LIU-SPS Orbit Correction ReviewWednesday 16 January 2013

Malika Meddahi

Elena Shaposhnikova

LIU-SPS orbit correction review

LIU-SPS Orbit Correction Review: Aims

Initial motivation: issues with the SPS orbit correction; day-to-day variation of beam orbit at high energy

Aim of review: - Examine the issues and observations - Effects all understood? All measurements done? What else is needed?- Review potential solutions

- Can dogleg non-closure be solved?- Is high energy orbit correction needed?- What can be done to improve the situation?

- Recommendations and proposal for the baseline in MTP

Main subjects discussed

• SPS injection orbit

• High energy orbit

• SPS extraction orbit

• Measurements in 2013

LIU-SPS Orbit Correction Review: Contributions

SPS injection orbit

- Summary

- The injection dogleg is optimised for the Q26 optics while still allowing proper Q20 optics orbit correction at injection energy.

- Orbit correction will be improved at high energy after LS1 thanks to coil reconfiguration of the corrector MDHD.11832.

- Due to possible Q20 limitations for ion injection (and for other areas, as RF noise and transition crossing), the benefits of using the Q20 optics for ions should be revised.

- Removal of dogleg is not recommended (useful for non-LHC beams) and not really needed. The dogleg introduces only static error.

SPS injection orbit

- Recommendation:

- No drastic changes are requested for the SPS injection orbit. Its performance is adequate, still using the Q26 MKP voltage and Q20 residual correction done using the calculated YASP corrector kick on the measured orbit.

- Follow-up / Actions:- Check that the higher beam position on the TIDV beam dump is not

an issue – Francesco Velotti - Done

- Upgrade MDHD.11832 during LS1- Jérémie Bauche

- If MDHD.11832 used then interlocking required - Jörg Wenninger – Verena Kain

- Revise the benefits of using the Q20 optics for ions – LIU-SPS team (Elena’s beam dynamics working group)

High energy SPS orbit

- Summary (1/2)• The quadrupole displacement is first established for orbit correction of non-LHC

beams (Q26 optics) and then the effect is checked for the LHC beam. Displaced quadrupoles give smaller orbit distortion/correction effect for the Q20 optics. The rms orbit is larger for the LHC beam by approximately a factor 2 due to different fractional tune.

• Yet-improved YASP with simultaneous minimisation of rms orbits in two different cycles with Q20 and Q26 should be developed.

• The LHC beam tune was optimised by minimising beam losses due to e-cloud in 2007, this value can be now reconsidered.

• The SPS orbit variation leads to trajectory drift at LHC injection and requires regular steering of the transfer lines ( weekly to daily ). The SPS orbit variations measured with the Q20 optics on the longer scale (weeks) were even in the opposite direction; no systematic measurements were done in the Q26 optics.

• The MSE effect is faster and leads to shot-by-shot variations. Slow drift could be corrected, but most difficulty comes from combination of these two effects which may lead to false steering. It is very important to reduce the effect of the MSE.

High energy SPS orbit

- Summary (2/2)• The need to changing the scraper jaw position with respect to the beam position

was recently traced to a possible drift of the system offset. Therefore, it can be treated separately from the orbit issue.

• A few identified HW nonconformities (shims, groundings) may lead to problems with orbit correction but less probably to their drift with time. Different improvements are planned during the LS1.

High energy SPS orbit

- Recommendation:

- A strategy has to be developed and implemented to minimise the rms orbits of both Q20 and Q26 (on two different cycles) at the same time - Yannis Papaphilippou - Jörg Wenninger

- Follow-up / Actions:- Continue the measurements and improvements on the MSE – Gilles

Le Godec- Propose alternative (long-term) solutions for powering the MSE –

Gilles le Godec- Install the sun glass BLMs in the SPS-to-LHC injection areas – Bernd

Dehning- Correct the offset drift of the scraper system during LS1 - EN/STI- Remove the equipment bad earth connections during LS1 - TE/VSC - Investigate the source of the measured dB/dt kick at position 3.26

during LS1- Jérémie Bauche

SPS extraction orbit

- Summary:- Using the reference orbit at high energy for automatic correction of

beam position and slope (instead of steering the TLs) would be the ideal solution. This can probably be done with the help of existing interlocked extraction bumpers in LSS4 and LSS6.

- This strategy would add additional constraints on the BPM precision and the bumper interlock system.

- The operational risks would have to be assessed. Simulations are needed to define the best strategy.

SPS extraction orbit

- Recommendation:

- There is no further action needed to correct the dogleg from orbit leakage or to reduce the Q20 orbit amplitude at extraction. Stability is more the issue than amplitude.

- However, if 4% horizontal emittance dilution from dispersion (TI2) is not accepted, it can be improved by correcting the average SPS orbit. A corrected orbit would also make scraping easier and more stable, and reduce the time needed for LHC setting up.

- Follow-up / Actions:

- Simulation to be done in order to define the best SPS extraction orbit correction strategy. In particular, investigate possibilities of correcting SPS orbit at extraction, e.g. via feedback system, using strong extraction bumpers or CODs, to improve stability and reduce time needed by LHC for TL steering– Eliana Gianfelice , Verena Kain, Karel Cornelis

Additional SPS measurements

- Recommendation:

- Perform additional measurements for understanding the SPS orbit behaviour at flat top

- Orbit at flat top in Q26 optics fast ramp cycle - For comparison with Q20- For testing a virtual correction in both optics at flat top using quad

alignments- Dispersion at flat top in Q26 optics fast ramp cycle

- To compare with Q20 and to see if it fits into the picture

- Follow-up / Actions:

- Summarise the outcomes of the measurements performed in 2013 – Hannes Bartosik