Very Preliminary proton MD summary

G. Arduini – BE/ABP

Acknowledgements: BI, Collective effects team, Cryo, Injection Team, OP, Vacuum Team

Special thanks to Massi and Experiments

• Complete the observations from the previous MD with 50 ns beam concerning electron cloud build-up:– Vacuum rise has been observed in all uncoated warm-warm and

warm-cold transitions (where vacuum pressure measurements exist) for bunch populations > 6×1010 p/bunch and with trains of 24 bunches. Differently from 150 ns beam pressure rise is observed also in vacuum pipe with single beam.

– Reduction by more than a factor 10 of the vacuum activity has been observed during “scrubbing” at 450 GeV from 29/10 to 4/11

– Clear signs of heat load due to electron cloud build-up in the arcs have been observed with 50 ns. No sign of it with 150 ns.

– No clear evidence of reduction of the heat load at 3.5 TeV after scrubbing need additional experiment (comparison with first fill performed with 50 ns, before the scrubbing)

• Compare the behaviour of the 75 ns beam with 50 ns beam in terms of vacuum rise, heat load and beam stability

Motivations

OverviewTime with beam [h]

Wed 17/11 Switch-over to proton settingsRF synchronization and captureInterlocks and Machine Protection checks (Beam Presence Flag, loss maps at 450 GeV)

15 (18)

Wed 17/11 – Thu 18/11

Injection setting-up for 75 ns beam 8 (8)

Thu 18/11 Injector tuning and abort gap cleaning verification 3 (3)Thu 18/11 – Fri 19/11

Ramp-up in intensity for 75 ns beam for beam stability, pressure rise and heat load measurements

21 (23)

Fri 19/11 Switch to 50 ns 6 (6)Fri 19/11 Test ramp to prepare ramp with 50 ns beam 3 (3)

Fri 19/11 – Sat 20/11

Ramp with 50 ns beam (9x12 bunches) 6 (8)

Sat 20/11 Ramp-up in intensity for 50 ns beam for beam stability, pressure rise and heat load measurements in comparison to 50 ns

3 (5)

Total effective time (time allocated for MD) 65(74)

• Major stops (~9 hours):– RF PS (Wed/Thu)– MKD (Fri/Sat)

• RF setting-up: some of the parameters are not yet remotely controllable and/or not cycle dependent expert intervention required in SR4

• Preparation in the injectors could be done only at the last minute due to problem on 80 MHz cavity in the PS not allowing to run ions and protons in parallel

• First asynchronous dump (beam 1). Luckily enough with pilot at 450 GeV. HW failure in the distribution of the triggers

Issues during the test

75ns – high intensity• Capture losses observed on beam 2 during Thursday are

understood Cavity 7B2 is showing some noise on the accelerating voltage in the presence of high intensity. Possible sources:

– Multipacting in the antenna pot or cable connector perturbing the field measurement (and the cavity feedback).

– Micro-quenches in the cavity causing a real field drop (and also perturbing the feedback).

• Might be triggered by multipacting/electron cloud in the cavity.• Conditioning at higher voltage might help.

A. Butterworth

Achieved 75ns• Filling while monitoring vacuum and cryogenics, all at 450GeV• 680 bunches/beam (8+14*48) 9 1010 p/b, batch spacing 1.85

us– Kept this beam for 2 hours for UFO investigations

• 680 bunches Beam1 (8+14*48) 11 1010 p/b, batch spacing 1.85 us

• 824 bunches Beam1 (8+17*48) 11 1010 p/b, batch spacing 1.005 us realized afterwards that this spacing is not compatible with operation of the fast BCT and possibly the damper. To be enforced for the future.

Achieved 75ns

Average bunch population ~0.9×1011 p. Total intensity ~6×1013 p/beam

Achieved 75ns

Except for first train (8 bunches) for all the other losses are located at the tail of the batch

Emittances with 680 bunches

Time evolution being analyzed. B1 affected by H instability at the tail of each batch Stabilized by chromaticity data being analyzed to understand origin.Bunch population = 1.1×1011 p – batch spacing 1.85 ms

Q’H,V=24Q’H,V=14 Q’H,V=14Q’H,V=24

Emittances with 680 bunchesHigh chromaticity seems to help controlling the beam also for tighter batch spacing (1.005 ms) and nominal bunch intensity.Bunch population = 1.1×1011 p – batch spacing 1.85 ms

Observed losses• Loss maps with 488 bunches for B1 (1011 p/bunch).

Effect of the observed pressure rise in the straight sections? (to be further analyzed)

75 ns vs. 50 ns

75 ns (8+48 b) – 1.85 ms spacing

50 ns (12+48 b) – 1.85 ms spacing

75 ns vs. 50 ns

75 ns up to 824 bunches (Beam 1).

50 ns up to 444 bunches (Beam 1)

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[W p

er h

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Qbs21L3 (calculated with T increase) Qbs33L6 (calculated with T increase)

Qbs13R7 (calculated with T increase) Qbs (IC+SR calculated with beam parameter)

Beam energy Intensity Beam1

Intensity Beam2

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[W p

er h

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Qbs21L3 (calculated with T increase) Qbs33L6 (calculated with T increase)

Qbs13R7 (calculated with T increase) Qbs (IC+SR calculated with beam parameter)

Beam energy Intensity Beam1

Intensity Beam2

L. Tavian

For both beams significant heat load in the beams screens of the triplets (particularly L8)

• 75 ns is certainly better than 50 ns but scrubbing is required in order to operate with large number of bunches and to ramp.

75 ns – 824 bunches

V. Baglin, G. Bregliozzi, G. Lanza

Some results – scrubbing with 50 ns

Before scrubbing (30/10): Heat load ~40 mW/m/beam

After scrubbing (19/11)Heat load <10 mW/m/beam. Only B2

-1

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[W p

er h

alf-c

ell],

[Te

V], [

1013

p]

Qbs21L3 (calculated with T increase) Qbs33L6 (calculated with T increase)

Qbs13R7 (calculated with T increase) Qbs (IC+SR calculated with beam parameter)

Beam energy Intensity Beam1

Intensity Beam2

L. Tavian

Same filling pattern (9x12 b) and bunch population (~1011 p). Scrubbing at 450 GeV effective also for 3.5 TeV in the arcs

• Transition from ions to protons took longer than expected (RF set-up required in SR4, access for problems in the injectors) some of the RF parameters to be made remotely controllable

• Analysis ongoing several data sets

• Less vacuum activity 75ns spacing as compared to 50 ns although we will need scrubbing (or solenoids) to avoid pressure rises in the straight sections to fill up the machine

• Heat load in beam screens the arcs for 75 ns beam hardly visible but important activity in the triplets in particular L8

• Comparison of 50ns at 3.5 TeV before and after scrubbing at 450 GeV clearly shows that the situation has improved significantly in the straight sections and in the arcs (heat load)

Preliminary summary

• Reserve

9x12 1x12+4x24

• Vacuum Interlock due to pressure increase on the penning gauges VGPB.773.6L7.R on the cold-warm transition of the Q6L7.R. Beams circulating in different vacuum chambers

• Unexpected (at least to me) for this number of bunches

Pressure rises with trains of 24 bunches

• Moved to e-cloud measurement–scrubbing mode on Sunday afternoon until Wednesday evening (with an interruption on Monday day-time for quench test at 3.5 TeV):– Pressure rise observed in cold-warm and warm-warm (uncoated)

transitions – Even stronger pressure rise when injecting trains of 36 bunches– Little or no dependence on bunch length– Cleaning seen for 12-24-24 (factor 2 in four hours)

• persistent after refilling– Cleaning with 36 bunches less evident due to losses generated by

beam instabilities

E-cloud measurements & scrubbing

12+2x24 12+2x24 12+36 12+36

• Systematic measurements of pressure rise in the straight sections and heat load in the arcs for different filling patterns to provide input for simulations and guide predictions:– Dependence on bunch intensity– Dependence on bunch train length– Dependence on bunch train spacing

• Very preliminary simulation results indicate that SEY~2.5 (assumed 1.7 so far)

E-cloud measurements

0.6x1011 p/bunch

0.8x1011 p/bunch

1.1x1011 p/bunch

12+1212+2412+36

• Comparison between pressure rise before and after scrubbing run for 12+36 bunches at 450 GeV (reduction by ~1 decade in ~3 days)

Scrubbing

04/11: max p @ LSS3 VGPB.2.5L3.B=8E-8 mbar

31/10: max p @ LSS3 VGPB.5L3.B = 5.5E-7 mbar

G. Bregliozzi, G. Lanza

• Not seen during runs with 104 bunches per beam with 150 ns spacing for comparison.

Heat load on beam screens (33L6)

L. Tavian

• After scrubbing: 1x12+4x24 bunches

• Reached saturation?

• Reduction?

Heat load on beam screens (33L6)e-cloud peak: ~37 mW/m per aperture

L. Tavian

• 12 bunches + 4 trains of 24 bunches spaced by 1.85 ms

• Build-up of the electron cloud over more than one train leading to instabilities and emittance blow-up along the trains

• Consistent with preliminary results of simulations for SEY~2.5

Beam stability at injection

F. Roncarolo

• 12 bunches + 1 train of 36 bunches

• Build-up occurs already in the first train of 36 bunches with the same effect (instability with approximately 1 s rise-time/blow-up)

Beam stability at injection

F. Roncarolo

E. Métral

• Can be stabilized by increasing chromaticity (up to 18 units) and by transverse emittance blow-up Can be used during a scrubbing period but how far can we go with larger number of bunches?

• How does it improve with scrubbing?

Beam stability at injection

F. Roncarolo

• Observed instabilities (H faster) with 1x12+4x24 bunches at flat-top when the damper is switched OFF. Not observed for 9x12 bunches for the same machine settings.

• Rise-time: few tenth of s (H), 1-2 s (V)

• Can be cured by the transverse feedback

Beam stability at flat-top

H. Bartosik, B. Salvant