Sunao Kawasaki

Gyrotron Backward Wave Oscillator Experiments with a Relativistic Electron Beam Using an X-Band Rectangular Waveguide

A mildly relativistic electron beam (500keV, 200A, 10ns) injected into an X-band rectangular waveguide immersed in a uniform axial magnetic field (4-10kG) produced magnetically tunable microwave radiation in the 9-13 GHz frequency range with an estimated output power of 1MW. The frequency range and tunability of the radiated microwave agreed with a theoretical model for a gyrotron backward wave oscillator taking into account the low energy component of the beam electron.

System Design of Heavy Ion Fusion Experiment

A brief description is given on the design of a high energy accelerator system for an intense heavy ion beam as an igniter of the inertial fusion. The compromise between the requirements for the final beam and the cost is the problem of principal concern. The flexibility and the reliability of the design, including the use of the system with the multiple purposes in the wide range of science other than the nuclear fusion, are also considered.

Resonance absorption of radiation field by an intense relativistic electron beam in inverse cyclotron maser geometry

Attenuation of the radiation field by an intense, mildly relativistic electron beam moving in a longitudinal magnetic field was studied experimentally in the frequency range of x‐band microwaves. Nearly complete absorption of the radiation externally injected along the beam was found to be near a particular value of the axial guide magnetic field. The interaction mechanism is identified as the coupling between the waveguide modes and the beam cyclotron wave propagating backwards. It is concluded that the absorption should be the inverse process of the electron cyclotron maser by a dense relativistic electron beam.

Higher Frequency Operation of Linear Accelerator

The high frequency operation of linacs is discussed and several trial designs for fusion material irradiction test facility in Japan are given. The size of linac namely the construction cost may be reduced by using 1 MW CW klystrons with the frequency of about 1 GHz. Preliminary results of the fabrication technique for the linac drift tube by copper coating are shown.

Compression System in ERA of IPP-Japan. : II. Experimental Result

During the adiabatic compression of an electron ring, negative mass instabilities have been observed. To interpret these experimental results, the pillbox model is applied to the closed cylindrical structure of the vacuum chamber, and the effects of the self-fields of the electron ring and beam loading are considered. Using such a model we can explain the experimental results.

Design study of fusion material irradiation test facility in Japan

Abstract The design studies of the testing facility for fusion material irradiation following the concept of FMIT have been carried out based on current technology for accelerators, fusion reactors and materials. The facility consists of three sub-facilities: accelerator, target assembly and service cell. Special consideration has been given to fulfill the specifications of high current accelerator and to perform highly reliable operation of two to three years without maintenance. Balance between remote maintenance and adoption of low activation materials is the key issue of this facility to raise the operational performance.

Accelerator component development for fusion material test device

Abstract Preparation of high current steady state ion source, fabrication of linac tanks by coating method, and development of high power high frequency power tube are described. The first one is the application of bombarded cathode to ion source with rather high operating pressure of 150 Pa, and the second is an application of coating technique primarily developed for tokamak divertor plate to linac cavity. Copper coating onto aluminium substrate is prepared and the measurements of the change of Q-value with coating thickness of 10 ∼ 30 μm is performed. The development of high power high frequency tube of 500 MHz frequency range for continuous operation is also described.

RFQ for Heavy Ion Fusion

RFQ is promising as low ß linac for heavy ion fusion. The bunching characteristics for 238U++l beams have been investigated and the primary results have been shown. There is a possibility of obtaining sufficiently narrow longitudinal emittance and acceleration of several MeV within reasonable distance.

Guiding of Intense Relativistic Electron Beams with an Axial Magnetic Field

Intense relativistic electron beams guided by an axial magnetic field are investigated under some experimental conditions. The beam envelope reveals a spatially periodic structure in the uniform axial field, and the wavelength of the periodicity cannot be explained by a simple rigid rotor model, but by taking the beam deceleration due to the beam potential into consideration. The rapid beam destruction at a hump region in the guiding field is observed and discussed.

Equilibrium and Destruction of a REB in a Magnetic Guide

A REB with a relatively small ¿/ ¿ (320 keV, 0.75 kA and 1.0 MeV, 1 kA) is injected into an axial magnetic guide in the injection system of ERA device of IPP-Nagoya. The beam surface envelope reveals an outstanding spatially periodic structure in the uniform field and the wave length and the REB parameters in the guide are found to be well consistent with the values predicted with a particular kind of the equilibrium model, proposed by Diament a few years ago. A rapid destruction of the REB during the passage through a magnetic hump and with an abrupt change of the surrounding metal wall radius is observed and discussed briefly.