Virtual Cathode lifetimes and floating potential measurements in a Polywell {\ texttrademark} fusion device

Physics of Plasmas, 2010

2000

The goal of the Penning Fusion eXperiment-Ions (PFX-I) is the production of thermonuclear conditions in a Penning trap by means of spatial and/or temporal compression of a high temperature plasma. The present approach involves the confinement of positive ions in a virtual cathode produced by a nonthermal (beam-like) electron plasma held within a Penning trap of modified geometry. We will report on the first evidence of ions trapped in this manner. Experimental evidence of the maintenance of the non-Maxwellian electron energy distribution needed to produce the virtual cathode and progress on optical diagnostics will also be presented.

Physics of Plasmas, 2019

An experiment on the formation of virtual electrode and ion sheath characteristics has been carried out in a hot cathode discharge plasma produced inside a cylindrical inertial electrostatic confinement fusion device. The plasma parameters such as electron temperature and plasma density are evaluated by using a Langmuir probe. Transition from a single potential well to multiple potential wells, i.e., virtual electrodes inside the cathode grid, is observed when the bias voltage applied to the cathode is increased from-1000 to-5000 V. An emissive probe has been used for the measurement of plasma potential due to its greater accuracy than the conventional Langmuir probe. Ion sheath potential structures and presheath characteristics for different cathode potentials have been investigated using the emissive probe and are found to be consistent with the Debye sheath model. A detailed discussion on the obtained results has been presented in this paper.

The Inertial Electrostatic Confinement Fusion Reactor (IEC Fusion) is a potential method for controlled fusion power. The IEC fusion reactor confines plasma via a strong electrostatic potential between two concentric grids as ions stream towards the center. The electrostatic potential between the outer grid and the inner grid is on the order of magnitude of tens of kilo volts, and the outer grid is usually grounded. Gas species such as Deuterium and Tritium are injected into a vacuum chamber housing the grids, usually at pressures on the order of a millitorr. Once ionized by the electric field, the ions accelerate radially toward the central grid, colliding with other ions of sufficient relative velocity to undergo fusion. Those ions that shoot through the center without fusing will decelerate and fallback towards the center, making another pass. This method of confinement therefore has two advantages: Plasma recirculates around the central grid making multiple passes and hence increasing the likelihood of fusion. Optimal fusion cross section is on the order of hundred million Kelvins, while difficult to achieve conventionally, it translates to only tens of kilo electron volts, which is fairly easy to achieve via electrostatics. There are also difficulties associated with IEC fusion. Several loss mechanisms limit its ultimate power output, the most significant being Coulomb interactions, causing bremsstrahlung radiation and thermalization of ion velocities, and ion-grid collisions. This thesis investigates the fusion performance of a cylindrical IEC device, this will be done via computational modelling, and iterative numerical simulations of performance parameters. A set of optimum design parameters will be derived from the simulations, and a preliminary design for an IEC device will be given. The results were not surprising, there is an optimum operating voltage of approximately 190 kV. The optimum pressure and chamber size is approximately 1 meter at 1 millitorr. The grid transparency has a dramatic effect on the performance as well, but this is material limited to 98%. A novel method of reducing grid collisions is being researched by the US Navy currently, in which electrons are trapped to form a virtual cathode, using magnetic fields. This is termed the Polywell.

Elektronika ir Elektrotechnika, 2014

A new inertial electrostatic confinement (IEC) fusion device is proposed. The device contains two ion guns which feed the plasma media by deuterium ions. The device is designed in three dimensions and the finite difference method is applied to satisfy the boundary values of the cylindrical chamber. It is the first time that both the ions and electrons are simulated in this geometry by particle in cell (PIC) technique. Ions and electrons can interact with six bar-sized cathodes of the chamber and each other as a result of many-body problem. The device has a central dc current-carrying rod, which generates a homogeneous magnetic field surrounding the six cathodes. Thus we expect a better confinement compared to the conventional devices. The simulation records the real-time position and momentum by using the electromagnetic equations together with the momentum equations. The dynamics of the particles is seen to be complicated with vibrations on the horizontal plane due to the field.

Physics of Plasmas, 2015

Theory for a gridded inertial electrostatic confinement (IEC) fusion system is presented that shows a net energy gain is possible if the grid is magnetically shielded from ion impact. A simplified grid geometry is studied, consisting of two negatively-biased coaxial current-carrying rings, oriented such that their opposing magnetic fields produce a spindle cusp. Our analysis indicates that better than break-even performance is possible even in a deuterium-deuterium system at bench-top scales. The proposed device has the unusual property that it can avoid both the cusp losses of traditional magnetic fusion systems and the grid losses of traditional IEC configurations.

arXiv (Cornell University), 2015

Theory for a gridded inertial electrostatic confinement (IEC) fusion system is presented that shows a net energy gain is possible if the grid is magnetically shielded from ion impact. A simplified grid geometry is studied, consisting of two negatively-biased coaxial current-carrying rings, oriented such that their opposing magnetic fields produce a spindle cusp. Our analysis indicates that better than break-even performance is possible even in a deuterium-deuterium system at bench-top scales. The proposed device has the unusual property that it can avoid both the cusp losses of traditional magnetic fusion systems and the grid losses of traditional IEC configurations.

Physics Letters A, 2017

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights • Deuterium plasma of a cylindrical inertial electrostatic confinement fusion device has been characterised using Langmuir probe and OES. • Plasma temperature is 3 eV in the case of hot cathode discharge whereas 10 eV in the case of cold cathode discharge. • The plasma density is two to three orders more in case of the hot cathode discharge than the cold cathode discharge. • The discharge modes such as "star" and "jet" are witnessed in the case of cold cathode discharge. • The observation of spontaneous oscillation along with the harmonics has been reported.

2019

The goal of this presentation is to describe a fusion reactor based on a magnetic bottle using magnetic confinement for electrons and electrostatic confinement for ions. It produces nuclear fusions with a yield, unfortunately, extremely low, this one being defined by: “Kinetic fusion products energy / Electric energy consumed”. This presentation relies on the Multiplasma particular simulator program version 1.10 (not public) developed by the author and used for the simulation of such reactor. The studied reactor supposes the use of a Deuterium/Tritium fuel. The problems of tritium regeneration, neutrons management relatively to materials and radiation hygiene are not addressed. This article is only concerned by the fusion aspect exclusively.

2004

Significant experimental and theoretical progress has been made in the U.S. heavy ion fusion program on high-current sources, injectors, transport, final focusing, chambers and targets for high energy density physics (HEDP) and inertial fusion energy (IFE) driven by induction linac accelerators. One focus of present research is the beam physics associated with quadrupole focusing of intense, space-charge dominated heavy-ion beams, including gas and electron cloud effects at high currents, and the study of long-distance-propagation effects such as emittance growth due to field errors in scaled experiments. A second area of emphasis in present research is the introduction of background plasma to neutralize the space charge of intense heavy ion beams and assist in focusing the beams to a small spot size. In the near future, research will continue in the above areas, and a new area of emphasis will be to explore the physics of neutralized beam compression and focusing to high intensitie...