components in previous Lucretia simulation.

After the meeting, T.Tauchi checked the sextupole components of QM16FF ( QEA-9) in Mika's presentation at the 11th ATF2 project meeting. As appended slides, two are similar values. So, Sha's values are in-consistent with them.

Next meeting is 18th May, 2011. K.Kubo will chair this meeting, since T.Tauchi will be absent for the ILC PAC meeting, Taipei.