Cleaning performance of LHC collimation system during the energy ramp

1. Cleaning performance of LHC collimation system during the energy ramp Elena Quaranta on behalf of the collimation team

2. Outline • Motivation of the study • SixTrack simulation during the ramp • General simulation setup • Energy and collimator setting changing • Collimator positions changing only • Energy changing only • Comparison of simulated cases • Measurement in the LHC (Nov. 2012) • Betatron loss maps during the ramp • SixTrackvs LHC measurements • Summary

3. Motivation of the study • Betatron cleaning performance of the collimation system deeply investigated so far at injection () and top energy () • Need of a better knowledge of the collimator efficiency during the energy ramp • Benchmark energy dependence of the cleaning inefficiency in SixTrack simulations Foresee collimator performance expected at higher energies for future configurations (e.g: after LS1)

4. SixTrack Simulation during the ramp Elena Quaranta

5. General simulation setup • 8 energies between and considered • particles tracked for 200 turns • Mathematicascript implemented to automatically generate the SixTrack input for a given energy and speed the procedure up • Simulations performed for B1 and B2 with initial loss in both H and V planes. • Results only for B1 and losses in H plane will be discussed, in order to compare with measurements • 2012 tight settings used for collimator half gap at the end point • Collimator position (in ) during the energy ramp obtained by linear interpolation of values from injection and flat top

6. Energy and Collimator Setting changing

7. Energy and Collimator Setting changing 1 TeV 450 GeV 4 TeV 2 TeV

8. Energy and Collimator Setting changing • Different factors may influence : • Impact parameter • Particle energy • Collimator positions relative to aperture Which role do these aspects play in determining the performance of the collimation system? How do they affect ?

9. Energy and Collimator Setting changing - Impact parameter modified - • Impact parameter changing Increasing the smearing of the halo in order to have at the same average impact parameter as at injection No significant modifications! • Separate simulations performed by varying only the energy or the position of the jaws to isolate the effects of the energy dependence of the scattering and the collimator movements with respect to the aperture

10. Collimator positions changing only • Energy kept constant at • Impact parameter at (value at ) • Collimators moved like in normal ramp(same position in that should have at equivalent energy in the ramp) Energy constant Coulomb scattering physics unchanged but… Collimators moving closer to beam center Scattering angles not enough to make particle reach the aperture so… decreases

11. Energy changing only • Energy increasing like in a normal ramp • Collimator half gap constant at position at • Distance from the beam (in units of ) set by: Multiple Coulomb scattering angle Change in particle-matter interaction inside jaw when energy increases Probability to hit TCSs Protons absorbed in collimation system increases so…

12. Comparison of simulated cases Good superposition of the two effects Statistical error

13. Measurements in the LHC (Nov. 2012) Elena Quaranta

14. Betatron loss maps during the ramp • 4 nominal proton bunches () + 4 pilot bunches () injected • Alternatively B1 and B2 excited in H plane at specified energies by ADT system • Duration of each excitation: 4s 2 TeV - simulated 2 TeV - measured Higher leakage in IR6 (cfr: IPAC13 – R. Bruce)

15. SixTrackvs LHC measurement Measurement Simulation TCP.C6L7.B1 TCSG.4R6.B1 TCTH.4L8.B1 MQ in Q8

16. SixTrackvs LHC measurement - Main issues - • Impossible to directly compare SixTrack results with BLMs data • BLMs signal related to hadronic showers coming out from primary interaction of protons inside the collimator material • Simulation output referred to number of particles absorbed in the jaw • To allow the comparison, SixTrack results re-normalized to the first value of the measurement (already normalized to max loss in TCP.C6L7.B1) in each collimator considered • Almost constant trend in the Dispersion Suppression: worsening of the inefficiency with the energy due to the scattering effect compensated by the tightening of the collimator • Performance in IR6 slightly overestimated by simulation results • Decreasing slope for tertiary collimators in IR8, in agreement with its opening during the ramp • Discontinuity in the line referred to TCTH IR8 around justified by statistical issue

17. Summary • LHC energy ramp simulated by SixTrack, tracking particles at intermediate energies, from injection to flat top • Different cases analyzed to better understand the aspects that mainly affect the collimator performance • Energy and collimator opening counter-acting each other in the determination of the cleaning inefficiency • Nov. 2012 (MD#4): data taken from BLMs signal, after ADT excitation of B1 and B2 in H plane • Very good agreement between simulation results and measurements, within uncertainty from BLMs vs losses of beam protons • Increased confidence in SixTrack ability to reproduce the energy dependence of collimator inefficiency • SixTrack well benchmarked to simulate future LHC scenarios at higher energies

18. Thanks for the attention! Questions? Comments? Remarks?