Chromaticity correction (without RCS.A78B2)

Thanks to: F. Roncarolo, E.Todesco, M.Lamont, J.Wenninger

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Outline & Measurement method

• Q raw data• Clean the data• Fit a sin function with variable A• Calculate Q’• Q’ function smoothing• Elaborate data depending on needs

Q’ decay at injection (state of art)

Q’ during rampQ’ decay at flat-topB3 to Q’ measurementsQ’ knob verification

(OP w/o RCS.A78B2)

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OP without RCS.A78B2

INJECTION• B3 decay

RAMP• Snapback• B3 variation

(momentum change)

FLATTOP• B3 decay

B2 compensation is calculated as for B1 then multiplied to a 8/7=1.14 factor

The RCS.A78B2/B3 function has been equally distributed on the other circuits

The B2 global_B3 knob has been multiplied by a 8/7=1.14 factor(effect of about 0.2 Q’ units)

RCS.A78B2/B3

sec

B3

Q’

min

sec

B3

~7 B3 units

Example of H corr

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B3 decay at injection

B1• Q’H ~ +2.5• Q’V ~ -2

B2• Q’H ~ +2.5• Q’V ~ -2

0.058 B3 units

B3 decay not correctly compensated (kind of

expected), but the good news is that there is no

visible difference between the beams

Dec_tau 600Dec_d 0.28dec_delta 0.32

Trims on lattice sext to get Q’~8 before going into the ramp

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B3 decay at injection

Example of horizontal corrections

The problems seen during the scrubbing were likely due to:• Not good control of the tune decay (due to lack of reproducibility)• High precision required over a much larger window than in standard operation

Q’ min

Jul 4th Aug 8thDec_tau 850 600Dec_d 0.32 0.28dec_delta 0.26 0.32

July 4th

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Ramping w/o RCS.A78B2

First ramp:At about 800 sec the B2Q’V starts growing and B2Q’H goes down then passes negative…B2 is dumped around 1080 sec after the ramp start

Third ramp:Both beams survive!Q’ (re-)measured along the ramp (small corrections implemented) and at flattop

Second ramp:Both beams survive the ramp, but are dumped about 30 sec after flattop is reached (electrical glitch caught by FMCM RD1.LR5)

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Ramp

• B3 compensation at injection not perfect, about 2/3 Q’ units are not into the snapback correction but in the lattice sextupole

• Q’ along the ramp is well controlled (+-2)

• No visible effect from the missing RCS

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Flattop

• Very good control of small (~0.05 units) B3 decay at flattop

• Small (visible on V??) effect from the missing RCS as the trim was reverted and not put back

• Tune decay not compensated (QFB during squeeze)

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B3 to Q’ measurement Old assumption: 1 B3 unit =

• -43 Q’ units in H• 35 Q’ units in V

Values measured during Run1

New measurements1 B3 unit =

B1• H ~ -42.6 Q’ unit• V ~ 35.3 Q’ unit

B2• H ~ -42 Q’ unit• V ~ 35 Q’ unit

0.3 B3 units swing in 10 stepscrosscheck with 1 unique step back (not shown)

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Q’ knob check

Knob measurements2 steps of 5 units

B1• H -> 2 to 12• V -> 15 to 5

B2• H -> 2.2 to 12.2• V -> 14 to 4

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Q’ today

+6 all along (~10)+8 the last point (~12)

+6 all along (~9)+8 the last point (~12)+10

(+13)

+12 (+15) +10(+13)

B1HB1V

B2HB2V

+12 (+15)+10

(+13)

+10(+13)

sec

sec

sec

sec

Q’

Q’

Q’

Q’

Linear Fit:

On-momentum tune

Chroma

Momentum- Offset

Problematic when frequency acquisition () and tune (Q) are not well aligned

Sine modulation of RF frequency Acquire Tune (Q) and momentum offset

Online Q’ estimate V1 -> the naïve approach

𝑄 (𝑡 )=𝑄on+𝑄′ .Δ𝑝𝑝

(𝑡)

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K.Fuchsberger

Individual Harmonic Fits on and

Δ𝑝𝑝

(𝑡 )=𝐴𝑝 . sin (𝜔 𝑡+𝜑𝑝)+𝐵𝑝

4 Fit parameters

Initial guess

4 Fit parameters

𝑄 (𝑡 )=𝐴𝑄 .sin (𝜔𝑡+𝜑𝑄)+𝐵𝑄

, with

Online Q’ estimate V2

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K.Fuchsberger

• Worked very reliably for several fills

• Next improvement steps:• Q’ trace (e.g. to

observe evolution during ramp)

• Feed Forward• Error Estimation

Online Q’

K.Fuchsberger

14Matteo Solfaroli

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Conclusions The exclusion of RCS.A78B2 has been fairly transparent (NO

difference between the beams)

B3 injection decay The B3 injection decay is correctly compensated for the operational

purpose (windows of about 1 hour at constant Q’) It would be a plus to verify the powering history dependence with

some additional measurements

Snapback & ramp Quite a good control of Q’ during ramp and snapback (+-2 units) A measurement with slower ramp start could maybe gives us more

info?? (details to be studied)

Decay @flat-top The correction for B3 decay at flat-top (0.05 units) has been

implemented and the Q’ is well controlled (tune decay not negligible, but corrected with the QFB during the squeeze (if used))