SPS scrubbing run in 2014 H. Bartosik, G. Iadarola, G. Rumolo LHC Performance Workshop (Chamonix 2014), 22/9/2014 Many thanks to: G. Arduini, T. Argyropoulos, T. Bohl, K. Cornelis, H. Damerau, J. Esteban Müller, B. Goddard, S. Hancock, W. Höfle, L. Kopylov, H. Neupert, Y. Papaphilippou, G. Papotti, E. Shaposhnikova, M. Taborelli and the SPS operator crew

Outline Introduction The 2014 SPS scrubbing run o Possible cycles o Scrubbing stages o Possible supercycle composition The doublet scrubbing beam o Motivation o Production scheme o Experience in MDs Scrubbing preparation o Beams from the PS o SPS setup o Measurements

Outline Introduction The 2014 SPS scrubbing run o Possible cycles o Scrubbing stages o Possible supercycle composition The doublet scrubbing beam o Motivation o Production scheme o Experience in MDs Scrubbing preparation o Beams from the PS o SPS setup o Measurements

Electron cloud in the SPS and scrubbing Strong limitation due to e-cloud in the past →Instabilities at injection + incoherent effects →Emittance blow-up along the batch →High chromaticity needed for beam stability →Pressure rise around the machine Situation improved gradually due to scrubbing →Requires days of dedicated running in high electron cloud conditions →Secondary Electron Yield reduction by the e-cloud itself Scrubbing runs since 2002 →Performed at 26 GeV in cycling mode (~40 s cycle length) →Typically limited by heating and/or outgassing →~1-2 weeks periods SPS scrubbing history 43.2 s 2002 (14d) 2003 (8d) 2004 (10d) 2006 (5d) 2007 (7d) 2008 (2.5d) 2012 (5d) 2009 (1.5d) Shutdown 400% 2000 (48 b x μm

SPS scrubbing run 2014 Goals for 2014: Qualify the loss of conditioning due to LS1 Recover 2012 performance with 25 ns beams Quantify amount of beam/time needed Test “doublet” scrubbing beam  to be used in the LHC in 2015 Qualification criterion  beam quality measurements Ideally, achieve by the end of the allocated scrubbing time: 25 ns, 4 batches, up to 1.3e11ppb, emittances below nominal, no blowup along the train as in 2012 basis for LIU strategy on e-cloud mitigation – coating vs scrubbing

From 2014 injector schedule (current version)

Scrubbing originally foreseen in two consecutive weeks (W39-40), before the start-up of the NA physics. Then split between Weeks 39 and 45  Finally spread over Week 45 plus an additional two-day mini-block in Week 50 Several reasons for splitting the scrubbing run into two blocks (requested by LIU-SPS): Gives time to analyze the first block’s results and adapt accordingly Untangling scrubbing from the machine commissioning, NA setup and vacuum conditioning of all the newly-installed or vented equipment Allows setting up scrubbing beams before the 2nd scrubbing block ⇒ the “doublet” beam – its potential to scrub the SPS can be explored already in 2014 (also in view of LHC scrubbing in 2015)

Pre-scrubbing cycles Over weeks 41 – 44 some experience will be already gained during the available parallel and dedicated MD time  Both single bunch and 25 ns beam (1 batch) on short flat bottom cycle (6BP) should be already set up  Work on recovery performance for nominal 25 ns beam might have already started (with the consequent scrubbing) 6 BPs (7.2 s) Inj. Dump

Scrubbing cycles We will need to accumulate dose and monitor the evolution of beam parameters for both coherent and incoherent effects  4 or more batches circulating in the machine at 26 GeV  Acceleration to 450 GeV should be fully set up and used for scrubbing qualification 18 BPs (21.6 s) 33 BPs (39.6 s) Inj. Dump Inj. Dump Inj. 19 BPs (22.8 s)

Planning (to be steered on the fly) MondayTuesdayWednesdayThursdayFriday SaturdaySunday Intensity ramp up at 26 GeV on intermediate flat bottom cycle (21.6 s) First scrubbing block Intensity ramp up at 26 GeV with 25 ns beams (ideally up to 5 injections – try to push bunch intensity up to 1.5x10 11 p/b?) Inj. Dump Possible supercycle (to be coordinated with physics in the PS complex) Inj. Week 45

Planning (to be steered on the fly) MondayTuesdayWednesdayThursdayFriday SaturdaySunday Intensity ramp up at 26 GeV on intermediate flat bottom cycle (21.6 s) First scrubbing block Intensity ramp up at 26 GeV with 25 ns beams (ideally up to 5 injections – try to push bunch intensity up to 1.5x10 11 p/b?) Study residual electron cloud effects on beam lifetime and quality for nominal beam (e.g. emittance growth, bunch shortening over long flat bottom) while gradually lowering vertical chromaticity setting for stability Inj. Dump Inj. Possible supercycle Studies on long flat bottom cycle (39.6 s) Week 45

Planning (to be steered on the fly) MondayTuesdayWednesdayThursdayFriday SaturdaySunday Intensity ramp up at 26 GeV on intermediate flat bottom cycle (21.6 s) First scrubbing block Intensity ramp up at 26 GeV with 25 ns beams (ideally up to 5 injections – try to push bunch intensity up to 1.5x10 11 p/b?) Study residual electron cloud effects on beam lifetime and quality for nominal beam (e.g. emittance growth, bunch shortening over long flat bottom) while gradually lowering vertical chromaticity setting for stability Acceleration and scrubbing qualification Studies on long flat bottom cycle (39.6 s) Scrubbing qualification (25 ns std and BCMS, up to 450 GeV) Possible supercycle for scrubbing + qualification Week 45

Planning (to be steered on the fly) MondayTuesday Second scrubbing block At this stage doublet beam could be ready including acceleration The goal is to accumulate the largest possible electron dose on the beam chambers The results of the tests with the doublet beam will be important for the LHC scrubbing in 2015 Wednesday Week 50 Possible supercycle Scrubbing with doublet (possibly with acceleration) Dedicated MD (scrubbing) 18 BPs (21.6 s) Inj. Dump

Outline Introduction The 2014 SPS scrubbing run o Possible cycles o Scrubbing stages o Possible supercycle composition The doublet scrubbing beam o Motivation o Production scheme o Experience in MDs Scrubbing preparation o Beams from the PS o SPS setup o Measurements

“Doublet” scrubbing beam: introduction Scrubbing with 25 ns beam allowed to lower the SEY of the dipole chambers well below the multipacting threshold for 50 ns  e-cloud free operation with 50 ns beams  Can we go to lower bunch spacing to scrub for 25 ns operation? Due to RF limitations in the PS it is impossible to inject bunch-to-bucket into the SPS with spacing shorter than 25 ns An alternative is to inject long bunches into the SPS and capturing each bunch in two neighboring buckets obtaining a (5+20) ns “hybrid” spacing Non adiabatic splitting at SPS injection

“Doublet” scrubbing beam: introduction Non adiabatic splitting at SPS injection 20 ns5 ns Scrubbing with 25 ns beam allowed to lower the SEY of the dipole chambers well below the multipacting threshold for 50 ns  e-cloud free operation with 50 ns beams  Can we go to lower bunch spacing to scrub for 25 ns operation? Due to RF limitations in the PS it is impossible to inject bunch-to-bucket into the SPS with spacing shorter than 25 ns An alternative is to inject long bunches into the SPS and capturing each bunch in two neighboring buckets obtaining a (5+20) ns “hybrid” spacing

“Doublet” scrubbing beam: introduction Close to the threshold all the electrons produced after a bunch passage are absorbed before the next one  small accumulation over subsequent bunch passages PyECLOUD simulation Std 25 ns beam e-cloud enhancement mechanism:

More e - production and shorter e - decay  accumulation possible PyECLOUD simulation Std 25 ns beam Doublet beam e-cloud enhancement mechanism: “Doublet” scrubbing beam: introduction

“Doublet” scrubbing beam: SPS simulation results MBA dipole magnet MBB dipole magnet Significantly lower multipacting threshold for large enough intensity per doublet

“Doublet” scrubbing beam: SPS simulation results Significantly lower multipacting threshold for large enough intensity per doublet Beam orbit modulation needs to be applied to condition a wide enough area of the chamber MBB - 26GeV Intensity per bunch of the doublet (b.l. 4 ns ) (b.l. 3 ns)

First machine tests have been conducted at the SPS at the end of run in order to validate the production scheme and obtain first indications about the e-cloud enhancement The production scheme has been successfully tested for a train of (2x)72 bunches with 1.7e11 p per doublet Time [ms] 200 MHz RF Voltage [MV] st inj. Measurements by to T. Argyropoulos and J. Esteban Muller “Doublet” scrubbing beam: first test at the SPS

Time [ms] 200 MHz RF Voltage [MV] st inj.2 nd inj. Profile of the first doublet First machine tests have been conducted at the SPS at the end of run in order to validate the production scheme and obtain first indications about the e-cloud enhancement The production scheme has been successfully tested for a train of (2x)72 bunches with 1.7e11 p per doublet The possibility of injecting a second batch without degrading the circulating beam has also been shown

“Doublet” scrubbing beam: first test at the SPS Measurement Simulation First results looked very encouraging, e-cloud enhancement confirmed by: Measurements with the electron cloud detectors (agreement with measured cloud profile gives an important validation for our simulation model and code)

25ns std. (1.6e11p/bunch ) (1.6e11p/doublet) 25ns “doublet” “Doublet” scrubbing beam: first test at the SPS First results looked very encouraging, e-cloud enhancement confirmed by: Measurements with the electron cloud detectors (agreement with measured cloud profile gives an important validation for our simulation model and code) Dynamic pressure measurements observed in the SPS arcs

First results looked very encouraging, e-cloud enhancement confirmed by: Measurements with the electron cloud detectors (agreement with measured cloud profile gives an important validation for our simulation model and code) Dynamic pressure measurements observed in the SPS arcs “Doublet” scrubbing beam: first test at the SPS Provided that we can produce and preserve a good quality (multiple batches, large bunch intensity), this beam will be used during the two-day mini-scrubbing run at the end of the 2014 run  Acquired experience will be very important for the definition of the LIU-SPS strategy with respect to e-cloud and scrubbing and for the LHC scrubbing in 2015 To be noted Need to commission the new transverse damper for doublets at injection SPS BQM software was updated for doublet beams

Outline Introduction The 2014 SPS scrubbing run o Possible cycles o Scrubbing stages o Possible supercycle composition The doublet scrubbing beam o Motivation o Production scheme o Experience in MDs Scrubbing preparation o Beams from the PS o SPS setup o Measurements

Beam requirements From the PS: Before first scrubbing week (W45): 25 ns beam (std. production scheme and BCMS, 72 b., up to 1.5e11 ppb) 50 ns beam (std. production scheme, 36 b., up to 1.7e11 ppb) – as backup In addition, before second scrubbing block (W50): 25 ns beam for doublet production (>1.5e11 ppb, long bunches at extraction) From earlier SPS setup and MDs: Before first scrubbing week (W45): Basic setup (injection, orbit, working point, RF, damper) of 26 GeV flat bottom cycle (with 25 or 50 ns beams, Q20) Setup of 25 ns LHC filling cycle Before second block (W50): Setup of “doublet” beam at 26GeV (capture of multiple batches, orbit, working point, RF, damper) and possibly acceleration

Measurements Tests which compromise the scrubbing efficiency should be kept to the minimum possible Collect as much data as possible to learn about ecloud effects and scrubbing in the SPS BCT/FBCT (to estimate beam dose) Longitudinal parameters (BQM, mountain range, faraday cage scope) Beam transverse oscillations o BBQ, LHC BPMs, Headtail monitor, fast pickup from HBWD feedback setup, new digitizers on BPW exponential pickups Beam transverse size o Wirescanners (bunch by bunch), BGI (?) Pressure along the ring (1 Hz rate) o Special attention to the a-C coated magnets Dedicated e-cloud equipment o Electron cloud monitors (MBA StSt, MBB StSt, MBB a-C, MBB copper) o Shielded pickup o In situ SEY measurement (if available) o Removable StSt sample (for lab SEY measurement) o COLDEX

Summary and conclusions In the past, SPS was strongly limited by e-cloud Scrubbing proved to be an effective mitigation for 25 ns beams up to nominal intensity 25 ns beams delivered to LHC in 2012 were well within design report specs Scrubbing run 2014 To recondition SPS after LS1, since large parts of the SPS were vented 1 st block: 7 days (week 45) Qualify the loss of conditioning due to LS1 Recover 2012 performance with 25 ns beams 2 nd block: 2(3) days (week 50) Test scrubbing with doublet (also in view of LHC in 2015) Experience gained will be needed for LIU decision about SPS coating Need to prepare beams from the PS and test instrumentation in SPS

Thanks for your attention!

No additional impedance heating is expected with the doublet beam (same total intensity) – Beam power spectrum is modulated with cos 2 function – Lines in the spectrum can only be weakened by the modulation “Doublet” beam: beam induced heating Thanks to C. Zannini