T. Uesugi

Advanced RF-KO slow-extraction method for the reduction of spill ripple

Two advanced RF-knockout (RF-KO) slow-extraction methods have been developed at HIMAC in order to reduce the spill ripple for accurate heavy-ion cancer therapy: the dual frequency modulation (FM) method and the separated function method. As a result of simulations and experiments, it was verified that the spill ripple could be considerably reduced using these advanced methods, compared with the ordinary RF-KO method. The dual FM method and the separated function method bring about a low spill ripple within standard deviations of around 25% and of 15% during beam extraction within around 2 s, respectively, which are in good agreement with the simulation results.

Source of spill ripple in the RF-KO slow-extraction method with FM and AM

The RF-knockout (RF-KO) slow-extraction method with frequency modulation (FM) and amplitude modulation (AM) has brought high-accuracy irradiation to the treatment ofa cancer tumor moving with respiration, because ofa quick response to beam start/stop. However, a beam spill extracted from a synchrotron ring through RF-KO slowextraction has a huge ripple with a frequency of around 1 kHz related to the FM. The spill ripple will disturb the lateral dose distribution in the beam scanning methods. Thus, the source ofthe spill ripple has been investigated through experiments and simulations. There are two tune regions for the extraction process through the RF-KO method: the extraction region and the diffusion region. The particles in the extraction region can be extracted due to amplitude growth through the transverse RF field, only when its frequency matches with the tune in the extraction region. For a large chromaticity, however, the particles in the extraction region can be extracted through the synchrotron oscillation, even when the frequency does not match with the tune in the extraction region. Thus, the spill structure during one period ofthe FM strongly depends on the horizontal chromaticity. They are repeated with the repetition f of the FM, which is the very source ofthe spill ripple in the RF-KO method. r 2002 Elsevier Science B.V. All rights reserved.

Development of FFAG Accelerator at KEK

The 150MeV proton FFAG accelerator is constructed and a beam is extracted at the final energy. This is the prototype FFAG for various applications such as proton beam therapy. We are now in preparation for using an extracted beam in the practical applications.

Electron Cooling of Bunched Beams

Experiments of electron cooling have been done with the HIMAC synchrotron in NIRS. Limitation on cooled beam‐sizes in longitudianl and transverse spaces were measured. The effect of space‐charge field and intra‐beam scattering are investigated.

Optical Matching of Slowly Extracted Beam with Transport System at HIMAC

Matching of twiss parameters between the ring and the transport line plays an important role in controlling the beam size. At HIMAC, thus, matching of twiss parameters was realized by using the simulation result. As a result, it was verified that the calculation result was in good agreement with the measurement of the beam size. The distribution of the beam profile in the transport line was also in good agreement with the particle tracking result. This paper describes the controllability of the slowly extracted beam and related development at HIMAC.