Comparison of Single and Collisional-Merging FRCs with Enhanced Magnetic Gradients in the FAT-CM*

The field-reversed configuration (FRC) is a compact toroid plasma characterized by a high beta and a self-generated toroidal current, making it a promising nuclear fusion reactor candidate. A specific device was designed to study the coalescence and reformation of colliding FRCs into a hotter, larger plasma. Two years prior to this work, the device was modified to increase the magnetic gradients in the formation sections, resulting in an increased translational velocity of the FRCs. This enhancement led to significantly hotter plasmas, with measured ion temperatures increasing from 50-70 eV before the modification to 100-300 eV after.

An experiment was conducted to characterize the single translated FRC following the modification. In these single translation experiments, ion temperatures ranging from 20 to 65 eV were observed when measurements were taken 0.3 m from the midplane in the direction of one of the formation sections. Measurements were performed from both formation sections. Line integrated average electron densities with the expected proportionality to the collisional densities were measured for the single translation experiments (2.1 × 10²⁰ − 4.6 × 10²⁰ 𝑚^-3). Toroidal flow could only be determined for the formation section nearest to the measurement point due to the FRC’s increasing drift from the z-axis during translation.

This study establishes a crucial baseline for future experiments with the device, providing valuable insights into the behavior of FRCs under modified conditions.