Masatsugu Nishi

Development of Signal Processing Methods for Imaging Buned Pipes

A new imaging technique for subsurface radars is described for reconstructing clear images of buried pipes in soil. The method developed has two signal processing stages; preprocessing and aperture synthesis. The preprocessing extracts signals scattered from the pipes by reducing clutter noise. The synthetic-aperture processing analyzes only the scattered signals derived by the first stage and reconstructs high-quality images in a short processing time. The imaging technique developed was successfully applied to the imaging of actual buried metallic pipes. It was experimentally confirmed that the new imaging method was capable of reconstructing clear images in a short time without losing image quality.

Advanced subsurface radar system for imaging buried pipes

A subsurface radar system for imaging buried pipes was developed. The system is capable of reconstructing clear pipe images under unfavorable conditions, such as large attenuation rate of the radio waves propagating in soil. The output power of a pulse generator, the amplifier gain, and average number are controlled by moving the observation depth to improve the detection capability. Fast image processing methods are also used. A 6.5-cm-diameter steel pipe, buried at a depth of 2.5 m, was clearly reconstructed as a color image averaged attenuation rate of 12.6 dB/m in the soil. A plastic pipe (6.5 cm in diameter), buried at a depth of 1 m, was also imaged by the system. >

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.

A compact proton synchrotron with combined-function lattice dedicated for cancer therapy

A compact proton synchrotron with combined function lattice has been designed as a dedicated machine for cancer therapy because of its merits of easy operation and low construction cost. The lattice has a six-fold symmetry and its radius of curvature and circumference are 1.9 m and 23.9 m, respectively. For the purpose of establishing a good reference design, we have constructed a model magnet based on the three-dimensional magnetic field calculation. A magnetic field measurement has been performed with use of a three-dimensional Hall-probe. In the present paper, the results of these developments is presented together with the outline of the reference design.

Performance of parallel plate ionization chamber for medical irradiation

We have developed parallel plate ionization chambers (PPIC) to measure not only the cumulative intensity but also the time structure of slow-extracted heavy-ion beams from a medical synchrotron. The characteristics of the PPIC with 3 mm and 1 mm gap distances for 760, 200, 111, and 55 Torr air were investigated with C/sup 6+/ beam (290 MeV/u) at HIMAC. The applied voltage to start the plateau region strongly depends on the beam intensity, and pressure of counter gas. The PPIC can be also used as a useful beam monitor for the time-structure measurement of heavy-ion beams.

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>>

Beam-Profile Control Using an Octupole Magnet

For medical irradiation, beams with a uniform distribution have been required. We have proposed a method to control the beam profile using an octupole magnet. We have installed an octupole magnet and confirmed its effectiveness at the Heavy Ion Medical Accelerator in Chiba (HIMAC) beam-transport line. A beam efficiency of 91% can be realized with a flatness of ±4% over the range of ±15 mm. The beam offset at the position of the octupole magnet is required to be within ±0.2 mm to realize this condition. This method is expected to have a beam efficiency higher than that of the ordinary method using wobbler magnets and a scatterer system.

A compact proton synchrotron for cancer treatments

A compact proton synchrotron for cancer treatments is presented. In the present synchrotron, the beam can be accelerated up to 270 MeV for the application to proton radiography as well as cancer treatments. In order to shorten the straight section for the extraction deflector such as a septum magnet, the deflections clue to the defocusing quadrupole and edge type bending magnets in the synchrotron lattice are utilized effectively. The beam is extracted by the resonant extraction scheme which features that the position and gradient of the extracted beam are constant and the rapid switching is possible. Then, the present synchrotron can be applied to various irradiation schemes such as the double scattering, wobbler and raster scanning methods.

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.

New operation scheme for low emittance storage rings

Abstract We have proposed a new operation scheme to ease the small dynamic aperture problem at beam injections into low emittance storage rings. Electron beams are injected into the storage ring in a high emittance mode. Then the operation mode is transferred into a low emittance mode, while keeping the betatron tunes constant. The new operation scheme facilitates enlargement of the dynamic aperture during beam injections. A very large dynamic aperture is not necessary in the low emittance storage mode. The new operation scheme can realize a storage ring with an emittance lower than the conventional one.