Koichi Kasuya

Method of processing ion energy distributions using a Thomson parabola ion spectrograph with a microchannelplate image converter camera

A Thomson parabola ion spectrograph (TP) is a very useful tool for the investigation of pulsed laser ablation. Measurements performed with the TP give useful information about physical processes, ion species and their energy distributions, as well as charge states. For ions with the lower charge states, q<20, complete information about energy distributions of all ionization states of ions can be obtained from a single laser shot. For ions with higher ionization states, parabolas generated in the TP interfere and it is impossible to get energy distributions for all the ion species. In this situation, the registered ions are composed of a few groups with different charge states and different energies. The TP enables the charge states and energetic ranges of different ion groups to be estimated. This presentation describes a method of processing experimental results, obtained from a TP, using a microchannelplate (MCP) image converter. Ion energy distributions for C1+–C6+ and Ta1+–Ta12+ are shown, and the eff...

New type of pulsed ion source with cryogenic anode

A magnetically insulated diode with a cryogenically refrigerated anode is proposed and a prototype of such a diode is constructed. H2O ice is produced on an anode which is cooled with liquid nitrogen. A small machine, consisting of a marx generator and a blumlein line, is used to extract ion beams from the diode. Proton beams of about 50 A and 70 keV are obtained with good reproducibility. Diode electrical characteristics and the extracted beam performance are also examined.

A new pulsed cryogenic proton source cooled by liquid helium

A new cryogenic proton source with liquid helium cooling system is presented. The anode is cooled down to about 4.2 K. A hydrogen ice is produced on the surface and used as the ion source. Proton beams of a current density 21 A/cm2 at 200 kV are extracted with good reproducibility. This new ion source is expected to be a proton source without contamination by nonprotonic ions.

Characteristics of a transverse-flow CO laser excited by RF-Discharge

We have developed a compact, efficient kW-class CO laser excited by transverse radio frequency (RF) discharge. The discharge and output characteristics of the RF-excited CO laser were investigated and were compared with those of the DC-excited one. The RF discharge power at 13.56 MHz was supplied to a discharge volume of 40H/spl times/35W/spl times/280L (mm/sup 3/). Utilization of the RF excitation instead of the DC excitation enhanced the maximum input power, the electrical conversion efficiency and the beam quality. Six gas conditions (pressure, temperature, flow speed, and the concentrations of CO, N/sub 2/, and O/sub 2/) were chosen as the experimental parameters. The optimum values of the gas parameters to maximize the output power were 50 torr, 200 K, 17 m/s, 5%, 12% and 0.4% respectively. The maximum output power obtained was 1.32 kW, with an electrical conversion efficiency of 27% and a slope efficiency of 39%. The specific laser power, which characterizes the scaling law of a transverse-flow laser, was 4.6 kW/m for the length, and 3.3 W/cm/sup 3/ for the volume. >

Electrical Discharge Channel in Sodium Vapor Initiated by Resonant Laser Light

A z-discharge channel in sodium vapor was initiated by a laser beam, which was tuned to the sodium D resonance line (λ=589 nm). Applying a voltage sufficiently lower than the self-breakdown voltage, the discharge of ~40 cm in length was initiated by laser radiation of modest power density. Streak-camera photographs showed that the laser-initiated discharge channel was produced just along the laser beam path. It was confirmed that the resonant laser light was very effective for the channel initiation.

Thomson parabola ion energy analyzer with a coincident and jitter‐free applied electric field ramp

A simple Thomson parabola ion energy analyzer for intense pulsed ion beam is demonstrated. Beam ions collimated by two apertures, are deflected by a time ramping electric field and a static magnetic field. The ramping electric field is produced with a stacked cable pulser powered by a voltage divider of the pulse power generator. As there is no additional switching tube and no high‐voltage generator other than the main machine, the analyzer has an electric field ramp that is coincident and has no jitter with the ion beam. A temporal history of ion beam energy is measured as an example and a reasonable agreement with the measured diode voltage is obtained.

Laser initiation of an electrical discharge channel in cesium contained gas

A high power laser light tuned to the resonance line (455.5 nm) of the cesium atom induced photoionization in argon buffer gas and initiated a channel discharge of 60 cm length. The time lag from the laser injection to the channel breakdown was observed and compared with numerical result based on a simple model of the discharge channel. It was confirmed that good agreement was obtained between both time lags. A simple model well described the fundamental characteristic of the channel breakdown.

Pulsed ion beam generation with cryogenic‐anode diode

Magnetically insulated ion diodes with a cryogenically refrigerated anode are proposed and their characteristics are examined. Proton beams of 7 A/cm2 and deuteron beams of 5 A/cm2, with energy of about 80 keV are extracted from a refrigerated H2O or D2O anode with good reproducibility and reasonable repetition rate.

Ablation rate estimation of inertial fusion reactor candidate material with intense ion beam and X-ray

Various candidate materials were collected from many sources. Some of them were irradiated with intense proton beams at Yokohama campus of Tokyo Institute of Technology (TITech), and some others were irradiated with intense nitrogen beams at Albuquerque site of Sandia National Laboratories (SNL). Intense X-rays of SNL were also used to irradiate other materials including the above collected ones. A series of numerical calculations of X-ray ablations was additionally performed at TITech, which results were compared with the experimental ones. Our aims were to supply necessary data for the future design of inertial fusion reactor chambers. One of the key issues in this field was the ablation thickness of the various chamber wall materials with typical inertial fusion reactions. We measured the ablation thickness of various samples, and we also observed the surface conditions of the samples before and after the irradiations with a microscope and an X-ray luminescence composition analyzer.

Vacuum ion source diagnostics at the Tokyo Institute of Technology

After a brief review of various diagnostics for vacuum ion sources measured data are presented for the particle distributions within the anode/cathode gap regions using passive spectroscopy, active laser interferometry, and resonant laser-induced fluorescence, while the extracted ion beams were observed by particle track detectors of both time-integrated and time-resolved types. Also measured were the prompt gamma-rays and the D-D neutrons when the beams hit the targets. The experimental arrangements of these diagnostics, together with some examples of the typical results obtained, are shown. It is discussed how various kinds of particles were distributed within the ion diodes, and how they were extracted from the source regions. >