Characterization of Magnetic Confinement and Plasma Parameters for a Stellarator Using Permanent Magnets*

MUSE, a stellarator constructed using permanent magnets, is a cutting-edge fusion device that employs rare earth magnets to confine plasmas. To gain insights into the plasma confinement mechanism, detailed mapping of magnetic flux surfaces was conducted. This mapping technique involved utilizing an oscillating rod coated with fluorescent powder. As the electron beam collided with the rod, it triggered the emission of photons, allowing for the visualization of magnetic surfaces. Additionally, Poincaré maps were generated by capturing images during electron beam shots, enabling a comprehensive analysis of plasma dynamics.

In this study, the characterization of the plasma was performed using single, double, and triple simple cylindrical Langmuir probes. These probes facilitated the measurement of current-voltage (I-V) curves, enabling a thorough investigation of plasma properties. Specifically, the radial profiles of electron temperature, electron density, and electrical potential were obtained as functions of various parameters, including heating power, neutral gas pressure, magnetic field strength, and rotational transform. The rotational transform, a crucial parameter describing the twisting or rotation of magnetic field lines within the plasma, played a pivotal role in understanding plasma behavior.