R.C. Kirkpatrick

Magnetized Target Fusion: An Overview

AbstractThe magnetized target fusion (MTF) concept is explained, and the underlying principles are discussed. The necessity of creating a target plasma and the advantage of decoupling its creation ...

A physics exploratory experiment on plasma liner formation

Momentum flux for imploding a target plasma in magnetized target fusion (MTF) may be delivered by an array of plasma guns launching plasma jets that would merge to form an imploding plasma shell (liner). In this paper, we examine what would be a worthwhile experiment to explore the dynamics of merging plasma jets to form a plasma liner as a first step in establishing an experimental database for plasma-jets-driven magnetized target fusion (PJETS-MTF). Using past experience in fusion energy research as a model, we envisage a four-phase program to advance the art of PJETS-MTF to fusion breakeven (Q ∼ 1). The experiment (PLX) described in this paper serves as Phase 1 of this four-phase program. The logic underlying the selection of the experimental parameters is presented. The experiment consists of using 12 plasma guns arranged in a circle, launching plasma jets toward the center of a vacuum chamber. The velocity of the plasma jets chosen is 200 km/s, and each jet is to carry a mass of 0.2 mg to 0.4 mg. A candidate plasma accelerator for launching these jets consists of a coaxial plasma gun of the Marshall type.

Implosion of solid liner for compression of field reversed configuration

The design and first successful demonstration of an imploding solid liner with height to diameter ratio, radial convergence, and uniformity suitable for compressing a field reversed configuration is discussed. Radiographs indicated a very symmetric implosion with no instability growth, with /spl sim/13x radial compression of the inner liner surface prior to impacting a central measurement unit. The implosion kinetic energy was 1.5 megajoules, 34% of the capacitor stored energy of 4.4 megajoules.

Experimental and Computational Progress on Liner Implosions for Compression of FRCs

Magnetized target fusion (MTF) is a means to compress plasmas to fusion conditions that uses magnetic fields to greatly reduce electron thermal conduction, thereby greatly reducing compression power density requirements. The compression is achieved by imploding the boundary, a metal shell. This effort pursues formation of the field-reversed configuration (FRC) type of magnetized plasma, and implosion of the metal shell by means of magnetic pressure from a high current flowing through the shell. We reported previously on experiments demonstrating that we can use magnetic pressure from high current capacitor discharges to implode long cylindrical metal shells (liners) with size, symmetry, implosion velocity, and overall performance suitable for compression of FRCs. We also presented considerations of using deformable liner-electrode contacts of Z-pinch geometry liners or theta pinch-driven liners, in order to have axial access to inject FRCs and to have axial diagnostic access. Since then, we have experimentally implemented the Z-pinch discharge driven deformable liner-electrode contact, obtained full axial coverage radiography of such a liner implosion, and obtained 2frac12 dimensional MHD simulations for a variety of profiled thickness long cylindrical liners. The radiographic results indicate that at least 16 times radial compression of the inner surface of a 0.11-cm-thick Al liner was achieved, with a symmetric implosion, free of instability growth in the plane of the symmetry axis. We have also made progress in combining 2frac12-D MHD simulations of FRC formation with imploding liner compression of FRCs. These indicate that capture of the injected FRC by the imploding liner can be achieved with suitable relative timing of the FRC formation and liner implosion discharges.

Magnetized target fusion-an overview

Summary form only given. Magnetized target fusion (MTF) consists of the hydrodynamic compression of a wall-confined, hot, magnetized DT plasma to ignition conditions. Even in the absence of self heating, parameter studies have shown that targets with gains as high as ten are possible. To reduce the radiative energy loss from the plasma so that conduction is the major energy loss mechanism, the initial density of the DT is much lower than that used for inertial confinement fusion (ICF). This makes the targets larger, and the reduced losses allow a lower compression rate, so that the implosion time can be long and the necessary power and intensity on target can be very low. The parameter space for MTF is intermediate in density and time scales between those of ICF and magnetic-confinement for fusion energy (MFE).

Experimental measurements of a converging flux conserver suitable for compressing a field reversed configuration for magnetized target fusion

Data are presented that are part of a first step in establishing the scientific basis of magnetized target fusion (MTF) as a cost effective approach to fusion energy. A radially converging flux compressor shell with characteristics suitable for MTF is demonstrated to be feasible. The key scientific and engineering question for this experiment is whether the large radial force density required to uniformly pinch this cylindrical shell would do so without buckling or kinking its shape. The time evolution of the shell has been measured with several independent diagnostic methods. The uniformity, height to diameter ratio and radial convergence are all better than required to compress a high density field reversed configuration to fusion relevant temperature and density.

Particle and heat transport in a dense wall-confined MTF plasma (theory and simulations)

Plasma beta in magnetized target fusion systems is sometimes much greater than 1, and the plasma may be in direct contact with the imploding liner. Plasma processes are strongly dominated by inter-particle collisions. Under such conditions, the plasma microturbulence, behaviour of α-particles, and plasma equilibria are very different from conventional fusion systems. This paper contains the most comprehensive analysis of the corresponding phenomena to date. Two-dimensional numerical simulations of plasma convection in the targets of a diffuse pinch type demonstrate an onset of convection in this configuration.

Magnetized Target Fusion

Magnetized target fusion (MTF) seeks to take advantage of the reduction of thermal conductivity through the application of a strong magnetic field and thereby ease the requirements for reaching fusion conditions in a thermonuclear (TN) fusion fuel. A potentially important benefit of the strong field is the partial trapping of energetic charged particles to enhance energy deposition by the TN fusion reaction products. The essential physics is described. MTF appears to lead to fusion targets that require orders of magnitude less power and intensity for fusion ignition than currently proposed (unmagnetized) inertial confinement fusion (ICF) targets do, making some very energetic pulsed power drivers attractive for realizing controlled fusion.

Pulsed Laser Effects Phenomenology

A comprehensive overview of the phenomenology associated with the interaction of intense laser beams with matter is presented. The beam is assumed to be incident on a solid or liquid target located within a transport medium. The discussion is first categorized by the type of this medium; namely, vacuum, gas, liquid, solid or particulate. Then the dependence of the interaction is further classified by the laser flux, pulselength, wavelength and the target properties. The various classes of behavior are discussed along with the conditions for their occurrence. Classes discussed include: slow bulk heating, transparent vapor from the target surface, secondary energy transport to the ablation surface, laser absorption at the critical surface, shock induced blowoff, photoelectric cross section dependence on temperature and density, laser supported combustion and detonation, contained vaporization and Mie scattering.

Progress with developing a target for magnetized target fusion

Summary form only given, as follows. Magnetized target fusion (MTF) is an approach to fusion where a preheated and magnetized plasma is adiabatically compressed to fusion conditions. Successful MTF requires a suitable initial target plasma with an embedded magnetic field of at least 5 T in a closed-field-line topology, a density of roughly 10/sup 18/ cm/sup -3/, a temperature of at least 50 eV, and must be free of impurities which would raise radiation losses. Target plasma generation experiments are underway at Los Alamos National Laboratory using the Colt facility; a 0.25 MJ, 2-3 /spl mu/s rise-time capacitor bank. In the first experiments, a Z-pinch is produced in a 2 cm radius by 2 cm high conducting wall using a static gas-fill of hydrogen or deuterium gas in the range of 0.5 to 2 torr. Follow-on experiments will use a frozen deuterium fiber along the axis (without a gas-fill). The diagnostics include B-dot probes, framing camera, gated OMA visible spectrometer, time-resolved monochrometer, silicon photodiodes, neutron yield, and plasma-density interferometer. Operation to date has been with drive currents ranging from 0.8 MA to 1.9 MA. Optical diagnostics show that the plasma produced in the containment region lasts roughly 20 to 30 /spl mu/s, and the B-dot probes show a broad current-profile in the containment region. The experimental design and data will be presented.Magnetized target fusion (MTF) is an approach to fusion where a preheated and magnetized plasma is adiabatically compressed to fusion conditions. Successful MTF requires a suitable initial target plasma with an embedded magnetic field of at least 5 T in a closed-field-line topology, a density of roughly 10/sup 18/ cm/sup -3/, a temperature of at least 50 eV, and must be free of impurities which would raise radiation losses. Target plasma generation experiments are underway at Los Alamos National Laboratory using the Colt facility; a 0.25 MJ, 2-3 /spl mu/s rise-time capacitor bank. The goal of these experiments is to demonstrate plasma conditions meeting the minimum requirements for a MTF initial target plasma. In the first experiments, a Z-pinch is produced inside a 2 cm radius by 2 cm high conducting cylindrical metal container using a static gas-fill of hydrogen or deuterium gas in the range of 0.5 to 2 ton. Thus far, the diagnostics include an array of 12 B-dot probes, a framing camera, a gated OMA visible spectrometer, a time-resolved monochrometer, filtered silicon photodiodes, neutron yield, and plasma-density interferometers. These diagnostics show that a plasma is produced in the containment region that lasts roughly 10 to 20 /spl mu/s with a maximum plasma density exceeding 10/sup 18/ cm/sup -3/. The experimental design and data are presented.