SPS scrubbing run in 2014 H. Bartosik, G. Iadarola, G. Rumolo LHC Performance Workshop (Chamonix...

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 2012-13 MDs

• Scrubbing preparation

o Beams from the PS

o SPS setup

o Measurements

Outline

• Introduction


o Possible cycles

o Scrubbing stages



o Motivation

o Production scheme



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. - 0.8x1011 p/b @inj.)

3.5 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)

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)

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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)

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Inj. Inj. Inj. Inj. Inj. Dump

Inj. Inj. Inj. Inj.

19 BPs (22.8 s)

Planning (to be steered on the fly)

Monday Tuesday Wednesday Thursday Friday Saturday Sunday

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 1.5x1011 p/b?)

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Possible supercycle (to be coordinated with physics in the PS complex)

Inj.

Week 45






• 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

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Possible supercycle

Studies on long flat bottom cycle (39.6 s)

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Week 45

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• 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


Monday Tuesday

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)


Outline

• Introduction


o Possible cycles

o Scrubbing stages



o Motivation

o Production scheme



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

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Non adiabatic splitting at SPS injection

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Non adiabatic splitting at SPS injection

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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


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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:

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More e- production and shorter e- decay accumulation possible

PyECLOUD simulation

Std 25 ns beam

Doublet beam

e-cloud enhancement mechanism:


“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

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Position [m]

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0.60e11ppb0.70e11ppb0.80e11ppb0.90e11ppb1.00e11ppb1.10e11ppb1.20e11ppb6btc 25ns1.20e11ppb

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 2012-13 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

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Measurements by to T. Argyropoulos and J. Esteban Muller

“Doublet” scrubbing beam: first test at the SPS


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First bunch (of 2 single) after the second inj.

After 1st inj.

After 2nd inj.

Profile of the first doublet

• First machine tests have been conducted at the SPS at the end of 2012-13 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


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”





• Dynamic pressure measurements observed in the SPS arcs




• Dynamic pressure measurements observed in the SPS arcs


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


o Possible cycles

o Scrubbing stages



o Motivation

o Production scheme



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

• 1st block: 7 days (week 45)

• Qualify the loss of conditioning due to LS1

• Recover 2012 performance with 25 ns beams

• 2nd 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!

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Frequency [GHz]

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25 ns beamdoublet beam

No additional impedance heating is expected with the doublet beam (same total intensity)– Beam power spectrum is modulated with cos2 function

– Lines in the spectrum can only be weakened by the modulation

“Doublet” beam: beam induced heating

Thanks to C. Zannini

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