Neutron production rate and plasma characteristics of spherically convergent beam fusion

Abstract

Experimental and simulation results of a spherical glow discharge for a portable neutron source are presented. The experimental device is a 45-cm-diameter, 31-cm-high stainless-steel cylindrical chamber, in which a spherical mesh-type anode 30 cm in diameter is installed. The spherical grid cathode consists of 2.0-mm-diameter stainlesssteel wire, which is made into an open spherical grid of 5-cm diameter. The system is maintained at a constant pressure of 1 to 15 mTorr by feeding hydrogen or deuterium gas. The basic characteristics of breakdown voltages versus pressure and electrostatic potential profiles were measured for hydrogen discharge. Using deuterium, a steady-state neutron production of 10 4 s -1 was observed at a discharge of 40 kV, 2 mA. Motions of ions and electrons in the device were simulated by using a particle code, which is one-dimensional in coordinate system and two-dimensional in velocity space. It was confirmed by both the measurement and simulation that a virtual anode is formed in the central part inside the grid cathode. © 2001 Scripta Technica, Electr Eng Jpn, 135(2): 1

Investigations of Ion Confinement by Direct Current Coaxial Glow Discharge

“…Miley et al [5], who studied the breakdown voltage characteristics as a function of pressure-electrode separation (pd), using a spherical cathode grid mounted concentrically within a grounded spherical vacuum vessel, which served as the anode. Yamauchi et al [2], using a pulsed discharge confirmed, by experimental measurements and simulation calculations, that a virtual anode is formed in the central part inside the grid cathode in a spherical glow discharge for a portable neutron source. Popov et al [6] studied the electron energy distribution function and the temperature of the electron groups using a Langmuir single probe, in a dc discharge tube with coaxial electrodes, for argon plasma.…”

“…When the virtual anode is formed, it causes recirculation for some of positive ions toward the grid cathode and decelerates more of ions to converge at the center; hence ion density is slightly decreased. After that ions are converged at the center from all directions, so the ion density is increased again until it reaches the center at r = 0 [2,7]. It is noticed from Figure 11 that values of ion density calculated using Poisson equation are different from and less than that obtained using the single and double probes.…”

“…When an external dc voltage is applied between the cylindrical transparent grid cathode and cylindrical vacuum chamber (anode), the ion beam will be accelerated toward the grid, crosses through it and moves in the radial direction toward the center, forming a central virtual anode with high ion density. This virtual anode decelerates ions to reach the center by reflecting some of the ions toward its injection position [2]. The electrical characteristics of the virtual anode cylindrical glow discharge for Helium gas are measured.…”

“…After the ion beam starts to collide neutral gas atoms producing large number of secondary electrons and positive ions. A virtual anode is formed and decelerates these ions to reach the axis, means their kinetic energy is decreased and hence the potential increased as the probe moves from r = 12 mm inward toward the plasma core until reaching its maximum value at location of the virtual anode [2], i.e. at 2 mm and 8 mm, for discharge currents 10 and 20 mA respecttively (right hand side in Figure 5).…”

“…In a negative grid dc coaxial glow discharge, ions of the gas species are produced by electron-impact ionization. The ion beam is accelerated and passes through the grid cathode, forming a virtual anode which decelerates the ions to arrive at the center of the device [2]. The ion beam collides with the neutral gas atoms after it passes the grid cathode, causing secondary electrons to be emitted.…”