Target Status Report Chris Booth & Paul Hodgson Sheffield 18 th Sept ember2008

Chris BoothUniversity of Sheffield 2 Current Status 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 fell through lower bearing. Same stator had run with old shaft & bearings for >500K actuations in Sheffield without problem. Earlier shafts with DLC coatings run >5M cycles. Unclear why failed setup was different. Weekly meetings Sheffield/RAL to try to identify cause of problem and best way forward.

Chris BoothUniversity of Sheffield 3 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 have been consulted and provided valuable expertise.

Chris BoothUniversity of Sheffield 4 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. Tom Bradshaw/Jim Rochford will try to map field inside stator with (low) DC current. Difficult job – high spatial precision needed. Will take time to prepare. But this stator ran well with other shaft! Implies not likely to be a stator problem!

Chris BoothUniversity of Sheffield 5 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 BoothUniversity of Sheffield 6 Tests of possible failure causes (3) Distortion of shaft ? Static: Metrology will perform precise measurements, but shafts are NOT perfectly straight. Always true? (Ti not rigid enough.) Dynamic: Wing Lau to model behaviour under acceleration. Andy to try to get high-speed camera. Poor 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. 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).

Chris BoothUniversity of Sheffield 7 Way forward Some things can be checked quickly. Others need a detailed study. Two likely problem areas are rigidity of shaft and surface coatings. We have 1 shaft (DLC coated, same batch as failure!) plus spare bearings (coated & uncoated). Will remove sharp edges from uncoated bearing set, electropolish to remove erosion damage, electroless nickel plate – very hard, smooth bearing surface. Company found who can do this within 2 weeks. Run existing shaft, new bearing. Inspect frequently for any start of damage. Preliminary result by Collaboration Meeting. In parallel, RAL engineering effort to look at improvements to design of shaft (rigidity, mass) and other components for more robust design.