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Scenarios for e-cloud studies with coated chambers in 2012

LIU-SPS e-cloud review, 11 January 2012, J. Bauche.

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Outline

Can we equip 2 MBB type magnets with pick-up probes through holes in the magnets?• 3D magnetic modeling of experimental set-up• Field quality degradation and mitigation measures• Simulation results• Conclusion and future work

Plans for installation of 2 half-cells with a-C coatings in 2012 • Current situation• Prospects and proposals for 2012

Can we install new coated chambers instead of doing the coating in-situ?• Impact of installing new chambers• Budget and resources• New coated chambers vs. coating in-situ

Conclusions

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Installation of e-cloud probes in MBB’s

3D magnetic modeling for the experimental set-up

Large model has required careful staged meshing to limit number of FE

E-cloud probe in the centre of the magnet requires drilling hole through half-yoke

Symetric holes on top and bottom half-yokes to avoid longitudinal effects

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Field quality degradation and mitigation measures Principle: flux density lost in the centre due to the hole is compensated at the magnet

ends with special pole shim sets

2 pole shim sets at each end of main dipoles to adjust magnetic length

Installation of e-cloud probes in MBB’s

Standard pole shim

Special pole shim

Standard pole shim cross-section

Special pole shim profile

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Simulation results Shim design optimization has been done at maximum current of LHC cycle (5750 A)

Installation of e-cloud probes in MBB’s

Δ ∫B.dl / ∫B0.dl [10-4] vs. horizontal position X in mid plane [mm]

Local field in probe centre and edges

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Relative integrated field errors at various coil currents

LHC cycle I max

(5750 A / ῀ 2 T)

CNGS - FT cycle I max

(4900 A / ῀ 1.8 T)

Non saturated iron

(2500 A / ῀ 1.8 T)

Installation of e-cloud probes in MBB’s

∫B.dl - ∫Bref.dl / ∫Bref.dl [10-4] vs. Horizontal position X [mm]

Saturation affects the correction efficiency of the special end shim in the range of 5.10-4. Results have been submitted for approval to BE/OP to check if this dynamic error is acceptable.

Drilling a hole on one single half-yoke could reduce the degradation of the field quality but would generate longitudinal effects needs further simulations (with shorter model!) before validation. It would however help saving a spare magnet…

Any solution will require a magnetic measurement to check if eddy current effects are negligible coating should be done in-situ afterwards!

Conclusion and future work

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Plans for installation of coated magnets in 2012

Situation of coated magnets installed in the SPS after this winter TS 2011-2012

Situation of spare dipoles after this winter TS 2011-2012

To ensure smooth operation during run 2012, we need 3 operational spares of each type

From on the mid of the run, we can reduce this number to 2 and recuperate the spares for coating in-situ

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Prospects and proposals for installation of additional coated magnets in the SPS in 2012

Plans for installation of coated magnets in 2012

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Coating the SPS by replacing the vacuum chambers

Installing new coated chambers in each of the 744 main dipoles of the SPS is equivalent to rebuilding a new accelerator. The machine characteristics (field quality, alignment, etc…) must be at least as good as what they are now. Any systematic error in reassembling the magnets could have a major impact on the performance and thus on the beam quality the SPS will provide afterwards, notably to the LHC.

This implies notably:– A careful (and probably long) preparation of the project with:

• A review (+ upgrade ?) of the specifications of the machine (tolerances on systematic / random bending strength and field uniformity errors, tolerances on alignment, etc…)

• Setting up a strong QA plan

• Hiring a large number of (competent) persons and training them to the magnet assembly process

– The development of non-polluting magnetic measurement techniques

– Most probably to build a new big building for setting up a sufficiently large workshop inside (depending on the requested cadencies to meet the timelines) and to design and purchase dedicated assembly, measurement and test equipment

– To store a large part of the magnets (building ?) before reinstallation as to be able to sort and distribute the magnets along the machine (w.r.t. individual errors)

– Etc…

Impact of installing new coated chambers

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Coating the SPS by replacing the vacuum chambers

Please refer to previous talks for details of the estimates:– Resources Needed for Coating Project - 19 May 2009 @ SUSG

– Estimates for strategies for coating with or without opening the magnets – 01 April 2010 @ TFSU

– Preliminary report of TFSU – 14 April 2010 @ LMC

In summary :– Budget: 13 to 18 MCHF for replacing the chambers vs. 4 to 5 MCHF for coating in-situ

(depending on cadency)

– Resources: 25 FTE for replacing the chambers vs. 13 FTE for coating in-situ

Remember extent and limits of these estimates:– Coating of only the main dipoles. Pumping port shieldings, quadrupoles and SSS not

included.

– Estimate given for the project done in one shot @ nominal cadency. Start up, end phases and possible splitting of the project in several stages not included in the budgets.

– Construction of new buildings for storage and workshop not included

Budget and resources

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Coating the SPS by replacing the vacuum chambers

Coating in situ– More advantageous regarding budget, resources and timelines

– Workshops enough larges already exist at CERN

– Technical justification for not using this method was the possible problem of ageing of the carbon layer. Is it still valid with the hollow cathode method?

New coated chambers:– Means rebuilding a new machine is much more risky!

– Is 4 times more expensive, requires 3-4 times more personnel

– Needs in addition the construction of new building(s)

– Is not needed for combining it with a major consolidation so far

– Do the accelerator complex present timelines allow to implement such a large scale project ?

New coated chambers vs. coating in-situ

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Conclusions

Additional simulations are needed to assert if the installation of probes to monitor the e-cloud through 2 MBB yokes is feasible.

Installing 2 half-cells of main magnets with coated vacuum chambers in 2012 is at the limit of the feasibility w.r.t. the available number of spares as well as the resources for doing the work. Any magnet that would have to be replaced during the run for maintenance reasons would strongly impact on the proposed coating program.

Except if there is a major technical reason not to use the in-situ coating method, the potential benefits of replacing the vacuum chambers for coating dipoles in the whole SPS do not balance the costs and risks it implies.

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Spare slides