Measurement of the transverse impedance of the TCSPM

Measurement of the transverse impedance of the TCSPM and TCSG collimators S. ANTIPOV, D. AMORIM, N. BIANCACCI, G. MAZZACANO, B. SALVANT

Many thanks to R. Bruce, L. Carver, A. Mereghetti, S. Redaelli, D. Valuch, and LHC-OP 7/28/2017 S. ANTIPOV, TCSPM RESULTS 2

Motivation N. Biancacci, et al. , Impedance Measurements of Low Impedance Collimator, HL-LHC TCC, 30. 03. 2017 7/28/2017 S. ANTIPOV, TCSPM RESULTS 3

TCSPM Collimator 3 stripes of different coatings to simulate different low impedance collimators N. Biancacci, et al. , Impedance Measurements of Low Impedance Collimator, HL-LHC TCC, 30. 03. 2017 7/28/2017 S. ANTIPOV, TCSPM RESULTS 4

Measurement procedure The measurement was carried out on 30/06 -01/07 during MD 1 Two collimators measured: ◦ TCSG. D 4 R 7. B 2 (CFC, orange line) ◦ TCSPM. D 4 R 7. B 2 (three stripes, blue line) Measurement procedure was changed during the MD: improved and treatable results were obtained TCSG full gap TCSPM stripe position D. Amorim 7/28/2017 S. ANTIPOV, TCSPM RESULTS 5

Changing the collimator half-gap from 4. 5 to 20 coll σ “Can we kick faster? ” – B. Salvant 7/28/2017 S. ANTIPOV, TCSPM RESULTS 6

Fitting and compensating the tune drift 1. Mo. Gr bulk Take the tune data, calculated by Sussix ◦ Using D. Amorim’s Python script 2. Separate the data into two subsets based on collimator position: ‘UP’ and ‘DOWN’ 3. For each subset subtract the average ◦ That leaves only the tune drift + random errors 4. Unify the datasets, and perform a polynomial fit 5. Apply the correction to both data subsets 7/28/2017 S. ANTIPOV, TCSPM RESULTS 7

Can reduce the uncertainty of the tune to 10 -5 Mo. Gr bulk ± 1 σ 7/28/2017 S. ANTIPOV, TCSPM RESULTS 8

Tune shifts from all stripes are clearly visible 7/28/2017 S. ANTIPOV, TCSPM RESULTS 9

Experimental data agrees with the model The model includes both RW and geometric contribution Model tune shifts (line) computed using the actual collimator setting, used during the MD 7/28/2017 S. ANTIPOV, TCSPM RESULTS 10

6. 0 sigma • Significant decrease of tune shift for Mo coating with respect to CFC • No major difference between Mo. Gr and Ti. N 7/28/2017 S. ANTIPOV, TCSPM RESULTS 11

4. 5 sigma • Significant decrease of tune shift for Mo coating with respect to CFC • No major difference between Mo. Gr and Ti. N 7/28/2017 S. ANTIPOV, TCSPM RESULTS 12

4. 0 sigma • Significant decrease of tune shift for Mo coating with respect to CFC • No major difference between Mo. Gr and Ti. N 7/28/2017 S. ANTIPOV, TCSPM RESULTS 13

3. 5 sigma • Significant decrease of tune shift for Mo coating with respect to CFC • Accounting for 20% beam loss before the measurement • See a small difference between Mo. Gr and Ti. N 7/28/2017 S. ANTIPOV, TCSPM RESULTS 14

Tune shift (x 10 -5) Material 3. 5 s 4. 0 s 4. 5 s 6. 0 s CFC 26. 8 ± 1. 6 16. 7 ± 1. 8 11. 3 ± 1. 6 7. 2 ± 1. 9 Mo. Gr 12. 7 ± 2. 2 8. 2 ± 1. 3 5. 4 ± 1. 8 3. 6 ± 1. 8 Ti. N 10. 2 ± 2. 8 7. 7 ± 1. 9 5. 4 ± 2. 5 3. 1 ± 1. 7 Mo 9. 5 ± 2. 0 5. 6 ± 1. 9 3. 5 ± 1. 8 2. 7 ± 1. 9 7/28/2017 S. ANTIPOV, TCSPM RESULTS 15

Two instabilities observed in B 2 during the test Fill Local time Plane Nb [1011] Q’ εn, x/y [um] m |l| τ [s] D [turns] Ioct [A] σb [m] Notes 5895 00: 23 H 1. 2 10/10 ~2. 5/~2. 5 0 2 9. 4 ? 376 0. 081 TCSPM algnement tests 5895 04: 25 H 0. 8 12. 7/7 2. 5/2 0 ? 12. 7 ? 276 0. 076 TCSG closing 7/28/2017 S. ANTIPOV, TCSPM RESULTS 16

Instability 1 Amplitude, a. u. Beam 2 went unstable in the H plane when the Q’ was reduced from 15 to ~10 0 20 Collimation σ 7/28/2017 S. ANTIPOV, TCSPM RESULTS N. Biancacci 17

Instability 1 The octupole current was above threshold for Gaussian beam Stability prediction for Gaussian beam is ~30 % lower than inferred from the observation 1. 2 x 1011 ppb, εn = 2. 0 μm, damper = 100 turn 7/28/2017 S. ANTIPOV, TCSPM RESULTS 18

Instability 2 Amplitude, a. u. TCSG moved below 4 σ N. Biancacci 0 20 Collimation σ 7/28/2017 S. ANTIPOV, TCSPM RESULTS 19

Instability 2 THE BEAM WAS EXPECTED TO GO UNSTABLE BELOW 4 SIGMA – WENT UNSTABLE AT 3. 9 Pre-MD estimates with 2016 coll. settings SIMULATION WITH THE ACTUAL COLLIMATOR SETTINGS CONFIRMS THE OBSERVATION Q’ setting 0. 8 x 1011 ppb, εn = 2. 5 μm, damper = 100 turn S. Antipov, et al. , Tune shift and stability predictions for the TCSPM MD, ABP-HSC Meeting, 08. 05. 17 7/28/2017 S. ANTIPOV, TCSPM RESULTS 20

Conclusion During the MD we were able to measure individual tunes at the level of or better (!) than 10 -5 The measured tune shifts agree with the predictions of the impedance model ◦ The observed instabilities in B 2 fit in the current model as well A clear reduction of the tune shifts can be seen with Mo, Mo. Gr, and Ti. N ◦ Ti. N and Mo. Gr are similar within the experimental uncertainties Measurements of single collimator tune shifts can be used to assess the impedances of individual collimators ◦ In particular, the "magic subset" to be selected for pre-HLLHC Results being checked with wire measurements (N. Biancacci and G. Mazzacano) 7/28/2017 S. ANTIPOV, TCSPM RESULTS 21

Backup 7/28/2017 S. ANTIPOV, TCSPM RESULTS 22

Individual tunes can be measured at the 10 -5 level Collimator Tune at 4. 5 σ Tune at 20 σ TCSG 0. 293618 ± 1. 1 x 10 -5 0. 293730 ± 1. 1 x 10 -5 TCSPM: Mo. Gr 0. 293619 ± 1. 8 x 10 -5 0. 293673 ± 1. 7 x 10 -5 TCSPM: Ti. N 0. 293663 ± 1. 2 x 10 -5 0. 293717 ± 1. 4 x 10 -5 TCSPM: Mo 0. 293657 ± 1. 3 x 10 -5 0. 293692 ± 1. 2 x 10 -5 7/28/2017 S. ANTIPOV, TCSPM RESULTS 23

Instability 1: Spectrogram N. Biancacci 7/28/2017 S. ANTIPOV, TCSPM RESULTS 24

Instability 1 Amplitude, a. u. Beam 2 went unstable in the H plane when the Q’ was reduced from 15 to ~10 7/28/2017 S. ANTIPOV, TCSPM RESULTS N. Biancacci 25

Instability 1 Beam 2 went unstable in the H plane when the Q’ was reduced from 15 to ~10 No exact measurement of beam emittance, only an estimate available 1. 2 x 1011 ppb, εn = 2. 5 μm, damper = 100 turn 7/28/2017 1. 2 x 1011 ppb, εn = 2. 0 μm, damper = 100 turn S. ANTIPOV, TCSPM RESULTS 26

Instability 2: Spectrogram 7/28/2017 S. ANTIPOV, TCSPM RESULTS 27

Two instabilities observed in B 1 when gradually lowering Q’ to 0 B 1 was kept intact during the impedance measurement test We lowered Q’ to try and observe the destabilizing effect of resistive transverse damper Fill Local time Plane Nb [1011] Q’ 5895 06: 01 H 1. 3 5895 06: 16 H 0. 8 7/28/2017 εn, x/y [um] m |l| τ [s] D [turns] Ioct [A] σb [m] Notes 5/5? 3. 2/2. 7 0 1 4. 4 ? 376 0. 075 After modulation 0/0 0 2 14. 7 ? 150 0. 075 2. 5/1. 7 S. ANTIPOV, TCSPM RESULTS 28