Impact of noise in the main circuits –orbit, beta* and tune ripple

D. Gamba, J. Coelo de Portugal, R. Tomas

99th HiLumi WP2 Meeting – 25/07/2017

Outline

§ Introduction§ Simulation procedure and results

§ A few simulation cross-checks§ Comparison between HL-LHC and LHC

§ Crosscheck with available measurements§ Conclusions

2

Introduction§ definition of PC performances being redefined by

WP6B:

§ Here we would like to re-verify the single particle effect due to errors on the different circuits.§ Come up with reasonable specification for PC stability.

3

Simulation procedure

1. Compute un-perturbed optics in MAD-X.2. Assign an absolute error of 1ppm of PC Irated to

one circuit at a time, then re-compute optics.3. Compute induced tune variation, β-beating and

orbit excursion.4. Give an estimate of best accelerator performance

assuming all “class 1” PC§ (0.1 ppm r.m.s. stability in current regime – bandwidth

[0-0.1] Hz.)§ Next: come up with specifications for new PC.

§ Unreasonable to ask better than 0.1 ppm r.m.s.

4

Optics analyzed

§ HL-LHC 1.3:§ β* = 20cm§ on_x1=255; phi_ir1 = 90; on_x5=255; § on_x2=170; phi_ir2 = 90; on_x8=-250; § on_lhcb=-1; on_alice=1;§ E = 7 TeV; σE = 1.08e-04; εN = 2.5 μm§ B1: Q1=62.3101, Q2=60.3200, DQ1=2.0621, DQ2=1.8465§ B2: Q1=62.3101, Q2=60.3200, DQ1=2.0132, DQ2=2.0634

§ LHC (runII/2016/opt_400_10000_400_3000_totem5.madx)§ β* = 40cm§ on_x1 =-185; on_x5 =185; on_x2 = 200; on_x8 = -250; § on_sep(1258)=0; on_o(1258) = 0;§ E = 6.5 TeV; σE = 1.13e-04; εN = 3.75 μm

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HL-LHC 1.3 – tune

6

Similar effectCompatible with previous studies

(see Paris Nov2017)

HL-LHC 1.3 – beam size

7

Taking into account β and D beating. With respect to unperturbed beam size.

Similar effect

Sensitive trim!

HL-LHC 1.3 – beam orbit

8

With respect to unperturbed beam size.

Seems related to crossing scheme.

Similar effect

Compatible with previous studies

(see Paris Nov2017)

(MBA12)

Main bends effect attenuated by induced ΔE?

9

�L

L= ↵c

�p

p0

Momentum compaction:SUMM_table.ALFA

Path length variationTWISS_table.DATA.T

Machine length:SUMM_table.LENGTH

To be applied to the next TWISS as “DELTAP” or

“PT” input*.

* One should be careful with the definitions of T/PT/DELTAP which are not well documented in MAD-X

Note that nominal

bunch length is about 8 cm.

Cross-check of T error with PTC_TWISS

§ Consider MB.A12 error§ Compute closed orbit with MAD-X§ Treat HL-LHC as a line in PTC (icase = 6)

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(MBA12)

Effect of energy: without/with correction

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No change

Comparison different MB induced errors

12

With respect to unperturbed beam.

Vertical orbit induced by MBA12 and MBA81?§ Apply MB.A12 error on lattice treated as a line and see where Y pops up.

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MB.A8R1.B1

… possibly due to fringe fields?… to be checked again in PTC (here MAD-X), eventually playing with HGAP/FINT

Nominal Y orbitY

[mm

]

LHC 40cm – tune

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AsymmetricImportant trim.“restoring” symmetry

LHC 40cm– beam size

15

Taking into account β and D beating. With respect to unperturbed beam size.

Most of the effects happen here.

LHC 40cm– beam orbit

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With respect to unperturbed beam size.

Related to crossing scheme.

As in HL-LHC

No vertical excitation

LHC PC specification

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Circuit Irated CLASS Stability ([0-0.1] Hz) ppm rmsMain bends 13 kA 1 0.1 (was 3 ppm peak-peak)Main quads 13 kA 1 0.1 (was 3 ppm peak-peak)Triplets 8/6 kA 1* 0.1* (was 5 ppm peak-peak)D1/D2;Insertion quads

4/5/6 kA 2 0.17** (was 5 ppm peak-peak)

Trims;Multipole correctors

600 A 3 0.33** (was 10 ppm peak-peak)

Orbit correctors 60/120 A 4 1.67** (was 50 ppm peak-peak)

Note: 3 ppm p-to-p ≈ 3 / (2 * sqrt(3)) = 0.87 ppm r.m.s

* In the LHC design report they were foreseen to be class 2.** Assuming factor 3/0.1 = 30 better than specification as for class 1.

Circuits precisions assumed

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HL-LHC

LHC

LHC TDR

LHC optimistic

LHC TDR

LHC optimistic + all 0.1 ppm

+ all 1 ppm

Overall computation (r.m.s)

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HL-LHC 1.3 (20cm β*)** LHC (40cm β*)

*Only known

PC:LHC TDR

Only known PC:

Optimistic LHC

Optimistic LHC +

0.1 ppm HL-LHC

OptimisticLHC +1 ppm

HL-LHC

LHC TDR Optimistic LHC

Δ H/V tune(10-5) 12.6/12.2 1.5/1.4 1.8/1.8 11/11 7.8/7.7 0.9/0.9

Δ Orbit at IP 1H/1V 5H/5V(10-3 σbeam)

8.4/8.312.0/9.0

1.0/1.01.4/1.0

1.4/1.11.8/1.1

10/4.312/4.6

7.5/4.35.1/0.6

0.9/0.50.6/0.1

Δ size at IP 1H/1V/5H/5V (10-4 σbeam)

2.4/2.02.5/2.1

0.3/0.20.3/0.2

0.3/0.30.4/0.3

1.4/1.63/2.3

0.6/0.80.9/1.4

0.1/0.10.1/0.2

Δ Orbit at collimators H/V(10-3 σbeam)

8.7/6.5 1.0/0.7 1.2/0.8 7.3/3.3 6.5/4.1 0.7/0.5

Δ size at collimators H/V(10-4 σbeam)

2.3/2.3 0.3/0.3 0.3/0.3 2.1/2.3 0.9/1.1 0.1/0.1

* See previous slide for assumed precisions** for 15cm β* one needs to scale up due to higher beta at triplets.

Can we see something in the LHC?

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§ Measuring the tune jitter from AC-dipole kicks (around 10 minutes per measurement set)

§ Hard to see the effect of the 𝛽∗, we need more statistics.§ With no triplet (ballistic) the effect is around 10%&.

§ Measurements seems x2 worse than “Optimistic LHC”

Tune jitter [𝟏𝟎%𝟓]

40cm 2016 40cm 2017 30cm(200m arcs)

25cm(600m arcs)

Ballisticoptics 2017

Beam 1 x 5±2 6±2 0±32 3±2 0.9±0.4

Beam 2 x 4±2 4±2 3±2 1.7±0.8 0.8±0.4

Beam 1 y 2.4±1.0 3.0±1.2 1.7±0.8 4±2 0±0.8

Beam 2 y 8±4 0±20 2.1±1.1 2.6±1.3 1.7±0.7

W. Average 3.8±1.5 3.9±1.7 2.1±1.0 2.6±1.1 0.8±0.4

Can we see something in the LHC?Losses at collimators?

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LHC simulations:

Can we see something in the LHC?Losses at collimators?

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LHC simulations:

Stability of main circuits in LHC

§ RB.A12 : 6.1808676362e-07§ RB.A23 : 1.72964004707e-07§ RB.A34 : 1.71225763164e-07§ RB.A45 : 1.33232467131e-07§ RB.A56 : 1.91227157209e-07§ RB.A67 : 1.79065705191e-07§ RB.A78 : 1.33945000149e-07§ RB.A81 : 1.81371559565e-07

§ RQD.A12 : 2.25494306069e-07§ RQD.A23 : 3.16447839007e-07§ RQD.A34 : 2.71206017397e-07§ RQD.A45 : 2.27288417406e-07§ RQD.A56 : 2.22046391423e-07§ RQD.A67 : 2.35416619213e-07§ RQD.A78 : 2.0096993093e-07§ RQD.A81 : 4.39526995513e-07

§ RQF.A12 : 2.23428534208e-07§ RQF.A23 : 2.87326102644e-07§ RQF.A34 : 2.50201699175e-07§ RQF.A45 : 2.39742199278e-07§ RQF.A56 : 2.23592578842e-07

§ RQF.A67 : 3.51132157367e-07§ RQF.A78 : 2.04801820609e-07§ RQF.A81 : 2.37581686397e-07

§ RTQX2.L2 : 2.24598733606e-07§ RTQX2.R2 : 2.4177249014e-07§ RTQX2.L8 : 2.55522985171e-07§ RTQX2.R8 : 2.39493058201e-07§ RTQX2.L1 : 3.13981652932e-07§ RTQX2.R1 : 2.50915251894e-07§ RTQX2.R5 : 2.2632214839e-07§ RTQX2.L5 : 2.4674245274e-07

§ RQX.L2 : 2.28912721764e-07§ RQX.R2 : 2.23970044637e-07§ RQX.L8 : 2.20920832604e-07§ RQX.R8 : 2.53642731065e-07§ RQX.L1 : 2.16450848768e-07§ RQX.R1 : 2.41465557872e-07§ RQX.R5 : 2.31886607475e-07§ RQX.L5 : 2.34358761454e-07

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Looking in Timber at Fill 5966 STABLE beam on 19/07/2017

r.m.s. of ΔI/Imean:

• May explain x2 in tune stability measurements.• no correlation with losses at BLMs seen, yet…

Conclusions§ From optics analysis, the tune stability of both LHC

and HL-LHC seems to be dominated by tripletsand arcs dipoles/quadrupoles.

§ In HL-LHC (20 cm) the tune stability might be not better than 1.5e-5 (assuming perfect triplets). § More realistic to be around 2e-5.

§ It looks like we are lucky having PC for the arcs which are much better than specifications (about 0.2 instead of 0.9 ppm r.m.s.)§ We need to make clear that we have a new specification

also for these PC (even though they will not be updated)§ We need systematic measurements to ensure we

have the effect under control.§ Could be interesting to look for loss spikes and/or to

induce them.§ Measure/Induce tune jitter with respect to triplet currents.

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