M. Shiho

Fe-based nanocrystalline FINEMET cores for induction accelerators

Abstract Pulse power modulators used for high repetition rate linear induction accelerators are generally composed of main switches using thyratrons, step-up pulse transformers, multistage magnetic pulse compression circuits and pulse forming lines. Fe-based amorphous cores are normally used for saturable reactors in linear induction accelerators, because the volume of the saturable reactor using Fe-based cores is small due to its high effective induction swing. However, there is a great demand to reduce the core loss in order to improve the efficiency of pulse power modulators. Recently, a new Fe-based nanocrystalline soft magnetic materials, FINEMET, that has both high saturation flux density and low core loss was developed. The dynamic magnetic characteristics of an insulated FINEMET core were measured using a high voltage pulse excitation circuit, and the total core volume and the total core loss for saturable reactors in a 2-stage magnetic pulse compression circuit were calculated. As the result, by using the FINEMET cores for saturable reactors in a magnetic pulse compression circuit, the total core loss becomes 68%, and the total core volume becomes 133%, of the conventional Fe-based amorphous cores.

Millimeter wave amplification in a free electron laser with a focusing wiggler

A mm wave amplifier experiment on a free electron laser was performed using an intense, mildly relativistic electron beam (0.7–0.9 MeV) with a combination of a focusing planar wiggler and a weak additional axial magnetic field in the so‐called ‘‘group 1’’ region. A beam transport ratio of over 80%, through the whole wiggler length, was realized. In an amplification experiment, a spatial growth rate of 56 dB/m was obtained at a frequency of 45 GHz, and a power saturation was observed at a level of 6 MW, where the total gain was estimated to be 52 dB. It was shown that the off‐axis component of the beam contributes considerably to the rf amplification in the focusing wiggler.

Charge exchange neutral particle mass and energy analyzer for the JT‐60 tokamak

Design considerations and experimental results are described for a charge exchange neutral particle mass and energy analyzer for JT‐60, which analyzes H, D, and He simultaneously up to a maximum energy of 110 keV. The analyzer has separately a 180° deflection magnet for momentum analysis and an electrostatic deflector for mass analysis. The way to control the effect of the electric fringe fields in order to expand the detectable energy range is studied by numerical simulation. The deflector is then designed, made of two triangular plates and three additional electrodes for the control of the fringe fields. The effect of the deflector is demonstrated experimentally. Energy and mass resolution and the relation between the incident ion energy and the magnetic field strength are measured. The results of the calibration experiments agree with the designed value.

A new FEL concept driven by a vacuum microfielf emitter

Abstract In order to reduce the scale and construction cost of free election lasers, it is necessary to investigate various new ideas with respect to electron beam generation, acceleration and radiation mechanism. In this paper, a microscale free electron laser is proposed which is driven by a very small diameter (less than a few μm) electron beam. The microscopic electron beam can be generated with a needle cathode, for an example, a Spindt cathode. By injecting the microscopic electron beam into a microdielectric channel, we generate radiations of several μm wavelength by Cherenkov emission, Smith-Purcell emission and so on. In the design of a microfield emitter FEL (MFE FEL). It is shown that a 2 mm long dielectric pipe with an electron beam of diameter 1 μm and with a current of 50 μA gives a one pass gain of 50% for a 10 μm wavelength radiation.

Active Beam Scattering Method for Measurement of Ion Temperature in JFT-2 Tokamak Plasma

The capability of determining ion temperature by neutral beam scattering was investigated, and the ion temperature of an ohmically-heated JFT-2 tokamak was determined using a neutral beam scattering system. In the scattering experiment, a continuous beam of 15 keV hydrogen atoms was used with a scattering angle of 4°C. The ion temperature obtained by this method agreed with that deduced from measurement of passive charge-exchange neutrals. The influence of impurities on the scattering spectrum was investigated, and it was found that the difference between the intensity estimated from Rutherford scattering theory and the observed intensity increased with the atomic number of the target particle. It was established that the fact that impurity ions did not contribute to the scattering intensity arose from the ionization of the neutral beam by collision with impurity ions.

Design study of mm to nm diameter electron beams for submillimeter-wave to X-ray free-electron lasers

Microfabricated field-emitter tips and arrays are promising candidates for an electron source of compact FELs. Examples are presented of moderate-energy high-brightness electron beams which are small in diameter and expected to be generated with the use of a Spindt cathode.

Multi-Channel Mass-Separated Neutral Particle Energy Analyser for Simultaneous Measurements of Hydrogen and Deuterium Atoms Emitted from Tokamak Plasma

A mass-separated neutral particle energy analyser able to carry out the simultaneous measurement of hydrogen and deuterium atoms emitted from a tokamak plasma was constructed. The analyser was calibrated for the energy and mass separation in the energy range from 0.4 keV to 9 keV. It was installed in the JFT-2 tokamak in order to investigate the behavior of deuterons and protons in a JFT-2 tokamak plasma heated by ion cyclotron wave and neutral beam injection. It was found that the energy spectrum could be determined with sufficient accuracy, and the ion temperature obtained from the energy spectrum was in good agreement with the ion temperature deduced from the Doppler broadening of the impurity ion line.

Laser-driven vehicles: from inner space to outer space

Laser supported propulsion of a micro-airplane with water-covered ablator is demonstrated. The repetitive use of overlay structure is experimentally demonstrated with specially-designed water supply. The various transparent overlay is investigated by the CIP-based hydrodynamic code and experiments by pendulum and semi-conductor load cell. The momentum coupling efficiency of 5000 N-sec/MJ has been achieved by ORION experiments that agree with the simulation code. With the maximum efficiency approximately 105 N- sec/MJ predicted by the simulation, 30 pulses of MJ laser can give the sound speed to 10tons airplane. The concept can also be used for driving a micro-ship inside human body and a robot under the accidental circumstance of nuclear power reactor in which large amount of neutron source makes electronic device useless.

JAERI millimeter wave FEL experiments with a focusing wiggler

Abstract The first results of the JAERI millimeter wave FEL experiments with a focusing wiggler are presented. The induction linac delivers a 1 MeV, 1 ∼ 3 kA beam in a wiggler whose magnets have a curved surface; the wiggler has 30 periods of 5 cm. We found that such a focusing wiggler is essential for beam transport at low energy and high current. The power and spectrum of the superradiant emission have been measured. The growth rate of the radiation is 0.4 dB/cm.

Experiments with field-emitter arrays for free electron micro-laser applications

Abstract Propagation characteristics of beams extracted from double-gated field-emitter arrays (FEAs) were investigated. The beams were accelerated to several keV in a 15-mm long gun region and the whole beam traversed a distance of 1 m. Separate images of emitting tips were formed, when operating the focus lens of FEAs, on a fluorescent screen located at the downstream end. The images became clearer when the beam focusing was assisted by either an electrostatic or magnetic lens arranged in the transport system. A quadrupole lens was employed to determine the emittance diagram of the beam. It was verified that beamlets emitted from the tips were distributed on a straight line in the transverse trace plane. Normalized emittance of the beam thus obtained was a few times 10 −7 π m rad, independently of the beam current within a measured range of 10 nA–50 μA.