High Intensity Beams in Existing Accelerators for CN2PY: SPS studies, PS issues E. Shaposhnikova Laguna-LBNO General Meeting CERN, Acknowledgments: T. Bohl, H. Damerau, R. Garoby, S. Gilardoni, B. Goddard, I. Efthymiopoulos 2/10/20121

Present and future SPS performance (in terms of beam power) OperationSPS recordAfter LIU (2020) AimStudy LHCCNGSLHCCNGSLHCpost-CNGS SPS beam energy [GeV] bunch spacing [ns] bunch intensity/ number of bunches SPS beam intensity/ * PS beam intensity/ * PS momentum [GeV/c] PS cycle length [s] /2.4* SPS cycle length [s] /7.2 SPS average current [ μ A] /1.6 SPS power [kW] /622 *Feasibility including operational viability (especially in the PS) remains to be demonstrated 2/10/20122

SPS intensity & limitations to reach 750 kW Beam power of 750 kW corresponds to 7x10 13 total intensity (“ultimate CNGS” intensity) extracted from the SPS every 6 s or to 8.4x10 13 per 7.2 s Two PS batches are injected into the SPS Maximum (record) PS intensity achieved at 14 GeV/c in the past: 3x10 13 in single PSB batch injection => 1.2 s PS cycle 4x10 13 in double PSB batch injection => 2.4 s PS cycle  Maximum (potential) SPS intensity at 14 GeV/c (no losses): – 6x10 13 injected in 1.2 s – 8x10 13 injected in 2.4 s  Maximum SPS intensity at 400 GeV/c with 3 s acceleration time (present), 5% losses (optimistic) and no limitations (unrealistic): – 7.6x10 13 every 7.2 s => 680 kW – doesn’t make sense – 5.7x10 13 every 6.0 s => 610 kW 2/10/20123

CERN-AB PAF 2/10/20124 => No gain with longer SPS cycle for maximum SPS intensity below 7x10 13 (CNGS target limitation) 2.4 s flat bottom (double batch injection from PSB to PS) POT per year [10 19 ] for 200 days of operation with 80% machine availability and beam sharing of 0.45/0.85

Main present limitations for high intensity CNGS-type beam In all machines: – Beam losses leading to radiation issues; already at the limit in PS → present (2012) operation with total intensity of 4x10 13 from the SPS – Losses during CERN intensity record (2004): 2/10/20125

PS limitations for high intensity beams (1/3) (H. Damerau, S. Gilardoni, S. Hancock, R. Steerenberg) Injection losses: – Direct losses due to aperture restrictions at the septum and for the circulating beam  Ongoing: re-design of the injection optics and vacuum chambers to improve aperture  Smaller physical emittances with Linac4 and PSB at increased energy of 2 GeV – Excessive stray radiation on top of injection region  New shielding will be installed during LS1 – Injection region has a difficult accessibility in case of septum failure due to radiation 2/10/20126

PS limitations for high intensity beams (2/3) (H. Damerau, S. Gilardoni, S. Hancock, R. Steerenberg) Extraction losses: – 5-turns extraction (operational today with 2.7x10 13 per PS extraction) CT extraction: intrinsic losses on the entire ring, up to 10% of the circulating beam. – Future HI beam cannot operate with such large losses MTE extraction: 2% losses due to debunched beam, well localized at the extraction septum. – Losses considered too large for extraction septum activation already with current CNGS intensities. Intervention in case of septum failure delayed due to cool-down. – Study ongoing to protect the septum. – 1-turn/fast extraction (operational with 8x10 12 in single bunch, 3x10 13 feasible with 8 bunches) Limited losses (below 2% at 20 GeV/c), if dp/p at extraction is not too large – Excessive stray radiation on top of extraction region  New shielding will be installed during LS1 2/10/20127 Relevant for future CNGS-like beams

PS limitations for high intensity beams (3/3) (H. Damerau, S. Gilardoni, S. Hancock, R. Steerenberg) Longitudinal losses: – Limited RF power at transition crossing (RF-phase jump) and during acceleration – Intensity limited to < 3.5x10 13 (CNGS Run1 experience, 2008) Machine operability – With high absolute losses, more time needed for cooling-down for any intervention. In particular, in case of failure in a very radioactive zone, risk of very long LHC down-time (weeks). – Ageing of materials due to stray radiation – Ageing of the Main Magnets due to radiation in the high-losses zones and limited number of spares. 2/10/20128

SPS limitations for high intensity CNGS-type beam Beam losses due to many different reasons (see below) Longitudinal beam stability (leading to uncontrolled longitudinal emittance blow-up) Maximum available RF power at 200 MHz (750 kW for full ring) and therefore voltage (7.5 MV) due to beam loading Beam induced heating of equipment Large transverse (vertical) emittance at injection Injection below transition No bunch-to-bucket transfer, debunched beam component Transverse damper (LHC beams: 40 MHz bandwidth) 2/10/20129

LHC and CNGS beams in the SPS FT/CNGS beam from PS: – practically debunched beam – 5-turn extraction – no bunch-to-bucket transfer – injection below transition 10 Nominal parameters of two main types of proton beam in the SPS 2/10/2012 high intensity run

LIU-SPS upgrades for LHC beam – can they help for CNGS-type beam? Main difference between the two (LHC and CNGS) beams: – CNGS beam: injection at 14 GeV/c and transition crossing → different beam control (LLRF) – CNGS beam fills whole SPS ring and LHC beam – only half → different requirements for beam power (continuous and pulsed regimes) – bunch spacing → multi-bunch effects (instabilities, heating) CNGS-type beam will profit from planned SPS upgrades: – Upgrade of the 800 MHz RF (2015): 1 → 2 cavities, new FB&FF – Upgrade of the 200 MHz RF (2020) : 4 → 6 cavities, new beam control – Impedance reduction (by 20% for 200 MHz RF , serigraphy of extraction kickers – 2015, + …) – Low γ t (transition energy) optics? – implemented for LHC beam 2/10/201211

LIU (LHC Injectors Upgrade) plans, also beneficial for the CNGS-type beam Linac4 Increase of injection energy in PSB (due to Linac4) Increase of injection energy in PS Replacement of RF system in the PSB Upgrade of FB systems (LLRF) in the PS Increased aperture and reinforced tunnel shielding in PS Improved beam instrumentation in all accelerators and transfer lines 2/10/201212

FT/CNGS acceleration cycle: voltage and power  At the moment maximum available voltage is used due to uncontrolled emittance blow–up during transition crossing - Any voltage reduction leads to beam losses 132/10/2012 RF voltage and bucket areaRF power present limit

Bunch length along the batch for high intensity beam (5.6x10 13 injected, 15% losses) (AB-Note RF, T. Bohl et al.) t=1.315 s t=3.286 s t=1.534 s, γ>γt t=4.163 s 142/10/2012

Possible LLRF improvements in the SPS (identified during high intensity run) Separate capture of each PS batch in the SPS (possible due to large bandwidth of the main 200 MHz TW RF system) would allow voltage capture modulation (0.8 MV increased to 2.5 MV) – optimum for beam loss reduction Variable gain of 1-turn-delay feedback Upgrade of the frequency range of the feed-forward system (below 26 GeV/c)  Will be implemented during the 200 MHz RF upgrade (after LS2, 2020) Use of the 800 MHz RF system during cycle => after LS1, /10/201215

LIU-SPS plans: 200 MHz RF cavities redistribution and power upgrade power: 1.4 MW pulsed each, ~800 kW cw E. Montesinos power: 1.0 MW pulsed each, ~ 800 kW cw 2/10/201216

Voltage for FT/CNGS acceleration cycle  Presently both voltage and power are at the limit: 7.5 MV used after transition crossing (due to uncontrolled longitudinal emittance blow-up)  Significant improvement for CNGS and fast LHC cycle with 6 cavities 4200 bunches spaced by 5 ns RF current 0.73 A - for N = 4.8x10 13 (nominal CNGS) 1.06 A – for N =7x /10/ Total voltage available for acceleration with Pmax=0.7 MW/cavity

Can new SPS optics improve CNGS beam stability (uncontrolled emittance blow-up)? Q20: low transition gamma (γ t =18) (optics: Y. Papaphilippou, H. Bartosik) Increase of slip factor η = 1/γ 2 - 1/γ t 2 above transition in respect to the nominal optics (γ t =22.8) Threshold of longitudinal instability N th ~ |η| Longitudinal instability threshold (single RF) s cales as N th ~ |η| ε 2 /E → less uncontrolled emittance blow-up after transition? But for the same bucket area required RF voltage V rf ~ |η| Slip factor η (~ beam stability) 182/10/2012 transition

Voltage program for FT/CNGS cycle in two optics Q26 – nominal optics (till now) Q20 – low transition gamma (1 week as operational for LHC beam) => Voltage above present limit of 7.5 MV even for 0.4 eVs Now after transition crossing some bunches have emittance > 0.6 eVs 192/10/2012 present limit

Specific studies required for high intensity CNGS-type beam PS: – Loss reduction and related activation – Transition crossing – RF limitations, beam transfer and Multi-Turn Extraction at 4x10 13 p/p – Operational compatibility with different users, spares policy… SPS: – Use of the 800 MHz RF system (Landau cavity) for beam stability – Optimum transition crossing – Need for collimation system for loss localisation – New optics with lower transition energy – Plans: beam studies in 2012 in collaboration with C. Lazaridis, T. Argyropoulos, J. E. Muller, T. Bohl 2/10/201220

Summary After the upgrades foreseen by the LIU project (to be completed by 2020) potentially higher intensity CNGS-type beam can be accelerated in the SPS Total intensity of 7x10 13 in the SPS ring is much higher than what is foreseen for the LHC beams by LIU project, nevertheless improvements should be expected for the CNGS-type beam from LIU upgrades, both in the SPS and its injectors (Linac4, 2 GeV PSB, …) Main limitations for higher intensity are due to beam losses in whole injector chain More studies are required in PS to see present limits and find remedies since CNGS-type beam is more demanding in terms of beam intensity than LHC beam. The new Multi-Turn Ejection scheme must be put into operation in the PS and improved to reduce beam loss in sector 16 (location of dummy septum and septum 16). Present main limitations in the SPS are due to beam losses from multi-bunch effects during transition crossing. Possible improvements to the LLRF have been identified, but they probably will not be implemented before 2018 (together with the 200 MHz RF upgrade which should also help) SPS plans for 2012: studies of high intensity in nominal and Q20 optics with the 800 MHz RF system in the SPS More (exotic) possibilities can be considered in future (injection at higher energy, bunch-to-bucket transfer…) 212/10/2012

Some references Increasing the proton intensity of PS and SPS, R. Cappi (editor) et al., CERN/PS (AE) Report of the High Intensity Protons working group, M. Benedikt et al., CERN-AB OP/RF MTE issues (2nd session of IEFC workshop – March ) RF studies of the high intensity CNGS beam in the SPS, T. Bohl et al., AB-Note-2005 MD Recent intensity increase in the CERN accelerator chain, E. Shaposhnikova et al., Proc. PAC 2005 Analysis of the maximum potential proton flux to CNGS, M. Meddahi, E. Shaposhnikova, CERN-AB SPS upgrade possibilities, E. Shaposhnikova, LHC performance workshop Chamonix 2010 Can the proton injectors meet the HL-LHC requirements after LS2? B. Goddard, LHC performance workshop Chamonix /10/201222