Weekly summary

Summary Weeks 27 & 28 (29) 5.07/19.07

Week 28: R. Bailey & M. Meddahi Week 29: M. Lamont & J. Wenninger

Week 30: R. Assmann & O. Brüning

for the OP team and for all colleagues from the various groups

8:30 meeting 1

LHC commissioning Week 27

Aims for the week● Deliver luminosity for physics:

– Luminosity of 1030 cm-2 s-1

– Stabilize performance in physics

● Transfer line and injection system setting up for >1012 p/beam

● Advance the understanding of sudden beam losses in stable beams

– Blow up emittance injected in LHC to ~nominal– Run with different collision schemes

LHC week 27

Beam losses in stable beamsOperation with higher intensity and crossing angle

sudden losses observed during stable beams– Most of time after luminosity scans– Hump presence? Sometime but not always? Is it the cause or the

symptom?– Observation of strong coherent oscillations which is certainly linked to

beam-beam effect - Werner Herr why beam-beam ?

- with single beam : not observed- with low intensity : not observed

beam-beam effects are probably not the origin of the problem, but the killer when it happens : Remember the SPS p-pbar where any source of modulation or noise on the beams led to heavy losses.

LHC week 27

Collision schemes considered for Studies● Single_10b_4_2_4 Probe the effect of long range

encounters– 4 colliding pairs in IP1, IP5 and IP8, 2 colliding pairs in IP2– 0 parasitic encounters– Max. 2 head-on collisions/bunch (not 3 as before)– Observed again sudden beam losses Long range encounters are not the source of the problem

● Single_10b_4_2_4 without crossing angle in IP 1 and 5 Probe crossing angle effect

– Crossing angle not needed could not be tested (collimation)

● Single_10b_4_2_4_rotated Probe the effect of bucket number

– As above but rotated to have 1*1 in IR8 instead of IR1 and 5 could not be tested (RF)

LHC week 27

Preparation towards > 1e12 p /beam 450 GeV

– Multi-bunch controlled longitudinal blow-up – Thomas Bohl, Joachim Tueckmantel, Urs Wehrle.4 single bunches were injected into the SPS, 2.4 s apart, bunch spacing was 2 ms, I_bunch ~1011 at injectionOptimization of the controlled long. emittance blow-up.

At 450 GeV, with 7.0 MV bunch lengths: 1.3 ns - 1.85 ns longitudinal emittances : 0.40 - 0.75 eVs.

For better optimization: TWC 800 MHz is required (this will be a new operational requirement) More beam time

needed– SPS transverse blow-up with transverse damper - Wolfgang Hofle

Octupoles are used in combination with an excitation by the damper around the tune frequency (small frequency modulation) Tuned the system for providing emittances of ~3 mm in H and V for both beams

LHC week 27

– Transverse emittance measurements across the SPS-TLs-LHC chain - Brennan Goddard – Chiara Bracco – Wolfgang Hofle -Federico Roncarolo, Jean-Jacques Gras, Anna Guerrero, Rhodri Jones, Enrico Bravin, OP crewsWith transverse blow-up: SPS H and V: ~3.3 mmTI 2 horizontal: ~3.6 mm - TI 2 Vertical: ~3.3 umTI8 horizontal : ~3.6 mm - TI8 Vertical : ~3.5 um LHC H & V B1: ~ 3.3 mm for each newly injected bunchLHC H & V B2: ~ 3.3 mm for each newly injected bunchBunch 1 measured after each injection of a new bunch blowup of the individual bunches on the flat bottom at about 1 mm/h - B2 V most affected

BTV screens in the dump lines : added to the screen matching application -– Fabio Follin provide useful emittance measurements

Preparation towards > 1e12 p /beam 450 GeV

LHC week 27

– LHC injection protection devices – Brennan Goddard

TDI settings verification as a function of TCP setting. Data to be fully analyzed for B1- For B2 TDI scan repeated with the offsets found in previous measurements: results coherent with earlier findings.

– Tail scans in TI 2 – Chiara BraccoTail scan performed for two collimators upstream of the TED with nominal bunch, with and without SPS beam scraping.Showing tails in H, with about 2% of the beam outside 4.5 sigma, coming from blowups in the SPS (losing at TCDI with large Dx)

– Trajectory consolidation in TI 2 and TI 8 - Brennan, Chiara, Malika, Volker, KajetanPerformed bare corrections allowed removing most of the correctors which have been added over the weeks wrt to May orbit referenceCorrected the injection oscillations into the LHC, minimising kicker strengths and overall trajectory

Preparation towards > 1e12 p /beam 450 GeV

LHC week 27

– Re-centering of the TL collimators in TI 2 and TI 87 collimator set up in TI 2 [6 in TI 8] around the new trajectory. Injected 12 (13) nominal bunches, final 8 with BLMs unmasked, to total intensity of 1.1e12 (setup beam flag -> FALSE)Dump of 12 (13) nominal bunches cleanInjection oscillations for B1 / B2 with the new steering looks OK - avoid correcting from now on. Oscillations are damped nicely with the transverse damper

– Multi bunch injection from the SPS into LHC– Still much work to be done in the SPS (orbit, transverse, settings…)

before injection into the LHC

– Sent 1 train of 4 bunches in TI 2 - will wait for SPS tidy up before continuing.

Preparation towards > 1e12 p /beam 450 GeV

LHC week 27

LHC commissioning Week 28

Aims for the week● Deliver luminosity for physics:

– Luminosity above 1030 cm-2 s-1

– Stabilize performance in physics– start multi bunch injection– Hump investigations

LHC week 28

General performance● Start of the week : operation with 8/9 bunches per beam, 9E10/b.

– 6 colliding pairs for ATLAS, CMS and LHCb.● Tuesday : switch to 12 bunch operation, 9E10/b.

– 8 colliding pairs for ATLAS, CMS and LHCb.– Peak luminosity 1.4E30 cm-2s-1

● Thursday : switch to 13 bunch operation, 9E10/b.– 8 colliding pairs for ATLAS, CMS and LHCb.– Stored energy : 660 kJ.– Peak luminosity : 1.6E30 cm-2s-1 for fill 1233 on Sunday.

– Expected luminosity 1.7E30 cm-2s-1 for nominal emittances.– Longest fill : 19 hours.

● Attempt to add an extra ½ intensity bunch for LHCf on Thursday.– Aborted, running late in the night, longer than expected beam position

interlock check.

10 LHC week 28

Record fill 1233

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In stable beams for 19 hoursL at end: 0.7E30 cm-2s-1

LHC week 28

Integrated L (M. Ferro-Luzzi)

12

ca. 70 nb-1 in last fill!

LHC week 28

● Beam intensity lifetimes in collision between 25 and 125 hours.– Initially lifetime degradation when switching on transverse damper on B2, fixed

by RF team during the week (better noise performance).– In the last fills dampers had positive or no effect on lifetime.– Fill with very equal TOTAL intensity tend to perform better.

● Losses in collisions.– Bunch intensity losses have still been observed in collisions, but they became

less frequent in the second half of the week.– Changes:

– Damper ON (but not always).– Larger Q split B1-B2 : from 0.003 to 0.005.– Manual luminosity optimization.

Beams in collisions

13 LHC week 28

TOTEM - roman pots

● Roman pots were moved into the beam during stable beams.– First to 30 sigma H and V.– Night Wednesday to Thursday: 25 sigma in V.– At 25 sigma candidate elastic events were observed.– No problems for operation, but some issues with stability of front-end

software (diagnostics only – interlocking not affected).

14 LHC week 28

Hump vs. GSM signal in the tunnel● Circulating beam (single nominal bunch) available at ~16:25

Started to switch OFF GSM network in the tunnel in the following order: – Sector 12 + TI2

Sector 23 Sector 34 sector 45 Sector 56 Sector 67 Sector 78 Sector 81 + TI8 + UX15

● By 17:24 all GSM transmitters in the tunnel were OFF No significant modification on the hump amplitude

By 18:00 the GSM network was re-established (for a total interruption of 1.5 h) This test was possible thanks to the contribution of IT/CS (A. Pascal, F. Chapron).

Test organized by G. Arduini on Thursday

LHC week 28

Hump vs. GSM signal in the tunnel

● Typical slow drift in frequency as observed in other occasions, but no significant change in amplitude

GSM OFF – B2V

GSM OFF – B2H

GSM ON – B2V

GSM ON – B2H

LHC week 28

● SPS multi-bunch cycle– SPS cycle with 4 injections is ready.– Adjusted extraction kicker delays to extract ALL 4 bunches.– Extraction to upstream TEDs for both B1 and B2.– Extraction to TI2 downstream ok.– Everything looking ok – next step is injection into the LHC.

● Multi-bunch injection into LHC– Delayed to after the technical stop. Suffered from booster MPS and SPS

vacuum.

Multi-bunch injection

17 LHC week 28

Ghost bunches● Small ghost bunches around main bunches reported by the

experiments.– Intensity at the level of 0.1% of the main bunch.

● Ghost bunches confirmed measurements of the RF group. – Bunches extend up to -80 ns. Spacing is 5 ns.– Abort gap population isbelow 5E6 p/bucket (exceptfor messy 80 ns).

18 LHC week 28

Capture losses

● After a problem to due an energy mismatch (build up by the orbit FB at injection), it was suggested by RF to adapt the RF frequency at injection to balance the energy errors of Ring1 and Ring2.– Injection fRF changed by +5 Hz.– Lower capture losses.– A better match could be obtained with orbit correctors after the technical

stop.– Capture losses will become more critical as we inject more beam !

19 LHC week 28

‘Big’ problems

● PS booster MPS problem.– Filling of LHC did not suffer too much, some refills were delayed.– Solved Wednesday evening.

● SPS vacuum problem : dipole in cell 406– Vacuum problem appeared Thursday in the SPS.– Survived the weekend, running just below the threshold of the ion pumps.

Multi-bunch injection tests foreseen Friday had to be postponed.

20 LHC week 28

Orbit in the ramp fill 1232

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● Orbit correction became unstable – seemed to be coming from IR4.● Orbit FB switches off.● Switch on worked, instability disappeared!

Very good stability50 mm rms !!

LHC week 28

● Orbit clean-up at injection– Injection orbit and corrector settings re-seeded wrt reference. RMS deviations

back to 0.1 mm, corrector settings cleaner (Saturday).● Orbit and separation effects at 3.5 TeV

– Following the orbit cleanup, the separation corrections no longer worked – luminosities were 0 at start of fill 1232 !

– Orbit changes have been propagated to 3.5 TeV by OFB (most likely).– New settings had to be found, because the older settings did not match.

Tedious in ALICE (3 hours !).– Inspection and comparison of the orbits in stable beams of a few fills of the

week revealed significant fill to fill differences in the IRs (up to 0.5-1 mm) – must establish stricter correction policy, refresh references more frequently and improve the separation bump collapse procedure/settings.

Orbit effects

22 LHC week 28

Week 29

● Technical stop (advancing according to schedule)– CMS cryo filters required cleaning CMS not back until Saturday

● Beam setting up and operation– One dump with pilot bunch at 450 GeV and at 3.5 TeV for dump validation.– One ramp with 1 bunch of 9E10 / beam to validate modifications of SMP

system (‘relaxed expert Setup Beam Flag limit [x4]).– Multi-bunch injection.– Energy matching ring1 and ring2.– Orbit and procedure clean-up at end of squeeze collisions.– Loss maps for collimation.– Orbit feedback tests.– 10 A/s for pre-cycle and ramp-down (tbc).– Could dream of 24 bunches per beam.

23 LHC week 29

Outlook beyond Week 28

● Deliver luminosity for physics:– Luminosity above 1030 cm-2 s-1

– Stabilize performance in physics– start multi bunch injection (ca 24 bunches per beam)– stable running (statistics and experience) for operation with beam energies above 1 MJ

LHC week 29