Computational Accelerator Physics 2002 - Beam Theory Group ...

0 20 40 60 80 100 120 140
12
x 10 -3 B3.
x 10 -4 B7.
-0.04
0.14
0.12
-0.06
0.1
-0.08
0.08
-0.1
0.06
0.04
-0.12
0.02
-0.14
0
Step 0 20 40 60 80 100 120 140
Step
Figure 9. Field errors (left right in Tesla at a reference radius of 17 mm) as a function
of the excitation step. First the decapole (outer layer coil) is ramped up to about 0.25 of its
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nominal field value (step 10). Then the octupole (inner layer coil) is powered up to its nominal
field value (100 A, step 20). Subsequently the octupole field is ramped up and down between
+100 (step 20, 60, 100) and -100 A (step 40, 80, 120).
6. Conclusions
A vector magnetization model for superconducting multi-filamentary wires in the coils
of accelerator magnets has been developed. It describes arbitrary excitational cycles, in
particular also excitations for which the magnetization is not parallel to the external field. The
model has been combined with numerical field computation for the calculation of field errors
in magnets with nested coil geometries and local saturation of the ferromagnetic yoke. The
material related input parameter is only the critical current density (which can be measured on
the strand level). Arbitrary excitational cycles can now be studied and optimized for machine
operation.
References
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