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During Magnetized Target Fusion (MTF), also known as Magnitoye Obzhatiye (MAGO) in Russia, preheated and magnetized target plasma is hydrodynamically compressed to fusion conditions. Because the magnetic field suppresses losses by electron thermal conduction in the fuel during the target implosion heating process, compression may take longer than traditional inertial confinement fusion. Hence, “liner-on-plasma” compressions, magnetically driven using relatively inexpensive electrical pulsed power, may be practical. A candidate target plasma, MAGO, was originated in Russia and is now under joint development by the All-Russian Scientific Research Institute of Experimental Physics (VNIIEF) and Los Alamos National Laboratory (LANL). Other possible target plasmas now under investigation at LANL include wall-supported, deuterium-fiber-initiated Z-pinches and compact toroids. Such target plasmas are undergoing detailed computational modeling. Also undergoing computational modeling are liner-on-plasma compressions of such target plasmas to fusion conditions. Experimental and computational investigation of liner implosions suitable for MTF continues. Results will be presented.

Experiments on measurements of the electron concentration and electrical conductivity in weakly non-ideal dense helium plasma were carried out by the interaction of plasma with a strong magnetic field. Explosively driven shock tubes were used for plasma generation. To obtain a strong magnetic field a solenoid was wound over the tube. To avoid plasma heating by the electrical field eddy current, a high level of conductivity was generated behind the reflected shock wave. Electron concentration was defined by measurements of Hall voltage. The four-point probe method was used to measure electrical conductivity. Experimental data are compared with the calculations.

Magnetized Target Fusion (MTF) target plasmas are being characterized at the Los Alamos National Laboratory Colt facility. The goal of this project is to demonstrate plasma conditions meeting the requirements for an MTF initial target plasma. In the experiments discussed, a z-directed current is driven through a polyethylene fiber that explodes, producing a plasma which is subsequently contained in a 2 cm radius by 2 cm high cylindrical metal wall. Technical limitations prevented the use of a cryogenically frozen deuterium fiber, as originally planned. Therefore, a polyethylene fiber was used to study plasma dynamics and to look for evidence that an exploding-fiber plasma would eventually become quiescent as the plasma expands and contacts the containing metal wall; i.e., becomes wall-confined and wall-stabilized.

In the MAGO system, plasma cooling due to the classical electron and ion thermal conduction is nonessential, owing to severe plasma magnetization. Drift flows of heat, particles and magnetic flux are more important. Their values are estimated during the preliminary heating stage, as well as during the subsequent implosion and ignition stages. The influence these flows have on plasma cooling can be significant and should not be neglected, especially during the subsequent implosion stage. Increasing plasma density or system size can reduce their impact. For electron and ion components, these flows can be taken into account as a form of the Hall and Leduc-Righi effects and heat transportation by current.

A comparative analysis is presented of the positive and negative features of systems using magnetic compression of the thermonuclear fusion target (MAGO/MTF) aimed at solving the controlled thermonuclear fusion (CTF) problem. The niche for the MAGO/MTF system, among the other CTF systems, in the parameter space of the energy delivered to the target, and its input time to the target, is shown. This approach was investigated at RFNC-VNIIEF for more than 15 years using the unique technique of applying explosive magnetic generators (EMG) as the energy source to preheat fusion plasma, and accelerate a liner to compress the preheated fusion plasma to the parameters required for ignition. EMG based systems produce already fusion neutrons, and their relatively low cost and record energy yield enable full scale experiments to study the possibility of achieving ignition threshold without constructing expensive stationary installations. A short review of the milestone results on the road to solving the CTF problem in the MAGO/MTF system is given.

There has been a recent rebirth of interest in the use of imploding liners to attain conditions for controlled thermonuclear fusion. Much of the latest interest has involved compression of plasmas in which magnetic fields provide thermal insulation from colder boundaries, rather than mechanical support of the plasma. This Magnetized Target Fusion” (MTF) vs. magnetic-confinement fusion benefits from the rapid and efficient compression of the plasma by liner implosion. Such implosions have been demonstrated in both theta-pinch and z-pinch forms, using cylindrical and quasi-spherical shells driven by fast capacitor banks. It has been almost thirty years since the last major effort on imploding liners for fusion, which was prompted by work in the Soviet Union and extended by the development of reversible, liquid-metal liner systems at the Naval Research Laboratory, Washington, DC. Here, we briefly review lessons learned and technical issues affecting both reactor embodiments and laboratory development of liner/plasma compression.

Perpendicular collisionless shock waves (CSW), in plasma consisting of two species of ions with initial zero β, are considered in 1-D stationary problem formulation. CSW is assumed composed of a narrow resistive front caused by anomalous resistance and heat conduction, followed by a stationary structure in which formation of self-consistent interaction of ion flows plays the principal role. CSW structure is determined for various Alfven-Mach numbers below critical value, for which the existence of such a solution is possible, and relative fractions of electron and ion heatings are found. It is shown that in two-flow CSW with Alfven-Mach numbers higher than some value, ions, having small velocity deviations from main flows and moving across fields of the obtained solution, experience parametric resonance and in this sense CSW may be considered unstable for these Alfven-Mach numbers.

The possibility of plasma acceleration in an exploding wire and its intensive heating in the presence of a strong axial magnetic field was shown in [1,2]. In [3] the simple model of plane stationary plasma flow through the magnetic field was solved. It was shown that when the initial velocity of the media is higher than the adiabatic velocity of sound, the velocity increases as the coordinate grows. Next, the model of stationary plasma flow crosswise to the axial magnetic field in a cylindrical geometry was developed. Experiments on wire explosions in an axial field of Bz = 50 T confirmed that a high temperature peripheral area is formed due to induced azimuthal currents. The measured plasma conductivity is 200 - 400 (Ohm-m)-1.

A proposed effort to study the interaction of imploding liner material with magnetized plasma is discussed. The experiments include forming magnetized plasmas within cylindrical or quasi-spherical metal shells 8 - 10 cm in diameter. The subsequent implosion of the metal shells (imploding liners) compresses the magnetized plasmas. The use of time-and-space-resolved spectroscopy is used to observe high atomic number boundary material mixing with the initial, low atomic number plasma. Magnetic pressure from a 10 - 15 megampere axial current discharge through the shells will drive the metal shell implosions. A variant of these proposed experiments, known as plasma working fluid compression, has been done. Triplets of sequential radiographs of such working-fluid compression experiments indicate that megabar fluid pressures were achieved. Our intended theoretical work will include 2-D MHD simulations of boundary material formation and mix during compression. Preliminary calculations as well as diagnostic schemes and issues will be discussed.

In all the experiments performed to date, the MAGO chambers had a central current-carrying post used for the introduction of the initial magnetic field into the chamber. The results of the first experiments on the capacitor bank facility CASCADE in which the initial magnetic field was not introduced into MAGO chamber, and the central current-carrying post was removed from the plasma heating compartment, are presented in the report. The experiments demonstrated the feasibility of obtaining high-temperature plasma in such chambers with neutron emission duration of 1-1.5 μs. The results may be very useful analyzing the mechanisms of the plasma preliminary heating in MAGO chambers and for testing the applied calculation techniques.