Injection Considerations for Scrubbing Run C. BRACCO, M.J. BARNES, W. BARTMANN, B. GODDARD, M. MEDDAHI, J. UYTHOVEN ACKNOWLEDGMENTS: M. DI 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 mm38 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: Procedures Measures 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  m and dump limit = +/-200  m  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 Castro M. Donze

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 Scrubbing run 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  m 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

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 operational  Same 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/STI  Continue 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 MKI8D MKI8C 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 MD M.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 breakdown  Maximum 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

2012 Scrubbing Run: Observations  The interlock levels were gradually increased during the run:  Tanks: 2∙10 -9 mbar  4∙10 -9 mbar  Interconnects: 1∙10 -8 mbar  4∙10 -8 mbar  No flashover and relatively low heating. TI8 Interconnects Highest values at MKI extremes (contribution from Q4)

LS1 Vacuum Related Upgrades Heating collar Heating collar control box  MKIs have background pressure of few x 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 H 2 into test tank (no magnet, only screen conductors connected to pulsed HV) – no increase in electrical breakdown rate up to mbar but no ionized gas! New NEG coated bypass tubes

Multipacting in Ceramic Tube During 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 Beam Prior 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 mbar Seuil 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 2 nd flashover); carry out extended MKI SoftStart  Carry out MKI sublimation (asap) if integrated vacuum above limits