Junichi Hirota

FINEMET-CORE LOADED UNTUNED RF CAVITY

Abstract A testing machine for an untuned RF cavity loaded with FINEMET cores was fabricated to realize a wide operation frequency range and a high accelerating gap voltage. The cavity performance was examined in low and high power tests. The operation frequency range was widened to 0.5–10 MHz, where the voltage standing wave ratio (VSWR) was lower than 2. A heat-up test showed the cavity could induce an accelerating gap voltage of 200–300 V/core, only by forced air cooling. Applications of the untuned RF cavity to various kinds of synchrotrons are discussed, based on the results of the performance tests.

A ferrite loaded untuned cavity for a compact proton synchrotron

A small untuned RF cavity using a doubly re-entrant resonator and Ni-Zn ferrite cores with highly complex permeability has been designed for a compact proton synchrotron. A new method for power feeding named as multiple power feeding (multi-feed coupling) as against to direct coupling was developed to increase the accelerating voltage. The RF power is fed into the cavity through a set of couplers with the same number as the ferrites. The coupler consists of one-turn loop which is wound on to each ferrite core. The effect of multi-feed coupling was verified by measurements of the VSWR and electric field in the accelerating gap using the low and the high power model cavities.

Novel Design for Electromagnet with Wide Excitation Range

A novel design for an electromagnet with a wide excitation range is described. The magnetic field distribution of an electromagnet usually deforms as the excitation approaches the saturation level. This effect can be minimized if the saturation of the ferromagnetic material is uniform; the integrated magnetic field along a flux line \intH ds in the pole is uniform for all flux lines crossing the gap area of interest. This condition can be realized by adding vacant portions into low flux density regions in iron poles, and thus the magnetic flux density in the iron region becomes uniform. This magnetic flux density equalizer can be applied to a variety of magnets: flat dipoles, n-indexed dipoles, quadrupoles and higher-order multipole magnets.

An untuned RF cavity using multifeed coupling

Abstract A ferrite-loaded untuned RF cavity was designed and fabricated as the accelerating structure for a compact proton synchrotron dedicated to cancer therapy. An invented power-feeding method, “multifeed coupling”, was used to achieve a gap voltage higher than 700 V with an applied RF power of 1.2 kW in the frequency range 1.5–8 MHz and a cavity length 0.4 m. The temperature in the ferrite cores had less than a 22°C rise from room temperature using only forced air cooling.

Resonant beam extraction with constant separatrix

A new scheme for slow beam extraction using nonlinear resonance is presented to realize small emittance. In the scheme, the amplitude of the betatron oscillations is increased by perturbations, while keeping the separatrix constant. As a measure of perturbation, the transverse filtered noise is studied in computer simulations. It is shown that the emittance of the extracted beam is vanishingly small. It is also shown that the time structure of the extracted current is not affected by the ripple in the magnet current.<<ETX>>

Energy varying resonant beam extraction from the synchrotron

Two different operating schemes for the energy varying beam extraction from the synchrotron are presented based on the resonant extraction scheme in which the transverse RF perturbation is applied for increasing the amplitude of the betatron oscillations with keeping the separatrix of the resonance constant. The first operating scheme is that the primary acceleration is followed by the second acceleration, during which the beam is extracted by the above extraction scheme. In order to keep the separatrix constant during the extraction, the currents of the magnets are ramped with keeping the mutual ratio. In the other operating scheme, the currents of the magnets are ramped from the injection energy level to the maximum level and the beam is extracted with a constant energy at an intermediate stage. The ramping pattern can be commonly used for the beam extraction at the different energy level.