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

2. 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

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

4. 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

5. 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

6. Integrated gradient (strength)
From central 10mm: IG0 = T
Model value (integrated By at x=1mm from z= mm): T
Measurement is ~1% lower

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

8. 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)

9. 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