Kai Masuda

Measurements of strongly localized potential well profiles in an inertial electrostatic fusion neutron source

Direct measurements of localized electric fields have been made by the laser induced fluorescence (LIF) method using the Stark effect in the central cathode core region of an inertial electrostatic confinement fusion (IECF) neutron (proton) source. These are expected to have various applications, such as luggage security inspection, non-destructive testing, land mine detection and positron emitter production for cancer detection, currently producing continuously about 107 n/s D-D neutrons. Since 1967, when the first fusion reaction was successfully proved to have taken place in a very compact IECF device, potential well formation due to the space charge associated with spherically converging ion beams has been a central key issue remaining to be clarified in beam-beam collision fusion, which is the major mechanism of the IECF neutron source. Many experiments, although indirect, have been done so far to clarify the nature of the potential well, but none of them has produced definitive evidence. The results found by the present LIF method show a double well potential profile with a slight dip for ion beams with relatively larger angular momenta, whereas for ions with smaller angular momenta, a much steeper potential peak develops.

Inertial electrostatic confinement fusion device with an ion source using a magnetron discharge

An inertial electrostatic confinement (IEC) fusion device is studied for a compact fusion neutron/proton source using a built-in magnetron ion source. The addition of an ion source to the IEC fusion device enhances fusion reactions by allowing a lower operating gas pressure and by providing a beam-like ion energy distribution. Under lower gas pressures, charge exchange collisions are reduced, resulting in longer ion lifetime and thus enhanced ion re-circulation. The performance characteristics of this IEC fusion device found in the experiments were compared with the numerical calculations and found qualitatively in good agreement. An improvement in normalized neutron yield (defined as neutron yield divided by the product of grid current and operating gas pressure), more than a factor of two, has been observed compared with the conventional glow-discharge driven IEC fusion device.

Lasing at 12 µm Mid-Infrared Free-Electron Laser in Kyoto University

Laser amplification using a 12 µm mid-infrared free-electron laser (MIR-FEL) was observed at the Institute of Advanced Energy (IAE), Kyoto University. A 25 MeV electron beam of 17 A peak current was used for the lasing experiment. A beam loading compensation method with an RF amplitude control in the thermionic RF gun was used to extend the macropulse duration against the backbombardment effect in the thermionic RF gun. As a result, an electron beam with a 4 µs duration was generated. A laser output with an intensity 50 times as high as the spontaneous emission intensity was observed. FEL gain was estimated to be 16% from the exponential growth of the laser output signal, and a cavity loss of 2.8% was estimated from the decay of the laser output signal. Three-dimensional (3D) FEL simulation was also performed to achieve the gain saturation in our FEL device.

Simulations of electron backstreaming in a microwave thermionic gun

Abstract Electron trajectories in a 4 + 1 2 RF gun were calculated by a 2-D simulation code newly developed with full Maxwellian equations with space charge effects taken into account self-consistently to evaluate RF gun performance characteristics, in particular, the effects due to backstreaming electrons. The energy spectra, and current profile of the backstreaming electrons were calculated to show appreciable concentration to the limited area of the cathode, and also that the high energy backstreaming electrons are mainly originated in the 4th cavity of the RF gun.

Conceptual design of a nuclear material detection system based on the neutron / gamma-ray hybrid approach

A nuclear material detection system based on neutron / gamma-ray hybrid approach has been proposed for the container inspection at the sea port. The neutron from the inertial electrostatic confinement fusion source will be used for a fast pre-screening process. The quasi-monochromatic gamma-ray beam from the laser Compton Backscattering source will be used for an isotope identification for the precise inspection. Nuclear resonance fluorescence method will be employed for the isotope identification because of its high selectivity and high penetration for the shielding.

Research and Development of the Humanitarian Landmine Detection System by a Compact Fusion Neutron Source

Results of 5 years task are described on the research and development of the advanced humanitarian landmine detection system by using a compact discharge-type fusion neutron source called IECF(inertial-electrostatic confinement fusion) device and dual sensors made of BGO and Nal. With 107 neutrons/s stably produced in CW mode, 10.8 MeV, gamma rays from (n, gamma) reaction with nitrogen atoms in the explosives (explosive simulant in our study) are measured for two kinds of explosives(TNT, RDX), under the conditions of three different buried depths, and soil moistures. Tentative detection probability for arid soil is found to be in excess of 80%.

Non-destructive inspection system for special nuclear material using inertial electrostatic confinement fusion neutrons and Laser Compton Scattering Gamma-rays

A study of a non-destructive inspection system for hidden special nuclear materials in the cargo container at the sea port has been carried out under a promotion of Japan Science and Technology. This inspection system consists of an active neutron detection method for a fast screening purpose and a nuclear resonance fluorescence (NRF) method for isotope identification. The inertial electrostatic confinement fusion device has been developed for a neutron source and two neutron detection methods, the Feynman-alpha method and high energy neutron detection method, have been examined to realize the fast screening system. Generation of a quasi-monochromatic gamma-ray beam from the laser Compton Backscattering by using a compact microtron electron accelerator and an NRF experiment on uranium target using a new type of scintillation detector, LaBr3(Ce), has been studied to realize the isotope identification system.

Performance Characteristics of an Inertial Electrostatic Confinement Fusion Device with a Triple-Grid System

Abstract Performance characteristics of an inertial electrostatic confinement fusion triple-grid system are experimentally studied to provide an ample fusion reaction rate under a lower-gas-pressure region to make the operation free from glow discharge restrictions between the discharge voltage, current, and gas pressure. With a filament to provide sufficient electrons, the operating gas pressure is found to reduce down to 1/5 for the same discharge current and voltage. Although the gas pressure region that was achieved still remains the region where the fusion reaction between the ion beam and background gas is dominant, the neutron yield normalized by the gas pressure in the triple-grid system shows higher value than the conventional single-grid system.

Particle-in-Cell Simulation of Inertial Electrostatic Confinement Fusion Plasma

Abstract A particle-in-cell calculation code was made to simulate the operation of an inertial electrostatic confinement (IEC) fusion device. The computation includes the effects of ionization by electron impact. Several techniques to save computational time are introduced in this program code. One of them is time-dependent fine space meshes used in the regions where the particles concentrate. Several superparticles that have similar radial position as well as similar energy are merged, while one superparticle is divided into several particles with a somewhat different velocity when the total number of superparticles decreases. The methods enable more precise determination of the characteristics of an IEC device in a shorter time than by previous methods.

Evaluation of thermal effects due to back-streaming electrons in the IAE RF gun

Back-streaming electrons in thermionic RF guns give a serious thermal effect to a cathode. In this study, the back-streaming beam power onto a thermionic cathode of the IAE RF gun was evaluated quantitatively by using an infrared radiation thermometer. Time evolutions of cathode surface temperature during RF macro-pulse were also calculated by using a simple 1-dimensional heat conduction model and results of a 2-dimensional particle simulation for several methods expected to reduce back-bombardment effect.