Preliminary summary of the LHC scrubbing run

in LBOC, 11/12/2012G. Arduini, H. Bartosik, G. Iadarola, G. Rumolo

Thanks to the machine Coordinators,Cryogenics, Damper, EN/STI, Injection,

Operation, Vacuum teams,ABP, RF and BI colleagues contributing to measurements

Aims of the 2012 scrubbing run

• Further reduce the SEY over the whole machine– Use a 25ns beam at 450 GeV, monitoring electron cloud observables

and beam quality evolution– Eventually ramp to 4TeV up to a few hundreds of bunches (for

beam-beam, e-cloud, and UFO studies and for 25ns pilot run and additional scrubbing!)

• Collect additional information on the evolution on the SEY as a function of the accumulated electron dose (especially in the low SEY region) and compare machine data with existing models

– Essential to validate models and establish strategies for the post-LS1 era

• In parallel, learn about other possible differences in 25ns vs. 50ns operation (concerning heating, stability, UFOs)

Scrubbing Overview

• Fast intensity ramp-up and overall excellent machine availability

• Beam under control (damper, chromaticity, octupoles) in spite of the record intensities (up to 2.7x1014 p, 2748 bunches per beam)

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Fills 3389 3407

Heat load evolution• The heat load on the beam screens was used on line for

estimating the efficiency of the scrubbing process

Thanks to L. Tavian

Heat load in sector 56

Main limitations

Smooth run, no fundamental showstopper was found Good scrubbing dose was maintained all along the scrubbing period.

The overall efficiency was determined by:• Vacuum pressure in the MKI region (during the initial

stages):o The interlock levels were gradually increased (tanks:

2∙10-9mbar 4∙10-9mbar, interconnects: 1∙10-8mbar 4∙10-8mbar)

• Cryogenics (with higher intensities):o Limited cooling power at stand alones in P6 and

8 required about 10’ between successive injectionso Try to dump the beams in conditions of lower heat

load (to avoid strong fluctuations on 120A current lead temperature precycle needed)

Other limitations• Vacuum pressures along the ring were continuously

monitored by the vacuum teamo Apart from MKIs and shortly ATLAS during the first

night, no significant slow down coming from pressure rises

Thanks to TE-VSC and EN-STI

Other limitations• Vacuum pressures along the ring were continuously

monitored by the vacuum teamo Apart from MKIs and shortly ATLAS during the first

night, no significant slow down coming from pressure rises

• TDIs had to be opened after each injection in order to keep heating and outgassing under control.

A. Lechner

Pressure runaway that triggered a manual dump

Other limitations• Vacuum pressures along the ring were continuously

monitored by the vacuum teamo Apart from MKIs and shortly ATLAS during the first

night, no significant slow down coming from pressure rises

• TDIs had to be opened after each injection in order to keep heating and outgassing under control.

A. Lechner

Other limitations• Vacuum pressures along the ring were continuously

monitored by the vacuum teamo Apart from MKIs and shortly ATLAS during the first

night, no significant slow down coming from pressure rises

• TDIs had to be opened after each injection in order to keep heating and outgassing under control.

o On 10/12 – last night of scrubbing – one jaw of the TDI in point 8 got stuck in open position (twice) The EN/STI piquet could remotely reset the motor

o LVDT reading of TDI.4L2 LU might trigger a warning/error, on the *LOWER* limit due to drift while cooling down. Access ongoing, exchange of one of LVDTs

Thanks to TE-VSC and EN-STI

Other limitations• Vacuum pressures along the ring were continuously

monitored by the vacuum teamo Apart from MKIs and shortly ATLAS during the first

night, no significant slow down coming from pressure rises

• TDIs had to be opened after each injection in order to keep heating and outgassing under control.

o On 10/12 – last night of scrubbing – one jaw of the TDI in point 8 got stuck in open position (twice) The EN/STI piquet could remotely reset the motor

o LVDT reading of TDI.4L2 LU might trigger a warning/error, on the *LOWER* limit due to drift while cooling down. Access ongoing, exchange of one of LVDTs

• No anomalous heating was observed on other sensitive elements (e.g. collimators) (larger bunch lengths and smaller bunch intensities)

Thanks to TE-VSC and EN-STI

Initially:• Transverse instability leading to beam dump

→ Injecting a single train of 72 bunches with chroma set to 2→ Injecting trains of 216 and 288 bunches, even with chroma set to

15!

Beam quality evolution

Thanks to R. De Maria,

W. Höfle, D. Valuch

During injection set up

Beam quality evolutionInitially:

• Transverse instability leading to beam dump → Injecting a single train of 72 bunches with chroma set to 2→ Injecting trains of 216 and 288 bunches, even with chroma set to

15!• Poor lifetime, however exhibiting signs of improvement

even within the same fillBeam 1 Fill 3389

Train spacing 3.7 ms 1 msTrains with 72 288 bunches

Beam 2

Q’ ~ 15 Q’ ~ 7

Q’ ~ 15 Q’ ~ 7

Beam quality evolutionBunch by bunch lifetime strongly improved within the first scrubbing fill (Fill 3389).

Filling scheme with minimum possible batch spacing and maximum number of bunches was employed for the following fills.

Between Friday Dec. 7th and Sunday Dec. 9th there were 10 scrubbing fills with more than 2000b. per beam.

Beam quality evolutionBeam lifetime (CCC monitoring)

Sunday 9 Dec

Thursday 6 Dec

Beam quality evolutionBeam lifetime – Fill 3390

Beam 1

Beam 2

Beam quality evolutionBeam lifetime – Fill 3390

Beam 1

Beam 2

Beam quality evolutionBeam lifetime – Fill 3398

Beam 1

Beam 2

Beam quality evolutionBeam lifetime – Fill 3398

Beam 1

Beam 2

Beam quality evolutionBeam lifetime – Fill 3405

Beam 1

Beam 2

Beam quality evolutionBeam lifetime – Fill 3405

Beam 1

Beam 2

Beam quality evolutionSummary of lifetimes

Scrubbing Scrubbing

Studies

Miscellaneous• Important transverse emittance blow up

→ Affecting only some bunches of the first injected train→ Seen with BSRT, confirmed with WS, both planes

• Effect suppressed by increasing the octupole strength from -0.5 to -2.0

Octupole setting -0.5

Octupole setting -2.0

Preliminary considerations• 3.5 days of scrubbing with 25ns beams at 450GeV were

carried out with high heat load (i.e. electron) rate

• e-cloud effects on the beam were visibly mitigated but not suppressed yet (seemingly confirmed by both heat load and beam lifetime measurements)

• Important information on the SEY evolution vs. electron dose collected for validation/improvement of our models and for enabling us to extrapolate to post-LS1 operation

• More data analysis (including transverse emittances from BSRT and stable phase shift) and interpretation ongoing + more information/additional scrubbing expected from MDs with ramps to 4 TeV

Thanks for your attention!