Target Operation and

Status Report

Chris Booth for Target Team

20th October 2008

Chris Booth University of Sheffield 2

At June Collaboration Meeting:• Target installed and running in ISIS.• Stators rebuilt to address problems with electrical

breakdown.• Demonstration actuator (plus replacement) to be

ready for July/August.Since then:

• Demonstrator actuator bearings failed after only few days continuous operation (1 Hz).

• Target in ISIS has continued to run successfully.• Programme established to determine cause of

failure and prevent recurrence, with increased engineering input.

Chris Booth University of Sheffield 3

ISIS Target – mainly positive!• Target operation in ISIS for beamline studies –

>120K pulses have revealed no problems.• Actuation & control have operated flawlessly – no

target drops.• Raising & lowering system works fine.• Software (DAQ & monitoring) run well, allows

remote monitoring.• Target behaviour stable and reproducible.• System operated by non-experts.• Plans for enhanced control system, with

computer interface, “on hold”. (Thesis, bearings, …!)

Chris Booth University of Sheffield 4

Electrical Breakdown Issue• All coils tested to 1 KV before assembly.• Kapton insulation around coils.

– Note! This also affects thermal behaviour!

• Assembled stators re-tested to 1 KV.• Switching spikes measured – only 60V (on top of

220V supply).• Capacitor bank & power supply split to provide

±110V – lower voltage to ground.• Question: Is kapton between coils & cooling

shims overkill? Should it be removed to lower temperature (and hence resistance)??

– Was original problem mechanical damage not punch through?

Heating increases resistance, reducing acceleration

Chris Booth University of Sheffield 6

Demonstrator Target Problem• Two new target drives delivered to RAL late July.• One ran in R78 – failed after ~340K actuations.• Serious damage to shaft & bearing surfaces.• Significant abraded material, though little or none

fell through lower bearing.• Same stator had run with old shaft & bearings for

>500K actuations in Sheffield without problem.• Earlier shafts with DLC coatings ran >5M cycles.• Unclear why failed setup was different.• Weekly meetings Sheffield/RAL to try to identify

cause of problem and best way forward.

Chris Booth University of Sheffield 7

Possible failure causes• Misalignment of bearings and shaft.• Partial demagnetisation of permanent magnets

causing non-axial forces.• Distortion of coils causing non-axial forces.• Poorer quality DLC coatings on shaft and/or

bearings.• Dynamic or static distortion of shaft.

All the above are addressed in the following slides. Several experts from RAL, Sheffield Materials and outside companies (as well as MICE) have been consulted and provided valuable expertise.

Chris Booth University of Sheffield 8

Tests of possible failure causes (1)Misalignment of bearings and shaft • Bearings have sharp edges. Misalignment of

bearings would cause edges to cut into shaft.• Metrology at RAL have checked both stators. Both are

well aligned.

Distortion of coils causing non-axial forces ?• With improved electrical insulation, recent coils have

looked less uniform.• Craig MacWaters/Paul Smith are trying to map field inside

stator with (low) DC current. • Difficult job – high spatial precision needed. Will take time

to complete.• But this stator ran well with other shaft! Implies not likely

to be a stator problem!

Chris Booth University of Sheffield 9

Tests of possible failure causes (2)Partial demagnetisation of permanent magnets • Field at surface of sectored magnets measured in

Sheffield. (Not easy, because of small scale!!)

• No sign of significant azimuthal asymmetry.

Chris Booth University of Sheffield 10

Tests of possible failure causes (3)Poor Diamond-Like Carbon (DLC) coatings ?• Discussions with coating company (TecVac), who have seen

photos of failed parts. • QC sample indicates adherence normal, but thickness

2-3 μm cf 5-6 μm normal.• Could be surface contamination or inadequate polishing prior

to coating – most likely explanation according to TecVac.• Overall, this may be the most likely cause of failure.• Sheffield surface expert: wire erosion damage causes poor

adhesion.• RAL metrology & Sheffield expert: may be better to have

dissimilar materials in contact (not both DLC).• DLC coated shaft plus nickel coated bearings may be better.

Chris Booth University of Sheffield 11

Tests of possible failure causes (4)

Distortion of shaft ?

• Static: Metrology will perform precise measurements, but shafts are NOT perfectly straight. Always true? (Ti not rigid enough.)

• Dynamic: Stephanie Yang/Wing Lau modelling behaviour under acceleration.

• Andy obtaining high-speed camera to study present performance.

• Is Sheffield shock-absorbing mounting a significant difference? (Check: camera.)

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Way forward (1)• Some things can be checked reasonably quickly. Others need

a detailed study.• Two likely problem areas are rigidity of shaft and surface

coatings.• Required alignment precision is not really known.• We have 1 shaft (DLC coated, same batch as failure!) plus

spare bearings (coated & uncoated).• We have removed sharp edges from uncoated bearing set, and

had them electropolished to remove erosion damage then electroless nickel plated – very hard, smooth bearing surface.

• Plan to run existing shaft + new bearing. Inspect frequently for any start of damage. Preliminary result in one – two weeks.

• In parallel, several engineering studies aimed at a more robust design.

Chris Booth University of Sheffield 13

Way forward (2)• Wing/Stephanie continue FE study of shaft – vibration

modes, heat generation in bearings, etc. (Input from and verification with camera results.)

• Jason Tarrant considering:– Alternative coatings for present shaft and bearings.– Radically different shaft design to improve rigidity, ease of

construction.– Shorter shaft, revised bearing positions.

• Paul Smith (with assistance from Jim Rochford & others) to do FEA study of coil/magnet system, to determine lateral forces as function of misalignments.

• Adam Dobbs examining effect of target orientation w.r.t. beam on beam loss.

• Andy – engineering schedule.

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Conclusion• Target operation in ISIS shows actuation, control,

infrastructure working correctly.• Reproducibility of build & quality control (of

coatings) are issues.• Two-pronged approach adopted:

– New bearing coatings to be tried very soon.– Expanded engineering support for target team.– Improved engineering rigour in revised design –

mechanical and magnetic FEA etc.– Improved QA for production (electrical, magnetic,

mechanical).

• New target to be tested prior to installation for 15th January.