Injection Considerations for Scrubbing RunC. BRACCO, M. J . BARNES, W. BARTMANN, B. GODDARD, M. MEDDAHI , J . UYTHOVEN

ACKNOWLEDGMENTS: M. D I CASTRO, M.DONZE, A. LECHNER, R. LOSITO, A. MASI , A. PERILLO MARCONE

Outline

TDI Heating 2012 Scrubbing run:

Procedures Observations

LS1 modifications 2015 scrubbing proposed strategy

MKI Vacuum activity 2012 Scrubbing run:

Procedures Observations

LS1 modifications 2015 scrubbing proposed strategy

TDI Heating

25 mm

38 mm

Beam

2

TDI IR8

Beam screen plastic deformation induced by heating (bake out, resistive wall heating) and blockage of sliding supporting structure

Jaw elastics deformation induced by heating during operation with high intensity beams

Not possible to define a direct correlation between LVDT drift and jaw’s Sagitta but “acceptable” drifts (no loss of protection) were estimated by measuring the position of the “warm” jaw wrt the beam.

2012 Scrubbing Run: ProceduresMeasures taken during 2012 scrubbing run to limit TDI heating:

Move TDI to parking position (+/- 55 mm) as soon as possible when intensity of circulating beam >1e14 protons

Move it out after 15 minutes and keep it out for at least 15 minutes (or time needed for cool down) for any intensity <1e14 protons

Monitor LVDT drifts, vacuum and temperature (cooling water):

LVDT drifts: warning limit = +/-165 mm and dump limit = +/-200 mm In and out water temperature dump limit: 1 degree Vacuum warning limit: 1e-7 mbar (IP2) and 1e-8 mbar (IP8)

A monitoring tool was prepared but not enough time for commissioning it not operational manual TIMBER analysis

Insure TDI protection during injection:

Make special scrubbing sequence for topping up. Put MKI in STANDBY before moving the TDI out

Operator dump, not automatic!

M. Di CastroM. Donze

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2012 Scrubbing Run: Observations

Clear correlation between pressure increase and TDI heating

LVDT drifts as during nominal operation Some mechanical issue (jaw stuck) probably due to the

frequent cycling of jaws

Scrubbingrun

A. Lechner

A. Lechner

TDI Modifications during Run1

Improved mechanics of the beam screen: stainless steel (304L) with increased thickness (6 mm) + additional reinforcement + flange for electrical contact instead of RF fingers + improved sliding of beam screen wrt tank (ceramic bearings)

Eight PT100 temperature sensors installed on the beam screen (two) and the jaws (six)

0.3 mm Ti coating on Al block to reduce SEY

Full system dismantled and remounted more reliable motor mechanics (“as new” system)

Still heating and vacuum activities are expected during the scrubbing run (no Cu and NEG coating could be applied on beam screen and jaws)

Details available in EDMS doc. N. 1342836

2015 Scrubbing Run Procedures

Same procedure as in 2012: Move TDI to parking position (+/- 55 mm) as soon as possible when intensity of circulating beam >1e14 protons

Move it out after 15 minutes and keep it out for at least 15 minutes (or time needed for cool down) for any intensity <1e14 protons

Sequence to put the MKI in STANDBY before moving the TDI out

Monitoring tool to be made operationalSame LVDT limits as in 2012 (no operational experience up to now to modify them)Direct temperature measurement (no water flow but new PT100 sensors) limits to be agreed

with EN/STIContinue monitoring vacuum, limits = 1e-7 mbar (1e-8 mbar?)

Vacuum and MKI Flashover

Q5 side of MKI8D

Solenoids on interconnects

Solenoids by Q4 & Q5

Pressure rise in MKI8C-D interconnect

MKI8C

MKI8DMKI8C spark

Q4 & Q5 solenoids OFF

Interconnect solenoids OFF

Pressure rise on Q5 side of MKI8D

High instantaneous pressure in the kicker magnet tank, and near the capacitively coupled end of the beam screen, when pulsing the kickers, increases the probability of an electrical breakdown

A prolonged pressure increases at the MKI, when pulsing the kickers, also increases the probability of an electrical breakdown

SIS interlock on instantaneous and integrated pressure

UFO MDM.J. Barnes, LBOC – 25/09/2012

Procedures on EDMS for Run 1 Vacuum thresholds MKI:

Nominal SIS thresholds: 2e-9 mbar for the magnets and 5e-9 for the interconnects

During scrubbing run: 4e-9 mbar for the magnets and 1e-8 mbar for the interconnects

If required: increase vacuum thresholds in steps of 2e-9 mbar for the magnets and 5e-9 mbar for the interconnects

Wait 3-4 hours before increasing thresholds again, no electrical breakdown has to occur during this time otherwise no further step in thresholds

If a second breakdown occurs step back to lower thresholds. Possible increasing again after 3-4 hours without breakdownMaximum upper limit for scrubbing run (HW limit to be set in the tunnel): 4e-8 mbar (Seuil Bas) and 5e-8 mbar (Seuil Haut)

at the magnet tank and 4e-7 mbar at interconnects with adjacent beam-line

If pressure > 4e-9 mbar and 1e-8 mbar extended SoftStart before next injection

If SIS vacuum-thresholds is reached on the vacuum integral sublimation needed before next injection

E-cloud solenoids on for injection, possible reducing the current with stable beams but this will probably increase the vacuum integral increase risk of need sublimation

SIS temperature interlock kept at its nominal value. It can be increase after positive soft-start.

Thresholds back to nominal after scrubbing run

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2012 Scrubbing Run: Observations The interlock levels were gradually increased during the run:

Tanks: 2 10∙ -9mbar 4 10∙ -9mbar Interconnects: 1 10∙ -8mbar 4 10∙ -8mbar No flashover and relatively low heating.

TI8 Interconnects

Highest values at MKI extremes (contribution from Q4)

LS1 Vacuum Related UpgradesHeating collar

Heating collar control box

MKIs have background pressure of few x 10-11 mbar; Penning gauges are an important part of the kicker magnet interlocks. A “problem” is that the very good MKI pressure level is at the limit of

measuring of the Penning. To avoid the Penning “going to sleep”, TE-VSC have installed heating collars, regulated by a “first prototype” control box.

Upgraded design of RF fingers Bypass tubes NEG coated ; MKI interconnects are NEG coated - no solenoids installed; BE-BI have NEG coated BTVSIs and BPTXs; TE-VSC have installed NEG cartridges, on the cold-warm transition, to supplement

existing ion pumps; TE-VSC have exchanged the ion pump, on the MKI interconnects, for a version which

has a NEG cartridge better pumping; New ceramic tubes will need conditioning with beam. SIS vacuum threshold studies -

in lab, with help of TE-VSC, inject H2 into test tank (no magnet, only screen conductors connected to pulsed HV) – no increase in electrical breakdown rate up to 10-7 mbar but no ionized gas!

New NEG coated bypass tubes

Multipacting in Ceramic TubeDuring Technical Stop 3, 2012, an MKI magnet (MKI8D) was replaced in the LHC. Immediately following the restart of the LHC the vacuum pressure close to this MKI, with beam present, was relatively high. The new ceramic tube required ~250 hours, with beam, to achieve a normalized pressure similar to the pre-replacement (~4E-24 mbar/p) level: this is thought to be due to the relatively high Secondary Electron Yield [SEY] (6 to 10) of the ceramic.

Proposed Strategy for MKIs Towards 25 ns BeamPrior to Scrubbing: Request that VSC increase “digital interlock” (relay #4) of Penning gauge, on each MKI tank, as follows:Seuil Bas : 1e-8 mbar 4e-8 mbarSeuil Haut: 2e-8 mbar 5e-8 mbar

During Scrubbing: Controlled increase of SIS interlock thresholds for MKI interconnects, from 5e-9mbar e.g. to 5e-8 mbar: if spark occurs, reduce thresholds and run extended SoftStart .

Controlled increase of SIS interlock thresholds for MKI tanks, e.g. from 2e-9mbar to 5e-9 mbar: if spark occurs, reduce thresholds and run extended SoftStart .

If the vacuum integral exceeds the SIS threshold a sublimation should be carried out as soon as reasonably possible, followed by an extended SoftStart.

After Scrubbing: Sublimate (some or all) MKIs. Mini HV conditioning.Reset MKI SIS thresholds.Request VSC reset “digital interlock” thresholds.

Conclusions

Improvements were applied to the TDI (Beam screen, temperature sensors, etc.) and MKI (NEG coating and cartridge, new screen design, etc.) during LS1.

Heating and vacuum/SEY activities are still expected during scrubbing run in 2015 (no NEG and CU coating of TDI beam screens and jaws, time for conditioning of MKI ceramic chambers)

Same strategy as used in 2012 for next scrubbing run: Monitor TDI heating (operational tool for: LVDT, temperature and vacuum) and MKI vacuum manual

beam dump by operator for TDI heating above limit and wait for cooling, no injection if MKI vacuum above thresholds

TDI to parking position (when MKI in STANDBY) asap with high intensity In case of MKI flashover: do not further increase vacuum thresholds (reduce thresholds in case of 2nd

flashover); carry out extended MKI SoftStart Carry out MKI sublimation (asap) if integrated vacuum above limits