A new device, the Inductive Plasma Accelerator, was employed to simultaneously form and accelerate two oppositely directed field reversed configurations (FRCs) where the relative velocity (600 km s−1) of the plasmoids was much larger than their internal thermal motion. Upon collision all of the FRC directional energy was observed to be rapidly thermalized concurrent with complete magnetic reconnection of the two FRCs. Upon merging, the resulting FRC was compressed to kilovolt ion temperatures exhibiting a configuration lifetime better than predicted by past scaling of in situ formed FRCs. With the improved FRC confinement scaling, a pulsed plasma device based on this approach capable of achieving fusion gain is examined. For an FRC with a poloidal flux 20 mWb or greater, the fusion energy yield per pulse exceeds the plasma energy for compression fields of 10 T or more. The scaling is insensitive to the compression chamber radial scale, providing for the possibility of a very compact fusion neutron source.

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NomenclatureB b , B bias = magnitude of preexisting (vacuum) axial magnetic field B  = amplitude of rf rotating magnetic field B z = axial magnetic field change due to RMF driven currents (superscript M denotes maximum) B ext = magnitude of magnetic field external (radially) to the FRC  = plasma pressure normalized to external (vacuum) field C = capacitance value  = classical skin depth = (2/ 0 ) 1/2 E = electric field vector (subscripts r, , z denote cylindrical components) e = unit of electron charge E k = propellant kinetic energy E k_RMF = kinetic energy derived from electromagnetic input E k_th = kinetic energy derived from conversion of plasma thermal energy E ion = ionization energy E  = energy input from Ohmic heating  = Hall scaling parameter F = force vector (subscripts r, , z denote cylindrical components) FRC = field reversed configuration  = magnetic flux I = current (subscripts r, , z denote cylindrical components) Isp = propellant specific impulse j = current density (subscripts r, , z denote cylindrical components) k = Boltzmann's constant  = plasma resistivity  e = thruster efficiency  = ratio of plasma radius to classical skin depth   0 = magnetic permeability in vacuum m = electron mass  ei = electron-ion collision frequency n = plasma density n e = electron density N = electron line density p = plasma pressure  = azimuthal cylindrical coordinate Q = circuit quality factor r = radial cylindrical coordinate r p = plasma radius r s = magnetic separatrix radius 1 AIAA Senior Member 2 AIAA Member 3 AIAA Member 2 Figure 1. ELF thruster operating on water vapor. RMF= rotating magnetic field T = plasma temperature T e = electron temperature  = RMF pulse length  = angular frequency of RMF  ce = electron angular frequency in rotating field  ci = ion angular frequency in rotating field z = axial cylindrical coordinate

The high flux source for the Pulsed High Density Experiment (PHDX) has been constructed, and fieldreversed configuration (FRC) plasmas are being produced. To diagnose FRC plasma temperatures three kinds of diagnostic systems have been set up on PHDX; λ = 632.8 nm He-Ne laser interferometer system at the midplane for total temperatureT total , 16 channel spectrometer for ion temperature T i and soft x-ray (SXR) measurement system for electron temperature T e viewed along z-axis, respectively. The SXR measurement system consists of five sets of collimators and AXUV100 photodiodes with directly deposited filters which have different bandpass regions. As a result of preliminary temperature diagnostics, the following plasma parameters are estimated during a relatively quiescent phase of FRCs; T total ∼ 50 eV, T i ∼ 50 eV and T e ∼ 25 eV. This result does not agree with the equilibrium relation of T total ≈ T i + T e , and it must be caused by plasma condition and our assumptions in the spectral analysis.

An experimental program has been initiated that will explore the very compact, high energy density regime of fusion based on the magneto-kinetic compression of the FRC. Of all fusion reactor embodiments, only the FRC has the simply-connected closed field, linear confinement geometry, and intrinsic high b required for magnetic fusion at high energy density. PHD takes advantage of the linear confining geometry by incorporating a traveling, burning plasmoid, significantly reducing the wall loading as well as keeping the formation well separated from the burn chamber. Being small, compact, and at high b greatly improves the exposed surface to reacting volume ratio. Being pulsed eliminates the need for flux sustainment, and provides for regulation of the average wall loading. A wide range of reactor scenarios are compatible with PHD including liquid metal walls with the prospect of direct energy conversion through cyclical wall compression/expansion.