Field mapping system and field adjustment for a 230-MeV proton cyclotron

To produce a 230 MeV proton beam, a new 4 T superconducting isochronous azimuthally varying-field (AVF) cyclotron, which is the smallest among AVF cyclotrons for proton beam therapy, is under development. In this project, to obtain the required field, a new mapping system was developed, and magnetic-field mapping and adjustments were conducted. The mapping system measures the field of the cyclotron using six Hall probes, whose positions are changed by a linear stage and a rotary stage. The results of field mapping tests conducted indicate that the system has sufficiently repeatability and reproducibility Further, the results of subsequent successful field measurements confirm that the field-adjustment methods are able to control the field.