T. Argyropoulos, H. Bartosik, T. Bohl, A. Burov, S. Cettour Cave, H.
Damerau, J. Esteban Muller, A. Guerrero, W. Höfle, G. Rumolo, Y.
Papaphilippou, B. Salvant, E. Shaposhnikova, D. Valuch
• Both optics in parallel for direct comparison
– Nominal optics (“LHCMD1”)
– low γt optics (“LHCFAST3”)
• Setting up of 50ns beams (double batch) with 4 batches
– Basic setup – orbit, tunes, chromaticity, kicker timings, RF-voltage program
– “Advanced setup” – transverse dampers, longitudinal feedback
• Measurements with nominal intensity (~1.3e11 ppb injected)
– Transverse emittance measurements in both cycles
– Longitudinal beam parameters in both optics
– Studies on transmission efficiency with nominal optics
• Measurements with ultimate intensity (~1.8e11 ppb injected)
– Longitudinal beam parameters in both optics
• Correcting orbit
– Quite high RMS orbit in vertical plane in Q20 optics for high energy part of cycle
 try to correct using available corrector strength next time … (problem for
transverse damper? See below …)
– Usual picture in nominal optics
• Tunes and chromaticity were adjusted in both cycles using Auto-Q
– Several iterations needed for chromaticity correction …
Low γt optics
Nominal optics
Courtesy W. Höfle
Q26
pos
BPH
BPV
BPH
BPV
BDH
BDH
BDV
BDV
name
20408
20508
20608
20708
21437 H1
21451 H2
21455 V1
22176 V2
position length
beta H
mu H
mu H
beta V
mu V
mu V
Dx
m
m
m
2pi
degrees m
2pi
degrees m
688.1194
0.275 103.0124 2.629762
0 21.04532 2.574098
4.762246
720.1171
0.275 21.05808 2.740457
102.7656 2.705568
0 2.175791
752.1148
0.275 102.9519 2.871766 87.1214 20.95317 2.816718
3.164567
784.1125
0.275 21.05617 2.982506
102.9587 2.948405 87.4213 1.088184
1018.584
2.32 72.84712 3.857974 442.1562 31.97077 3.857227
2.766706
1021.164
2.32 63.6318 3.864006 444.3279 37.4709 3.869101
2.520029
1022.884
1.46
57.943 3.868515
41.59403 3.876037 421.369 2.355577
1253.827
1.46 62.05857 4.785832
38.5286 4.695524 716.3843 2.675021
Q26 optics:
phase advance between pick-ups close to 90 degrees (87 degrees)
programming of feedback phase via LSA, assuming 90 degrees phase advance between PUs
H1,H2:
LSA 144 degrees
delta with respect to theory:
+8, +10 degrees
V1: LSA -7 degrees
delta with respect to theory:
-15 degrees
V2: LSA -80 degrees
delta with respect to theory:
- 7 degrees
Example H: 0.13*1.5*360 + 90 + 444 – 144 = 460 should be 90 +n x 360 mod -1 for damping
beam (notch/1TD + PUK) – 144
differences to theory can either be due to actual phase advance error with respect to model or it
is a damper setting-up error; pretty good though
Courtesy W. Höfle
Q20
pos
BPH
BPV
BPH
BPV
BDH
BDH
BDV
BDV
name
20408
20508
20608
20708
21437 H1
21451 H2
21455 V1
22176 V2
position length
beta H
mu H
mu H
beta V
mu V
mu V
Dx
m
m
m
2pi
degrees m
2pi
degrees m
688.1194
0.275 103.6715 2.02085
0 32.43247 1.99135
1.926628
720.1171
0.275 32.47134 2.108193
103.8512 2.090135
0 0.707269
752.1148
0.275 103.8069 2.206964 67.0008 32.2824 2.177651
1.19788
784.1125
0.275 32.37378 2.294389
102.9175 2.277217 67.3496 1.473792
1018.584
2.32 79.00912 2.970619 341.9168 43.66215 2.973393
2.429263
1021.164
2.32 71.33171 2.97609 343.8863 48.79656 2.982293
2.20275
1022.884
1.46 66.52994 2.980064
52.53837 2.987701 323.1237 2.051741
1253.827
1.46 69.85252 3.677835
49.36182 3.630155 554.4072 2.386917
Q20 optics:
phase advance between pick-ups are 67 degrees
programming of feedback phase via LSA, assuming 90 degrees phase advance between Pus fails
H1,H2:
LSA 65 degrees
V1: LSA -90 degrees
V2: LSA 65 degrees
could not be well adjusted
 H1,H2,V1 could be well adjusted but not V2
 we need to change the way we program the pick-up mixing for the Q20 optics, more function
generators needed or special FPGA firmware (preferred way is more function generators)
 also a not-explained delay error was corrected for V1, to be followed up
• 4 batches of 36 bunches with ~1.3e11 ppb injected
• Similar transmission in both optics (~95%)
Nominal optics
Low γt optics
• Transverse emittances were measured mainly in vertical plane
(BWS.519) in order to identify emittance blow-up
– Wirescans in PS (all batches at extraction) and SPS at extraction using the
bunch selection mode (STANDARD with gating), slots 1-900 selected
– Inconsistencies were observed which are currently investigated with BI expert
(very small emittances measured in SPS in some cases, clearly below the PS
values)
– Switching between Q20 and Q26 not automatic (optics functions need to be
selected/set manually)
– Clearly more experience with emittance measurement of multi bunch/multi
batch beams needed
• Similar (avg.) emittances for both optics
–
–
–
–
–
PS: average emittance εy,n=1.45μm
SPS: average Q20 optics εy,n=1.45μm
SPS: average Q26 optics εy,n=1.40μm
Smallest emittance in SPS: 1μm !?!
To be investigated …
•
No major beam dynamics issues with ultimate intensity (1.8e11 ppb injected)
–
–
–
–
•
No time for optimization and transverse emittance measurements
No obvious problem in transverse plane for both optics
Beam stable longitudinally in Q20 with 800MHz on but without longitudinal emittance blow-up
Beam slightly unstable longitudinally in Q26 with 800MHZ on  normally emittance blow-up
needed, but not applied during MD for direct comparison
Transmission around 90% in both cycles without optimization (tunes not corrected,
dampers, …) - no controlled longitudinal emittance blow-up in nominal optics
• Kicker heating had to be monitored permanently …
• Vacuum and BLM interlocks when increasing the bunch intensity and going to 4
batches (ultimate intensity 1 batch around 4:10, 4 batches around 4:40)
– BLM, mainly in Q20 optics (cycle optimization lnot done at this point due to lack of time!!)
– Vacuum interlocks because of ZS outgassing, sparks, …
• Some issues were encountered in setup of Q20 beam
– Transverse damper setup – modifications in LSA needed?
– Vertical orbit at high energy  to be followed up
• Inconsistencies in multi bunch/multi batch emittance measurements
– To be understood
• From beam dynamics point of view no obvious show stopper for 50ns
multi batch in Q20 – very promising!!
– Further MDs with injection into LHC should be done
• Further studies with ultimate intensity 50ns beams for both optics
needed
– Optimization for high intensities: tunes, dampers, RF, …
– Emittance measurements
– Longitudinal beam characteristics
• What happens with 25ns beams in Q20 optics?