• W. Beeckman
  Sigmaphi, Vannes
• J. Simkin
  Vector Fields Ltd., Oxford
• M.N. Wilson
  Oxford Instruments, Accelerator Technology Group, Oxford, Oxon

A tender for the study and construction of a large superconducting split solenoid for the C400 carbon therapy cyclotron was issued by IBA in March 2008 and awarded to Sigamphi. Although the current density is moderate, the large radius and average field imply quite a high level of hoop stress. Simple formulas range between 140 and 180 MPa and, with such large values and uncertainties, it was felt necessary to perform a finite element analysis of the structure. Average fields in a cyclotron are very well modeled using an axially symmetrical structure and the stress was therefore studied using the stress module of the Vector Fields Opera2d suite. Different models were tried with different levels of details. A comparison is made between them as well as with the analytical results.