Minutes of the HL-LHC WP2 Task 2.4
2nd (EVO) meeting on Wednesday 13/06/2012 (10:30-12:30 max, 6/R-018)
Task 2.4 members: Alexey Burov (AB), Alessandro Drago (AD), Alessandro Gallo (AG), Andrea Mostacci (AM), Alessandro Vivoli (AV), Benoit Salvant (BS), Bruno Spataro (BrunoS), David Alesini (DA), Deepa Angal-kalinin (DAK), Elias Metral (EM), Elena Shaposhnikova (ES), Fabio Marcellini (FM), Fritz Caspers (FC), Frank Zimmermann (FZ), Giovanni Rumolo (GR), Hugo Alistair Day (HD), John Jowett (JJ), Luigi Palumbo (LP), Mauro Migliorati (MM), Michaela Schaumann (MS), Michel Martini (MichelM), Mikhail Zobov (MZ), Nicolas Mounet (NM), Oliver Boine-Frankenheim (OBF), Olga Zagorodnova (OZ), Rainer Wanzenberg (RW), Uwe Niedermayer (UN), Wolfgang Hofle (WH).
Present/Excused: AB, AD, AG, AM, AV, BS, BrunoS, DA, DAK, EM, ES, FM, FC, FZ, GR, HD, JJ, LP, MM, MS, MichelM, MZ, NM, OBF, OZ, RW, UN, WH => Someone else (I forgot and did not correctly wrote all the names of the present people)?
1) Comments on the last minutes + Actions
- Any comment? No.
- Information from MZ => Presentation he gave at the ECLOUD12 Workshop dedicated to the e-cloud suppression with clearing electrodes at DAFNE: http://agenda.infn.it/getFile.py/access?contribId=47&sessionId=10&resId=0&materialId=slides&confId=4303 => To be presented at the next meeting?
- For those interested, here is the talk I gave at IPAC12 discussing collective effects in the LHC (and its injectors): http://emetral.web.cern.ch/emetral/THYB03_Talk.pdf.
- LHC MDs next week => I know that MZ will be there. Other people plan to go. Did you contact NM or ES?
2) Some IBS studies for the current LHC, nominal LHC and HL-LHC and set-up of a benchmarking case with all the IBS contributors (Michaela Schaumann with JJ): pdf
- MichaelaS presented IBS simulation results for protons for:
- LHC in 2012 => Using the CTE (Collider Time Evolution) program (details on this program given in the talk and back-up slides => IBS effects simulated but no Beam-Beam). Results published in CERN-ATS-Note-2012-044 PERF.
- HL-LHC => Using MADX based on ATS optics.
- Benchmark case proposal (for all the people who want to study IBS effects).
- LHC in 2012:
- At injection:
- Loss mechanisms = debunching (particles leave bucket) and then hit the physical aperture.
- Highest losses but smaller transverse and longitudinal emittance blow up for bunches with larger initial bunch length (1.5ns).
- Blow-up and losses increase with smaller initial emittances.
- The high particle losses of the blown-up bunches decrease the expected luminosity much more, even if their emittance blow-up is slower
=> A compromise for the blow-up of the longitudinal emittance has to be found, to optimize the initial luminosity (and luminosity lifetime later).
- Physics (@ 4 TeV):
- Loss mechanisms = Sum of debunching and luminosity losses.
- Significant differences in debunching losses: they become more important for greater bunch lengths.
- Total losses dominated by luminosity burn-off.
- Smaller initial transverse emittances lose more and grow faster.
- Small initial bunch length grow faster.
- HL-LHC:
- HL-LHC beam parameters from https://espace.cern.ch/HiLumi/WP2/task4/SitePages/Home.aspx + collisions with round beams @ 7 TeV:
- betastar = 0.1 m.
- 1/2 x-angle = 290 microrad (IP1&5).
- FLAT MACHINE = with neither x-angles nor bumps.
- RF voltage = 16 MV @ 400 MHz. For the reduced bunch length case with 25 ns spacing and additional RF system with 24 MV @ 800 MHz is necessary.
- ATS version of the nominal LHC is used for the analysis.
- ATS optics:
- 31 Optics files with betastar values from 11m to 0.1m.
- The squeeze to smaller betastar creates high -values in the arcs around IP1&5.
- Increasing the beta-function in arcs starts for betastar <= 0.4 m.
=> IBS studies made for different betastar and different beam parameters.
- At injection:
- 1 eV longitudinal emittance.
=> Growth rates increase with increasing intensity and decreasing transverse emittance.
- The 3 IBS growth rates (l, x and y) were obtained for both beams considered (25 ns and 50 ns). The worst case is for the 50 ns beam with 3.5E11 p/b, 3 microm, 1 eVs => 8.06 h for l, 9.70 h for x and nothing in y.
- Physics @ 7 TeV:
- IBS growth rates vs. betastar:
- l growth rate improves with smaller betastar.
- x growth rate increases with betastar smaller than ~ 40 cm.
- Local contributions of the IBS growth:
- l: cumulative sum increases approximately linearly.
- x: local growth rates are increased for the high-beta regions in the arcs around IP1&5, while the contribution of the straight sections is almost zero, due to the small dispersion.
- y: growth very small and negative (damping).
- Conclusion and future plans:
- Stronger IBS effects for the beam parameters of the 50 ns spacing (as the growth rates increase with increasing intensity and decreasing transverse emittance).
- IBS growth rates are higher at injection due to the smaller longitudinal emittance.
- Throughout the squeeze to low betastar with the ATS optics, the l IBS growth rate improves by ~ 20%, whereas the h IBS growth rate increases by ~ 20% => Goes in the wrong way for the luminosity as it is better to have the smallest transverse emittance growth and allow maybe a bunch length increase.
- The IBS growth times @ 7 TeV for betastar = 10 cm in a flat machine (with MADX):
- 25 ns (2.2E11 p/b, 2.5 microm, 7.5 cm):
- l growth-time: 21.6 h.
- x growth-time: 16.7 h.
- y growth-time: Nothing.
- 50 ns (3.5E11 p/b, 3.0 microm, 7.5 cm):
- l growth-time: 17.0 h.
- x growth-time: 15.5 h.
- y growth-time: Nothing.
- Note: y IBS growth rate very small and negative (damping) as calculations done for a flat machine => If x-angle and vertical dispersion is introduced, this behaviour may change!
- Plans for the future:
- Simulations with CTE for ATS optics.
- Calculations and Simulations based on the SLHC optics (SLHCV3.1b): IBS growth rates at injection and in physics.
- Redo the calculations with MADX shown in this presentation with bumps and crossing angles in the machine (CTE does not use this information in the IBS calculations).
- Benchmark case proposal:
- Nominal optics V6.503.
- 2.5 microm transverse emittance.
- 1.6E11 p/b.
- 1.35 ns (=10.1 cm) rms bunch length.
- betastar = (0.6, 3, 0.6, 3) m for IP1,2,5,8.
- 1/2 x-angle = 142 microrad.
=> Results:
- l growth-time: 23.8 h (with CTE) and 27.7 h (with MADX).
- x growth-time: 30.1 h (with CTE) and 29.3 h (with MADX).
- y growth-time: -2.98E5 h (with CTE) and 2.43E3 h (with MADX).
- Many plots of the beam evolution...
3) CMS chamber (RW): ppt
- RainerW made a first comparison between the old (see LHC project Note 418) and new geometry proposed (with a smaller radius), looking at the loss and kick parameters. With the shortest bunch length which we have to consider (4 cm) the RF heating would be significantly increased.
- To be continued and documented.
4) Actions to be taken for the next meeting
- Old actions.
5) Miscellaneous
- The next (3rd) meeting (initially foreseen for 27/06/12 but then postponed) will finally take place in 05/09/2012 between 10:30 and 12:30 in room 6-R-018 => Agenda:
1) Operating Experience with Electron Cloud Clearing Electrodes at DAFNE (MZ, Ecloud12 talk).
2) Negative mass effect in nonlinear oscillatory system and its influence on stability of coherent betatron oscillations.
3) Relevant MD results and current LHC performance / issues (EM).
- See preliminary agendas for the next meetings.
Minutes by E. Metral, 03/08/2012.