DA Studies with
Crossing angles and higher order corrections
Emilia Cruz
On behalf of the JAI FCC Team
February 9th, 2017
Status after Barcelona
• Solved problems:
– Sixtrack problems with thick lattice, runs ok with thin lattice.
– Corrected crossing and dispersion scripts
• Unsolved problems---Minimum DA is still 0
– No errors and no crossing
Works ok. 80 sigma (Roman)
– No errors, crossing:
Works ok.
– Crossing, errors inner triplet:
4 sigma average, minimum 0 sigma.
– New cor_crossing script (Roman)
7-8 sigma average, minimum still 0 sigma.
9th Feb 2016, E.Cruz-Alaniz, JAI
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Possible Solutions
1.
Compare results good seeds – bad seeds.
2.
Explore which multipoles are causing problems.
3.
Explore coupling and correct it.
4. Correct directly higher orders : b3,a3,.. (Rogelio)
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Possible Solutions
1.
Compare results good seeds – bad seeds.
-
2.
No optical differences between bad seeds and good seeds. No consistent bad seeds
along all the angles.
Explore which multipoles are causing problems.
-
3.
No particular order was the problem. Results failed (0 DA) from the first order.
Explore coupling and correct it.
-
Current approach corrects the coupling. Not responsible for DA loss.
4. Correct directly higher orders : b3,a3,.. (Rogelio)
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Possible Solutions
1.
Compare results good seeds – bad seeds.
-
2.
No optical differences between bad seeds and good seeds. No consistent bad seeds
along all the angles.
Explore which multipoles are causing problems.
-
3.
No particular order was the problem. Results failed (0 DA) from the first order.
Explore coupling and correct it.
-
Current approach corrects the coupling. Not responsible for DA loss.
4. Correct directly higher orders : b3,a3,.. (Rogelio)
9th Feb 2016, E.Cruz-Alaniz, JAI
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Further useful corrections
•
Corrected error table:
– Adjusted to corresponding aperture.
•
Correct momentum-Voltage
– Results on momentum (4D) -> Cavities off – Deltap=0
– Results off momentum (6D) -> Cavities on – Deltap=2.7e-4
•
Correct directly higher orders : b3,a3,.. (Rogelio)
Include non-linear correctors to the corrector scheme.
CERN trip talk to E. Maclean experience in LHC and HL
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Minimize RDTs
Method to increase DA: Reduce non-linear effects of the errors in
the IT by minimizing resonance driving terms for different orders.
LHC report 349
HL-LHC IR non-linear correction and options
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Method
•
Add non linear correctors to the lattice:
- Normal and skew
- Left and right of the IR.
•
Current location is set next to MQX3
•
Make python routine that calculate strengths for each corrector to minimize
corresponding RDTs.
•
Include this routine to the tracking mask file calculating the correctors strengths for
each of the 60 seeds followed by other corrections (coupling correction, crossing,
chromaticity and tune,…)
•
Calculate DA for:
- On/off momentum studies
- Different correctors (b3/a3/b4/a4…)
- Different locations of correctors.
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Results: On momentum
minDA(no corr)=6.4σ
minDA(a3/b3)=7.9σ
minDA(a3/b3/a4/b4)=8.5σ
minDA(a3/b3/a4/b4)=39.9σ
•
•
For on-momentum studies we get a non-zero DA even without the use of non-linear
correctors.
Correction works very well to increase minimum DA, particularly for b6 correction.
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Results: Off momentum
minDA(no corr)=0σ
minDA(a3/b3)=4σ
minDA(a3/b3/a4/b4)=6.8σ
minDA(a3/b3/a4/b4)=6.9σ
•
•
•
For off-momentum we get again 0 DA without non-linear correctors.
DA < 1σ for 4 seeds.
With the use of non-linear corrections we get a non 0 DA and increasing min DA with
further corrections.
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DA results
Correction
On_momentum
Off_momentum
None
6.4σ
0σ
b3/a3
7.9σ
4σ
b3/a3/b4/a4
8.5σ
6.8σ
b3/a3/b4/a4/a6
39.9σ
6.9σ
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DA results
Correction
On_momentum
Off_momentum
None
6.4σ
0σ
b3/a3
7.9σ
4σ
b3/a3/b4/a4
8.5σ
6.8σ
b3/a3/b4/a4/a6
39.9σ
6.9σ
• On-momentum. All positive values.
• On-momentum. b6 correction seem to increase (a lot?) the min DA. Check studies.
• Off-momentum. Without non-linear correctors the DA goes back to zero. Fails for
4 seeds.
• Off-momentum. With correctors we get positive DA. Encouraging results.
• Could optimize location? But instead prioritize 0 DA result.
• Need to address zero-DA still to assure stability of the machine.
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Address zero DA
• We have the same problem of zero DA.
• Not as bad. It only happens for 4 seeds and results are consistent for all angles (same 4
seeds).
•
Look for origin (no indication):
- Compare W functions between bad seeds and good seeds. No difference.
Good seed on left
Bad seed on right
- h-terms for bad seeds don’t seem to have higher values.
h1200 (left) and h1300
(right) bad seeds (red)
compare to other seeds
(yellow)
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Address zero DA
•
Look for origin (indication?):
- Compare hpq00 terms between LHC and FCC for 60 seeds. LHC and FCC have
similar results for lower orders (left) but for higher orders (particularly h6000) FCC
has much higher values. Higher orders are responsible of loss of DA?
- Beta-beating higher for one of the 4 bad seeds. Other ones look normal but worth
trying correcting beta beating.
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Conclusions and Further work
• New results with updated error table and without non-linear correctors:
- On-momentum studies: 6σ min DA
- Off-momentum studies: 0σ min DA
• Adding non-linear correctors.
- On-momentum: Encouraging results. DA increases up to 39σ min DA
- Off-momentum : Encouraging results. DA increases up to 6.9σ min DA
• Investigate origin of 0 DA. So far no clear indication but looking forward to next results.
• Try further studies/correction:
- Correct beta beating
- Comparison of footprint between FCC and HLLHC
- Does thick tracking produce the same result?
• Much to do around non-linear correctors if needed higher DA. Optimize location?
Further correctors?
• Any other suggestion is more than welcome!
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Thanks!
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Bad seeds
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Bad seeds
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Possible Solutions
3.
Explore coupling and correct it (Roman, D. Boutin)
–
–
–
–
Tracking jobs already have a coupling correction (Roman)
Another coupling correction was done by D. Boutin, presented in Barcelona meeting.
Check strength of coupling: Calculate minimum tune approach for all seeds (Rogelio)
Running script, matching tunes as close as possible and then measuring difference for
all 60 seeds.
Before correction
Coupling Correction (Roman)
ΔQ < 0.040
–
–
ΔQ < 0.0025
Coupling very low, not responsible for DA loss
Try 4th option…
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