HiLumi LHC FP7 High Luminosity Large Hadron Collider Design Study - PDF document

CERN-ACC-SLIDES-2014-0069 HiLumi LHC FP7 High Luminosity Large Hadron Collider Design Study Presentation Recommendations (from Collective Effects Considerations) for the LHC 2015 Run M´ etral, E (CERN) 25 March 2014 The HiLumi LHC Design Study is included in the High Luminosity LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404. This work is part of HiLumi LHC Work Package 2: Accelerator Physics & Performance . The electronic version of this HiLumi LHC Publication is available via the HiLumi LHC web site <http://hilumilhc.web.cern.ch> or on the CERN Document Server at the following URL: <http://cds.cern.ch/search?p=CERN-ACC-SLIDES-2014-0069> CERN-ACC-SLIDES-2014-0069

RECOMMENDATIONS (FROM COLLECTIVE EFFECTS CONSIDERATIONS) FOR THE LHC 2015 RUN Elias Métral for the HSC section and collaborators (many thanks!)  Reminder of the recommendations for 2012  Experience from 2012  Recommendations for 2015 § Plan A § Plan B Elias Métral, LBOC, 25/03/2014 /19 1

RECOMMENDED VALUES FOR 2012 VS. ONES OF 2011 Minimizes the amount of octupoles needed and better for beam lifetime Used at the end of 2011 Proposed value for 2012 Chromaticities ~ + 2 ~ + 1 ( ≥ 0, as low as possible) Octupoles’s current [A]: 200 ~ 450 IoctD = - IoctF Rms bunch length [cm] (4- 9 (1.2) ~ 10 (~ 1.35) sigma bunch length [ns]) As the complex tune + reduced ADT gain shift with the tight After we reached the same (as much as possible collimators’ settings performance as last year to avoid unnecessary will be ~ 2.3 times with the same bunch length noise) higher (for RF heating reason with MKI mainly) Elias Métral, LBOC, 25/03/2014 /19 2

EXPERIENCE FROM 2012 (1/9) Measurements WHY? EOSI could not be Led to the decision cured until end of to change the sign of the Run I the octupoles => Instability at the End-Of-Squeeze => Instability in Adjust “MYC” = LOF > 0 as of 07/08/12 (fill # 2926) with ~ 500 A + high chroma (~ 15-20) + higher damper gain in the vertical plane (~ 50 turns) Elias Métral, LBOC, 25/03/2014 /19 3

EXPERIENCE FROM 2012 (2/9)  Why beam instabilities? The beam (some bunches) can cross regions of reduced (minimum) Landau damping area due to the interplay between the Landau octupoles (sign important) and BBLR and/or BBHO => Several strategies possible 1) Try and avoid the regions of reduced Landau damping area => Led to the idea to change the sign of the LOF (see StephaneF, LMC#141, 11/07/2012) and use LOF > 0 2) Try and go as fast as possible through critical areas => Led to the idea to improve the collision process (see XavierB, LMC#146, 29/08/2012). Can we do more? 3) Try and increase the instability rise-time => Optimization of the collimators positions (see R. Bruce, LBOC, 25/02/14) & materials (long term) and optics (ongoing) => Optimization of the ADT (bunch-by-bunch, done) and chromaticities (not yet done) Elias Métral, LBOC, 25/03/2014 /19 4

EXPERIENCE FROM 2012 (3/9)  Chromaticity (should) play a significant role in the instabilities - 50 ns - 1.7E11 p/b - No Landau - H-plane  Instability rise-time ~ 1.4 s - 50 turns ADT Elias Métral, LBOC, 25/03/2014 /19 5

EXPERIENCE FROM 2012 (4/9) - 25 ns - 1.7E11 p/b - No Landau - H-plane  Instability rise-time ~ 1.4 s - 50 turns ADT Elias Métral, LBOC, 25/03/2014 /19 6

EXPERIENCE FROM 2012 (5/9)  Reminder on AlexeyB’s past results § Old ADT § New (bbb – flat gain) ADT damper gain 1.4  50 turns Q’ Chroma. of ~ 2 units good again … Elias Métral, LBOC, 25/03/2014 /19 7 7

EXPERIENCE FROM 2012 (6/9) What were the exact / real values? Elias Métral, LBOC, 25/03/2014 /19 8 8

EXPERIENCE FROM 2012 (7/9)  Effects on chromaticity => … + Landau octupoles + BB Measurements Simulations => A good measurement and control of the (real, total) chromaticities will be needed to achieve the highest performance in the LHC Elias Métral, LBOC, 25/03/2014 /19 9

EXPERIENCE FROM 2012 (8/9)  Some more detail about the change of the LOF polarity End of squeeze Similar situation for the most critical cases => - Im ( Δ Q) This change alone could not (and did not) solve the EOSI Re ( Δ Q) Elias Métral, LBOC, 25/03/2014 /19 10

EXPERIENCE FROM 2012 (9/9) Adjust Better here => This change should improve the situation in Adjust (depends also on the instability rise time and time spent there) Elias Métral, LBOC, 25/03/2014 /19 11

RECOMMENDATIONS FOR 2015 (1/8)  There are 3 main phases in the LHC currently (without e-cloud!) 1) 1-beam regime 2) 2-beam regime through BBLR (during the squeeze) 3) 2-beam regime through BBHO (& BBLR) 1) 1-beam regime § LOF < 0 produces the largest area of Landau damping § Opening of collimators and low chromaticity minimize the amount of LOF needed § Some cases in 2012 where only ~ - 20 A in LOF sufficient 2) 2-beam regime through BBLR (during the squeeze) § Depends critically on beam and machine parameters § Leads to variations between the different bunches § Where we had the main pb in 2012 and the instability could not be cured Elias Métral, LBOC, 25/03/2014 /19 12

RECOMMENDATIONS FOR 2015 (2/8) 3) 2-beam regime through BBHO (& BBLR) § BBHO produces the largest source of Landau damping § OK once in HO and the impedance of collimators could even be increased there (by putting the collimators closer to the beam after HO) Elias Métral, LBOC, 25/03/2014 /19 13

RECOMMENDATIONS FOR 2015 (3/8)  The proposed strategy (PLAN A) is to maximize the LHC performance (to reach the highest brightnesses): Collide and squeeze as already proposed / discussed in the past => Go directly from 1-beam regime to BBHO-regime and have the BBLR-regime afterwards, i.e. replace sequence 1-2-3 by 1-3-2 To be decided after MDs => Maybe safer to start with the 2012 high chromas (~ 15-20 units) => Proposition: 1) LOF < 0 and low chromaticities (~ 1-2 units) IF controllable 2) Squeeze until β * ≈ 3m (to have no BBLR => Works also if emittance 2 times larger) 3) Collide (as fast as possible) with the collimators opened as much as possible 4) Continue the squeeze until the required β * γ β * d drift ≈ ϑ Fullc . a . ε norm Elias Métral, LBOC, 25/03/2014 /19 14