Katsumi Masugata

APPLICATIONS OF INTENSE PULSED ION BEAM TO MATERIALS SCIENCE

In addition to being initially developed as an energy driver for an inertial confinement fusion, an intense, pulsed, light‐ion beam (LIB) has been found to be applied to materials science. If a LIB is used to irradiate targets, a high‐density ‘‘ablation’’ plasma is produced near the surface since the range of the LIB in materials is very short. Since the first demonstration of quick preparation of thin films of ZnS by an intense, pulsed, ion‐beam evaporation (IBE) using the LIB‐produced ablation plasma, various thin films have been successfully prepared, such as of ZnS:Mn, YBaCuO, BaTiO3, cubic BN, SiC, ZrO2, ITO, B, C, and apatite. Some of these data will be presented in this paper, with its analytic solution derived from a one‐dimensional, hydrodynamic, adiabatic expansion model for the IBE. The temperature will be deduced using ion‐flux signals measured by a biased ion collector. Reasonable agreement is obtained between the experiment and the simulation. High‐energy LIB implantation to make chemical co...

SYNTHESIS OF NANOSIZE POWDERS OF ALUMINA BY ABLATION PLASMA PRODUCED BY INTENSE PULSED LIGHT-ION BEAM

Nanosize powders of alumina have been synthesized by high‐density ablation plasma produced by the irradiation of an intense, pulsed, light‐ion beam on an aluminum target in oxygen. Diameters of the powders, which are observed to be spherical, are typically 5–25 nm. At 1 Torr of oxygen, nanosize powders of aluminum are synthesized with those of a small amount of γ‐alumina. At 10 Torr of oxygen, on the other hand, γ‐alumina powders are produced with a small amount of aluminum powders. Annealing characteristics in nitrogen have also been studied on the transition from γ‐ to α‐alumina.

Mechanism of microwave generation by virtual cathode oscillation

A simple model is developed to describe the virtual cathode oscillation. With this model, it is found that the frequency dependence of the microwave power gain is determined by the phase relation between the oscillating electric field and the modulated electron beam current. Analytical expressions are given for the frequency dependence of the gain and for estimation of the maximum efficiency of microwave energy extraction from the electron beam.

Effect of longitudinal magnetic field on microwave efficiency of virtual cathode oscillator

The effect of a longitudinal magnetic field on the microwave efficiency of a virtual cathode oscillator is investigated by particle-in-cell simulations. The mechanism of the oscillation associated with microwave emission is physically understood. It is found that the reflection of the electron beam back to the diode region is important to the oscillation. When a longitudinal magnetic field is applied, the residence time of the electrons in the potential well is lengthened, resulting in a large energy spread of the electron beam, which reduces the output power of the microwave.

Preparation of BaTiO3 thin films by backside pulsed ion‐beam evaporation

Barium titanate (BaTiO3) thin films were successfully prepared in situ on Al/SiO2/Si(100) substrates by backside deposition from intense, pulsed, ion‐beam evaporation using a 1.3 MeV, 50 ns, 25 J/cm2 ion beam. Good morphology of the films prepared was observed, where no droplets appear compared to normal frontal‐side deposition. The deposition rates were typically 100 nm/shot. The films were perovskite polycrystals. The capacitance of the thin films (at 1 kHz) increased from 3 to 10 nF/mm2 with increasing substrate temperature from 25 to 250u2009°C, respectively.

Characteristics of pulsed power generator by versatile inductive voltage adder

A pulsed power generator by inductive voltage adder, versatile inductive voltage adder (VIVA-I), which features a high average potential gradient (2.5 MV/m), was designed and is currently in operation,. It was designed to produce an output pulse of 4 MV/60 ns by adding 2 MV pulses in two-stages of induction cells, where amorphous cores are installed. As a pulse forming line, we used a Blumlein line with the switching reversed, where cores are automatically biased due to the presence of prepulse. Good reproducibility was obtained even in the absence of the reset pulse. Within ∼40% of full charge voltage, pulsed power characteristics of Marx generator, pulse forming line (PFL), transmission line (TL), and induction cells were tested for three types of loads; open-circuit, dummy load of liquid (CuSO 4 ) resistor, and electron beam diode. In the open-circuit test, ∼2.0 MV of output voltage was obtained with good reproducibility. Dependences of output voltage on diode impedances were evaluated by using various dummy loads, and the results were found as expected. An electron-beam diode was operated successfully, and ∼18 kA of beam current was obtained at the diode voltage of ∼1 MV.

Diagnosis of high‐brightness ion beams produced in point pinch diodes

Diagnosis and evaluation have been carried out of the ion beam and anode plasma produced in a ‘‘point pinch diode.’’ From the measurement of a highly resolved Thomson‐parabola mass spectrometer, the ions accelerated in the diode gap contain (a) protons, (b) highly ionized carbon and oxygen ions, and (c) singly ionized medium mass ions such as carbon, oxygen, CO+2, OH+, H2O+. Time‐integrated x‐ray and particle pinhole images show the spot size of the electron beam on the plasma to be less than 0.5 mm in diameter, in which fine structures are found with size less than 0.1 mm. A Kα satellite line of Alu2009V is observed with a crystal spectrograph, which indicates the existence of Al4+ in the plasma.

New configuration of a virtual cathode oscillator for microwave generation

A new configuration of a virtual cathode oscillator is proposed for high‐power microwave generation. Analysis and simulation are carried out to investigate the characteristics of this configuration. In the numerical simulation, the microwave output power of ∼564 MW is obtained with an electron beam of 300 keV in electron energy and 15 kA in beam current, giving a beam‐to‐microwave efficiency of ∼12.5%. The significant features of the new configuration are (1) the microwave output power is not affected by an electron energy spread up to 6%; and (2) no significant change of the oscillation frequency is observed when the beam current changes from 10 to 20 kA.

Three-dimensional, tight focusing of intense pulsed light-ion beam by spherical plasma focus diode

A new type of ion-beam diode, self-magnetically insulated, spherical plasma focus diode (SPFD), was developed. With the SPFD, three-dimensional focusing of an intense pulsed light-ion beam was obtained. Experiments and simulations were carried out to study the behavior of the SPFD. In the experiments, diagnostic results of the Rutherford scattering pinhole camera and the shadow-box showed that the ion beam was focused into a small cylindrical area with ∼0.5 mm in diameter and ∼2.5 mm in length. The average ion-beam current density at the anode surface was found to be ∼2 kA/cm 2 . In the simulations, it was observed that most of the diode gap is well insulated by the self-magnetic field induced by the diode current. The electron sheath in the diode gap significantly enhances the ion flow from the anode. As a result, the ion current density is several times higher than the single-species space-charge limited value.

Development of high voltage step-up transformer as a substitute for a Marx generator

A new type of pulse transformer has been developed as a substitute for a Marx generator. In the transformer amorphous metallic cores are utilized with windings of cylindrical conductors. As a result, low leakage inductance is realized with high breakdown strength. The coupling coefficient of the transformer is estimated to be more than 0.99. By using the transformer of winding ratio of 1:3, a Blumlein pulse forming line of capacitance 20 nF is successfully charged up to 270 kV by using a capacitor bank of 240 nF, 90 kV. High speed charging of charging time=250 ns is realized with high efficiency of energy transfer (energy transfer efficiency from the capacitor bank to the pulse forming line was evaluated to be 76%).