Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /311 TMCI Intensity Threshold for LHC Bunch(es) in the SPS u Executive summary u TMCI measurements in the SPS in 2002, 2003 and 2007 (and 2008) u TMCI in H and V with the current SPS transverse impedance model u Simulation of the effect of space charge (for coupling between -2 and -3!) u Simulation studies for the nominal LHC bunch Scan in chromaticity Lower gammaT (19 instead of 22.8) u Conclusion and future work u Appendix E. Mtral for the Impedance Team* ( https://impedance.web.cern.ch/impedance/ ) * B. Salvant defended his PHD thesis Impedance Model of the CERN SPS and Aspects of LHC-Bunch Stability recently and gave an A & T seminar on 18/03/2010:ptpt Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /312 EXECUTIVE SUMMARY (1/3) 1)Can we reach ultimate intensity in 1 LHC bunch (~ 1.8E11 p/b) with the present SPS? => The answer is: We should be very close as we did it during an MD in 2006 (see037.pdf). Exact beam parameters should be re-checked!http://cdsweb.cern.ch/record/ /files/ab pdf Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /313 EXECUTIVE SUMMARY (2/3) 2)What is the transverse single-bunch limit with 1 bunch? => For small chromaticity, it should be very close to 1.8E11 p/b => Increasing chromaticity or playing with linear coupling could help to increase the intensity but then one has to be careful with slow losses etc. =>Transverse feedback could also help (studied now by W. Hofle): Interesting paper by M. Karliner and K. Popov (2004), Theory of a feedback to cure transverse mode coupling instability (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TJM-4D97G81- 3&_user=107896&_coverDate=02%2F01%2F2005&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId= &_rerunOrigin=google&_acct=C &_version=1&_urlVersion=0&_userid=107896&md5=953bb510b190e75f77d40bece8f2908d#S ECX1 ) - Refs. to S. Myers work, discussions on issues encountered at LEP - Illustrations are given for VEPP-4 and LEP => A factor 3-5 of intensity increase could be expected with negative chromaticity + resistive feedback! To be studied in detail => Double harmonic RF system?: Simulations are running Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /314 EXECUTIVE SUMMARY (3/3) 3)What is the transverse single-bunch limit with many bunches? => Should be studied in detail as the TMCI threshold could be lower (as mentioned by Elena => See S. Bergs work, => Interplay between impedance and ecloud for TMCI? In practice, we know that we need to have xix ~ and xiy ~ to have stability with nominal LHC beam. Is it only for the TMCI-like instability from ecloud or a combined effect with the vertical impedance? Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /315 TMCI measurements in the SPS in 2002 and 2003 G. Rumolo et al.: pdf pdf Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /316 REMINDER: Nominal LHC beam in the SPS (1/3) Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /317 REMINDER: Nominal LHC beam in the SPS (2/3) ~ 3.6 p at 450 GeV/c (i.e. 4 72 = 288 bunches with ~ 1.24 p/b) In 2006 Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /318 Example of bunch length with nominal (4 72 bunches) beam but low intensity (~ 2.5E13 p) Full (4 ) bunch length [ns/100] V 200MHz [10 4 V] V 800MHz [10 3 V] Beam momentum [GeV/c] Must enter in the LHC 2.5 ns bucket REMINDER: Nominal LHC beam in the SPS (3/3) Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /319 Instability suppressed by increasing the chromaticity TMCI measurements in the SPS in 2003 (1/5) Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 / st trace (in red) = turn 2Last trace = turn 150Every turn shown HeadTail Travelling-wave pattern along the bunch TMCI measurements in the SPS in 2003 (2/5) Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 / st trace (in red) = turn 2Last trace = turn 150Every turn shown TMCI measurements in the SPS in 2003 (3/5) Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 / st trace (in red) = turn 2Last trace = turn 150Every turn shown TMCI measurements in the SPS in 2003 (4/5) Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 / st trace (in red) = turn 2Last trace = turn 150Every turn shown TMCI measurements in the SPS in 2003 (5/5) Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3114 First HEADTAIL simulations (with simplified impedance) 1 st trace = turn 1Last trace = turn 50Every turn shown Flat chamber Travelling-wave pattern along the bunch HeadTail Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3115 Measured picture close to the simulated one Head HEADTAIL SIMULATION MEASUREMENT Tail Head Comparison between simulations and SPS meas. Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3116 TMCI measurements in the SPS in 2007 Stable beam N b [0; 6] & [6.3;7.6] p Unstable beam N b [6; 6.3] p Unstable beam N b > p Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3117 Chosen elements : BPHs (CST 3D simulations) - 96 BPVs (CST 3D simulations) km beam pipe (analytical calculations for a round pipe including indirect space charge, transformed with Yokoya factor) - 20 kickers (situation during 2006 run, analytical calculations with Tsutsui model) - 2 TW 200 MHz cavities (4 sections of 11 cells) without couplers (CST 3D simulations) - 2 TW 200 MHz cavities (5 sections of 11 cells) without couplers (CST 3D simulations) Simulation of the V-TMCI with the current SPS imp. model Additional assumptions: - all impedances lumped in one location - no space charge, no linear coupling, no chromaticity - no amplitude detuning - linear longitudinal restoring force Mode spectrum as a function of bunch current 1 st small instability: Nb= p/b 2 nd large instability: Nb= p/b stableunstablestable unstable Strong damping For beam with smaller long. emittance Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3118 Chosen elements : BPHs (CST 3D simulations) - 96 BPVs (CST 3D simulations) km beam pipe (analytical calculations for a round pipe including indirect space charge, transformed with Yokoya factor) - 20 kickers (situation during 2006 run, analytical calculations with Tsutsui model) - 2 TW 200 MHz cavities (4 sections of 11 cells) without couplers - 2 TW 200 MHz cavities (5 sections of 11 cells) without couplers stable Strong damping Additional assumptions: - all impedances lumped in one location - no space charge, no linear coupling, no chromaticity - no amplitude detuning - linear longitudinal restoring force For beam with smaller long. emittance Simulation of the H-TMCI with the current SPS imp. model Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3119 Reminder: Measured coherent tune shifts vs. intensity over the last years ~ 90% explained by simulations with current impedance model ~ 60% explained by simulations with current impedance model Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3120 Chosen elements : BPHs (CST 3D simulations) - 96 BPVs (CST 3D simulations) km beam pipe (analytical calculations for a round pipe including indirect space charge, transformed with Yokoya factor) - 2 TW 200 MHz cavities (4 sections of 11 cells) without couplers (CST 3D simulations) - 2 TW 200 MHz cavities (5 sections of 11 cells) without couplers (CST 3D simulations) Simulation of the V-TMCI without any kicker Additional assumptions: - all impedances lumped in one location - no space charge, no linear coupling, no chromaticity - no amplitude detuning - linear longitudinal restoring force For beam with smaller long. emittance Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3121 Simulation of the effect of space charge (on BB imp.) => Done for the BB impedance model: The SC effect seems to be small (even if the SC tune shift is much bigger than Qs) =>To be redone with our latest impedance model For beam with smaller long. emittance Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3122 Simulation studies for the ~ nominal LHC bunch (with ~ nominal long. emittance) (1/3) Non linear bucket Vertical plane Initial 0.31 eVs final 0.37 eVs Vrf=2 MV Initial bunch length 1 sigma=0.27 m Final bunch length 1 sigma=0.22 m Threshold = p/b Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3123 Simulation studies for the ~ nominal LHC bunch (with ~ nominal long. emittance) (2/3) Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3124 Non linear bucket Horizontal plane Initial 0.31 eVs final 0.37 eVs Vrf=2 MV Initial bunch length 1 sigma=0.27 m Final bunch length 1 sigma=0.22 m Threshold > p/b Simulation studies for the ~ nominal LHC bunch (with ~ nominal long. emittance) (3/3) Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3125 Threshold = p/b Simulation studies for the ~ nominal LHC bunch (with ~ nominal long. emittance) with xiy> 0 y = 2/26 ~ Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3126 Simulation studies for the ~ nominal LHC bunch (with ~ nominal long. emittance) with xiy< 0 (1/2) y = - 2/26 ~ Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3127 Simulation studies for the ~ nominal LHC bunch (with ~ nominal long. emittance) with xiy< 0 (2/2) Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3128 Simulation studies for the ~ nominal LHC bunch (with ~ nominal long. emittance) => Scan in xiy HEADTAIL sim. Meas. in 2001 (02/PAPERS/WEPRI084.pdf ) 1E10 p/b Beam with smaller long. emittance in the meas.! Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3129 Threshold = p/b Simulation studies for the ~ nominal LHC bunch (with ~ nominal long. emittance) with smaller gammaT (1/2) 19 instead of ~ 22.8 Initial 0.27 eVs Final 0.28 eVs Vrf=2 MV Initial bunch length 1 sigma=0.27 m Final bunch length 1 sigma=0.245 m Non linear bucket Vertical plane Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 / instead of ~ 22.8 Initial 0.27 eVs Final 0.28 eVs Vrf=2 MV Initial bunch length 1 sigma=0.27 m Final bunch length 1 sigma=0.245 m Non linear bucket Horizontal plane Simulation studies for the ~ nominal LHC bunch (with ~ nominal long. emittance) with smaller gammaT (2/2) Threshold > p/b Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3131 Conclusion and future work u The kickers are not the only contributors in the transverse plane! u The impedance model is improved everyday and many checks still need to be performed on the current model + add other equipments (800 MHz, pumping ports, ZS: ongoing) u For the nominal longitudinal emittance (i.e eVs instead of ~ 0.2 eVs), the single-bunch intensity threshold is close to the ultimate (from measurements we did in the past => To be redone this year) u Several possibilities to increase the TMCI intensity threshold: impedance reduction (correct identification before!), increase chromaticity (be careful with slow losses!), linear coupling, increase the slip factor eta, feedback, double harmonic RF? u CAUTION with many bunches: Effect of multi-bunch on the TMCI intensity threshold (as mentioned by Elena) => Was studied in the past by S. Berg: To be looked at in detail Combined effect impedance and ecloud? Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3132 Appendix Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3133 Benchmark between HEADTAIL and MOSES in the case of a Broad-Band resonator impedance Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3134 Effect of (direct) space charge on TMCI (1/2) Example on the case of a BB resonator impedance (considering a coupling between modes 0 and -1) => K.N. Ng and A. Burov, HB1999 workshop, 1999 Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3135 Effect of (direct) space charge on TMCI (2/2) Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3136 Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3137 Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3138 Elias Mtral, SPSU Study Group and Task Force on SPS Upgrade meeting, 25/03/2010 /3139