Magnetized target fusion (MTF) is a potentially low cost path to fusion, intermediate in plasma regime between magnetic and inertial fusion energy. It requires compression of a magnetized target plasma and consequent heating to fusion relevant conditions inside a converging flux conserver. To demonstrate the physics basis for MTF, a field reversed configuration (FRC) target plasma has been chosen that will ultimately be compressed within an imploding metal liner. The required FRC will need large density, and this regime is being explored by the FRX–L (FRC-Liner) experiment. All theta pinch formed FRCs have some shock heating during formation, but FRX–L depends further on large ohmic heating from magnetic flux annihilation to heat the high density (2–5×1022 m−3), plasma to a temperature of Te+Ti≈500 eV. At the field null, anomalous resistivity is typically invoked to characterize the resistive like flux dissipation process. The first resistivity estimate for a high density collisional FRC is shown here. The flux dissipation process is both a key issue for MTF and an important underlying physics question.
We describe the experiment and technology leading to a target plasma for the magnetized target fusion research effort, an approach to fusion wherein a plasma with embedded magnetic fields is formed and subsequently adiabatically compressed to fusion conditions. The target plasmas under consideration, field-reversed configurations ͑FRCs͒, have the required closed-field-line topology and are translatable and compressible. Our goal is to form high-density (10 17 cm Ϫ3 ) FRCs on the field-reversed experiment-liner ͑FRX-L͒ device, inside a 36 cm long, 6.2 cm radius theta coil, with 5 T peak magnetic field and an azimuthal electric field as high as 1 kV/cm. FRCs have been formed with an equilibrium density n e Ϸ(1 to 2)ϫ10 16 cm Ϫ3 , T e ϩT i Ϸ250 eV, and excluded flux Ϸ2 to 3 mWb.
Magneto-inertial fusion (MIF) approaches take advantage of an embedded magnetic field to improve plasma energy confinement by reducing thermal conduction relative to conventional inertial confinement fusion (ICF). MIF reduces required precision in the implosion and the convergence ratio.
The focus of the field-reversed configuration (FRC) experiment with a liner (FRX-L) is the formation of a target FRC plasma for magnetized target fusion experiments. An FRC plasma with density of 1023m−3, total temperature in the range of 150–300 eV, and a lifetime of ≈20μs is desired. Field-reversed θ-pinch technology is used with programed cusp fields at θ-coil ends to achieve non-tearing field line reconnections during FRC formation. Well-formed FRCs with density between (2–4)×1022m−3, lifetime in the range of 15–20μs, and total temperature between 300–500 eV are reproducibly created. Key FRC parameters have standard deviation in the mean of 10% during consecutive shots. The FRCs are formed at 50 mTorr deuterium static fill using 2 kG net reversed bias field inside the θ-coil confinement region, with external main field unexpectedly ranging between 15–30 kG. The high-density FRCs confinement properties are approximately in agreement with empirical scaling laws obtained from previous experiments with fill pressure mostly less than 20 mTorr. Analyses in this paper reveal that reducing the external main field modulation and∕or extending the θ-coil length in the FRX-L device are critical in achieving higher FRC parameters for application in magnetized target fusion.
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