First Plasmas and Diagnostics in MUSE Permanent Magnet Stellarator*

The Multipolar Unicoil Stellarator Experiment (MUSE) is the first optimized quasi-axisymmetric (QA) stellarator that uses permanent magnets (PM) and planar coils to create the helical magnetic fields for plasma confinement. After design and construction [1], the first experiments planned on MUSE are as follows. An electron beam (EB) and fluorescent rods are used for flux surface mapping and compared to Poincare plots to confirm the magnetic field, map error fields and magnetic islands, and calibrate magnetic permeability. Then, hydrogen gas is exposed to tesla coil and biased electrode glow heating to ionize, and then helicon radio frequency heating (HRFH) to create the plasma. Diagnostics are used to test the profiles of the plasma, effectiveness of HRFH operating regimes and antenna modes, flow damping and ripple from the optimized B field, and energy transfer and confinement. Diagnostics include single, double, and triple Langmuir probes (LP1, LP2, LP3), a double tipped Mach probe, Hall probes, Rogowski coils, Mirnov coils, diamagnetic loops, and flux loops. These experiments represent the first attempt to quantify plasma characteristics in a PM QA stellarator. Subsequent studies include imaging and correcting error fields as well as numerical analysis of HRFH and flow dynamics.

[1] T. Qian, et. al., Nucl. Fusion 62 084001 (2022)