In the Heavy Ion Medical Accelerator in Chiba

Sciences (NIRS), recent results of the development on two ECR ion sources named NIRS-ECR and NIRS-HEC are described. It was found that the elements of the gases used for producing a specific charge state of C ions affect the beam intensity. In the efforts for increasing the beam intensity at NIRS-HEC, it was shown that the ion-density distribution at the extraction slit should be matched with the extraction aperture. In order to optimize the ion-density distribution, three sextupole magnets with inner diameters of 46, 66, and 80mm were tested. Two-frequency heating of the plasma was tested by introducing an additional microwave power with variable-frequency. Generally, it enhances the beam intensity, but the additional microwave induces complicated effects on the behaviour of the source. The results suggest that the frequency of the additional microwave should be tuned finely in order to get a good performance.