CLIC PMQ High-strength prototype Magnetic measurements Stage 1: Non-magnetic support Ben Shepherd May 2012

Non-magnetic test rig First phase of testing – no steel components (ballscrews / rails) PMs are moved in and out by hand, position fixed using plastic shims Field measurements carried out using movable Hall probe PM movement Aluminium frame Steel poles PMs

Gradient versus stroke Consistently about 1.4T/m less than model Plastic shims inserted in various combinations Stroke range: 0-66.5mm 07 x scan.xlsx Shim Thickness.xlsx

08 xz scan.xlsx Gradient profile Measured gradient vs longitudinal position (x on the bench; z in the model) Matches the model with a 4.9mm offset

Gradient quality & comparison with model Point-by-point measurements are noisy Fit cubic function to field Bfit = a3x3 + a2x2 + a1x + a0 Then: G/G0 – 1 = (a3x2 + a2x) / a1 Created 2D model with asymmetry – moved top section down 0.4mm Distance between poles: 26.92mm Reproduce observed gradient quality (+2%) Needs some improvement... 0.4mm 12 x scan.xlsx

Integrated gradient (strength) From central 10mm: IG0 = 7.200 T Model value (integrated By at x=1mm from z=4.9-185.9mm): 7.277 T Measurement is ~1% lower

Force measurements Measure torque needed to turn ballscrew using torque wrench – convert into horizontal force Measurement precision – 2-5% At zero stroke: 11.5-12kN Modelled force at zero stroke ~17kN This mechanism pulls one side away first – could be reason for discrepancy

Attempt to ‘fix’ poles Pole misalignment is likely source of poor field quality Corroborated by physical measurements: inscribed diameter out by up to 0.23mm Took core section out to ‘re-set’ pole positions Set correctly, measured with CMM, dowelled in place Placed back in rig  same problem  Poles are moving (slightly) as PMs are brought in Decided to move on with assembly of complete magnet Poles should be much more rigidly held 27.03mm 27.26mm (nominal: 27.20mm)

Summary: measurements, phase 1 Gradient vs stroke Slightly lower than expected (1.4T/m difference) Difference less at high gradient – could be due to slight inward movement of poles Integrated gradient About 1% less than expected, but still within spec for 120% of CLIC nominal (14.4T) Field quality +2% in ±11.5mm – spec is ±0.1% in ±11.5mm Should be better for phase 2 Maximum force required to pull PMs out 12kN – model 17kN Discrepancy could be due to slight rotation of PMs