MEASUREMENT OF BEAM PHASE USING PHASE PROBE AT THE NIRS-930 CYCLOTRON

Abstract

The NIRS-930 cyclotron of the National Institute of Radiological Sciences (NIRS) has been used for production of short-lived radio-pharmaceuticals for PET, research of physics, developments of particle detectors in space, and so on[1]. The NIRS-930 has twelve trim coils for generation of the isochronous fields. Until recently, currents of the twelve trim coils had been adjusted only by monitoring the output beam intensity. In order to exactly produce the isochronous fields, a phase probe has been installed in the NIRS-930. The beam phase excursion could be reduced within 10 degree. INTRODUCTION The NIRS-930 (Km=110 MeV, Kf=90 MeV) has been used for radio isotope manufacturing of short-lived radiopharmaceuticals, such as Cu, Ge, Mg I At. In such an operation, long hours duration of stable high intensity beam was required. And, the beam of various particles and energies were required for various experiments such as biological and physical experiments. The generation of the isochronous fields is necessary in the operation with parameter of various particle and energy. The NIRS-930 has twelve trim coils for generation of the isochronous fields. The currents of the twelve trim coils had been adjusted only by monitoring the output beam intensity before installation of the phase probe. The isochronous field was indefinite because the beam phase was not able to be measured. Therefore, a phase probe has been newly installed in order to exactly produce the isochronous fields. PHASE PROBE FOR NIRS-930 This phase probe was a product by SHI (Sumitomo Heavy industries) with reference to design of a phase probe for cyclotron at TIARA (Takasaki Ion Accelerators for Advanced Radiation Application). This phase probe was composed of pairs of 10 upper and lower electrodes, size of which is 40 ~ 93 mm (azimuthal width) x 58 mm (radial length). The radial position of the 10 sets phase probe and radial distribution of magnetic field generated by each twelve trim coils in the NIRS-930 is shown in Fig. 1. Until now, only dispersion of beam phase was measured for adjustment of current of the trim coil. That beam phase measurement was not calibrated with acceleration phase, a zero was output of phase probe P1 that is innermost electrode in this measurement. In order to adjust the acceleration phase for an ideal phase, it is necessary to calibrate with acceleration phase. Figure 1: The radial distribution of magnetic field generated by trim coils at maximum current (in the main magnetic average field of 8.8 [kGauss]) and radial position of the phase probe. P2 P3 P4 P5 P6 P7 P8 P9 P10 P1 C1 C2 C3 C4 C5 C6 C7 C8 C9 C11