For the collisional merging field reversed configurations (FRCs), it is desired to have both FRCs to be tuned approximately same, as well as to optimize each FRC to have high temperature, and high translation speed so as to retain most of the equilibrium flux after traveling a distance to the middle plane for merging. The present study reports the experimental study of a single-translated FRC (field-reversed configuration) in the KMAX-FRC device with various diagnostics, including a triple probe, a bolometer, several magnetic probe arrays, and a novel 2D internal magnetic probe array. According to the measurements conducted in the present study, a maximum toroidal magnetic field equal to ~1/3 of the external magnetic field inside the FRC separatrix radius is observed, and the typical parameters of a single-translated FRC near the device’s mid-plane are n e ~ 2-4×1019 m-3, T e ~ 8 eV, T i ~ 5 eV , R s ~ 0.2 m , l s ~ 0.6 m, and Φ p(RR) ~ 0.2 mWb . The 2D magnetic topology measurement revealed, for the first time, the time evolution of the overall internal magnetic fields of a single-translated FRC, and an optimized operation regime is given in the paper.

A novel FRC axial compression experiment with high-speed translated θ-pinch plasma was conducted in the KMAX device. The translated north FRC was decelerated and compressed by an oncoming θ-pinch plasmastream, and the dynamic process was revealed by a 2D magnetic probe array. The FRC separatrix length is compressed to one-third of the initial value while the radius expands by ~57%, resulting in the an ~ 16% increase in the electron temperature and ~26% in the density, which matches the calculation from an adiabatic compression model. The good agreement is explained by the fast compression and particle supplementation owing to the compression with plasma. The results reported in this work may contribute to the understanding of electron heating in collision-merged FRC and provide a new compression method for the magneto-inertial fusion concept.

Pseudospark switches are widely used in pulsed power applications. In this paper, we present the design and performance of a 500 Hz repetition rate high-voltage pulse generator to drive TDI-series pseudospark switches. A high-voltage pulse is produced by discharging an 8 µF capacitor through a primary windings of a setup isolation transformer using a single metal-oxidesemiconductor field-effect transistor (MOSFET) as a control switch. In addition, a self-break spark gap is used to steepen the pulse front. The pulse generator can deliver a high-voltage pulse with a peak trigger voltage of 7.8 kV, a peak trigger current of 63 A, a full width at half maximum (FWHM) of ∼ 30 ns, and a rise time of 5 ns to the trigger pin of the pseudospark switch. During burst mode operation, the generator achieved up to a 500 Hz repetition rate. Meanwhile, we also provide an AC heater power circuit for heating a H 2 reservoir. This pulse generator can be used in circuits with TDI-series pseudospark switches with either a grounded cathode or with a cathode electrically floating operation. The details of the circuits and their implementation are described in the paper. K: Pulsed power; Trigger concepts and systems (hardware and software); Plasma generation (laser-produced, RF, x ray-produced) 1Corresponding author.

A series of experimental results of field-reversed configurations (FRCs) on a KMAX (Keda Mirror with AXisymmetricity) tandem mirror machine are reported. Single-side FRC translation processes with three different gas species were measured by avalanche photodiodes. Consistent with the theoretical prediction, the measured FRC speeds were inversely proportional to the square root of the ion mass. However, the speeds of the hydrogen FRC increased even in a uniform magnetic field region while the speeds of the helium and argon FRCs decreased. Possible mechanisms are discussed. The speed of the second pass due to the reflection of the mirror fields was found to be ∼1/3 of the first pass speed. The internal magnetic fields were measured for a colliding-merging argon FRC, and the results show that, even for very slowmoving FRCs, merging can occur.

The field-reversed configuration (FRC) is a compact toroidal plasma system related to the research of alternative fusion reactors. Improving the FRC formation, which is critical to the improvement of its overall quality, is reported in this paper by using a plasma gun to assist the pre-ionization process. For the single-translated FRC, the poloidal magnetic flux increases around 30%, accompanied by an increase in the separatrix radius and plasma density, while its translation speed is found to decrease slightly. The estimated increase in particle inventory is more than 60%. The improvement of these parameters also extends the lifetime of the FRC.