Search

We are planning experiments using a field reversed configuration plasma injected into a metal cylinder, which is subsequently electrically imploded to achieve a fusing plasma. Diagnosing this plasma is quite challenging due to the short timescales, high energy densities, high magnetic fields, and difficult access. We outline our diagnostic sets in both a phase I study (where the plasma will be formed and translated), and phase II study (where the plasma will be imploded). The precompression plasma (diameter of only 8–10 cm, length of 30–40 cm) is expected to have n∼1017 cm−3, T∼100–300 eV, B∼5 T, and a lifetime of 10–20 μs. We will use visible laser interferometry across the plasma, along with a series of fiber-optically coupled visible light monitors to determine the plasma density and position. Excluded flux loops will be placed outside the quartz tube of the formation region, but inside of the diameter of the θ-pinch formation coils. Impurity emission in the visible and extreme ultraviolet range will b...

Research on forming, compressing, and accelerating milligram‐range compact toroids using a meter diameter, two‐stage, puffed gas, magnetic field embedded coaxial plasma gun is described. The compact toroids that are studied are similar to spheromaks, but they are threaded by an inner conductor. This research effort, named marauder (Magnetically Accelerated Ring to Achieve Ultra‐high Directed Energy and Radiation), is not a magnetic confinement fusion program like most spheromak efforts. Rather, the ultimate goal of the present program is to compress toroids to high mass density and magnetic field intensity, and to accelerate the toroids to high speed. There are a variety of applications for compressed, accelerated toroids including fast opening switches, x‐radiation production, radio frequency (rf) compression, as well as charge‐neutral ion beam and inertial confinement fusion studies. Experiments performed to date to form and accelerate toroids have been diagnosed with magnetic probe arrays, laser interf...

A technique is demonstrated whereby the delivered mass and flow rate versus time of a short rise‐time gas delivery system may be accurately determined. The gas mass M that flows past a point in a gas delivery system by an arbitrary time t=tp may be accurately measured if that point is sealed off with a fast closing valve within a time interval short compared to the mass flow time scale. If the injected mass is allowed to equilibrate in a known volume after being cut off from its source, a conventional static pressure measurement before and after injection, and application of the ideal gas law suffices. Repeating for many different values of tp, and assuming reproducibility, the injected mass time history M(t) characteristic of the system without the fast closing valve may be determined. The flow rate versus time dM(t)/dt may then be determined by numerical differentiation. Mass flow measurements are presented for a fast delivery system for which the flow of argon through a 3.2‐mm‐i.d., 0.76‐mm‐thick coppe...

Interferometric measurements of the line‐averaged free electron density of plasma compact toroids as part of preliminary toroid formation experiments are presented. These experiments are in preparation for compact toroid acceleration experiments to be performed at Phillips Laboratory’s High Energy Plasma Division. The primary instrument used was a Michelson (double pass) interferometer operating with a HeNe laser at a wavelength of 633 nm. Density measurements of hydrogen and argon plasmas are correlated with magnetic field and spectroscopic measurements to characterize the toroid mass, velocity, and impurity distribution.

Experiments with coaxial plasma guns at currents in excess of ten megamperes have resulted in the production of high‐voltage pulses (0.5 MV) and hard x radiation (10–200 keV). The x‐radiation pulse occurs substantially after the high‐voltage pulse suggesting that high‐energy electrons are generated by dynamic processes in a very high speed (≳106 m/s), magnetized plasma flow. Such flows, which result from acceleration of relatively low‐density plasma (10−4 vs 1.0 kg/m3) by magnetic fields of 20–30 T, support high voltages by the back electromotive force‐u×B during the opening switch phase of the plasma flow switch. A simple model of classical ion slowing down and subsequent heating of background electrons can explain spectral evidence of 30‐keV electron temperatures in fully stripped aluminum plasma formed from plasma flows of 1–2 × 106 m/s. Similar modeling and spectral evidence indicates tungsten ion kinetic energies of 4.5 MeV and 46 keV electron temperatures of a highly stripped tungsten plasma.

Detailed calculations of the formation, guide, and mirror applied magnetic fields in the FRC compression-heating experiment (FRCHX) were conducted using a commercially available generalized finite element solver, COMSOL Multiphysics(®). In FRCHX, an applied magnetic field forms, translates, and finally captures the FRC in the liner region sufficiently long to enable compression. Large single turn coils generate the fast magnetic fields necessary for FRC formation. Solenoidal coils produce the magnetic field for translation and capture of the FRC prior to liner implosion. Due to the limited FRC lifetime, liner implosion is initiated before the FRC is injected, and the magnetic flux that diffuses into the liner is compressed. Two-dimensional axisymmetric magnetohydrodynamic simulations using MACH2 were used to specify optimal magnetic field characteristics, and this paper describes the simulations conducted to design magnetic field coils and compression hardware for FRCHX. This paper presents the vacuum solution for the magnetic field.