An embodiment of the magnetized target fusion concept in a spherical geometry with stand-off drivers

Abstract

In order to maximize the K-line radiation from imploding gas puff loads driven by high current, pulsed power generators such as the DECADE Module 2 (DM2), initial puff diameters of 5-10 cm are required to provide implosion times of 200-300 ns. To date, such implosions have been found to produce lower-than-predicted yields. Lack of uniformity in the initial current flow through the neutral gas is offered as one of the possible reasons. If so, sufficient pre-ionization of the gas should mitigate this problem.A uv source was designed to pre-ionize a 7-cm diameter argon gas puff to be employed on the DM2 generator at Primex Physics International Company. The source is a 19-cm diameter cylinder consisting of two flashboards bent into semi-circles. The flashboard plasma is directed toward the axis of the cylinder which is co-linear with the axis of the gas nozzle. The plane of the flashboard is located 18 cm from the nozzle exit so that the ionizing uv is emitted at 60-80" angles and promptly illuminates the gas while the flashboard plasma arrives at the PRS load region about 4 ps later. The pre-ionization is measured absolutely using a high-sensitivity interferometer with which we can discriminate between phase shifts due to neutral argon and those due to free electrons as a function of space and time. Pre-ionization levels in the I-10% range were measured near the outer edge of the DM2 nozzle rendering this outer layer sufficiently conductive to carry the DM2 current.In addition to the DM2 application, it is anticipated that a version of this uv pre-ionization scheme will be utilized on neon gas puffs driven by the NRL Hawk generator.An innovative fusion scheme, embodying the principles of magnetized target fusion (MTF), in which the initial magnetized target and a plasma liner containing a cold fuel layer are introduced into the reactor vessel in a stand-off manner, is discussed. Two compact toroids containing fusionable materials are introduced into a spherical reactor target chamber in a diametrically opposing maimer. Embedded in the compact toroids are force-free magnetic fields in Woltjer-Wells-Taylor's state of minimum energy, which are known experimentally to be extraordinarily stable. They collide in the center to form an initial magnetized target plasma. A spherical distribution of plasma jets are then launched fiom the periphery of the vessel, coalescing to form a converging spherical plasma liner. On impact with the central plasma, the plasma liner sends a shock wave through it, shock heating it to some elevated temperature (above 100 eV) which sets the initial adiabat for subsequent compression. The high temperature immediately raises the electrical conductivity of the plasma to the extent that it traps the magnetic flux inside the central plasma. The central plasma is further compressed by the plasma liner and heated nearly adiabatically to conditions for thermonuclear burn, the magnetic flux being compressed with it. The thermal loss rate, greatly reduced by the high magnetic fields, are sufficiently lo...

One-dimensional radiation-hydrodynamic scaling studies of imploding spherical plasma liners

“…Imploding spherical plasma shells, or "liners," formed by an array of convergent high-Mach-number (M) plasma jets, are potentially attractive for forming cm-and µs-scale high-energy-density (HED) plasmas for scientific studies and as a standoff driver magneto-inertial fusion [1,2,3,4] (MIF). The Plasma Liner Experiment (PLX) [5] at Los Alamos National Laboratory (LANL) plans to merge thirty high-M dense plasma jets in spherically-convergent geometry to explore the feasibility of forming imploding spherical plasma liners.…”

Plasma Liner with an Intermediate Heavy Shell and Thermal Pressure Drive

“…An advantage of the plasma liner approach in general [8][9][10], and the heavy liner approach in particular (this paper) is that there is no need for any direct material connections of the primary energy source and the target and, therefore, the "stand-off" problem is solved.…”

“…Potentially more attractive solution is offered by the concept of the plasma liner [8,9], in which very high Mach number jets would be generated by plasma guns situated on the walls of the explosion chamber and merge near the target, to form a 3D pusher for the target. This approach, in principle, allows avoiding the use of any material structures connecting the target with the "external world."…”

Magneto-Inertial Fusion

“…To test the possibility of a standoff driver [34,35] (one without physical leads to the liner thus avoiding repetitive hardware destruction), a plasma liner formed from multiple plasma jets [17,18] is being pursued again at LANL, i.e., plasma-jet-driven MIF or PJMIF, funded by an ARPA-E for the next 3 years under its accelrating low-cost plasma heating and assembly (ALPHA) program. A 2.7-meter diameter spherical vacuum chamber is the centerpiece of the plasma liner experiment (PLX) at LANL, which has also conducted basic plasma shock experiments [19,20,36,37] using two plasma railguns that were developed by HyperV Technologies Corporation.…”